Chlorophyll a Fluorescence

The biochemical basis of heat/drought tolerance was investigated by comparing the response of antisense and sense transgenic soybean plants (containing the L-D 1pyrroline-5-carboxylate reductase gene) with non-transgenic wild-type plants. The plants were subjected to a simultaneous drought and heat stress of 2 days, whereafter they were rewatered at 251C. During this time the sense plants only showed mild symptoms of stress compared to the antisense plants which were severely stressed. Upon stress, nicotinamide adenine dinucleotide phosphate (NADP þ) levels decreased in antisense while it increased in sense plants. Recovery with respect to NADP þ levels was best in sense plants. Sense plants had the highest ability to accumulate proline

When sprayed as a post-emergent, foliar herbicide propanil destroyed Echinochloa crus-galli (L.) with little or no visible injury to rice., confirming its selective contact action. In treated rice leaves there was, however, a temporary decrease in dry weight, pigments, proteins and photosynthetic products followed by complete recovery in 4-5 days. In both rice and E. crusgalli, at lower concentrations propanil inhibited the electron flow in a manner similar to that of DCMU, but at higher concentrations it damaged the primary electron donor.

... Michael E. Loik a , ¶ , Travis E. Huxman c , b , Erik P. Hamerlynck d , b and Stanley D. Smith b. ... 19. ME Loik, CD St. Onge and J. Rodgers, Post-fire recruitment of Yucca brevifolia and Yucca schidigera in Joshua Tree National Park, California. ...

Continuous measurements of the surface water CO 2 partial pressure (pCO 2) and the chlorophyll a fluorescence were performed in the Baltic Sea using a fully automated measurement system deployed on a cargo ship. The ship commuted regularly at two day intervals between the Mecklenburg Bight (Luebeck) and the Gulf of Finland (Helsinki). The pCO 2 data collected during June 2003 and September 2004 were used to identify biological production events such as the spring bloom and the midsummer cyanobacteria bloom in five different sub-regions. To quantify the net biomass production, the decrease of the total CO 2 , N C T (normalized to a uniform alkalinity), during the production periods was calculated using the pCO 2 , temperature and salinity records and the mean alkalinity. Taking into account the CO 2 air/sea exchange and the formation of dissolved organic carbon, a simple mass balance yielded the net production of particulate organic carbon which represents the total biomass. The chlorophyll a concentrations obtained from the fluorescence data showed peaks that in most cases coincided with the production maxima and thus supported the interpretation of the pCO 2 data. The production during both the spring bloom (2004) and the midsummer nitrogen fixation period (2003) increased by a factor of about three from the southwest to the northeast. For the spring bloom our estimates were significantly higher than those based on the winter nutrient supply and Redfield C / N and C / P ratios. This indicated the existence of additional nutrient sources such as dissolved organic nitrogen, early nitrogen fixation and preferential P mineralization. Midsummer N C T minima were observed only in 2003 and used to quantify the nitrogen fixation activity and to characterize its interannual variability.

Young plants of two Brazilian Green Dwarf coconut ecotypes from contrasting regions in relation to climate (UGD, from a hot and humid climate and JGD, from a hot and dry climate) were submitted to three consecutive drying/recovery cycles, under greenhouse conditions to determine the photosynthetic limitations encountered during the recovery phase of water deficiency. Three hypotheses were tested: (1) non-stomatal factors contribute to the incomplete recovery of net photosynthesis rate (A), (2) photochemical impairment is an important component of the non-stomatal limitations to A and (3) the two coconut ecotypes respond differently to the drought recovery. In each drying/recovery cycle, irrigation was suppressed until A reached zero. Then the plants were rewatered and the recovery was accompanied for 8 days. After 4 days of rewatering, CO 2 and light response curve parameters were used to discriminate the stomatal and non-stomatal factors contributing to the incomplete recovery of A. Upon rewatering for 4 days, the pre-dawn leaf water potential of the stressed plants increased from −1.20 to −0.15 MPa on average. Only small differences were detected in the intercellular to atmospheric CO 2 concentration ratio but A did not recover completely to the control values. In both ecotypes, light and CO 2-saturated A, carboxylation efficiency, maximum quantum yield of PSII and maximum electron transport rate were significantly lower in stressed plants in comparison with the well-watered ones. Relative stomatal limitation (L S) ranged from 16 to 20% without significant differences between treatments and between ecotypes. The relative mesophyll limitation (L m) was significantly higher in JGD in cycle 1 but this changed after repeated drought stress, decreasing to values significantly lower than those in UGD in the other two cycles. The results showed that after 4 days of rewatering stressed plant stomatal limitations were comparable to that of well-watered control plants (∼20%). However A did not recover completely after drought stress due to non-stomatal factors. Important differences between the ecotypes were identified. The ecotype JGD presented smaller L m , faster recovery of the apparent quantum efficiency of CO 2 assimilation, adjustment of some carbon balance components and signs of photosynthetic capacity acclimation after repeated drying/recovery cycles.

The cold stress effect on early vigour and photosynthesis efficiency was evaluated for five industrial chicory varieties with contrasting early vigour. The relationships between the growth and physiological parameters were assessed. The varieties were examined at three growth temperatures: 16 (reference), 8 (intermediate) and 4 °C (stress). The effect was measured using physiological processes (growth, photosynthesis, chlorophyll a fluorescence), and pigment content. The analysis of the measured growth parameters (dry leaf and root mass, and leaf area) indicated that temperature had a significant effect on the varieties, but the overall reaction of the varieties was similar with lowering temperatures. The photosynthesis and chlorophyll a fluorescence measurements revealed significant changes for the photosynthesis (maximum net photosynthesis, quantum efficiency, light compensation point and dark respiration) and chlorophyll a fluorescence parameters (photochemical and non-photochemical quenching) with lowering temperatures for Hera and Eva, two extremes in youth growth. No significant differences could be found between the extremes for the different temperatures. The pigment content analysis revealed significant differences at 4 °C in contrast to 16 and 8 °C, especially for the xanthophyll/carotenoid pool, suggesting a protective role. Subsequently, the relationship between the physiological processes was evaluated using principal component analysis. At 4 °C, 2 principal components were detected with high discriminating power for the varieties and similar classification of the varieties as determined in the growth analysis. This provides a preview on the possible relationships between photosynthesis and growth for industrial chicory at low temperatures.

The photosynthetic characteristics of four transgenic rice lines over-expressing rice NADP-malic enzyme (ME), and maize phosphoenolpyruvate carboxylase (PC), pyruvate,orthophosphate dikinase (PK), and PC+PK (CK) were investigated using outdoor-grown plants. Relative to untransformed wild-type (WT) rice, PC transgenic rice exhibited high PC activity (25-fold increase) and enhanced activity of carbonic anhydrase (more than two-fold increase), while the activity of ribulose-bisphosphate carboxylase/oxygenase (Rubisco) and its kinetic property were not significantly altered. The PC transgenic plants also showed a higher light intensity for saturation of photosynthesis, higher photosynthetic CO(2) uptake rate and carboxylation efficiency, and slightly reduced CO(2) compensation point. In addition, chlorophyll a fluorescence analysis indicates that PC transgenic plants are more tolerant to photo-oxidative stress, due to a higher capacity to quench excess light energy via photochemical and...

A field test of wych elm (Ulmus glabra Huds.) trees micropropagated in tissue culture was established to compare their photosynthetic characteristics with those from control grafted scions. Measurements were made at the sixth growing season after planting. The results showed similarities between the two stock types in terms of height, diameter at breast height, and leaf morphology. Grafted trees, which were markedly less rejuvenated than micropropagated trees, performed better in many of the light absorption and leaf gas exchange attributes including maximum CO 2 assimilation rate at saturating photosynthetic photon flux density (P max ), apparent quantum yield of photosynthesis (a), transpiration rate (E), and stomatal conductance (g s ). In the grafts, the direct effect of photosynthesis could be clearly identified by a significantly lower specific leaf area and a higher content of leaf dry mass. Chlorophyll a fluorescence parameters showed nonstressed growth patterns in both stock types. Rates of the maximal photochemical efficiency of photosystem II (F v /F m ), potential electron capacity ('area'), and variable-to-initial fluorescence ratio (F v /F 0 ) were higher in micropropagated elms. Findings from this study indicate that micropropagated elm stock is ready for testing on a larger scale.

The aim of this educational review is to provide practical information on the hardware, methodology, and the hands on application of chlorophyll (Chl) a fluorescence technology. We present the paper in a question and answer format like frequently asked questions. Although nearly all information on the application of Chl a fluorescence can be found in the literature, it is not always easily

The aim of this educational review is to provide practical information on the hardware, methodology, and the hands on application of chlorophyll (Chl) a fluorescence technology. We present the paper in a question and answer format like frequently asked questions. Although nearly all information on the application of Chl a fluorescence can be found in the literature, it is not always easily

Survival and recovery of the seagrass Halophila ovalis (R.Br.) Hook during and after light deprivation was investigated to assist in the interpretation of recent losses of Halophila spp. in Queensland, Australia. Light deprivation experiments were conducted in outdoor aquaria and in situ at two water depths. Halophila ovalis plants were deprived of light for a maximum of 30 days, and recovery processes were investigated for up to 18 days following 15 days of light deprivation. Measurements of H. ovalis biomass, storage carbohydrate concentrations, chlorophyll a+b concentrations, stable carbon isotopes ratios (δ13C) and chlorophyll a fluorescence parameters (F0, Fm and Fv/Fm) were made during and at the end of the light deprivation and recovery periods. Biomass declined after 3–6 days in the dark and complete plant death occurred after 30 days. During the recovery period, biomass continued to decline for a short duration of time before stabilising. Sugar concentrations declined rapidly for the first 2 days of light deprivation before stabilising, then increased rapidly during the recovery period. Chlorophyll a+b concentrations were sensitive to very small differences in light availability: concentration decreased in total darkness, remained unchanged at 0.1% of surface irradiance and increased at 0.5% of surface irradiance. Photochemical efficiency of photosystem II (Fv/Fm) remained unchanged during the light deprivation and recovery periods. The lack of response in δ13C during light deprivation indicated the cessation of carbon fixation. Decreased sugar utilisation after 2 days of light deprivation indicated a reduction in respiration and growth. Starch concentrations did not change during light deprivation, suggesting the inhibition of starch utilisation by anaerobic conditions within the plant. Plant death after 30 days was notably faster than previously reported for other species of seagrass. The rapid die-off may be due to a shortage of available carbohydrates or due to a build-up of the phytotoxic end products of anaerobic respiration. Overall, H. ovalis has a very limited tolerance to light deprivation when compared to larger species of seagrass. Consequently, the persistence of this species in coastal marine environments may be dependent upon the occurrence and duration of transient light deprivation events.

This study uses chlorophyll a fluorescence to examine the effect of environmentally relevant (1-4 h) exposures of thermal stress (35-45 8C) on seagrass photosynthetic yield in seven tropical species of seagrasses. Acute response of each tropical seagrass species to thermal stress was characterised, and the capacity of each species to tolerate and recover from thermal stress was assessed. Two fundamental characteristics of heat stress were observed. The first effect was a decrease in photosynthetic yield ( F v / F m ) characterised by reductions in F and F mV . The dramatic decline in F v / F m ratio, due to chronic inhibition of photosynthesis, indicates an intolerance of Halophila ovalis, Zostera capricorni and Syringodium isoetifolium to ecologically relevant exposures of thermal stress and structural alterations to the PhotoSystem II (PSII) reaction centres. The decline in F mV represents heat-induced photoinhibition related to closure of PSII reaction centres and chloroplast dysfunction. The key finding was that Cymodocea rotundata, Cymodocea serrulata, Halodule uninervis and Thalassia hemprichii were more tolerant to thermal stress than H. ovalis, Z. capricorni and S. isoetifolium. After 3 days of 4 h temperature treatments ranging from 25 to 40 8C, C. rotundata, C. serrulata and H. uninervis demonstrated a wide tolerance to temperature with no detrimental effect on F v / F mV qN or qP responses. These three species are restricted to subtropical and tropical waters and their tolerance to seawater temperatures up to 40 8C is likely to be an adaptive response to high temperatures commonly occurring at low tides and peak solar irradiance. The results of temperature experiments suggest that the photosynthetic condition of all seagrass species tested are likely to suffer irreparable effects from short-term or episodic changes in seawater temperatures as high as 40-45 8C. Acute stress responses of seagrasses to elevated seawater temperatures are consistent with observed reductions in above-ground biomass during a recent El Niño event. Crown

Florescence assessments of Sunflower (Helianthus annuus L.) genotypes in field under drought stress environment were studied. Climate change and low precipitation represents the main constraints in sunflower production in Pakistan. In present investigation two sunflower genotypes, viz S.28111 and SF0049 were selected to study their photosynthetic performance through non-destructive technique in field. Three treatments were applied to impose drought in plants i.e. irrigation after 6 days (D1), irrigation after 8 days (D2) and irrigation after 16 days (D3) with control irrigation after 4 days. Results revealed that drought stresses altered the electron transport rate through PSII (Fm/Fo), photochemical quenching (qP), efficiency of photosystem II (ΦPSII), linear electron transport rate (rETR), non-photochemical quenching (NPQ), size and number of active reaction centre of photosynthetic apparatus (Fv/Fo), driving forces (DFABS and DFCS) and performance indexes (PIABS and PICS) parameters that depends on the efficiency and yield of energy transfer and primary photochemistry. However, S.28111 maintained substantial quantum yield and enhanced photosynthetic performance under drought stress environment compared to SF0049. It is suggested that the assessment of photochemistry of PSII offers a practical and sensitive field screening regarding test for drought stress tolerance in sunflower. Results are discussed in relation to photosynthetic performance and florescence responses of sunflower genotypes in the drought stress environment.

In order to detect early effects of plant contamination by fluoride emission on two tropical grasses, Chloris gayana and Panicum maximum, previously cultivated under greenhouse conditions, were exposed to a single source of fluoride emission at a station at 1.1 km from an aluminum smelter in Ouro Preto, MG, Brazil. Controls were placed at a reference station 78 km from the fluoride source. During an 8-day period of exposure leaf injury, ionic permeability, photosynthetic rates, stomatal conductance, transpiration, chlorophyll a fluorescence and chlorophyll, soluble carbohydrates and fluoride contents were evaluated. Plants at the Ouro Preto station showed an increase in fluoride content, leaf injury and ionic permeability. Symptoms of injury by fluoride exposure were visible after 3-4 days in both species. High electrolyte leakage and correlation coefficients between the total ionic permeability and the fluoride content in leaves indicate a fluoride effect on the structural and/or functional integrity of the cellular membranes. Leaf fluoride injuries were quite different in the two species. In C. gayana necroses were limited to the leaf tips, while in P. maximum damages were observed in the whole leaf, suggesting a higher susceptibility of this latter species to fluoride. Nonetheless, neither grass showed statistical differences with respect to photosynthetic rates, stomatal conductance, transpiration, chlorophyll a fluorescence and chlorophyll content in leaves without any apparent fluoride injury. Plants at the Ouro Preto station showed a significant decrease in reducing sugar content between 3 and 5 days of exposure to fluoride, but thereafter reducing sugar content increased reaching the content of control plants. Fluoride exposed plants also showed a remarkable starch content reduction, remaining always much lower than those at the reference station. r

Young plants of two Brazilian Green Dwarf coconut ecotypes from contrasting regions in relation to climate (UGD, from a hot and humid climate and JGD, from a hot and dry climate) were submitted to three consecutive drying/recovery cycles, under greenhouse conditions to determine the photosynthetic limitations encountered during the recovery phase of water deficiency. Three hypotheses were tested: (1) non-stomatal factors contribute to the incomplete recovery of net photosynthesis rate (A), (2) photochemical impairment is an important component of the non-stomatal limitations to A and (3) the two coconut ecotypes respond differently to the drought recovery. In each drying/recovery cycle, irrigation was suppressed until A reached zero. Then the plants were rewatered and the recovery was accompanied for 8 days. After 4 days of rewatering, CO 2 and light response curve parameters were used to discriminate the stomatal and non-stomatal factors contributing to the incomplete recovery of A. Upon rewatering for 4 days, the pre-dawn leaf water potential of the stressed plants increased from −1.20 to −0.15 MPa on average. Only small differences were detected in the intercellular to atmospheric CO 2 concentration ratio but A did not recover completely to the control values. In both ecotypes, light and CO 2 -saturated A, carboxylation efficiency, maximum quantum yield of PSII and maximum electron transport rate were significantly lower in stressed plants in comparison with the well-watered ones. Relative stomatal limitation (L S ) ranged from 16 to 20% without significant differences between treatments and between ecotypes. The relative mesophyll limitation (L m ) was significantly higher in JGD in cycle 1 but this changed after repeated drought stress, decreasing to values significantly lower than those in UGD in the other two cycles. The results showed that after 4 days of rewatering stressed plant stomatal limitations were comparable to that of well-watered control plants (∼20%). However A did not recover completely after drought stress due to non-stomatal factors. Important differences between the ecotypes were identified. The ecotype JGD presented smaller L m , faster recovery of the apparent quantum efficiency of CO 2 assimilation, adjustment of some carbon balance components and signs of photosynthetic capacity acclimation after repeated drying/recovery cycles.

The in-vitro acclimatization of Phalaenopsis plantlets under photoautotrophic conditions, with 0 (control), 3.43, 6.86 and 13.72 mM uniconazole (UCZ) treatments for 30 days was investigated before the plantlets were transferred to ex-vitro environments for 14 days. The physiological and growth characters of in-vitro acclimatized, and ex-vitro adapted plantlets were measured. Chlorophyll a (Chl a ), chlorophyll b (Chl b ), total chlorophyll (TC) and total carotenoid (C x+c ) content in plantlets treated with 6.86 mM UCZ were maintained at higher levels than those in plantlets of the control, by 1.82, 1.85, 1.83 and 1.93 times, respectively, leading to enrichment of the pigments in ex-vitro conditions. The maximum quantum yield of PSII (F v /F m ), photon yield of PSII (F PSII ), photochemical quenching (qP) and non-photochemical quenching (NPQ) in UCZ treated plantlets and in ex-vitro adaptation were not significantly different. Proline was accumulated in the control plantlets in both in-vitro acclimatization and ex-vitro conditions, while proline in those plantlets with UCZ treatments was maintained at a low level, which was defined by unstressed conditions. Net photosynthetic rate (P n ) in 6.86 mM UNZ treated plantlets peaked at a higher level than that of the control plantlets, both in-vitro and ex-vitro, by 3.27 and 2.93 times, respectively. In addition, proline content and P n were inversely related in both in-vitro acclimatization and ex-vitro adaptation. The P n in UCZ acclimatized plantlets was negatively correlated with plant dryweight. In-vitro photoautotrophic Phalaenopsis plantlets were successfully acclimatized using a 6.86 mM UCZ treatment which caused them to adapt quickly to ex-vitro environments.

High temperatures and high atmospheric vapor pressure deficits (VPDs) are usually encountered in greenhouses in hot climates. For citrus, these environmental conditions can lead to decreases in photosynthetic activity with detrimental effects on plant growth. The aim of this study was to evaluate the use of reflective aluminized polypropylene shading nets on photosynthetic performance of citrus plants, by measuring CO 2 assimilation, transpiration rate, stomatal conductance and chlorophyll a fluorescence. Incident photosynthetically active radiation (PAR) levels and leaf temperatures were reduced when the reflective nets were used. Higher stomatal conductance and higher CO 2 assimilation rates were observed in shaded plants, so that integrated daily net CO 2 uptake was approximately 20% higher than in exposed plants. The better performance of shaded plants, however, was observed only during the middle of the day, being PAR-limited in early morning and late afternoon. The reflective net was also effective in preventing photoinhibition of photosynthesis in shaded plants, which sustained higher maximum (F v /F m ) and effective ðDF=F 0 m Þ quantum yield with higher apparent electron transport rates (ETRs) than exposed plants. Observed photoinhibition in exposed plants was transient, probably reflecting photosynthetic regulatory responses to excess absorbed light energy. Therefore, the results clearly showed that photosynthetic performance of citrus cultivated in greenhouses can be improved by the use of reflective nets. Favorable effects comprised not only the maintenance of proper stomatal aperture for gas exchange but also a better functioning of the photosystem II (PSII) under nonphotoinhibitory conditions. # 2002 Published by Elsevier Science B.V.

To investigate the ability of pioneer and late-successional species to adapt to a strong light environment in a reforestation area, we examined the activities of antioxidant enzymes in relation to photosystem II, chlorophyll a fluorescence and photosynthetic pigment concentration for eight tropical tree species grown under 100% (sun) and 10% (shade) sunlight irradiation. The pioneer (early-succession) species (PS) were Cecropia

The response of barley (Hordeum vulgare L. cv. Akcent) to various photosynthetic photon flux densities (PPFDs) and elevated [CO2] [700 μmol (CO2) mol−1; EC] was studied by gas exchange, chlorophyll (Chl) a fluorescence, and pigment analysis. In comparison with barley grown under ambient [CO2] [350 μmol (CO2) mol−1; AC] the EC acclimation resulted in a decrease in photosynthetic capacity, reduced stomatal conductance, and decreased total Chl content. The extent of acclimation depression of photosynthesis, the most pronounced for the plants grown at 730 μmol m−2 s−1 (PPFD730), may be related to the degree of sink-limitation. The increased non-radiative dissipation of absorbed photon energy for all EC plants corresponded to the higher de-epoxidation state of xanthophylls only for PPFD730 barley. Further, a pronounced decrease in photosystem 2 (PS2) photochemical efficiency (given as FV/FM) for EC plants grown at 730 and 1 200 μmol m−2 s−1 in comparison with AC barley was related to the reduced epoxidation of antheraxanthin and zeaxanthin back to violaxanthin in darkness. Thus the EC conditions sensitise the photosynthetic apparatus of high-irradiance acclimated barley plants (particularly PPFD730) to the photoinactivation of PS2.

An aggregate flux event was observed by ship and by four underwater gliders during the 2008 subpolar North Atlantic spring bloom experiment (NAB08). At the height of the diatom bloom, aggregates were observed as spikes in measurements of both particulate backscattering coefficient (b bp ) and chlorophyll a fluorescence. Optical sensors on the ship and gliders were cross-calibrated through a series of simultaneous profiles, and b bp was converted to particulate organic carbon. The aggregates sank as a discrete pulse, with an average sinking rate of $ 75 m d À 1 ; 65% of aggregate backscattering and 90% of chlorophyll fluorescence content was lost between 100 m and 900 m. Mean aggregate organic carbon flux at 100 m in mid-May was estimated at 514 mg C m À 2 d À 1 , consistent with independent flux estimates. The use of optical spikes observed from gliders provides unprecedented coupled vertical and temporal resolution measurements of an aggregate flux event.

After briefly describing my early collaborative work at the University of Allahabad, that had laid the foundation of my research life, I present here some of our research on photosynthesis at the University of Illinois at Urbana-Champaign,randomly selected from light absorption to NADP+ reduction in plants, algae, and cyanobacteria. These include the fact that (i) both the light reactions I and II are powered by light absorbed by chlorophyll (Chl) a of different spectral forms; (ii)nlight emission (fluorescence, delayed fluorescence, andnthermoluminescence) by plants, algae, and cyanobacteria providesndetailed information on these reactions and beyond; (iii) primary photochemistry in both the photosystems I (PS I) and IIm(PS II) occurs within a few picoseconds; and (iv) most importantly, bicarbonate plays a unique role on the electron acceptor
side of PS II, specifically at the two-electron gate of PS II. Currently, the ongoing research around the world is, and should
be, directed towards making photosynthesis better able to deal with the global issues (such as increasing population, dwindling resources, and rising temperature) particularly through genetic modification. However, basic research is necessary to
continue to provide us with an understanding of the molecular mechanism of the process and to guide us in reaching our goals of increasing food production and other chemicals we need for our lives.

This chapter investigates the use of chlorophyll a fluorescence to better understand changes in the regulation of photosynthetic electron transport. It describes the different electron pathways utilised by photosynthetic organisms, including pathways used in photosynthesis as well as alternative electron cycling (AEC). The major photoprotective processes are described, in particular, non-photochemical quenching (NPQ) and its three components, energy-dependent quenching (qE), state-transition quenching (qT), and photoinhibition (qI). Fluorescence and NPQ responses to light stress are compared across a higher plant, diatom and cyanobacteria. Photosynthesis is a complex interaction of complementary processes making the identification and isolation of a particular photosynthetic pathway or process inherently difficult. Therefore, we describe the use of chemicals which allow for the differentiation of mechanistic photosynthetic processes, such as electron transport pathways, CO2 fixation and the use of trans-thylakoid proton gradients, which can be effectively understood and quantified using chlorophyll fluorescence detection techniques.

The sensitivity of three foliose lichen species to urban environments with different air pollution loads and climatic conditions was tested using chlorophyll a fluorescence (Chl a F) PAM measurements. Transplants of Xanthoria parietina (L.) Th. Fr., Flavoparmelia caperata (L.) Hale and Parmotrema perlatum (Huds.) M. Choisy collected in a pristine site of the Classic Karst (Trieste, NE Italy) were exposed for 12 weeks (August-December 2008) at that site (control, A), and in two urban sites with heavy traffic in Trieste (B) and Udine (C). Concentrations of the main gaseous pollutants were monitored by passive samplers in A (NO 2 , O 3 ), and by pollution monitoring stations in B and C (NO X , NO 2 , SO 2 , O 3 ). In the laboratory, Kautsky curves were induced under standardized conditions at species-specific PPFD values before exposure, after 6 weeks and at the end of the exposure. Significant decrease in F v /F m was only observed in P. perlatum transplants exposed in B, possibly as a consequence of the dry conditions of that site. Non-photochemical quenching (NPQ) was negatively affected in all three species, although with different intensity, in both urban sites, but more intensively in C than in B. Chl a F data shows clearly that (i) the decrease of NPQ was modulated by time exposure to NO X as well as by NO X concentration, and (ii) the species response to pollutants was related to species ecology: X. parietina, which is more nitro-and xerophytic than the other two species, tolerated better the transplant environmental conditions, confirming recent floristic observations carried out in several urban areas of Central Europe.

The main objective of this study was to evaluate the effects of drought and re-watering on 10 varieties of barley (Hordeum vulgare L.) originating from Morocco. Five varieties obtained from the National Institute of Agricultural Research (INRA) of Morocco and five landraces (local varieties defined by high stress tolerance, high yield stability, an intermediate yield and low-input demand) collected at five localities in the south of Morocco were used in the present study. After 2 weeks of growth, drought stress was initiated by withholding water for 2 weeks followed by 1 week of re-watering. The polyphasic OJIP fluorescence transient was used to evaluate photosystem II (PSII) criteria at the end of the first week of drought stress (moderate drought), at the end of the second week (severe drought) and the end of the recovery phase. Drought and re-watering had little effect on the maximum quantum yield of primary photochemistry ϕ Po (=F V /F M ). The photosynthetic performance index (PI) is the product of an antenna, reaction center and electron transport dependent parameter. It revealed differences between varieties as a function of drought and re-watering. For the screening for drought stress tolerance, changes in the PI during a 2-week drought stress treatment were analysed and a new parameter was defined: the drought factor index (DFI) = log(PI week 1 /PI control ) + 2 log(PI week 2 /PI control ). The DFI of the tested varieties correlated with their drought tolerance. Another parameter that was analysed was the relative water content. It decreased during the drought stress treatment varying between 61% and 78.2% at the end of the drought period. During the subsequent recovery period, it increased in a species-dependent manner (65.1-94.1%). A third parameter studied were changes in the initial fluorescence rise. The fluorescence rise during the first 300 s (L-band) can give information on the energetic connectivity between PSII units whereas changes in the rise during the first 2 ms (K-band) offer information on developing limitations on the donor side of PSII. Changes in respectively the L and K-bands of the fluorescence transients OJIP were shown to have predictive value with respect to the vitality of leaves and the tolerance of the varieties to drought stress.

Formate is known to cause significant inhibition in the electron and proton transfers in photosystem II (PSII); this inhibition is uniquely reversed by bicarbonate. It has been suggested that bicarbonate functions by providing ligands to the non-heme iron and by facilitating protonation of the secondary plastoquinone Q B . Numerous lines of evidence indicate an intimate relationship of bicarbonate and formate binding of PSII. To investigate the potential amino acid binding environment of bicarbonate/formate in the Q B niche, arginine 257 of the PSII D1 polypeptide in the unicellular green alga Chlamydomonas reinhardtii was mutated into a glutamate (D1-R257E) and a methionine (DQ-R257M). The two mutants share the following characteristics. (1) Both have a drastically reduced sensitivity to formate. (2) A larger fraction of Q 3 A persists after flash illumination, which indicates an altered equilibrium constant of the reaction Q 3

The relationship between CO 2 exchange and relative electron-transport rate through photosystem II (ETR, measured using chlorophyll a¯uorescence) was determined for a moss and a green algal lichen, photobiont probably Trebouxia sp., in the ®eld in Antarctica. Net photosynthesis (NP) and dark respiration (DR) were measured over temperatures from zero to 25°C and gross photosynthesis (GP) calculated (GP NP + DR). The strong response of DR to temperature in these organisms resulted in substantial changes in CO 2 exchange rates. The moss Bryum argenteum Hedw. showed a strong, linear relationship between GP and ETR. This was an unexpected result since mosses are C 3 plants and, in higher plants, this group normally has a curvilinear GP versus ETR relationship. It is suggested that suppression of DR in the light might be involved. The lichen, Umbilicaria aprina Nyl., had nonlinear relationships between ETR and GP that were dierent at each measurement temperature. In some cases the lowest ETR was at the higher CO 2 exchange rates. It is suggested that these relationships are the result of strong quenching mechanisms that are inversely proportional to GP. The results support a growing impression that the relationships between ETR and CO 2 exchange are complex in these organisms and dierent from those found for higher plants.

Four clones of robusta coffee representing drought-tolerant (14 and 120) and drought-sensitive (46 and 109A) genotypes were submitted to a slowly imposed water deficit. Sampling and measurements were performed when predawn leaf water potential (Ψ pd ) approximately −2.0 and −3.0 MPa was reached. Regardless of the clone evaluated, drought led to sharper decreases in stomatal conductance than in photosynthesis, which was accompanied by significant declines in internal to ambient CO 2 concentration ratio. Little or no effect of drought on chlorophyll a fluorescence parameters was observed. Regardless of the stress intensity, starch decreased remarkably. This was not accompanied by significant changes in concentration of soluble sugars, with the exception of clone 120 in which a rise in sucrose and hexose concentrations was found when Ψ pd reached −3.0 MPa. At Ψ pd = −2.0 MPa, activity of acid invertase increased only in clone 120; at Ψ pd = −3.0 MPa, it increased in clones 14, 46 and 120, while activity of sucrose synthase declined, but only in clone 109A. Drought-induced decrease in ADP-glucose pyrophosphorylase activity was found only in clones 14 and 46, irrespective of stress intensity. At Ψ pd = −3.0 MPa, maximal extractable and activation state of sucrose-phosphate synthase (SPS) decreased in all clones with the exception of clone 120, in which SPS activity was maintained in parallel to a rising activity of fructose-1,6-bisphosphatase. Changes in SPS activity could neither be explained by the CO 2 decrease linked to stomatal closure nor by differences in leaf water status.

In temperate climates, plants are more frequently exposed to sudden and strong decrease of temperature combined with high light intensity that compromise the photosynthetic efficiency and, often, the development and their survival. To investigate deeper the effects of such a photo-oxidative cold shock on photosynthesis of mandarin (Citrus reticulata Blanco) we used transient fluorescence analysis and gas exchange techniques. Mandarin plants were acclimated at 13 8C or grown at 25 8C for 30 days, then single leaves were exposed for 6 h at 5 8C and 1200 mmol photons m À2 s À1 and again exposed for 72 h under growth conditions. Acclimated leaves showed lower photosynthesis and higher total carotenoid contents than non-acclimated leaves. The photo-oxidative cold shock inhibited photosystem II (PSII) efficiency, as suggested by the reduction of F v /F m ratios, in all leaves. Carotenoid content was reduced in non-acclimated leaves. A time-dependent increase in the initial fluorescence level (F 0 ) and a faster decline in F v /F m ratio indicated a stronger PSII inhibition in non-acclimated leaves in comparison with acclimated leaves. The chlorophyll a fluorescence kinetic showed in all leaves complex changes in the O-J, J-I and I-P phases. The I and P steps of the fluorescence rise were particularly affected in non-acclimated leaves. Photosynthesis, fluorescence and pigment contents, measured in leaves maintained for 2 h in the dark and then returned for 72 h to growth conditions, showed a different pattern of recovery between leaves. Photosynthesis and fluorescence completely recovered in acclimated leaves after 72 h under growth conditions. On the contrary, non-acclimated leaves still showed very low values of photosynthesis and F v /F m , suppression of the sigmoidal shape of fluorescent transients and further reduction of chlorophyll contents, indicating the presence of irreversible damages to PSII and, probably, an anticipated senescence. It is suggested that carotenoids have a relevant role in protecting leaves of mandarin from the effects of a photo-oxidative cold shock. #

Aquatic primary productivity is frequently limited by the availability of nutrients. The ability to identify factors limiting algal growth is of considerable importance to our understanding of the ecology of aquatic plants and to water management practices. Methods used to identify limiting resources in the past have included a) analysis of nutrient availability, b) elemental composition and cell quotas for various nutrients, c) bio-assays monitoring growth of test species or of natural populations following nutrient enrichment and d) measurements of various physiological parameters, such as enhancement of respiration and dark carbon fixation rates and perturbation of photosynthetic rate following re-supply of nutrients.

Recycling of wood-ash to boreal forests has been suggested to prevent depletion of essential soil nutrient or reduce the negative effects of acidification of surface waters. The aim of this investigation was to study the effects of different concentrations of wood-ash (5, 10 and 12.5 g l −1 diluted in cultivating medium) on chlorophyll a fluorescence in Euglena gracilis and Chlamydomonas reinhardtii under laboratory conditions. The green alga C. reinhardtii was more susceptible to wood-ash solutions than the flagellate E. gracilis. Two different forms of wood-ash solutions were tested. In the first solution no adjustment of pH was made and after 7 days of incubation with wood-ash the pH for the different wood-ash concentrations (5, 10 and 12.5 g l −1) were 8, 9 and 11, respectively. In the second solution, the pH was adjusted to 7. The results show that no negative effect on fluorescence yield (F v /F m), relative electron transport rate (ETR), photochemical quenching (qP) or non-photochemical quenching (NPQ) was observed in E. gracilis. In contrast, C. reinhardtii displayed strong inhibition at concentrations of 10 and 12.5 g l −1 with non-adjusted pH. The negative effects of high pH on photochemical activity in C. reinhardtii could either be related to (1) the destruction of the pH across the thylakoid membranes or (2) other parts in the photosynthetic systems that are negatively affected by changing pH. The results indicate that elevated pH levels due to wood-ash application could be an environmental stress factor to phytoplankton communities and may lead to loss of diversity among primary producers in aquatic ecosystems. If wood-ash application was to become general practice in or near aquatic ecosystems a rapid change in pH induced by wood-ash must be avoided.

All photosynthetic organisms endeavour to balance energy supply with demand. For sea ice 27 diatoms, as with all marine photoautotrophs, light is the most important factor for 28 determining growth and carbon fixation rates. Light varies from extremely low to often 29 relatively high irradiances within the sea ice environment, meaning that sea ice algae require moderate physiological plasticity that is necessary for rapid light acclimation and photoprotection. This study investigated photoprotective mechanisms employed by bottom Antarctic sea ice algae in response to relatively high irradiances to understand how they acclimate to the environmental conditions presented during early spring, as the light climate begins to intensify and snow and sea ice thinning commences. The sea ice microalgae displayed high photosynthetic plasticity to increased irradiance, with a rapid decline in photochemical efficiency that was completely reversible when placed under low light. Similarly, the photoprotective xanthophyll pigment diatoxanthin (Dt) was immediately activated, but reversed during recovery under low-light. The xanthophyll inhibitor, dithiothreitol (DTT), and state transition inhibitor, sodium fluoride (NaF) were used in underice in situ incubations and revealed that non-photochemical quenching via xanthophyll cycle activation was the preferred method for light acclimation and photoprotection by bottom sea ice algae. This study showed that bottom sea ice algae from the east Antarctic possess a high level of plasticity in their light acclimation capabilities and identified the xanthophyll cycle as a critical mechanism in photoprotection and the preferred means by which sea ice diatoms regulate energy flow to PSII.

In floriculture, marketing and product distribution are critical issues for all countries. The production area and selling markets may be very far from each others with long transportation periods. The storage and packaging systems play an important role in preserving quality and reducing costs. The aim of this work was to evaluate the possibility to use vacuum packaging for storage cut Eucalyptus parvifolia Cambage foliage without compromising the ornamental quality. Experiments were performed to compare vacuum packaging system with conventional wet storage (cut branches placed in water). Vacuum packs and cut branches were placed in water and stored at 4°C for 3, 4, 5 or 6 days. After storage the vase life was evaluated at 20°C in a postharvest evaluation room. During the experiments, vase life, relative water content (RWC), chlorophyll content, chlorophyll a fluorescence and ethylene production were determined. Results showed that short time of storage in vacuum packs slightly damaged the leaves of cut eucalyptus with chlorophyll content reduction. Cut eucalyptus conventionally stored, instead, did not show chlorophyll decline. Ethylene production, a marker of stress conditions, increased with prolonged storage. Cut branches, wet or vacuum stored for 3 days, showed the same vase life and similar quality characteristics. This period of time can be sufficient for transportation of this floriculture items and vacuum packaging can be suggested as packaging system for increasing the truck loading capacity. The increase of load per unit of surface during transport gives a significant cost reduction.

Assessments of photosynthetic activity in marine plants can now be made in situ using a newly developed, submersible, pulse-amplitude modulated (PAM) fluorometer: Diving-PAM. PAM fluorometry provides a measure of chlorophyll a fluorescence using rapid-light curves in which the electron-transport rate can be determined for plants exposed to ambient light conditions. This technique was used to compare the photosynthetic responses of seagrasses near Rottnest Island, Western Australia. Several fluorescence parameters were measured as a function of time of day and water depth; electron-transport rate (ETR), quantum yield, photochemical quenching and non-photochemical quenching and Photosystem II (PSII) photochemical efficiency (F v :F m ratio) were measured. Results indicate that recent light-history plays a crucial role in seagrass photosynthetic responses. Maximum ETR of Posidonia australis, Amphibolis antarctica and Halophila ovalis is influenced by the irradiance during the diurnal cycle, with low rates at dawn and dusk (<10 μmol electron m−2 s−1), highest rates in late morning (40 to 60 μmol electron m−2 s−1) and a mid-day depression. Maximum ETR and PSII photochemical efficiency varied widely between seagrass species and were not correlated. A comparison of photochemical to non-photochemical quenching indicated that seagrasses in shallow water receiving high light have a high capacity for non-photochemical quenching (e.g. light protection) compared to seagrasses in deep water. These results indicate that in situ measurements of photosynthesis will provide new insights into the mechanisms and adaptive responses of marine plants.

Surface property distributions were mapped in the Mississippi River plume during May and August 1993 while following surface drifters. Prevailing winds were the primary factor controlling the orientation of the plume. In May, under typical southeasterly winds, the plume turned anticyclonically towards the coast, while in August, under anomalous westerly winds, the plume turned east. Remote imagery of sea surface temperature and suspended sediments confirmed the direction of the plume. Optimally interpolated maps of surface salinity, temperature, chlorophyll a fluorescence, and transmissivity from underway sampling, and periodic nutrient samples, reveal the plume structure. In May concentrations of nitrate, silicate, and phosphate decreased linearly with increasing salinity. Chlorophyll a increased to peak concentrations of 10 μg 1-1 in the plume, although higher pigment biomass was observed near the coast. In August nitrate and silicate concentrations decreased conservatively near the mouth of SW Pass, except where pigment biomass was enhanced in a convergent surface front. Surface nutrient concentrations in the plume also decreased with increasing salinity. The observations provide the first Lagrangian view of surface property distributions in the Mississippi River plume, and indicate that significant temporal variability exists in physical and biological properties within a day after waters are discharged from the river delta.

The interactions among water content, chlorophyll a fluorescence emission, xanthophyll interconversions and net photosynthesis were analyzed during dehydration in desiccation-tolerant Frullania dilatata (L.) Dum. and desiccation-intolerant Pellia endiviifolia (Dicks) Dum. Water loss led to a progressive suppression of photosynthetic carbon assimilation in both species. Their chlorophyll fluorescence characteristics at low water content were: low photosynthetic quantum conversion efficiency, high excitation pressure on photosystem II and strong non-photochemical quenching. However, dissipation activity was lower in P. endiviifolia and was not accompanied by a rise in the concentration of de-epoxidised xanthophylls as F. dilatata. The photosynthetic apparatus of F. dilatata remained fully and speedily recuperable after desiccation in as indicated by the restoration of chlorophyll fluorescence parameters to pre-desiccation values upon rehydration. A lack of recovery upon remoistening of P. endiviifolia indicated permanent and irreversible damage to photosystem II. The results suggest that F. dilatata possesses a desiccation-induced zeaxanthin-mediated photoprotective mechanism which might aid photosynthesis recovery when favourable conditions are restored by alleviating photoinhibitory damage during desiccation. This avoidance mechanism might have evolved as an adaptative response to repeated cycles of desiccation and rehydration that represent a real threat to photosynthetic viability.

Increased temperature, atmospheric CO 2 and change in precipitation patterns affect plant physiological and ecosystem processes. In combination, the interactions between these effects result in complex responses that challenge our current understanding. In a multi-factorial field experiment with elevated CO 2 (CO2, FACE), nighttime warming (T) and periodic drought (D), we investigated photosynthetic capacity and PSII performance in the evergreen dwarf shrub Calluna vulgaris and the grass Deschampsia flexuosa in a temperate heath ecosystem. Photosynthetic capacity was evaluated using A/C i curves, leaf nitrogen content and chlorophyll-a fluorescence OJIP induction curves. The PSII performance was evaluated via the total performance index PI total , which integrates the function of antenna, reaction centers, electron transport and end-acceptor reduction according to the OJIP-test.

Industrial waste substrata, rich in heavy metals, are poorly suited for plant growth. Efforts are made to establish an appropriate plant cover to reduce erosion and further contamination. Grasses are the usual solution, as they grow fast, thrive on poor substrata and have well-developed root systems. Some of them are also highly dependent on mycor-Plant Soil (2008) 305:267-280 basis of chlorophyll a fluorescence and was useful to show differences between waste substrata, inocula and coexisting plant species. The interactions between mycorrhizal and non-mycorrhizal plants were studied under greenhouse conditions and at least no negative effect of this coexistence was found.