In plants and many other organisms, phytochelatin synthase (PCS) catalyzes the synthesis of phyto... more In plants and many other organisms, phytochelatin synthase (PCS) catalyzes the synthesis of phytochelatins from glutathione in the presence of certain metals and metalloids. We have used budding yeast (Saccharomyces cerevisiae) as a heterologous system to characterize two PCS proteins, LjPCS1 and LjPCS3, of the model legume Lotus japonicus. Initial experiments revealed that the metal tolerance of yeast cells in vivo depends on the concentrations of divalent cations in the growth medium. Detailed in vivo (intact cells) and in vitro (broken cells) assays of PCS activity were performed with yeast expressing the plant enzymes, and values of phytochelatin production for each metal tested were normalized with respect to those of cadmium to correct for the lower expression level of LjPCS3. Our results showed that lead was the best activator of LjPCS1 in the in vitro assay, whereas, for both assays, arsenic, iron, and aluminum were better activators of LjPCS3 and mercury was similarly active with the two enzymes. Most interestingly, zinc was a powerful activator, especially of LjPCS3, when assayed in vivo, whereas copper and silver were the strongest activators in the in vitro assay. We conclude that the in vivo and in vitro assays are useful and complementary to assess the response of LjPCS1 and LjPCS3 to a wide range of metals and that the differences in the C-terminal domains of the two proteins are responsible for their distinct expression levels or stabilities in heterologous systems and patterns of metal activation.
• Despite the multiple roles played by antioxidants in rhizobia–legume symbioses, little is known... more • Despite the multiple roles played by antioxidants in rhizobia–legume symbioses, little is known about glutathione peroxidases (GPXs) in legumes. Here the characterization of six GPX genes of Lotus japonicus is reported.• Expression of GPX genes was analysed by quantitative reverse transcription–polymerase chain reaction in L. japonicus and Lotus corniculatus plants exposed to various treatments known to generate reactive oxygen and/or nitrogen species.• LjGPX1 and LjGPX3 were the most abundantly expressed genes in leaves, roots and nodules. Compared with roots, LjGPX1 and LjGPX6 were highly expressed in leaves and LjGPX3 and LjGPX6 in nodules. In roots, salinity decreased GPX4 expression, aluminium decreased expression of the six genes, and cadmium caused up-regulation of GPX3, GPX4 and GPX5 after 1 h and down-regulation of GPX1, GPX2, GPX4 and GPX6 after 3–24 h. Exposure of roots to sodium nitroprusside (a nitric oxide donor) for 1 h increased the mRNA levels of GPX4 and GPX6 by 3.3- and 30-fold, respectively. Thereafter, the GPX6 mRNA level remained consistently higher than that of the control. Immunogold labelling revealed the presence of GPX proteins in root and nodule amyloplasts and in leaf chloroplasts of L. japonicus and other legumes. Labelling was associated with starch grains.• These results underscore the differential regulation of GPX expression in response to cadmium, aluminium and nitric oxide, and strongly support a role for GPX6 and possibly other GPX genes in stress and/or metabolic signalling.Despite the multiple roles played by antioxidants in rhizobia–legume symbioses, little is known about glutathione peroxidases (GPXs) in legumes. Here the characterization of six GPX genes of Lotus japonicus is reported.Expression of GPX genes was analysed by quantitative reverse transcription–polymerase chain reaction in L. japonicus and Lotus corniculatus plants exposed to various treatments known to generate reactive oxygen and/or nitrogen species.LjGPX1 and LjGPX3 were the most abundantly expressed genes in leaves, roots and nodules. Compared with roots, LjGPX1 and LjGPX6 were highly expressed in leaves and LjGPX3 and LjGPX6 in nodules. In roots, salinity decreased GPX4 expression, aluminium decreased expression of the six genes, and cadmium caused up-regulation of GPX3, GPX4 and GPX5 after 1 h and down-regulation of GPX1, GPX2, GPX4 and GPX6 after 3–24 h. Exposure of roots to sodium nitroprusside (a nitric oxide donor) for 1 h increased the mRNA levels of GPX4 and GPX6 by 3.3- and 30-fold, respectively. Thereafter, the GPX6 mRNA level remained consistently higher than that of the control. Immunogold labelling revealed the presence of GPX proteins in root and nodule amyloplasts and in leaf chloroplasts of L. japonicus and other legumes. Labelling was associated with starch grains.These results underscore the differential regulation of GPX expression in response to cadmium, aluminium and nitric oxide, and strongly support a role for GPX6 and possibly other GPX genes in stress and/or metabolic signalling.
Alfalfa (Medicago sativa) plants were exposed to drought to examine the involvement of carbon met... more Alfalfa (Medicago sativa) plants were exposed to drought to examine the involvement of carbon metabolism and oxidative stress in the decline of nitrogenase (N 2 ase) activity. Exposure of plants to a moderate drought (leaf water potential of 21.3 MPa) had no effect on sucrose (Suc) synthase (SS) activity, but caused inhibition of N 2 ase activity (243%), accumulation of succinate (136%) and Suc (158%), and up-regulation of genes encoding cytosolic CuZn-superoxide dismutase (SOD), plastid FeSOD, cytosolic glutathione reductase, and bacterial MnSOD and catalases B and C. Intensification of stress (22.1 MPa) decreased N 2 ase (282%) and SS (230%) activities and increased malate (140%), succinate (168%), and Suc (1435%). There was also up-regulation (mRNA) of cytosolic ascorbate peroxidase and down-regulation (mRNA) of SS, homoglutathione synthetase, and bacterial catalase A. Drought stress did not affect nifH mRNA level or leghemoglobin expression, but decreased MoFe-and Fe-proteins. Rewatering of plants led to a partial recovery of the activity (75%) and proteins (.64%) of N 2 ase, a complete recovery of Suc, and a decrease of malate (248%) relative to control. The increase in O 2 diffusion resistance, the decrease in N 2 ase-linked respiration and N 2 ase proteins, the accumulation of respiratory substrates and oxidized lipids and proteins, and the up-regulation of antioxidant genes reveal that bacteroids have their respiratory activity impaired and that oxidative stress occurs in nodules under drought conditions prior to any detectable effect on SS or leghemoglobin. We conclude that a limitation in metabolic capacity of bacteroids and oxidative damage of cellular components are contributing factors to the inhibition of N 2 ase activity in alfalfa nodules.
The composition of antioxidant enzymes, especially superoxide dismutase (SOD), was studied in one... more The composition of antioxidant enzymes, especially superoxide dismutase (SOD), was studied in one nontransgenic and three transgenic lines of nodulated alfalfa plants. Transgenic lines overproduced MnSOD in the mitochondria of nodules and leaves (line 1-10), MnSOD in the chloroplasts (line 4-6), and FeSOD in the chloroplasts (line 10-7). In nodules of line 10-7, the absence of transgene-encoded FeSOD activity was due to a lack of mRNA, whereas in nodules of line 4-6 the absence of transgene-encoded MnSOD activity was due to enzyme inactivation or degradation. Transgenic alfalfa showed a novel compensatory effect in the activities of MnSOD (mitochondrial) and FeSOD (plastidic) in the leaves, which was not caused by changes in the mRNA levels. These findings imply that SOD activity in plant tissues and organelles is regulated, at least partially, at the posttranslational level. All four lines had low CuZnSOD activities and an abundant FeSOD isozyme, especially in nodules, indicating that FeSOD performs important antioxidant functions other than the scavenging of superoxide radicals generated in photosynthesis. This was confirmed by the detection of FeSOD cDNAs and proteins in nodules of other legumes such as cowpea, pea, and soybean. The cDNA encoding alfalfa nodule FeSOD was characterized and the deduced protein found to contain a plastid transit peptide. A comparison of sequences and other properties reveals that there are two types of FeSODs in nodules.
The antioxidant composition and relative water stress tolerance of nodulated alfalfa plants (Medi... more The antioxidant composition and relative water stress tolerance of nodulated alfalfa plants (Medicago sativa L. ¿ Sinorhizobium meliloti 102F78) of the elite genotype N4 and three derived transgenic lines have been studied in detail. These transgenic lines overproduced, respectively, Mn-containing superoxide dismutase (SOD) in the mitochondria of leaves and nodules, MnSOD in the chloroplasts, and FeSOD in the chloroplasts. In general for all lines, water stress caused moderate decreases in MnSOD and FeSOD activities in both leaves and nodules, but had distinct tissue-dependent effects on the activities of the peroxide-scavenging enzymes. During water stress, with a few exceptions, ascorbate peroxidase and
IEEE Workshop on Statistical Signal and Array Processing, 1996
We previously presented a blind 2D RAKE receiver for (direct sequence spread spectrum) CDMA that ... more We previously presented a blind 2D RAKE receiver for (direct sequence spread spectrum) CDMA that cancels strong multi-user access interference (MAI) and optimally combines multipath. After passing the output of each antenna through a matched filter based on the spreading waveform of the desired user, one estimates the signal plus interference spatio-frequency correlation matrix during that portion of the bit interval where the fingers of the RAKE occur, and the interference alone spatio-frequency correlation matrix during that portion of the bit interval away from the fingers. A reduced complexity scheme that outperforms the previous algorithm in a MAI dominant environment is presented based on a data adaptive transformation to a beamspace of dimension equal to the effective number of spatial degrees of freedom taken up by the desired user's multipath
Asilomar Conference on Signals, Systems & Computers, 1995
A blind adoptive beamforming scheme is developed for CDMA that cancels strong multi-user access i... more A blind adoptive beamforming scheme is developed for CDMA that cancels strong multi-user access interference and optimally combines multipath based on the following observation: after passing the output of each antenna through a matched filter corresponding to the PN sequence of the desired user, one can isolate periods of time when the cochannel interference dominates. This allows one to estimate the spatio-frequency correlation matrix of the co-channel interference alone. The weight vector yielding the optimum signal to interference plus noise ratio for bit decisions is the "largest" generalised eigenvector of the signal plus interference spatio-frequency correlation matrix in the metric of the spatio frequency correlation matrix of the co-channel interference alone. Simulations are presented demonstrating the efficacy of the procedure.
We previously presented a blind 2D RAKE receiver for CDMA that cancels strong multi-user access i... more We previously presented a blind 2D RAKE receiver for CDMA that cancels strong multi-user access interference and optimally combines the desired user's multipath. After passing the output of each antenna through a matched filter based on the spreading waveform of the desired user, one estimates the signal plus interference space-frequency (space-time) correlation matrix during that portion of the bit interval where the fingers of the RAKE occur, and the interference alone space-frequency (space-time) correlation matrix during that portion of the bit interval away from the fingers. The vector of space-frequency (space-time) weights yielding the optimum signal to interference plus noise ratio for bit decisions is the “largest” generalized eigenvector of the resulting matrix pencil. A reduced complexity scheme was also previously presented based on a data adaptive transformation to a beamspace of dimension equal to the effective number of spatial degrees of freedom taken up by the desired user's multipath. A decision directed adaptation of this scheme for a commercial cellular CDMA system based on the IS-95 standard is presented herein. Only the uplink from mobile to base is considered
Accurate channel state information and time/frequency synchronization are challenging to acquire ... more Accurate channel state information and time/frequency synchronization are challenging to acquire in mobile ad hoc cooperative set-ups, where resource-constrained relaying terminals rapidly (dis)join cooperation. This paper derives low-complexity differential modulations and cooperative transmission schemes so that detection at the receiver is feasible without channel knowledge or synchronization information. A simple distributed doubly-differential (DD) time-division multiplexing (TDM) scheme using diagonal spacetime (ST) unitary codes is derived to bypass multiple carrier frequency offsets (CFOs) and collect space diversity. Precoded differential orthogonal frequency division multiplexing (OFDM) transmissions are derived to additionally bypass timing offsets and collect multipath diversity using either DD diagonal or single-differential (SD) orthogonal ST block codes (OSTBCs). DD diagonal mappings suffer from considerable coding gain and signal-to-noise ratio (SNR) loss due to unitary constellation constraints and noise enhancement at the receiver. SD-OSTBCs achieve higher performance with reduced decoding complexity, at the cost of reduced CFO mitigation range. Simple and robust non-coherent selective and adaptive transmissions are also included, showing that full space and multipath diversity can still be achieved even with decoding errors at relays. Simulations corroborate theoretical claims.
Space technology and applications international forum (STAIF - 97), 1997
ABSTRACT A novel wideband beamforming technique for cellular CDMA systems is presented. The propo... more ABSTRACT A novel wideband beamforming technique for cellular CDMA systems is presented. The proposed algorithm asymptotically provides the optimum combination of space-time samples for maximizing the SINR for the {ital Signal with the Desired Code} (SDC) by canceling strong {ital Multi-User Access Interference} (MUAI) and optimally combining the multipath. In contrast to previously proposed techniques, bit synchronization for the SDC is not required. The algorithm presented herein asymptotically provides the respective time of arrivals of the multipaths within a bit period, and the optimum beamformers for extracting each multipath. Subsequently space-time weights for combining the fingers across both space and time while canceling the MUAIs are found. {copyright} {ital 1997 American Institute of Physics.}
IEEE GLOBECOM 2007-2007 IEEE Global Telecommunications Conference, 2007
When a terminal is recruited to cooperate with other neighboring terminals, its channel state and... more When a terminal is recruited to cooperate with other neighboring terminals, its channel state and carrier frequency offset (CFO) may be unknown to the destination. Under these circumstances, this paper considers the use of distributed double-differential (DD) modulation, which simplifies receiver implementation because it by-passes channel and CFO estimation. Two double-differential codecs are proposed transmitting: i) across orthogonal channels using time-division multiplexing, achieving rate and error performance similar to that of co-located multi-antenna DD systems; or ii) simultaneously, benefiting from the distinct CFOs across terminals and bypassing the need of ordering protocols. Both (i)-(ii) approaches are considered in adaptive-and selective-relaying cooperation protocols demonstrating that maximum spatial diversity is achievable. Simulations corroborate the theoretical error performance claims.
This article addresses the simultaneous estimation of the azimuth and elevation angles of multipl... more This article addresses the simultaneous estimation of the azimuth and elevation angles of multiple co-channel signals incident upon an array of antennas. A new closed-form algorithm that is applicable with filled circular arrays (FCAs) is presented. The algorithm, which is called FCA-ESPRIT, is applicable with any FCA geometry, e.g., FCAs constructed using rectangular, hexagonal, polar, or random sampling lattices. The only constraint imposed on the FCA geometry is that the spacing between adjacent sensors should be half a wavelength or less on average across the entire aperture. The algorithm provides automatically paired azimuth and elevation angle estimates by solving a set of ESPRIT-like equations wherein the unknowns have the form sin(θ i)ejφ(i) (where θi and φ i are the elevation and azimuth angles of the ith source, respectively). The algorithm provides arrival angle estimates via a closed-form procedure-it does not require computationally expensive search or optimization procedures
IEEE Transactions on Wireless Communications, 2007
We consider broadcasting to multiple destinations with uneven quality receivers. Based on their q... more We consider broadcasting to multiple destinations with uneven quality receivers. Based on their quality of reception, we group destinations in tiers and transmit using hierarchical modulations. These modulations are known to offer a practical means of achieving variable error protection of the broadcasted information to receivers of variable quality. After the initial broadcasting step, tiers successively rebroadcast part of the information they received from tiers of higher-quality to tiers with lower reception capabilities. This multi-tier cooperative broadcasting strategy can accommodate variable rate and error performance for different tiers but requires complex demodulation steps. To cope with this complexity in demodulation, we derive simplified pertier detection schemes with performance close to maximumlikelihood and ability to collect the diversity provided as symbols propagate through diversified channels across successive broadcastings. Error performance is analyzed and compared to (non)-cooperative broadcasting strategies. Simulations corroborate our theoretical findings.
An algorithm is presented for estimating the quantities needed by a space-time RAKE receiver for ... more An algorithm is presented for estimating the quantities needed by a space-time RAKE receiver for DS-CDMA to achieve maximum SINR for the desired user. The proposed algorithm, which is applicable in the case of either periodic or aperiodic spreading codes, asymptotically provides the exact time of arrival of each dominant multipath within a bit period, and the optimum beamformer for extracting each multipath. This is achieved by using cyclostationarity to exploit the difference between the respective spectra of the desired user and each multiuser access interferer at the output of the correlator based on the desired user's code. Estimates of the relative time delay and optimal beamformer for each RAKE finger are used by the spacetime RAKE receiver to optimally combine the desired user's multipath while simultaneously canceling strong multiuser access interference. Simulations of a near-far scenario are presented demonstrating the efficacy of the proposed algorithm.
International Conference on Acoustics, Speech, and Signal Processing, 1995
The problem addressed is that of narrowband digital cellular communications in the presence of mu... more The problem addressed is that of narrowband digital cellular communications in the presence of multipath and co-channel interferers having the same symbol rate and same overall signal characteristics as the desired source. For a given signal source, an algorithm is presented for blindly estimating the weight vector yielding the optimum SINR at the beamformer output. The instrumental quantity, denoted Sxx(f), is the Fourier transform of the expected value of the zero-lag autocorrelation matrix for one symbol period. The proposed scheme employs the PRO-ESPRIT algorithm to exploit the relationship between the timing offset and optimum beamforming weight vector for each source and the principal generalized eigenvalues and eigenvectors of the matrix pencil {Sxx(1/T0), Sxx(O)}, where 1/T0 is the symbol rate. Simulations are presented showing the rapid convergence of the algorithm and an improvement of several dB over the subspace-constrained Phase-SCORE algorithm
International Conference on Acoustics, Speech, and Signal Processing, 1997
A novel wideband beamforming technique for cellular CDMA systems is presented. The proposed algor... more A novel wideband beamforming technique for cellular CDMA systems is presented. The proposed algorithm asymptotically provides the optimum combination of space-time samples to maximize the SINR for the signal with the desired code (SDC) by optimally combining its multipath and canceling strong multiuser access interference (MUAI). In contrast to previously proposed techniques, code synchronization for the SDC is not required. The algorithm presented asymptotically provides the exact time of arrivals of the multipaths within a bit period, and subsequently the optimum space-time weights for combining the fingers across both space and time. The instrumental property exploited in this technique is the fact that although the respective spectra of the SDC and MUAI components at the output of the matched filter are statistically equal, the respective spectra of their squared values differ
International Conference on Acoustics, Speech, and Signal Processing, 1996
We previously presented a blind 2D RAKE receiver for CDMA that cancels strong multi-user access i... more We previously presented a blind 2D RAKE receiver for CDMA that cancels strong multi-user access interference and optimally combines multipath. After passing the output of each antenna through a matched filter based on the spreading waveform of the desired user, one estimates the signal plus interference spatio-frequency correlation matrix during that portion of the bit interval where the fingers of the RAKE occur, and the interference alone spatio-frequency correlation matrix during that portion of the bit interval away from the fingers. The weight vector yielding the optimum signal to interference plus noise ratio for bit decisions is the “largest” generalized eigenvector of the resulting matrix pencil. However, even when the number of elements comprising the array is relatively small, this spatio-frequency correlation matrix pencil is of large dimension. In addition to detracting from the real-time applicability of the scheme, this slows up the time to convergence. A reduced complexity scheme is presented based on a data adaptive transformation to a beamspace of dimension equal to the effective number of spatial degrees of freedom taken up by the desired user's multipath
We discuss a new approach to self-organization that leads to novel adaptive algorithms for genera... more We discuss a new approach to self-organization that leads to novel adaptive algorithms for generalized eigen-decomposition and its variance for a single-layer linear feedforward neural network. First, we derive two novel iterative algorithms for linear discriminant analysis (LDA) and generalized eigen-decomposition by utilizing a constrained least-mean-squared classification error cost function, and the framework of a two-layer linear heteroassociative network performing a one-of-m classification. By using the concept of deflation, we are able to find sequential versions of these algorithms which extract the LDA components and generalized eigenvectors in a decreasing order of significance. Next, two new adaptive algorithms are described to compute the principal generalized eigenvectors of two matrices (as well as LDA) from two sequences of random matrices. We give a rigorous convergence analysis of our adaptive algorithms by using stochastic approximation theory, and prove that our algorithms converge with probability one.
Blind space-time RAKE receivers for classical DS-CDMA that cancel strong multiuser access interfe... more Blind space-time RAKE receivers for classical DS-CDMA that cancel strong multiuser access interference while optimally combining the desired user's multipath are presented. The delay spread is assumed to be fraction of a symbol interval as in the IS-95 CDMA standard. The post-correlation symbol interval is segmented into that which encompasses the RAKE fingers and that away from the RAKE fingers. The signal-plus-interference and interference-alone space-time correlation matrices are estimated during the former and latter, respectively. Reduced-dimension space-time RAKE receivers are investigated for alleviation of the computational burden of computing the largest generalized eigenvector of the resulting matrix pencil. Theoretical analysis and supporting simulations reveal that if the space and time compressing transformations are designed judiciously, reduced-dimension two-dimensional (2-D) RAKE receivers offer faster convergence at the expense of only a slight loss in asymptotic signal-to-interference-plus-noise ratio (SINR) relative to the full-dimension space-time RAKE receiver. Applications to the IS-95 uplink are also presented along with supporting simulations.
In plants and many other organisms, phytochelatin synthase (PCS) catalyzes the synthesis of phyto... more In plants and many other organisms, phytochelatin synthase (PCS) catalyzes the synthesis of phytochelatins from glutathione in the presence of certain metals and metalloids. We have used budding yeast (Saccharomyces cerevisiae) as a heterologous system to characterize two PCS proteins, LjPCS1 and LjPCS3, of the model legume Lotus japonicus. Initial experiments revealed that the metal tolerance of yeast cells in vivo depends on the concentrations of divalent cations in the growth medium. Detailed in vivo (intact cells) and in vitro (broken cells) assays of PCS activity were performed with yeast expressing the plant enzymes, and values of phytochelatin production for each metal tested were normalized with respect to those of cadmium to correct for the lower expression level of LjPCS3. Our results showed that lead was the best activator of LjPCS1 in the in vitro assay, whereas, for both assays, arsenic, iron, and aluminum were better activators of LjPCS3 and mercury was similarly active with the two enzymes. Most interestingly, zinc was a powerful activator, especially of LjPCS3, when assayed in vivo, whereas copper and silver were the strongest activators in the in vitro assay. We conclude that the in vivo and in vitro assays are useful and complementary to assess the response of LjPCS1 and LjPCS3 to a wide range of metals and that the differences in the C-terminal domains of the two proteins are responsible for their distinct expression levels or stabilities in heterologous systems and patterns of metal activation.
• Despite the multiple roles played by antioxidants in rhizobia–legume symbioses, little is known... more • Despite the multiple roles played by antioxidants in rhizobia–legume symbioses, little is known about glutathione peroxidases (GPXs) in legumes. Here the characterization of six GPX genes of Lotus japonicus is reported.• Expression of GPX genes was analysed by quantitative reverse transcription–polymerase chain reaction in L. japonicus and Lotus corniculatus plants exposed to various treatments known to generate reactive oxygen and/or nitrogen species.• LjGPX1 and LjGPX3 were the most abundantly expressed genes in leaves, roots and nodules. Compared with roots, LjGPX1 and LjGPX6 were highly expressed in leaves and LjGPX3 and LjGPX6 in nodules. In roots, salinity decreased GPX4 expression, aluminium decreased expression of the six genes, and cadmium caused up-regulation of GPX3, GPX4 and GPX5 after 1 h and down-regulation of GPX1, GPX2, GPX4 and GPX6 after 3–24 h. Exposure of roots to sodium nitroprusside (a nitric oxide donor) for 1 h increased the mRNA levels of GPX4 and GPX6 by 3.3- and 30-fold, respectively. Thereafter, the GPX6 mRNA level remained consistently higher than that of the control. Immunogold labelling revealed the presence of GPX proteins in root and nodule amyloplasts and in leaf chloroplasts of L. japonicus and other legumes. Labelling was associated with starch grains.• These results underscore the differential regulation of GPX expression in response to cadmium, aluminium and nitric oxide, and strongly support a role for GPX6 and possibly other GPX genes in stress and/or metabolic signalling.Despite the multiple roles played by antioxidants in rhizobia–legume symbioses, little is known about glutathione peroxidases (GPXs) in legumes. Here the characterization of six GPX genes of Lotus japonicus is reported.Expression of GPX genes was analysed by quantitative reverse transcription–polymerase chain reaction in L. japonicus and Lotus corniculatus plants exposed to various treatments known to generate reactive oxygen and/or nitrogen species.LjGPX1 and LjGPX3 were the most abundantly expressed genes in leaves, roots and nodules. Compared with roots, LjGPX1 and LjGPX6 were highly expressed in leaves and LjGPX3 and LjGPX6 in nodules. In roots, salinity decreased GPX4 expression, aluminium decreased expression of the six genes, and cadmium caused up-regulation of GPX3, GPX4 and GPX5 after 1 h and down-regulation of GPX1, GPX2, GPX4 and GPX6 after 3–24 h. Exposure of roots to sodium nitroprusside (a nitric oxide donor) for 1 h increased the mRNA levels of GPX4 and GPX6 by 3.3- and 30-fold, respectively. Thereafter, the GPX6 mRNA level remained consistently higher than that of the control. Immunogold labelling revealed the presence of GPX proteins in root and nodule amyloplasts and in leaf chloroplasts of L. japonicus and other legumes. Labelling was associated with starch grains.These results underscore the differential regulation of GPX expression in response to cadmium, aluminium and nitric oxide, and strongly support a role for GPX6 and possibly other GPX genes in stress and/or metabolic signalling.
Alfalfa (Medicago sativa) plants were exposed to drought to examine the involvement of carbon met... more Alfalfa (Medicago sativa) plants were exposed to drought to examine the involvement of carbon metabolism and oxidative stress in the decline of nitrogenase (N 2 ase) activity. Exposure of plants to a moderate drought (leaf water potential of 21.3 MPa) had no effect on sucrose (Suc) synthase (SS) activity, but caused inhibition of N 2 ase activity (243%), accumulation of succinate (136%) and Suc (158%), and up-regulation of genes encoding cytosolic CuZn-superoxide dismutase (SOD), plastid FeSOD, cytosolic glutathione reductase, and bacterial MnSOD and catalases B and C. Intensification of stress (22.1 MPa) decreased N 2 ase (282%) and SS (230%) activities and increased malate (140%), succinate (168%), and Suc (1435%). There was also up-regulation (mRNA) of cytosolic ascorbate peroxidase and down-regulation (mRNA) of SS, homoglutathione synthetase, and bacterial catalase A. Drought stress did not affect nifH mRNA level or leghemoglobin expression, but decreased MoFe-and Fe-proteins. Rewatering of plants led to a partial recovery of the activity (75%) and proteins (.64%) of N 2 ase, a complete recovery of Suc, and a decrease of malate (248%) relative to control. The increase in O 2 diffusion resistance, the decrease in N 2 ase-linked respiration and N 2 ase proteins, the accumulation of respiratory substrates and oxidized lipids and proteins, and the up-regulation of antioxidant genes reveal that bacteroids have their respiratory activity impaired and that oxidative stress occurs in nodules under drought conditions prior to any detectable effect on SS or leghemoglobin. We conclude that a limitation in metabolic capacity of bacteroids and oxidative damage of cellular components are contributing factors to the inhibition of N 2 ase activity in alfalfa nodules.
The composition of antioxidant enzymes, especially superoxide dismutase (SOD), was studied in one... more The composition of antioxidant enzymes, especially superoxide dismutase (SOD), was studied in one nontransgenic and three transgenic lines of nodulated alfalfa plants. Transgenic lines overproduced MnSOD in the mitochondria of nodules and leaves (line 1-10), MnSOD in the chloroplasts (line 4-6), and FeSOD in the chloroplasts (line 10-7). In nodules of line 10-7, the absence of transgene-encoded FeSOD activity was due to a lack of mRNA, whereas in nodules of line 4-6 the absence of transgene-encoded MnSOD activity was due to enzyme inactivation or degradation. Transgenic alfalfa showed a novel compensatory effect in the activities of MnSOD (mitochondrial) and FeSOD (plastidic) in the leaves, which was not caused by changes in the mRNA levels. These findings imply that SOD activity in plant tissues and organelles is regulated, at least partially, at the posttranslational level. All four lines had low CuZnSOD activities and an abundant FeSOD isozyme, especially in nodules, indicating that FeSOD performs important antioxidant functions other than the scavenging of superoxide radicals generated in photosynthesis. This was confirmed by the detection of FeSOD cDNAs and proteins in nodules of other legumes such as cowpea, pea, and soybean. The cDNA encoding alfalfa nodule FeSOD was characterized and the deduced protein found to contain a plastid transit peptide. A comparison of sequences and other properties reveals that there are two types of FeSODs in nodules.
The antioxidant composition and relative water stress tolerance of nodulated alfalfa plants (Medi... more The antioxidant composition and relative water stress tolerance of nodulated alfalfa plants (Medicago sativa L. ¿ Sinorhizobium meliloti 102F78) of the elite genotype N4 and three derived transgenic lines have been studied in detail. These transgenic lines overproduced, respectively, Mn-containing superoxide dismutase (SOD) in the mitochondria of leaves and nodules, MnSOD in the chloroplasts, and FeSOD in the chloroplasts. In general for all lines, water stress caused moderate decreases in MnSOD and FeSOD activities in both leaves and nodules, but had distinct tissue-dependent effects on the activities of the peroxide-scavenging enzymes. During water stress, with a few exceptions, ascorbate peroxidase and
IEEE Workshop on Statistical Signal and Array Processing, 1996
We previously presented a blind 2D RAKE receiver for (direct sequence spread spectrum) CDMA that ... more We previously presented a blind 2D RAKE receiver for (direct sequence spread spectrum) CDMA that cancels strong multi-user access interference (MAI) and optimally combines multipath. After passing the output of each antenna through a matched filter based on the spreading waveform of the desired user, one estimates the signal plus interference spatio-frequency correlation matrix during that portion of the bit interval where the fingers of the RAKE occur, and the interference alone spatio-frequency correlation matrix during that portion of the bit interval away from the fingers. A reduced complexity scheme that outperforms the previous algorithm in a MAI dominant environment is presented based on a data adaptive transformation to a beamspace of dimension equal to the effective number of spatial degrees of freedom taken up by the desired user's multipath
Asilomar Conference on Signals, Systems & Computers, 1995
A blind adoptive beamforming scheme is developed for CDMA that cancels strong multi-user access i... more A blind adoptive beamforming scheme is developed for CDMA that cancels strong multi-user access interference and optimally combines multipath based on the following observation: after passing the output of each antenna through a matched filter corresponding to the PN sequence of the desired user, one can isolate periods of time when the cochannel interference dominates. This allows one to estimate the spatio-frequency correlation matrix of the co-channel interference alone. The weight vector yielding the optimum signal to interference plus noise ratio for bit decisions is the "largest" generalised eigenvector of the signal plus interference spatio-frequency correlation matrix in the metric of the spatio frequency correlation matrix of the co-channel interference alone. Simulations are presented demonstrating the efficacy of the procedure.
We previously presented a blind 2D RAKE receiver for CDMA that cancels strong multi-user access i... more We previously presented a blind 2D RAKE receiver for CDMA that cancels strong multi-user access interference and optimally combines the desired user's multipath. After passing the output of each antenna through a matched filter based on the spreading waveform of the desired user, one estimates the signal plus interference space-frequency (space-time) correlation matrix during that portion of the bit interval where the fingers of the RAKE occur, and the interference alone space-frequency (space-time) correlation matrix during that portion of the bit interval away from the fingers. The vector of space-frequency (space-time) weights yielding the optimum signal to interference plus noise ratio for bit decisions is the “largest” generalized eigenvector of the resulting matrix pencil. A reduced complexity scheme was also previously presented based on a data adaptive transformation to a beamspace of dimension equal to the effective number of spatial degrees of freedom taken up by the desired user's multipath. A decision directed adaptation of this scheme for a commercial cellular CDMA system based on the IS-95 standard is presented herein. Only the uplink from mobile to base is considered
Accurate channel state information and time/frequency synchronization are challenging to acquire ... more Accurate channel state information and time/frequency synchronization are challenging to acquire in mobile ad hoc cooperative set-ups, where resource-constrained relaying terminals rapidly (dis)join cooperation. This paper derives low-complexity differential modulations and cooperative transmission schemes so that detection at the receiver is feasible without channel knowledge or synchronization information. A simple distributed doubly-differential (DD) time-division multiplexing (TDM) scheme using diagonal spacetime (ST) unitary codes is derived to bypass multiple carrier frequency offsets (CFOs) and collect space diversity. Precoded differential orthogonal frequency division multiplexing (OFDM) transmissions are derived to additionally bypass timing offsets and collect multipath diversity using either DD diagonal or single-differential (SD) orthogonal ST block codes (OSTBCs). DD diagonal mappings suffer from considerable coding gain and signal-to-noise ratio (SNR) loss due to unitary constellation constraints and noise enhancement at the receiver. SD-OSTBCs achieve higher performance with reduced decoding complexity, at the cost of reduced CFO mitigation range. Simple and robust non-coherent selective and adaptive transmissions are also included, showing that full space and multipath diversity can still be achieved even with decoding errors at relays. Simulations corroborate theoretical claims.
Space technology and applications international forum (STAIF - 97), 1997
ABSTRACT A novel wideband beamforming technique for cellular CDMA systems is presented. The propo... more ABSTRACT A novel wideband beamforming technique for cellular CDMA systems is presented. The proposed algorithm asymptotically provides the optimum combination of space-time samples for maximizing the SINR for the {ital Signal with the Desired Code} (SDC) by canceling strong {ital Multi-User Access Interference} (MUAI) and optimally combining the multipath. In contrast to previously proposed techniques, bit synchronization for the SDC is not required. The algorithm presented herein asymptotically provides the respective time of arrivals of the multipaths within a bit period, and the optimum beamformers for extracting each multipath. Subsequently space-time weights for combining the fingers across both space and time while canceling the MUAIs are found. {copyright} {ital 1997 American Institute of Physics.}
IEEE GLOBECOM 2007-2007 IEEE Global Telecommunications Conference, 2007
When a terminal is recruited to cooperate with other neighboring terminals, its channel state and... more When a terminal is recruited to cooperate with other neighboring terminals, its channel state and carrier frequency offset (CFO) may be unknown to the destination. Under these circumstances, this paper considers the use of distributed double-differential (DD) modulation, which simplifies receiver implementation because it by-passes channel and CFO estimation. Two double-differential codecs are proposed transmitting: i) across orthogonal channels using time-division multiplexing, achieving rate and error performance similar to that of co-located multi-antenna DD systems; or ii) simultaneously, benefiting from the distinct CFOs across terminals and bypassing the need of ordering protocols. Both (i)-(ii) approaches are considered in adaptive-and selective-relaying cooperation protocols demonstrating that maximum spatial diversity is achievable. Simulations corroborate the theoretical error performance claims.
This article addresses the simultaneous estimation of the azimuth and elevation angles of multipl... more This article addresses the simultaneous estimation of the azimuth and elevation angles of multiple co-channel signals incident upon an array of antennas. A new closed-form algorithm that is applicable with filled circular arrays (FCAs) is presented. The algorithm, which is called FCA-ESPRIT, is applicable with any FCA geometry, e.g., FCAs constructed using rectangular, hexagonal, polar, or random sampling lattices. The only constraint imposed on the FCA geometry is that the spacing between adjacent sensors should be half a wavelength or less on average across the entire aperture. The algorithm provides automatically paired azimuth and elevation angle estimates by solving a set of ESPRIT-like equations wherein the unknowns have the form sin(θ i)ejφ(i) (where θi and φ i are the elevation and azimuth angles of the ith source, respectively). The algorithm provides arrival angle estimates via a closed-form procedure-it does not require computationally expensive search or optimization procedures
IEEE Transactions on Wireless Communications, 2007
We consider broadcasting to multiple destinations with uneven quality receivers. Based on their q... more We consider broadcasting to multiple destinations with uneven quality receivers. Based on their quality of reception, we group destinations in tiers and transmit using hierarchical modulations. These modulations are known to offer a practical means of achieving variable error protection of the broadcasted information to receivers of variable quality. After the initial broadcasting step, tiers successively rebroadcast part of the information they received from tiers of higher-quality to tiers with lower reception capabilities. This multi-tier cooperative broadcasting strategy can accommodate variable rate and error performance for different tiers but requires complex demodulation steps. To cope with this complexity in demodulation, we derive simplified pertier detection schemes with performance close to maximumlikelihood and ability to collect the diversity provided as symbols propagate through diversified channels across successive broadcastings. Error performance is analyzed and compared to (non)-cooperative broadcasting strategies. Simulations corroborate our theoretical findings.
An algorithm is presented for estimating the quantities needed by a space-time RAKE receiver for ... more An algorithm is presented for estimating the quantities needed by a space-time RAKE receiver for DS-CDMA to achieve maximum SINR for the desired user. The proposed algorithm, which is applicable in the case of either periodic or aperiodic spreading codes, asymptotically provides the exact time of arrival of each dominant multipath within a bit period, and the optimum beamformer for extracting each multipath. This is achieved by using cyclostationarity to exploit the difference between the respective spectra of the desired user and each multiuser access interferer at the output of the correlator based on the desired user's code. Estimates of the relative time delay and optimal beamformer for each RAKE finger are used by the spacetime RAKE receiver to optimally combine the desired user's multipath while simultaneously canceling strong multiuser access interference. Simulations of a near-far scenario are presented demonstrating the efficacy of the proposed algorithm.
International Conference on Acoustics, Speech, and Signal Processing, 1995
The problem addressed is that of narrowband digital cellular communications in the presence of mu... more The problem addressed is that of narrowband digital cellular communications in the presence of multipath and co-channel interferers having the same symbol rate and same overall signal characteristics as the desired source. For a given signal source, an algorithm is presented for blindly estimating the weight vector yielding the optimum SINR at the beamformer output. The instrumental quantity, denoted Sxx(f), is the Fourier transform of the expected value of the zero-lag autocorrelation matrix for one symbol period. The proposed scheme employs the PRO-ESPRIT algorithm to exploit the relationship between the timing offset and optimum beamforming weight vector for each source and the principal generalized eigenvalues and eigenvectors of the matrix pencil {Sxx(1/T0), Sxx(O)}, where 1/T0 is the symbol rate. Simulations are presented showing the rapid convergence of the algorithm and an improvement of several dB over the subspace-constrained Phase-SCORE algorithm
International Conference on Acoustics, Speech, and Signal Processing, 1997
A novel wideband beamforming technique for cellular CDMA systems is presented. The proposed algor... more A novel wideband beamforming technique for cellular CDMA systems is presented. The proposed algorithm asymptotically provides the optimum combination of space-time samples to maximize the SINR for the signal with the desired code (SDC) by optimally combining its multipath and canceling strong multiuser access interference (MUAI). In contrast to previously proposed techniques, code synchronization for the SDC is not required. The algorithm presented asymptotically provides the exact time of arrivals of the multipaths within a bit period, and subsequently the optimum space-time weights for combining the fingers across both space and time. The instrumental property exploited in this technique is the fact that although the respective spectra of the SDC and MUAI components at the output of the matched filter are statistically equal, the respective spectra of their squared values differ
International Conference on Acoustics, Speech, and Signal Processing, 1996
We previously presented a blind 2D RAKE receiver for CDMA that cancels strong multi-user access i... more We previously presented a blind 2D RAKE receiver for CDMA that cancels strong multi-user access interference and optimally combines multipath. After passing the output of each antenna through a matched filter based on the spreading waveform of the desired user, one estimates the signal plus interference spatio-frequency correlation matrix during that portion of the bit interval where the fingers of the RAKE occur, and the interference alone spatio-frequency correlation matrix during that portion of the bit interval away from the fingers. The weight vector yielding the optimum signal to interference plus noise ratio for bit decisions is the “largest” generalized eigenvector of the resulting matrix pencil. However, even when the number of elements comprising the array is relatively small, this spatio-frequency correlation matrix pencil is of large dimension. In addition to detracting from the real-time applicability of the scheme, this slows up the time to convergence. A reduced complexity scheme is presented based on a data adaptive transformation to a beamspace of dimension equal to the effective number of spatial degrees of freedom taken up by the desired user's multipath
We discuss a new approach to self-organization that leads to novel adaptive algorithms for genera... more We discuss a new approach to self-organization that leads to novel adaptive algorithms for generalized eigen-decomposition and its variance for a single-layer linear feedforward neural network. First, we derive two novel iterative algorithms for linear discriminant analysis (LDA) and generalized eigen-decomposition by utilizing a constrained least-mean-squared classification error cost function, and the framework of a two-layer linear heteroassociative network performing a one-of-m classification. By using the concept of deflation, we are able to find sequential versions of these algorithms which extract the LDA components and generalized eigenvectors in a decreasing order of significance. Next, two new adaptive algorithms are described to compute the principal generalized eigenvectors of two matrices (as well as LDA) from two sequences of random matrices. We give a rigorous convergence analysis of our adaptive algorithms by using stochastic approximation theory, and prove that our algorithms converge with probability one.
Blind space-time RAKE receivers for classical DS-CDMA that cancel strong multiuser access interfe... more Blind space-time RAKE receivers for classical DS-CDMA that cancel strong multiuser access interference while optimally combining the desired user's multipath are presented. The delay spread is assumed to be fraction of a symbol interval as in the IS-95 CDMA standard. The post-correlation symbol interval is segmented into that which encompasses the RAKE fingers and that away from the RAKE fingers. The signal-plus-interference and interference-alone space-time correlation matrices are estimated during the former and latter, respectively. Reduced-dimension space-time RAKE receivers are investigated for alleviation of the computational burden of computing the largest generalized eigenvector of the resulting matrix pencil. Theoretical analysis and supporting simulations reveal that if the space and time compressing transformations are designed judiciously, reduced-dimension two-dimensional (2-D) RAKE receivers offer faster convergence at the expense of only a slight loss in asymptotic signal-to-interference-plus-noise ratio (SINR) relative to the full-dimension space-time RAKE receiver. Applications to the IS-95 uplink are also presented along with supporting simulations.
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Papers by Javier Ramos