An mRNA species, HVA1, has been shown to be rapidly induced by abscisic acid (ABA) in barley aleu... more An mRNA species, HVA1, has been shown to be rapidly induced by abscisic acid (ABA) in barley aleurone layers (Hong, Uknes and Ho, Plant Mol Biol 11: 495-506, 1988). In the current work we have investigated the expression of riVAl in other organs of barley plants. In developing seeds, HVA1 mRNA is not detected in starchy endosperm cells, yet it accumulates in aleurone layers and embryo starting 25 days after anthesis, and its level remains high in these organs in dry seeds. Although the levels of HVA1 mRNA are equivalent in the dry embryos of dormant and nondormant barley seeds, upon imbibition HVA1 mRNA declines much slower in the dormant than in the nondormant embryos. The HVA1 mRNA and protein levels are highly induced by ABA treatment in all organs of 3-day-old seedlings. However, the induction in the leaf of 7-day-old seedlings is less than one tenth the level observed in the leaf of 3-day-old seedlings. In the leaf, HVA1 mRNA and protein are induced mainly at the base. These observations indicate that the expression of HVA 1 is under developmental regulation. Besides the HVA 1 protein, a smaller protein (p20) of approximately 20 kDa cross-reacting with anti-HVA1 polyclonal antibodies, is induced by ABA in barley seedlings but not in seeds. HVA1 mRNA is induced by drought, NaC1, cold or heat treatment. Similar to ABA treatment, the drought induction of HVA1 occurs in all the tissues of 3-day-old seedlings, but the induction decreases dramatically in the leaf of 7-day-old plants. The significance of organ-specific, developmentally regulated, and stress-induced expression of HVA1 is discussed.
ABSTRACT Lowering the sucrose content in the medium causes a decrease in growth of tobacco callus... more ABSTRACT Lowering the sucrose content in the medium causes a decrease in growth of tobacco callus cultures. At low sucrose concentrations the cultures developed a darker-green color, and produced a higher number of shoots in a shorter time. The shoots formed were of improved morphology. Our results might indicate that the osmolarity of the medium affects both greening and shoot formation in some tobacco callus cultures. Some differences were found between genetic lines in their responses to the shoot inducing media.
ABSTRACT The effects of amitrole on four tobacco lines were studied, using two biological systems... more ABSTRACT The effects of amitrole on four tobacco lines were studied, using two biological systems: germinating seeds and tissue cultures. Both differentiating and non-differentiating cultures were employed. Similar herbicide concentrations (2.5–7.5 × 10−5 M) caused bleaching and inhibited growth and differentiation in both systems. Evidences were found, supporting the notion that amitrole has several modes of action. Putative amitrole resistant mutants were isolated from differentiating and non-differentiating calli. These mutants exhibited various phenotypes of resistance. The advantages of plants' tissue cultures for selecting herbicide resistant mutants are demonstrated and discussed.
In order to study genes involved in latestages of flower development, we wereinterested in isolat... more In order to study genes involved in latestages of flower development, we wereinterested in isolating petal- orstamen-specific genes, particularly onesexpressed at a low level, as they mayinclude regulatory genes. To this end, asubtracted and equalized cDNA library oftomato petals and stamens was constructed.Approximately 650 clones of this librarywere found to represent 84 different genes.Northern analyses performed on 43 clonesdemonstrated that
Tomato fruit production is severely hampered by both extremely high and low temperatures, mainly ... more Tomato fruit production is severely hampered by both extremely high and low temperatures, mainly due to impaired microsporogenesis and pollination under these conditions. Even mild temperature stress, leading to partial damage to pollen viability can result in the production of under-fertilized puffy fruits of poor quality, while severe stress can abolish fruit set completely. Genetic or transgenic parthenocarpy that enables fertilization-independent fruit development offers a solution for tomato yielding under conditions unfavorable for pollen production and/or fertilization. A transgenic processing tomato UC82 line, expressing rolB specifically during early stages of fruit development was compared to the parental line with respect to yield and fruit quality under extreme temperatures. Under both high and low temperatures the transgenic line performed significantly better than the parental line. Its yield was significantly higher mainly due to a higher number of fruits that did develop, and also because of increased fruit weight. While the UC82 fruits developed under high temperatures were very puffy and severely malformed, the transgenic fruits maintained improved jelly fill and were of smooth and regular shape. Interestingly, under high temperatures the improved jelly fill in the transgenic line was accompanied by a higher number of seeds, suggesting that not only the developing seeds promote development of the placental tissue but also that proliferation of this tissue supports better seed development.
Changes in the degree of fatty acid (FA) desaturation are implicated in plant responses to variou... more Changes in the degree of fatty acid (FA) desaturation are implicated in plant responses to various abiotic stresses, including heat, salt and drought. However, it is still not known whether decreased levels of linolenic acid, found in many plants subjected to salt and drought stress, reflect a mechanism of defence or damage. We addressed this question by generating tobacco cells and plants ectopically overexpressing two FA desaturases: the cytosolic FAD3 or the plastidic FAD8. A remarkable increase in the ratio of total linolenic to linoleic acids resulted from overexpression of FAD3, whereas ectopic overexpression of FAD8 induced an increased ratio mainly in the plastidic lipids. Here we present evidence that overexpressing FAD8 imposes much greater heat sensitivity than does FAD3 overexpression, in both cultured cells and whole plants. Overexpression of either FAD3 or FAD8 increases tolerance to drought in tobacco plants and to osmotic stress in cultured cells. These findings suggest that a drought-induced decreased level of linolenic acid reflects damage. Our results point to the potential of exploiting FAD overexpression as a tool to ameliorate drought tolerance.
We describe here a novel plant-specific gene, Lefsm1 (fruit SANT/MYB-like 1) harboring a single S... more We describe here a novel plant-specific gene, Lefsm1 (fruit SANT/MYB-like 1) harboring a single SANT/MYB domain. The expression of Lefsm1 is specific to the very early stages of tomato (Lycopersicon esculentum) fruit development. Ectopic expression of Lefsm1 results in severe developmental alterations manifested in retarded growth, and reduced apical dominance during tomato and Arabidopsis seedling development. A promoter sequence residing 1.0 kb upstream to the translation initiation codon confers the organ-specific expression of the gene. Lefsm1 belongs to a novel small gene family consisting of five to six members in tomato, Arabidopsis and rice. The SANT/MYB domain of LeFSM1 and its orthologs in Arabidopsis and rice differs from that of all other plant or animal MYB proteins and from the SANT domains found in part of the chromatin remodeling proteins. Together, our results indicate that Lefsm1 is a founding member of a small family of proteins containing a novel MYB/SANT domain which is likely to participate in the regulation of a plant-specific developmental program.
The molecular signals for the development of the ovary into fruit following ovule fertilization a... more The molecular signals for the development of the ovary into fruit following ovule fertilization are not clear. However, in many species, including tomato ( Lycopersicon esculentum Mill.), auxins and auxin transport inhibitors can substitute for fertilization as activators of fruit set, suggesting that this plant hormone plays a key role in this process. In agreement, transgenes for auxin biosynthesis expressed under ovary- or ovule-specific promoters were shown earlier to enable parthenocarpic (i.e. seedless) fruit development. In the present study, we tested an alternative approach for the induction of parthenocarpy that is based on ovary-specific expression of the Agrobacterium rhizogenes-derived gene rolB. This gene was chosen because rolB transgenic plants manifest several syndromes characteristic of auxin treatment. Tomato plants transformed with a chimeric construct containing the rolB gene fused to the ovary- and young-fruit-specific promoter TPRP-F1 developed parthenocarpic fruits. Fruit size and morphology, including jelly fill in the locules of the seedless fruits, were comparable to those of seeded fruits of the parental line. Although it is not known whether ROLB signals for the same cassette of genes involved in fertilization-dependent fruit development, it clearly activates a battery of genes that enable successful completion of seedless fruit development in tomato.
ABSTRACT Non-differentiated tissue cultures (calli) and differentiated tissues (shoots) of tobacc... more ABSTRACT Non-differentiated tissue cultures (calli) and differentiated tissues (shoots) of tobacco were found to differ in their sensitivity to chloramphenicol (CAP). This phenomenon is especially manifested in darkness and in an illumination regime lacking u.v. and blue light. When the latter are included, CAP's photodegradation products are shown to appear. It seems that one of the main photodegradation pathways is through the production of p-nitro-benzaldehyde (p-NBA) which is further degraded. The possibility that either acetylation or physiological nitration of CAP is the cause for the differential tolerance was eliminated. The chromatographic and radiographic results indicate that in vivo degradation of CAP occurs both in calli and in shoot cultures. One of the in vivo degradation products is CAP-base.
ABSTRACT Non-differentiated tissue cultures (calli) of tobacco were found to be more sensitive to... more ABSTRACT Non-differentiated tissue cultures (calli) of tobacco were found to be more sensitive to chloramphenicol (CAP) than differentiated tissues (shoots). The difference is especially manifested in darkness and at an irradiation regime lacking u.v. and blue light. Photodegradation of CAP solutions was demonstrated at moderate light fluence rates (6–15 Wm−2). The evidence indicates that the final products of photodegradation may be toxic or non-toxic according to the irradiation regime. The implication of the present findings in establishing a selection system for resistance to chemicals, and especially CAP, using plant tissue cultures, is discussed.
A full-length cDNA clone encoding a novel fructokinase, LeFRK4, was isolated from a tomato (Lycop... more A full-length cDNA clone encoding a novel fructokinase, LeFRK4, was isolated from a tomato (Lycopersicon esculentum Mill.) flower cDNA library. The putative protein shares 62.6 and 55.5% amino acid identity with the two known tomato fructokinases, LeFRK1 and LeFRK2, respectively, and possesses three signature patterns of the pfkB family of carbohydrate kinases, two substrate recognition sites and an ATP-binding domain.
A petunia cell line, 1ECB, was previously isolated by the stepwise selection procedure, for resis... more A petunia cell line, 1ECB, was previously isolated by the stepwise selection procedure, for resistance to methotrexate (MTX), an antimetabolite for the enzyme dihydrofolate reductase (DHFR). Using ammonium sulfate precipitates of cell lysates of cell line 1ECB and its parental cell line (WT), it was found that the mutant has an increase of 400 fold in 3H-MTX binding capacity and a decrease in the affinity for MTX binding, at two orders of magnitude, in comparison with the WT. In addition, the DHFR specific activity in the mutant increased only moderately (5-to/0-fold), this activity is extremely sensitive to MTX inhibition as compared to the WT. It is evident that the MTX resistance of line 1ECB results mainly from overproduction of an MTX-binding protein which differs from the WT DHFR by four biochemical criteria. This protein may serve as a trap for the excess amounts of MTX to which the cells are exposed.
Cell suspensions of Petunia hybrida were subjected to a selection procedure in which the concentr... more Cell suspensions of Petunia hybrida were subjected to a selection procedure in which the concentration of the selective agent, methotrexate (MTX), was gradually elevated. In mammalian cells, this procedure frequently results in MTX-resistant mutants due to amplification of the gene coding for dihydrofolate reductase (DHFR), the target protein of MTX.
In plant cells methotrexate (MTX) may exert its toxic effect through several mechanisms, includin... more In plant cells methotrexate (MTX) may exert its toxic effect through several mechanisms, including inhibition of its target protein dihydrofolate reductase. Resistance based on a mechanism operating before MTX binds to proteins should confer protection to plant cells. A methotrexate-resistant cell line of Nicotianaplumbaginifolia was isolated by a stepwise selection procedure. This cell line survived in the presence of 10/~M MTX which is 50-100 fold higher than the lethal dose for the wild type cells. Neither alteration in kinetic characteristics of dihydrofolate reductase, nor elevated binding capacity of 3H-MTX to target protein(s), were observed. However, in comparison with wild type ceils, markedly lower amounts of intracellular 3H-MTX were found after the selected cell line was incubated with 3H-MTX, indicating that either reduced uptake or enhanced efflux of MTX is the major reason for MTX-resistance in this cell line.
The denatured protein profiles of developing tomato (Lycopersicon esculentum Mill.) fruits, from ... more The denatured protein profiles of developing tomato (Lycopersicon esculentum Mill.) fruits, from the anthesis stage up to fruits at 30% of their final diameter, were examined in a pat-2ipat-2 parthenocarpic line and in its near isogenic Bon-partheno-carpic line. At anthesis no differences were ...
Strigolactones are a new group of plant hormones that play a pivotal role in the regulation of ab... more Strigolactones are a new group of plant hormones that play a pivotal role in the regulation of aboveground plant architecture. However, the mechanisms governing their regulation of plant growth and development are unknown. We characterized the effect of a synthetic strigolactone (GR24) on tomato (Solanum lycopersicon) roots and present evidence for its relationship with the plant hormone auxin. We demonstrate that strigolactones interfere with the inhibitory effect of exogenously applied auxin on root elongation. This GR24-induced root elongation is conveyed via an increase in root cell length accompanied by a reduction in cell diameter, and it occurs despite strigolactone's reduction of cell division (detected as reduction of CYCB1;1 transcript). In addition, high concentrations of strigolactone lead to asymmetric root growth and inhibition of root-hair elongation. Exogenous application of NAA or IAA was unable to restore symmetric root growth and roothair elongation in the presence of strigolactone. However, application of NPA, an auxin-efflux inhibitor, did restore root-hair elongation in the presence of strigolactone. Similarly, exogenous application of 2,4-D, a synthetic auxin that is not secreted by efflux carriers, restored root-hair elongation and symmetric growth in the presence of strigolactone. Nevertheless, 2,4-D was unable to prevent root elongation by strigolactones. Therefore, strigolactones' effect on root growth and root-hair elongation appears to be mediated via an effect on auxin-efflux carriers. Nevertheless, more than one mechanism may govern strigolactones' effect on root growth.
Journal of Experimental Botany, Vol. 43, No. 249, pp. 471-478, April 1992 ... Isolation of MTX-re... more Journal of Experimental Botany, Vol. 43, No. 249, pp. 471-478, April 1992 ... Isolation of MTX-resistant Cell Line NP-19 of ... SARA SHABTAI1, MEIRA ZIV2 and RIVKA BARG1'3 ... 1 Department of Plant Genetics and Breeding, Institute of Field and Garden Crops, ...
An mRNA species, HVA1, has been shown to be rapidly induced by abscisic acid (ABA) in barley aleu... more An mRNA species, HVA1, has been shown to be rapidly induced by abscisic acid (ABA) in barley aleurone layers (Hong, Uknes and Ho, Plant Mol Biol 11: 495-506, 1988). In the current work we have investigated the expression of riVAl in other organs of barley plants. In developing seeds, HVA1 mRNA is not detected in starchy endosperm cells, yet it accumulates in aleurone layers and embryo starting 25 days after anthesis, and its level remains high in these organs in dry seeds. Although the levels of HVA1 mRNA are equivalent in the dry embryos of dormant and nondormant barley seeds, upon imbibition HVA1 mRNA declines much slower in the dormant than in the nondormant embryos. The HVA1 mRNA and protein levels are highly induced by ABA treatment in all organs of 3-day-old seedlings. However, the induction in the leaf of 7-day-old seedlings is less than one tenth the level observed in the leaf of 3-day-old seedlings. In the leaf, HVA1 mRNA and protein are induced mainly at the base. These observations indicate that the expression of HVA 1 is under developmental regulation. Besides the HVA 1 protein, a smaller protein (p20) of approximately 20 kDa cross-reacting with anti-HVA1 polyclonal antibodies, is induced by ABA in barley seedlings but not in seeds. HVA1 mRNA is induced by drought, NaC1, cold or heat treatment. Similar to ABA treatment, the drought induction of HVA1 occurs in all the tissues of 3-day-old seedlings, but the induction decreases dramatically in the leaf of 7-day-old plants. The significance of organ-specific, developmentally regulated, and stress-induced expression of HVA1 is discussed.
ABSTRACT Lowering the sucrose content in the medium causes a decrease in growth of tobacco callus... more ABSTRACT Lowering the sucrose content in the medium causes a decrease in growth of tobacco callus cultures. At low sucrose concentrations the cultures developed a darker-green color, and produced a higher number of shoots in a shorter time. The shoots formed were of improved morphology. Our results might indicate that the osmolarity of the medium affects both greening and shoot formation in some tobacco callus cultures. Some differences were found between genetic lines in their responses to the shoot inducing media.
ABSTRACT The effects of amitrole on four tobacco lines were studied, using two biological systems... more ABSTRACT The effects of amitrole on four tobacco lines were studied, using two biological systems: germinating seeds and tissue cultures. Both differentiating and non-differentiating cultures were employed. Similar herbicide concentrations (2.5–7.5 × 10−5 M) caused bleaching and inhibited growth and differentiation in both systems. Evidences were found, supporting the notion that amitrole has several modes of action. Putative amitrole resistant mutants were isolated from differentiating and non-differentiating calli. These mutants exhibited various phenotypes of resistance. The advantages of plants' tissue cultures for selecting herbicide resistant mutants are demonstrated and discussed.
In order to study genes involved in latestages of flower development, we wereinterested in isolat... more In order to study genes involved in latestages of flower development, we wereinterested in isolating petal- orstamen-specific genes, particularly onesexpressed at a low level, as they mayinclude regulatory genes. To this end, asubtracted and equalized cDNA library oftomato petals and stamens was constructed.Approximately 650 clones of this librarywere found to represent 84 different genes.Northern analyses performed on 43 clonesdemonstrated that
Tomato fruit production is severely hampered by both extremely high and low temperatures, mainly ... more Tomato fruit production is severely hampered by both extremely high and low temperatures, mainly due to impaired microsporogenesis and pollination under these conditions. Even mild temperature stress, leading to partial damage to pollen viability can result in the production of under-fertilized puffy fruits of poor quality, while severe stress can abolish fruit set completely. Genetic or transgenic parthenocarpy that enables fertilization-independent fruit development offers a solution for tomato yielding under conditions unfavorable for pollen production and/or fertilization. A transgenic processing tomato UC82 line, expressing rolB specifically during early stages of fruit development was compared to the parental line with respect to yield and fruit quality under extreme temperatures. Under both high and low temperatures the transgenic line performed significantly better than the parental line. Its yield was significantly higher mainly due to a higher number of fruits that did develop, and also because of increased fruit weight. While the UC82 fruits developed under high temperatures were very puffy and severely malformed, the transgenic fruits maintained improved jelly fill and were of smooth and regular shape. Interestingly, under high temperatures the improved jelly fill in the transgenic line was accompanied by a higher number of seeds, suggesting that not only the developing seeds promote development of the placental tissue but also that proliferation of this tissue supports better seed development.
Changes in the degree of fatty acid (FA) desaturation are implicated in plant responses to variou... more Changes in the degree of fatty acid (FA) desaturation are implicated in plant responses to various abiotic stresses, including heat, salt and drought. However, it is still not known whether decreased levels of linolenic acid, found in many plants subjected to salt and drought stress, reflect a mechanism of defence or damage. We addressed this question by generating tobacco cells and plants ectopically overexpressing two FA desaturases: the cytosolic FAD3 or the plastidic FAD8. A remarkable increase in the ratio of total linolenic to linoleic acids resulted from overexpression of FAD3, whereas ectopic overexpression of FAD8 induced an increased ratio mainly in the plastidic lipids. Here we present evidence that overexpressing FAD8 imposes much greater heat sensitivity than does FAD3 overexpression, in both cultured cells and whole plants. Overexpression of either FAD3 or FAD8 increases tolerance to drought in tobacco plants and to osmotic stress in cultured cells. These findings suggest that a drought-induced decreased level of linolenic acid reflects damage. Our results point to the potential of exploiting FAD overexpression as a tool to ameliorate drought tolerance.
We describe here a novel plant-specific gene, Lefsm1 (fruit SANT/MYB-like 1) harboring a single S... more We describe here a novel plant-specific gene, Lefsm1 (fruit SANT/MYB-like 1) harboring a single SANT/MYB domain. The expression of Lefsm1 is specific to the very early stages of tomato (Lycopersicon esculentum) fruit development. Ectopic expression of Lefsm1 results in severe developmental alterations manifested in retarded growth, and reduced apical dominance during tomato and Arabidopsis seedling development. A promoter sequence residing 1.0 kb upstream to the translation initiation codon confers the organ-specific expression of the gene. Lefsm1 belongs to a novel small gene family consisting of five to six members in tomato, Arabidopsis and rice. The SANT/MYB domain of LeFSM1 and its orthologs in Arabidopsis and rice differs from that of all other plant or animal MYB proteins and from the SANT domains found in part of the chromatin remodeling proteins. Together, our results indicate that Lefsm1 is a founding member of a small family of proteins containing a novel MYB/SANT domain which is likely to participate in the regulation of a plant-specific developmental program.
The molecular signals for the development of the ovary into fruit following ovule fertilization a... more The molecular signals for the development of the ovary into fruit following ovule fertilization are not clear. However, in many species, including tomato ( Lycopersicon esculentum Mill.), auxins and auxin transport inhibitors can substitute for fertilization as activators of fruit set, suggesting that this plant hormone plays a key role in this process. In agreement, transgenes for auxin biosynthesis expressed under ovary- or ovule-specific promoters were shown earlier to enable parthenocarpic (i.e. seedless) fruit development. In the present study, we tested an alternative approach for the induction of parthenocarpy that is based on ovary-specific expression of the Agrobacterium rhizogenes-derived gene rolB. This gene was chosen because rolB transgenic plants manifest several syndromes characteristic of auxin treatment. Tomato plants transformed with a chimeric construct containing the rolB gene fused to the ovary- and young-fruit-specific promoter TPRP-F1 developed parthenocarpic fruits. Fruit size and morphology, including jelly fill in the locules of the seedless fruits, were comparable to those of seeded fruits of the parental line. Although it is not known whether ROLB signals for the same cassette of genes involved in fertilization-dependent fruit development, it clearly activates a battery of genes that enable successful completion of seedless fruit development in tomato.
ABSTRACT Non-differentiated tissue cultures (calli) and differentiated tissues (shoots) of tobacc... more ABSTRACT Non-differentiated tissue cultures (calli) and differentiated tissues (shoots) of tobacco were found to differ in their sensitivity to chloramphenicol (CAP). This phenomenon is especially manifested in darkness and in an illumination regime lacking u.v. and blue light. When the latter are included, CAP's photodegradation products are shown to appear. It seems that one of the main photodegradation pathways is through the production of p-nitro-benzaldehyde (p-NBA) which is further degraded. The possibility that either acetylation or physiological nitration of CAP is the cause for the differential tolerance was eliminated. The chromatographic and radiographic results indicate that in vivo degradation of CAP occurs both in calli and in shoot cultures. One of the in vivo degradation products is CAP-base.
ABSTRACT Non-differentiated tissue cultures (calli) of tobacco were found to be more sensitive to... more ABSTRACT Non-differentiated tissue cultures (calli) of tobacco were found to be more sensitive to chloramphenicol (CAP) than differentiated tissues (shoots). The difference is especially manifested in darkness and at an irradiation regime lacking u.v. and blue light. Photodegradation of CAP solutions was demonstrated at moderate light fluence rates (6–15 Wm−2). The evidence indicates that the final products of photodegradation may be toxic or non-toxic according to the irradiation regime. The implication of the present findings in establishing a selection system for resistance to chemicals, and especially CAP, using plant tissue cultures, is discussed.
A full-length cDNA clone encoding a novel fructokinase, LeFRK4, was isolated from a tomato (Lycop... more A full-length cDNA clone encoding a novel fructokinase, LeFRK4, was isolated from a tomato (Lycopersicon esculentum Mill.) flower cDNA library. The putative protein shares 62.6 and 55.5% amino acid identity with the two known tomato fructokinases, LeFRK1 and LeFRK2, respectively, and possesses three signature patterns of the pfkB family of carbohydrate kinases, two substrate recognition sites and an ATP-binding domain.
A petunia cell line, 1ECB, was previously isolated by the stepwise selection procedure, for resis... more A petunia cell line, 1ECB, was previously isolated by the stepwise selection procedure, for resistance to methotrexate (MTX), an antimetabolite for the enzyme dihydrofolate reductase (DHFR). Using ammonium sulfate precipitates of cell lysates of cell line 1ECB and its parental cell line (WT), it was found that the mutant has an increase of 400 fold in 3H-MTX binding capacity and a decrease in the affinity for MTX binding, at two orders of magnitude, in comparison with the WT. In addition, the DHFR specific activity in the mutant increased only moderately (5-to/0-fold), this activity is extremely sensitive to MTX inhibition as compared to the WT. It is evident that the MTX resistance of line 1ECB results mainly from overproduction of an MTX-binding protein which differs from the WT DHFR by four biochemical criteria. This protein may serve as a trap for the excess amounts of MTX to which the cells are exposed.
Cell suspensions of Petunia hybrida were subjected to a selection procedure in which the concentr... more Cell suspensions of Petunia hybrida were subjected to a selection procedure in which the concentration of the selective agent, methotrexate (MTX), was gradually elevated. In mammalian cells, this procedure frequently results in MTX-resistant mutants due to amplification of the gene coding for dihydrofolate reductase (DHFR), the target protein of MTX.
In plant cells methotrexate (MTX) may exert its toxic effect through several mechanisms, includin... more In plant cells methotrexate (MTX) may exert its toxic effect through several mechanisms, including inhibition of its target protein dihydrofolate reductase. Resistance based on a mechanism operating before MTX binds to proteins should confer protection to plant cells. A methotrexate-resistant cell line of Nicotianaplumbaginifolia was isolated by a stepwise selection procedure. This cell line survived in the presence of 10/~M MTX which is 50-100 fold higher than the lethal dose for the wild type cells. Neither alteration in kinetic characteristics of dihydrofolate reductase, nor elevated binding capacity of 3H-MTX to target protein(s), were observed. However, in comparison with wild type ceils, markedly lower amounts of intracellular 3H-MTX were found after the selected cell line was incubated with 3H-MTX, indicating that either reduced uptake or enhanced efflux of MTX is the major reason for MTX-resistance in this cell line.
The denatured protein profiles of developing tomato (Lycopersicon esculentum Mill.) fruits, from ... more The denatured protein profiles of developing tomato (Lycopersicon esculentum Mill.) fruits, from the anthesis stage up to fruits at 30% of their final diameter, were examined in a pat-2ipat-2 parthenocarpic line and in its near isogenic Bon-partheno-carpic line. At anthesis no differences were ...
Strigolactones are a new group of plant hormones that play a pivotal role in the regulation of ab... more Strigolactones are a new group of plant hormones that play a pivotal role in the regulation of aboveground plant architecture. However, the mechanisms governing their regulation of plant growth and development are unknown. We characterized the effect of a synthetic strigolactone (GR24) on tomato (Solanum lycopersicon) roots and present evidence for its relationship with the plant hormone auxin. We demonstrate that strigolactones interfere with the inhibitory effect of exogenously applied auxin on root elongation. This GR24-induced root elongation is conveyed via an increase in root cell length accompanied by a reduction in cell diameter, and it occurs despite strigolactone's reduction of cell division (detected as reduction of CYCB1;1 transcript). In addition, high concentrations of strigolactone lead to asymmetric root growth and inhibition of root-hair elongation. Exogenous application of NAA or IAA was unable to restore symmetric root growth and roothair elongation in the presence of strigolactone. However, application of NPA, an auxin-efflux inhibitor, did restore root-hair elongation in the presence of strigolactone. Similarly, exogenous application of 2,4-D, a synthetic auxin that is not secreted by efflux carriers, restored root-hair elongation and symmetric growth in the presence of strigolactone. Nevertheless, 2,4-D was unable to prevent root elongation by strigolactones. Therefore, strigolactones' effect on root growth and root-hair elongation appears to be mediated via an effect on auxin-efflux carriers. Nevertheless, more than one mechanism may govern strigolactones' effect on root growth.
Journal of Experimental Botany, Vol. 43, No. 249, pp. 471-478, April 1992 ... Isolation of MTX-re... more Journal of Experimental Botany, Vol. 43, No. 249, pp. 471-478, April 1992 ... Isolation of MTX-resistant Cell Line NP-19 of ... SARA SHABTAI1, MEIRA ZIV2 and RIVKA BARG1'3 ... 1 Department of Plant Genetics and Breeding, Institute of Field and Garden Crops, ...
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