Amino acids (AAs) play significant roles in metal binding, antioxidant defense, and signaling in plants during heavy metal stress. In the present study, the essential amino acids (EAAs), non-essential amino acids (NEAAs), as well as the enzymes of proline and cysteine biosynthetic pathways were studied in contrasting arsenic accumulating rice genotypes grown in hydroponic solutions with addition of arsenate (As^V) or arsenite (As^III). Under a mild As stress, the total AAs content significantly increased in both the rice genotypes with a greater increase in a low As accumulating rice genotype (LAARG; IET-19226) than in a high As accumulating rice genotype (HAARG; BRG-12). At the equimolar concentration (10 μM), As^III had a greater effect on EAAs than As^V. Conversely, As^V was more effective in inducing a proline accumulation than As^III. Among NEAAs, As significantly induced the accumulation of histidine, aspartic acid, and serine. In contrast, a higher As concentration (50 μM) reduced the content of most AAs, the effect being more prominent during As^III exposure. The inhibition of glutamate kinase activity was noticed in HAARG, conversely, serine acetyltransferase and cysteine synthase activities were increased which was positively correlated with the cysteine synthesis.

This study was carried out to understand the mechanism of protection of plants under cold stress by exogenous 24-epibrassinolide (EBR). The eggplant (Solanum melongena L.) seedlings were pretreated with five concentrations of EBR (0, 0.05, 0.1, 0.2 and 0.4 °M) and then exposed to day/night temperatures of 10/5 °C for 8 d. The results show that EBR, especially 0.1 °M EBR, dramatically alleviated growth suppression and a decrease in chlorophyll content and photosynthetic rate caused by the cold stress. In addition, EBR also decreased malondialdehyde content and O₂ ^.- production rate induced by the cold stress, and increased the activities of superoxide dismutase, guaiacol peroxidase, catalase, and ascorbate peroxidase, and proline content. The results of the present study suggest that exogenous EBR could improve cold tolerance of eggplant by regulating photosynthesis and antioxidative systems.

Tobacco (Nicotiana tabacum L.) plants were cultured in vitro photoautotrophically at three levels of irradiance (PAR 400-700 nm): low (LI, 60 µmol m^-2 s^-1), middle (MI, 180 µmol m^-2 s^-1) and high (HI, 270 µmol m^-2 s^-1). Anatomy of the fourth leaf from bottom was followed during leaf development. In HI and MI plants, leaf area expansion started earlier as compared to LI plants, and both HI and MI plants developed some adaptations of sun species: leaves were thicker with higher proportion of palisade parenchyma to spongy parenchyma tissue. Furthermore, in HI and MI plants palisade and spongy parenchyma cells were larger and relative abundance of chloroplasts in parenchyma cells measured as chloroplasts cross-sectional area in the cell was lower than in LI plants. During leaf growth, chloroplasts crosssectional area in both palisade and spongy parenchyma cells in all treatments considerably decreased and finally it occupied only about 5 to 8 % of the cell cross-sectional area. Thus, leaf anatomy of photoautotrophically in vitro cultured plants showed a similar response to growth irradiance as in vivo grown plants, however, the formation of chloroplasts and therefore of photosynthetic apparatus was strongly impaired.

We investigated the effect of water stress on yield and quality of tomato plants overexpressing Solanum lycopersicum thylakoid-bound ascorbate peroxidase gene (StAPX). APX activity, hydrogen peroxide content, net photosynthetic rate of tomato leaves, and yield and nutrition quality of tomato fruits were measured under soil moisture 70, 60, and 50 % of full field capacity. Results show that the capability of APX for scavenging hydrogen peroxide induced by water stress was higher in the transgenic than the wild type (WT) plants. The yield of fruits of the transgenic tomato plants was higher than that of WT plants under water stress and the fruit nutrition quality was not different. These results indicate that overexpression of StAPX might improve water stress tolerance in the transgenic tomato plants.

Interactions between indole-3-acetic acid (IAA), abscisic acid (ABA), and ethylene (ET) in the photoperiodic flower induction of a short-day (SD) plant Pharbitis nil were investigated. It was shown that both IAA and ABA applied just before and during the first half of the 16-h-long inductive night inhibited flower induction in P. nil. Ethylene is also thought to be a strong flowering inhibitor of SD plants but only when it is applied in the second half of the inductive night. The application of IAA just before the inductive night decreased the content of endogenous ABA in cotyledons only during the first half of the inductive night. Additionally, the application of 2-aminoethoxyvinylglycine (AVG) - an ethylene biosynthesis inhibitor - partially reversed the inhibitory effect of IAA and ABA on flowering. The results suggest that the mechanisms of P. nil flower inhibition by IAA and ABA might be independent. However, both the hormones influenced ethylene production which directly inhibited flowering. We also show that ABA applied on the cotyledons of P. nil seedlings just before the inductive night caused a clear increase in the expression of PnACS1 and PnACS2 genes (encoding enzymes involved in ethylene biosynthesis) from the first hours after its application. The transcripts of PnACO1 and PnACO3 genes were also increased but their maximal values were shifted in relation to the PnACS1 and PnACS2. The data presented here strongly support the idea that both IAA and ABA inhibit P. nil flowering through the modulation of ethylene biosynthesis.

The present research is aimed towards molecular marker assisted pyramiding Tomato leaf curl virus (ToLCV) disease resistance genes into two ToLCV susceptible tomato (Solanum lycopersicum L.) cvs. Pbc and H-86 (resistance genes recipient parents). Resistance gene donors were EC-538408 (Solanum chilense) and EC-520061 (S. peruvianum) in the case of cv. Pbc, and EC-520061 (S. peruvianum) and H-24 (S. lycopersicum) in the case of cv. H-86. A ToLCV resistance gene associated co-dominant simple sequence repeat (SSR) marker SSR-218 was used to discriminate between homozygotes and heterozygotes at the seedling stage prior to pollination, which enabled the rejection of nontarget back crosses and pyramiding progenies of the crosses PbcxEC-520061 and H-86xEC-520061, whereas SSR-306 was used for the cross PbcxEC-538408. Ty-2 gene cleaved amplified polymorphic sequences (CAPS) marker was used for the cross H-86xH-24. Out of 279 pyramiding progenies of the cross PbcxEC-538408/PbcxEC-520061, total 91 plants showed the presence of both resistance allele 1 and 2 along with both susceptibility alleles, and in 243 pyramiding progenies of the cross H-86xEC-520061/H-86xH-24, total 82 plants showed the presence of both resistance allele 1 and Ty-2 along with both susceptible alleles. The pyramiding lines that carried both pyramided resistance genes were resistant to tomato leaf curl disease throughout its life cycle.

Drought is one of the main environmental stresses and many investigators identified beneficial effects of both silicon and selenium on plant growth and development. To examine the effects of Si and Se on rice (Oryza sativa L.) responses to drought, two cultivars Giza 177 and IET 1444 pretreated with 1.5 mM Si or 0.03 mM Se were then exposed to a water stress until leaf rolling was observed. The enhanced growth of Se or Si pre-treated plants was associated with a significant increase in the content of proline and glycine betaine in both shoots and roots. Furthermore, the transcription factors (TFs), dehydration responsive element-binding protein DREB2A, and NAC5 [no apical meristem (NAM), Arabidopsis thaliana activating factor (ATAF), and cup-shaped cotyledon (CUC)] were over-expressed in the drought stressed rice shoots. Notably, a pretreatment with either Se or Si significantly enhanced the expression of both TFs, DREB2A, NAC5, as well as the expression of the ring domain containing OsRDCP1 gene and some drought specific genes, such as OsCMO coding rice choline monooxygenase and dehydrin OsRAB16b. Expression of TFs and the studied genes was markedly enhanced in the Si-stressed shoots of cv. IET 1444 which favors its drought tolerance.

Durum wheat (Triticum turgidum L. var. durum) is mainly produced under rainfed but often sub-optimal moisture conditions in the Mediterranean basin. A set of 114 durum wheat recombinant inbred lines (RILs) developed from the cross of cultivars Omrabi5 × Belikh2 were tested for the ability to tolerate moisture deficiency at the germination and early seedling growth stage. The stress was imposed by exposing the germinating grain to 12 % polyethylene glycol. It induced a measurable reduction in root length, shoot length, and the percentage of normal seedlings. The germination and seedling growth of Belikh2 were more strongly inhibited than those of Omrabi5, and both parents were outperformed by > 50 % of the RILs. A quantitative trait locus (QTL) analysis was carried out by first assembling a linkage map from 265 informative microsatellites. Composite interval mapping revealed nine QTL spread over seven chromosomes. Five of these were associated with coleoptile length, and one of the five explained nearly 29 % of the relevant phenotypic variance. The coleoptile length was significantly correlated with the seedling growth, plant height, and thousand kernel mass derived from field-grown plants of the same RIL population.

In order to study chloroplast biogenesis, we chose natural variegated Epipremnum aureum (golden pothos) and regenerated pale yellow, variegated and green plants from all three types of tissue explants. The percentage of three types of regenerated shoots from three different explants was very close. Regenerated plants have been maintained for a year and show no sign of a colour switch. By comparing their protein profiles, two major differences between pale yellow and green plants were observed at the 15 and 40 to 50 kDa proteins. Moreover, pale yellow plants had unexpected high molecular mass proteins (greater than 60 kDa). Both variegated and green plants had more chlorophyll (Chl) a than Chl b, the ratios were about 1.46 and 1.93, respectively. In contrast, the pale yellow plants not only had less total Chl, but also the reduction of Chl a was much greater than Chl b, resulting in a higher content of Chl b than Chl a. Microscopic analysis revealed that pale yellow plants contained predominantly undeveloped chloroplasts with low Chl contents, even though their mesophyll cells were similar to green and variegated plants. PCR amplification of chloroplast DNA with 14 universal chloroplast primers did not reveal any difference among these regenerated plants.

In vitro flowering protocols were developed for a limited number of early flowering pea (Pisum sativum L.) cultivars. This work was undertaken to understand the mechanisms regulating in vitro flowering and seed-set across a range of pea genotypes. Its final goal is to accelerate the generation cycle for faster breeding novel genotypes. We studied the effects of in vivo and in vitro applications of the antigibberellin Flurprimidol together with radiation of different spectral compositions on intact plants, plants with the meristem removed, or excised shoot tip explants. Based on our results, we present a simple and reliable system to reduce generation time in vitro across a range of pea genotypes, including mid and late flowering types. With this protocol, more than five generations per year can be obtained with mid to late flowering genotypes and over six generations per year for early to mid flowering genotypes.

The MYB, MYC, and WD40 transcription factors (TFs) are known to regulate the expression of structural biosynthetic genes at different steps depending on the plant species. In this work, we used an agroinfiltration protocol with Tobacco rattle virus (TRV) constructs containing partial sequences from MYB or WD40 for virus-induced gene silencing (VIGS) to demonstrate their participation in the regulation of anthocyanin biosynthesis in chilli pepper (Capsicum eximium) fruits. The accumulation of anthocyanins in chilli pepper fruits of plants transformed with TRV2-MYB and TRV2-WD40 constructs was significantly reduced compared to the control or empty TRV2-transformed plants. A significant reduction in gene expression of both TFs was also detected. The expressions of the chalcone synthase (CHS), chalcone isomerase (CHI), flavonoid 3',5'-hydroxylase (F3'5'H), dihydroflavonol 4-reductase (DFR), and UDP-glucose:flavonoid 3-O-glucosyltransferase (3GT) genes were decreased in the plants transformed with the TRV2-MYB construct but not the transcription of flavanone 3-hydroxylase (F3H). When chilli pepper plants were infected with the TRV2-WD40 construct, a significant reduction in CHS, F3H, F3'5'H, DFR and 3GT expression, but not in CHI in the fruits was observed.

In this work, the response of the halophytic shrub Prosopis strombulifera to lowering an osmotic potential (Ψ_o) to -1.0, -1.9, and -2.6 MPa generated by NaCl, Na₂SO₄, and the iso-osmotic combination of them was studied at 6, 12, and 24 h after reaching such values in the growing media. By analyzing the content of abscisic acid (ABA) and related metabolites and transpiration rates, we observed that ABA content varied depending on type of salt, salt concentration, organ analyzed, and age of a plant. ABA content in leaves was much higher than in roots, presumably because of rapid biosynthesis and transport from roots. Leaves of Na₂SO₄-treated plants had the highest ABA content at Ψ_o -2.6 MPa (24 h) associated with sulfate toxicity symptoms. Significant content of ABA-glucose ester (ABA-GE) was found in both the roots and leaves, whereas only low content of phaseic acid (PA) and dihydrophaseic acid (DPA). The roots showed high ABA-GE accumulation in all treatments. The highest content of free ABA was correlated with ABA-GE glucosidase activity. The results show that ABA-GE and free ABA work together to create a specific stress signal.

Cold-responsive (COR) genes participate in the response of plants to low-temperature stress. In this study, we isolated and characterized a cold-responsive and light-inducible gene COR15B from Arabidopsis thaliana. Chloroplast damage caused by mutations (albino mutants seca1, secy1, and tic20) or by a norflurazon (NF) treatment resulted in a reduction of COR15B transcription. A semi-quantitative RT-PCR analysis shows that COR15B was induced by the salt stress in an abscisic acid-dependent manner. An over-expression of COR15B in Arabidopsis resulted in transgenic lines more sensitive to the NaCl treatment than the wild type. However, COR15B knockdown did not significantly affect the sensitivity of the cor15b mutant to the salt stress. Furthermore, we found that the expression of COR15A, a homologous gene of COR15B, was significantly elevated in cor15b mutant plants. All these results suggest that plants acquire the ability to fully express COR15B only after development of functional chloroplasts. The expressional reprogramming and functional backup may exist between COR15 homologues in Arabidopsis.

The present study was carried out to examine the effects of seed soaking in 1 mM ascorbic acid (AA) or 1 mM proline on the growth, content of photosynthetic pigments and proline, relative water content, electrolyte leakage, antioxidant enzymes and leaf anatomy of Hordeum vulgare L. Giza 124 seedlings grown in greenhouse under 100 or 200 mM NaCl. The plants exposed to the NaCl stress exhibited a significant reduction in growth, relative water content, leaf photosynthetic pigments, soluble sugars, as well as alterations in leaf anatomy. However, the treatment with AA or proline ameliorated the stress generated by NaCl and improved the above mentioned parameters. NaCl increased electrolyte leakage, proline content, and activities of antioxidant enzymes (SOD, CAT, and POX). The antioxidant enzymes and leaf anatomy exhibited considerable changes in response to AA or proline application in the absence or presence of NaCl.

We studied the influence of inorganic nitrogen sources (NO₃ ^- or NH₄ ⁺) and potassium deficiency on expression and activity of plasma membrane (PM) H⁺-ATPase in sorghum roots. After 15 d of cultivation at 0.2 mM K⁺, the plants were transferred to solutions lacking K⁺ for 2 d. Then, K⁺ depletion assays were performed in the presence or absence of vanadate. Further, PMs from K⁺-starved roots were extracted and used for the kinetic characterization of ATP hydrolytic activity and the immunodetection of PM H⁺-ATPase. Two major genes coding PM H⁺-ATPase (SBA1 and SBA2) were analyzed by real-time PCR. PM H⁺-ATPase exhibited a higher V_max and K_m in NH₄ ⁺-fed roots compared with NO₃ ^- -fed roots. The optimum pH of the enzyme was slightly lower in NO₃ ^- -fed roots than in NH₄ ⁺-fed roots. The vanadate sensitivity was similar. The expressions of SBA1 and SBA2 increased in roots grown under NH₄ ⁺. Concomitantly, an increased content of the enzyme in PM was observed. The initial rate of K⁺ uptake did not differ between plants grown with NO₃ ^- or NH₄ ⁺, but it was significantly reduced by vanadate in NH₄ ⁺-grown plants.

Two of the abundant transcripts encoding type 2 metallothionein (MT) proteins designated as MET2a and MET2b were selected in our previous study due to their high abundance (16.05 %) in the suppression subtractive hybridization library and their involvement in fruit development and maturation. The present study involves the isolation of the full-length cDNA encoding MET2a and MET2b from the ripening oil palm fruit mesocarp, examining their expression pattern compared to the other two previously reported type-3 MT members (MT3-A and MT3-B) in various oil palm organs including different vegetative and reproductive tissues. The full-length cDNA sequences of MET2a and MET2b were 571 and 553 bp and they were designated as EgMT2a and EgMT2b, respectively. The sequences of the EgMT2a and EgMT2b were then compared for sequence similarities in the database using both BLASTN and BLASTX programs. Their sequences were homologous (67-77 %) with several type-2 MTs in plants. All four MT encoding genes were differentially expressed in the ripening oil palm mesocarp tissues, but undetectable in the vegetative tissues examined. All MT genes examined were significantly up-regulated in the mature developmental stages of oil palm fruit mesocarp, except for EgMT2b which was expressed only at 17 weeks after anthesis. The type 2 MT proteins are related to a greater degree to the late fruit-ripening stage than the type 3 MT proteins consistent with their reported functions in homeostasis or detoxification. The findings in the present study contribute to better understanding the molecular mechanisms involved in fruit ripening in oil palm.

Heavy metal toxicity in soils has been considered as major constraints for oilseed rape (Brassica napus L.) production. In the present study, toxic effects of chromium (Cr) were studied in 6-d-old seedlings of four different cultivars of B. napus (ZS 758, Zheda 619, ZY 50, and Zheda 622). The elevated content of Cr inhibited seedling growth, decreased the content of photosynthetic pigments, and activities of antioxidant enzymes, as well as increased the content of malondialdehyde and reactive oxygen species in all the cultivars. The Cr content in different parts of plants was higher in Zheda 622 than in other cultivars. The electron microscopic study showed changes in ultrastructure of leaf mesophyll and root tip cells at 400 μmol Cr, and these changes were more prominent in Zheda 622. An increased size and number of starch grains and number of plastoglobuli, damaged thylakoid membranes, and immature nucleoli and mitochondria were observed in leaves. In roots, enlarged vacuoles, disrupted cell walls and cell membranes, an increased number of mitochondria and a size of nucleolus, as well as plasmolysis (in Zheda 622) were observed. On the basis of these findings, it can be concluded that cv. Zheda 622 was more sensitive to Cr as compared to other three cultivars.

Seasonal dimorphism (summer/winter) has been so far studied only in a few plants and has been focused on summer drought stress. However, Thymus sibthorpii in the study area appears to be affected by winter chilling stress and not by summer drought stress. Thus, the winter leaves were thicker and more compact compared to the summer leaves and they had more stomata and peltate hairs, more sclerenchymatous fibers, vacuoles with phenolics, and chloroplasts than the summer leaves. In addition, their chloroplasts possessed large grana and starch grains. In the summer leaves, cell vacuoles in mesophyll did not contain phenolics, and chloroplasts were devoid of starch grains and had large plastoglobuli. Physiological measurements revealed higher net photosynthetic rate and chlorophyll content in the winter leaves than in the summer leaves. Proline and soluble sugar content along with antioxidative enzyme (superoxide dismutase, peroxidase, ascorbate peroxidase, glutathione reductase) activities were increased in the winter leaves.

Selenium (Se) is essential for health of humans, animals, and plants. Especially wheat is a major source of Se in the terrestrial food chain. In this study, an element analysis was optimized and the content of Ca, Mg, K, S, P, Fe, Se, Mn, Cu, Zn, and Mo in leaves, roots, and seeds were measured during growth of wheat (Triticum aestivum L. cv. Manu) in Hoagland nutrient solution with 5 and 15 μM Na₂SeO₄. Se was transported to all investigated tissues and accumulated in the seeds in proportion to used amounts. The supplementation of Se, independently of concentration, weakly modified the micro- and macro-elements content in the seedlings. In the flag-leaf stage, an increase of the Mo and S content in the shoots and the S and Cu content in the roots was found. Moreover, in the generative phase, a decrease in Ca and Fe in the roots was registered. Increased Se in the nutrient solution strongly stimulated the Se accumulation in the seeds.

Exposure to low temperatures is one of the most important factors that generate abiotic stress in plants, and the rapid accumulation of soluble sugars belongs to significant metabolic responses to cold stress. The accumulation of soluble sugars may be at least partially triggered by an increased rate of starch degradation. The analysis of transcript profiles and starch degrading enzyme activities in leaves of two potato cultivars was performed during a 12-h exposure to 2 °C. An induction of β-amylase expression and activity as well as an accumulation of reducing sugars were observed in cv. Desiree. No accumulation of reducing sugars and no significant changes in the β-amylase activity were initially observed in cv. Russet Burbank. Surprisingly, an increased α-amylase activity was observed in the last hours of the experiment, which was accompanied by an increased amount of reducing sugars. The results indicate that the leaves of Desiree and Russet Burbank potatoes growing under cold stress may degrade starch via different pathways.

Self-grafted and pumpkin rootstock-grafted cucumber plants were subjected to the following four treatments: 1) aerated nutrient solution alone (control), 2) nutrient solution with 10 mM Ca(NO₃)₂ (Ca), 3) nutrient solution with 90 mM NaCl (NaCl), and 4) nutrient solution with 90 mM NaCl + 10 mM Ca(NO₃)₂ (NaCl+Ca). The NaCl treatment decreased the plant dry mass and content of Ca²⁺ and K⁺ but increased the Na⁺ content in roots and shoots. Smaller changes were observed in pumpkin rootstock-grafted plants. Supplementary Ca(NO₃)₂ ameliorated the negative effects of NaCl on plant dry mass, relative growth rate (RGR), as well as Ca²⁺, K⁺, and Na⁺ content especially for pumpkin rootstock-grafted plants. Supplementary Ca(NO₃)₂ distinctly stimulated the plasma membrane (PM) H⁺-ATPase activity which supplies the energy to remove excess Na⁺ from the cells. The expressions of gene encoding PM H⁺-ATPases (PMA) and gene encoding a PM Na⁺/H⁺ antiporter (SOS1) were up-regulated when Ca(NO₃)₂ was applied. The pumpkin rootstock-grafted plants had higher PM H⁺-ATPase activity as well as higher PMA and SOS1 expressions than the self-grafted plants under NaCl + Ca treatment. Therefore, the addition of Ca²⁺ in combination with pumpkin rootstock grafting is a powerful way to increase cucumber salt tolerance.

C-repeat binding factor (CBF), also called the dehydration-responsive element binding factor 1 (DREB1), can be induced by low-temperature (LT), and plays an important role in abiotic stress tolerance in higher plants. In present study, two new homologous genes of CBF from Prunus mume (PmCBFb and PmCBFc) have been identified and characterized. The complete coding sequences of PmCBFb and PmCBFc were 714 and 723 bp, respectively. They encoded putative proteins of 237 and 240 amino acids. Neither of them had introns. Genome PCR sequencing showed that PmCBFb was arranged in tandem with PmCBFa (another CBF/DREB1 homolog in P. mume) within a region of nearly 4 kb. Promoter prediction analyses indicated that multiple types of cis-elements related to abiotic stress and irradiance existed in the putative promoter region of PmCBFb. LT treatment of seedlings showed that the expression of PmCBF genes were induced by 2 °C within 30 min, and their expression reached a peak after 8-12 h. In addition, PmCBFa and PmCBFb appeared more sensitive to LT than PmCBFc. However, the exact roles of PmCBF genes in plant cold tolerance need to be further investigated.

Endogenous salicylic acid (SA) functions in plant response to an aluminum stress were assessed. We used different Arabidopsis thaliana genotypes including snc1 with a constitutively high content of SA, sid2 and nahG (transgenic lines) both with a low content of SA, SA insensitive mutant npr1-1, and snc1/nahG (i.e., the nahG expression in the snc1 background) with a similar SA content as in wild type (WT) plants. Results show that the snc1 plants displayed obvious growth retardation of roots and shoots under the Al³⁺ stress, whereas the sid2, nahG, and npr1-1 plants exhibited alleviated symptoms in comparison with the WT plants. The Al³⁺ content increased in all the tested genotypes with the increasing AlCl₃ concentration applied, but no significant variations were detected among the tested genotypes. The snc1 had much higher superoxide dismutase and peroxidase activities, and a lower catalase activity and the ratio of reduced to oxidized glutathione accompanied by higher accumulations of H₂O₂ and malondialdehyde compared with the WT plants. These changes were largely reversed by the introduction of nahG; the sid2, nahG, and npr1-1 plants were less affected than WT plants in all the above-mentioned parameters. The Al³⁺ stress significantly enhanced malate exudation in all the tested genotypes, but no significant correlation was observed between the SA-involved response to the Al³⁺ stress and the malate exudation. Based on these data, it was concluded that the SA-related functions in Arabidopsis response to the Al³⁺ stress were associated with the control of oxidative stress, but not of malate exudation.

Plant growth regulators (PRG)-assisted phytoremediation is a technique that could enhance the yield of heavy metal accumulation in plant tissues. So far, a small number of experiments have helped identify three groups of plant hormones that may be useful for this purpose: auxins, cytokinins, and gibberellins. Studies have shown that these hormones positively affect the degree of accumulation of metallic impurities and improve the growth and stress resistance of plants. This review summarizes the present knowledge about PGRs' impact on phytoextraction yield.

Transcription factors play vital roles in stress signal transduction and gene expression modulation. The sequence analysis shows that MdCBF1 from Malus domestica Borkh. cv. Fuji contained an AP2 core domain of 56 amino acids. By comparison of deduced amino acid sequences of CBF related proteins, we deduced that MdCBF1 is a CBF transcription factor gene which belongs to AP2/EREBP family, DREB-A1 subfamily. Further, we reported that transgenic Arabidopsis thaliana plants expressing the MdCBF1 gene exhibited stronger growth than wild type plants under freezing stress. The analysis of RT-PCR for stress-responsive genes implied that MdCBF1 over-expressing plants had a higher expression of COR15a, RD29A, and RD29B genes than wild type plants. Collectively, our results indicate that MdCBF1 might play an important role in the response of transgenic Arabidopsis plants to freezing stress.

MYB transcription factors (TFs) are known to have important functions in regulating the biosynthesis of secondary metabolites in plants. In this study, LeMYB1, a member of the MYB gene family of Lithospermum erythrorhizon, was cloned via the rapid amplification of cDNA ends. The alignment of the predicted translations of LeMYB1 with other MYB proteins revealed that LeMYB1 contained an N-terminal R2R3 repeat and a high degree of amino acid identity to NtMYBJS1 which is involved in jasmonic acid signalling and phenylpropanoid biosynthetic pathway regulation. To determine the expression pattern of LeMYB1, its promoter was cloned and the sequence analysis was performed. The results revealed a number of potential regulatory motifs related to tissue-specific gene expression and abiotic and biotic stress responses. Real-time PCR results suggest that LeMYB1 was induced transiently during the early stage when L. erythrorhizon cells were transferred from a B5 growth medium to a M9 production medium for shikonin formation. Exogenous methyl jasmonate (MeJA), an effective inducer of shikonin biosynthesis, induced the rapid LeMYB1 expression. In contrast, a treatment with ibuprofen (IBU), an inhibitor of jasmonate biosynthesis, significantly inhibited the LeMYB1 expression. Another inhibitor of shikonin formation, 2,4-dichlorophenoxyacetic acid (2,4-D), also markedly repressed the expression of LeMYB1. Tissue-specific expression analysis showed that LeMYB1 mRNA was predominantly accumulated in roots where shikonin was synthesized. Thus, the LeMYB1 gene may be a valuable member of the R2R3-MYB family in L. erythrorhizon and is possibly involved in the regulation of shikonin biosynthesis.

ApKUPs are typical high-affinity potassium (K⁺) transporters of Alternanthera philoxeroides which are involved in its response to K⁺ starvation and abiotic stresses. In this study, the overexpression of ApKUP3 gene in rice resulted in enhanced K⁺ nutrition and drought tolerance of transgenic plants. Compared with wild-type (WT) plants, the transgenic plants showed a better growth performance and a strengthened K⁺ accumulation under different K⁺ supplies. The ApKUP3 overexpression in the rice plants also enhanced tolerance to a drought stress, as evidenced by a reduced leaf water loss and an increased total leaf chlorophyll content, stomatal conductance, net photosynthetic rate, and activities of superoxide dismutase, peroxidase, and ascorbate peroxidase (APX). Moreover, the transcription of genes involved in the antioxidation defense system were higher in the transgenic plants than in the WT plants upon the drought stress.

Indian mustard (Brassica juncea L. cv. Vitasso) plants exposed to 10, 30, 50 and 100 µM of Cd for 5 d in hydroponic culture were analysed with reference to the distribution of Cd²⁺, the accumulation of biomass and antioxidants and antioxidative enzymes in leaves. Cd induced a decrease in plant biomass. The maximum accumulation of Cd occurred in roots followed by stems and leaves. Cd induced a decrease in catalase (CAT) and guiacol peroxidase (GPX) activities but an increase in ascorbate peroxidase (APX) and monodehydroascorbate reductase (MDHAR) activities. Enhancement in dehydroascorbate reductase (DHAR) activity was also at 10 µM Cd. Glutathione reductase (GR) activity showed pronounced stimulation after all treatments, but glutathione S-transferase (GST) and glutathione peroxidase (GPOX) activities decreased. The effectiveness of ascorbate-glutathione cycle (AGC) was determined by the ratio of ascorbate to H₂O₂. This ratio decreased in the Cd-treated leaves which indicated that the cycle was disordered.

This study was carried out to better understand the role of 24-epibrassinolide (EBR) in thermotolerance of melon (Cucumis melo L.). The melon seedlings were pretreated with various concentrations of EBR (0, 0.05, 0.1, 0.5, 1.0, and 1.5 mg dm^-3) as foliar spray and then exposed to a high temperature (HT) stress. Exogenous EBR (0.5-1.5 mg dm^-3) alleviated HT-caused growth suppression. In parallel, 1.0 mg dm^-3 EBR attenuated the decrease in chlorophyll content, net photosynthetic rate, stomatal conductance, maximum quantum efficiency of photosystem (PS) II, quantum yield of PS II, and photochemical quenching of chlorophyll a fluorescence in HT-stressed plants, and inhibited transpiration rate and non-photochemical quenching. Furthermore, exogenous EBR also significantly reduced the content of malondialdehyde (MDA) and increased the content of soluble proteins and free proline, and activities of antioxidant enzymes including superoxide dismutase, guaiacol peroxidase, catalase, and ascorbate peroxidase under the HT stress. The results show that protective effects of EBR against the HT stress in the melon seedlings were most likely mediated through the improvement of photosynthesis and the stimulation of antioxidant capacity.

Sulfur dioxide (SO₂) is a well-known and widespread air pollutant but it also acts as signaling molecule in various processes in animals. However, there is limited information on the role of SO₂ in plants except of its toxicity. Here we studied the role of SO₂ on stomatal movements in sweet potato (Ipomoea batatas) leaves. SO₂, generated by Na₂SO₃/NaHSO₃ solutions, was applied on epidermal strips. We found that the SO₂ donor induced stomatal closure in a dose-dependent manner. Rapid increases in endogenous hydrogen sulfide and nitric oxide content levels were observed in leaves after the treatment with the SO₂ donor. The SO₂-induced stomatal closure was reversed by the H₂S scavenger hypotaurine and the NO-specific scavenger cPTIO. Our results indicate that the SO₂-induced stomatal closure was likely mediated by the H₂S and NO signaling pathways.