The effects of lead toxicity on leaf gas exchange, chlorophyll content, chlorophyll fluorescence, chloroplast ultrastructure, and opening of stomata were examined in tobacco (Nicotiana tabacum L.) plants. Plants were grown in a growth chamber for 7 d in Hoagland nutrient solution supplemented with 0.0 (control), 5, 10, 25, 50, 100, 300 and 500 μM Pb(NO₃)₂. Plants treated with 5, 10, and 25 μM Pb(NO₃)₂ exhibited no abnormalities. Root and shoot growth, net photosynthetic rate and stomatal conductance were significantly reduced in plants treated with 100, 300 and 500 μM Pb(NO₃)₂. In plants treated with 500 μM Pb(NO₃)₂, the majority of stomata were closed. The effect of Pb(NO₃)₂ on chlorophyll content and chlorophyll fluorescence parameters was negligible. However, in plants exposed to 100, 300, and 500 μM Pb(NO₃)₂, the mesophyll cells showed altered chloroplasts with disrupted thylakoid membranes.

The seedling response to high Cu concentrations (1 and 10 μM CuSO₄ . 5 H₂O) was studied in Aegilops triuncialis, Ae. geniculata, Ae. cylindrica and Haynaldia villosa. The negative effect of Cu on the root growth was recorded at both concentrations, while the shoot growth was inhibited at 10 μM. The most tolerant was Ae. triuncialis, followed by Ae. geniculata. Ae. cylindrica and H. villosa were more sensitive.

Cytophysiological and cytogenetic characteristics of cell suspension culture of Panax japonicus var. repens were studied in relation to the accumulation of ginsenosides (GSs). The minimal time of cell number doubling was 1.3 ± 0.1 d and cell number increased 7 to 8-fold during growth cycle. The cell culture can be considered as aneuploid with about tetraploid (46-60 chromosomes) modal class. Upon long-term cultivation, the total content of GSs considerably increased and maximal concentration of GSs was 2.2 %(d.m.). The ratio of seven major GSs only slightly altered both over each and different subcultures. The overall amount of GSs of Rg-group significantly exceeded that of Rb-group. Cell volume and the number of large cellular aggregates with the higher proportion (by 20 %) of parenchymal cells increased late in the subculture. In this time the population contained about 20 % of the cells with doubled amount of nuclear DNA and accompanied with elevation in the GS content. These data prompted us to suggest that biosynthesis of GSs has a link with cell differentiation.

The aim of this study was to evaluate the growth and development of Aechmea blanchetiana Baker L.B. Sm. in vitro on medium with 0.0, 0.145, 1.45 and 14.5 μM Cu and 0.0, 2.75, 27.5 and 275 μM Zn. Significant accumulation of Cu and Zn occurred at 14.5 μM Cu and 27.5 and 275 μM Zn, respectively, and there were no significant changes in contents of the other macro- and micronutrients. Superoxide dismutase (SOD) activity significantly changed in the presence of both metals. Spermine content increased as Zn concentration increased and decreased with increasing concentrations of Cu. There was an accumulation of H₂O₂ in the leaf tissue of plants grown in 1.45 and 14.5 μM Cu and 27.5 and 275 μM Zn. A. blanchetiana was found tolerant to the Cu and Zn in concentrations used in this study and displays the capacity to accumulate these metals.

The oxidative processes and antioxidative system in cucumber (Cucumis sativus L.) fruit were determined during development and senescence. Four distinct developmental stages could be delineated during fruit maturation: immature (3-8 d after anthesis, DAA), mature (9-16 DAA), breaker (17-22 DAA), and yellow (35-40 DAA). The electrolyte leakage, malondialdehyde content, superoxide anion production rate, and hydrogen peroxide content increased continuously during fruit development and senescence. Superoxide dismutase and peroxidase activities consistently increased during fruit maturation, and the catalase activity displayed a single peak at the mature stage. Ascorbate peroxidase and glutathione reductase activities declined during fruit development, but both were activated in yellow fruit. Monodehydroascorbate reductase activity declined and dehydroascorbate reductase (DHAR) activity increased during fruit growth. DHAR was repressed in yellow fruit. Ascorbate dramatically accumulated and its redox state increased, whereas glutathione was degraded and its redox state declined, with fruit maturation.

Rice (Oryza sativa L.) seedlings inhibited the growth of hypocotyls and roots of cress (Lepidium sativum L.) seedlings when both seedlings were grown together. Two growth inhibiting substances were found in the culture solution in which rice seedlings were hydroponically grown for 14 d. One growth inhibitor was further purified. This suggests that the rice seedlings may produce growth inhibiting substances, acting as allelochemicals to other plants, and release them from their roots into the environment.

Salix alba L. and Populus×euroamericana cv. Robusta cuttings were grown in 10 μM Cd(NO₃)₂ (direct treatment) or in Knop solution and afterwards in Cd(NO₃)₂ (indirect treatment). Cd impact on rooting of directly treated plants and its impact on normally formed roots and shoots of indirectly treated plants were studied. The cumulative length, number and biomass of willow roots, pigment and starch contents, leaf net photosynthetic rate and dry mass/leaf area ratio of willow leaves were positively influenced by indirect treatment. However, indirectly treated poplars were more sensitive to Cd than directly treated ones. Indirect treatment lowered root Cd uptake in willow, Cd accumulation in cuttings of both species and Cd accumulation in poplar shoots. Cd-caused structural changes were similar in both species and in both treatments. Root apices, rhizodermis and cortex were the most seriously damaged root parts. In directly treated willow, the structure of central cylinder (0.5 - 1 cm from apex) remained unchanged in contrast to indirectly treated plants. Formation of cambium close to the apex indicated shortening of root elongation zone of indirectly treated plants. Directly Cd-treated poplar roots exhibited unusual defence activity of root apical meristem and accumulation of darkly stained material around central cylinder.

Short-term responses of Sedum alfredii roots to Cd exposure was compared in Cd hyperaccumulator (HE) and nonhyperaccumulating ecotype (NHE). Cadmium exposure significantly inhibited root elongation and induced loss of plasma membrane integrity and lipid peroxidation of roots tips in the NHE, whereas these effects were much less pronounced in the HE plants. A strong accumulation of reactive oxygen species with increasing Cd concentration was noted in the NHE root tips, but not in HE. After Cd exposure, a dose-dependent decrease in oxidized glutathione and marked increase in reduced glutathione and non-protein thiols were observed in root tips of HE, but were not seen in the NHE plants. These results suggest that the HE tolerates high Cd in the environment through the differential adaptations against Cd-induced oxidative stress.

The effects of carbon dioxide supply within the range of 1-5 % (along with purified air), on cell culture of Panax ginseng were investigated in a balloon type bubble bioreactor containing 4 dm³ of Murashige and Skoog (MS) medium supplemented with 7.0 mg dm^-3 indolebutyric acid, 0.5 mg dm^-3 kinetin and 30 g dm^-3 sucrose. A 1 % CO₂ supply was found beneficial for the production of cell mass; however, increasing CO₂ concentration to 2.5 and 5 % decreased the biomass accumulation. CO₂ enrichment was not beneficial for saponin production and 1, 2.5, and 5 % CO₂ supply resulted in decrease in saponin accumulation up to 11.6, 19.5, and 50.6 %, respectively.

The leaf structure and chloroplast ultrastructure of kidney tea (Orthosiphon stamineus Benth.) was studied in in vitro culture on standard MS medium supplemented with or without plant growth regulators (PGRs). The cytokinin N⁶-benzyladenine (BA) negatively affected the structure of the palisade parenchyma and chloroplast ultrastructure and increased the stomatal frequency of the adaxial epidermis. The auxin indole-3-butyric acid (IBA) did not modify the morphology of regenerated leaf tissues as well as the chloroplast ultrastructure. The effect of both PGRs applied in combination was manifested in well-differentiated mesophyll parenchyma, typical chloroplast ultrastructure and increased stomatal frequency on both leaf surfaces. This protocol can be suggested for further ex vitro propagation.

An ascorbate-deficient semi-dwarf mutant asfL-1 was detected in 250 Gy γ-ray treated grass pea (Lathyrus sativus L.) cv. BioR-231. The mutant contained only 42 % of leaf and 20 % of root ascorbate content of mother control (MC). I investigated the possible causes of ascorbate deficiency and its effect on growth and antioxidant defense in control and 150 mM NaCl-treated seedling after 60 d growth period. Ascorbate deficiency was due to significant reduction in activities of monodehydroascorbate reductase and dehydroascorbate reductase as well as increase in ascorbate oxidase, leading to considerable decrease in redox state. Despite low ascorbate pool and decrease in ascorbate peroxidase activity, shoot and root biomass production in asfL-1 mutant were similar to MC plants, even at NaCl treatment. High accumulation of glutathione (GSH) coupled with high activities of GSH reductase, catalase, GSH peroxidase and peroxidase in both tissues of the mutant permitted efficient recycling of GSH and scavenging of H₂O₂ through well integrated catalase/peroxidase system, despite high superoxide dismutase activity under NaCl treatment. The collapse of this system led to inhibition of growth in NaCl-treated mother plants. Together, the results suggested that asfL-1 plants undertook a major reshuffle in its antioxidant defense machinery, which effectively counterbalanced the negative impact of ascorbate deficiency and remained unperturbed by NaCl treatment to maintain normal growth and biomass production.

In this study, we report a function of myo-inositol-O-methyltransferase (Imt1) in response to low temperature stress using transgenic Arabidopsis thaliana. Imt1 gene was constructed identical to the Imt1 gene from a halophyte Mesembryanthemum crystallinum. After cold stress, the Imt1 transgenic plants exhibited stronger growth than the wild type plants. The elevated cold tolerance of the Imt1 over-expressing plants was confirmed by the lower electrolyte leakage and accumulation of malondialdehyde, but higher proline and soluble sugar contents in transgenic than wild type plants.

The aim of this study was to test the hypothesis that salinity can affect indirectly the nitrate acquisition by a negative modulation triggered by glutamine accumulation. Cowpea plants were exposed to a mild NaCl concentration (50 mM) in order to restrict growth and N-demand. After 21 d, pretreated plants and control plants were supplied with 0, 5 and 10 mM of Ca(NO₃)₂ for 3 d in absence of NaCl. Salt pretreated plants showed a great limitation in acquisition of NO₃ ^-, indicated by decline in the nitrate uptake rate, NO₃ ^- accumulation, nitrate reductase activity and protein content. The restriction of NO₃ ^- utilization was positively associated with increased glutamine synthetase activity and glutamine accumulation, especially in roots.

A micropropagation protocol for Bacopa monniera (L.) Wettst., a medicinally important plant, has been developed. Direct organogenesis without callus formation was induced by culturing node, internode and leaf explants on growth regulator free Murashige and Skoog (MS) medium. MS medium supplemented with an antibiotic trimethoprim (TMP) and a fungicide bavistin (BVN) produced axillary shoots from node and adventitious shoot buds on the surface of all explants. The combination of 200 mg dm^-3 TMP and 200 mg dm^-3 BVN induced the optimum frequency of shoot formation as well as shoot number. Presence of both TMP and BVN induced multiple axillary shoot formation from the nodal segments and this ability was maintained for four subcultures.

Cucumber seedlings were pretreated with 3 μM 5-aminolevulinic acid (ALA) followed by cultivation at normal (25/18 °C) or high (42/38 °C) day/night temperature to investigate the protective effects of ALA on heat stress in plants. Heat elevated the contents of malondiadehyde (MDA), superoxide radical (O₂ ^.-) and hydrogen peroxide (H₂O₂) in leaves of all plants but less in ALA-pretreated plants. Heat treatment resulted in higher antioxidant enzyme activities and proline and soluble sugar contents and weaker growth inhibition in ALA-pretreated plants than in those treated with heat alone. These results indicate that ALA pretreatment increased the tolerance of seedlings to heat stress.

Distribution of cadmium between roots and shoots of barley was manipulated by the cadmium concentration (0.01 and 0.005 mM Cd²⁺), pH (4.6 and 5.9) as well as treatment duration. The prolongation of treatment increased dry mass and content of cadmium in plants. The cadmium is accumulated mainly in roots. Presence of both, 0.005 mM Cd²⁺ and 100 mM NaCl in medium at pH 5.9 (Cd-NaCl plants) resulted in the most severe growth inhibition of plants, but about one half accumulation of cadmium in roots then in a case of only Cd-treated plants. In the Cd-NaCl plants, the net photosynthetic and transpiration rates were less reduced then in a case of only NaCl-treated plants. The treatments also influenced uptake of Ca, Cd, Cu, K, Mg, Na and Zn predominantly in roots.

The effect of AlCl₃ on the antioxidant system of rice roots and the role of applied antioxidants ascorbic acid (AsA) and glutathione (GSH) in AlCl₃-inhibited growth of rice roots were investigated. AlCl₃ treatment resulted in a rapid inhibition of root growth but had no effect on lipid peroxidation and antioxidative enzyme activities in rice roots. AlCl₃ treatment resulted in lower content of H₂O₂, AsA, and GSH than in controls. Exogenous AsA or GSH counteracted growth inhibition of rice roots induced by AlCl₃. AlCl₃ treatment increased syringaldazine peroxidase (SPOX) activities and lignin content in rice roots. Exogenous AsA or GSH prevented the decrease in H₂O₂ content and the increase in SPOX activities and lignin content in rice roots caused by AlCl₃. Results suggest that lignification induced by low AsA or GSH content may explain the mechanism of Al-inhibited growth of rice roots.

The effects of exogenous 24-epibrassinolide (EBR) on the growth, oxidative damage, antioxidant system and ion contents in eggplant (Solanum melongena L.) seedlings under salt stress were investigated. Eggplant seedlings were exposed to 90 mM NaCl with 0, 0.025, 0.05, 0.10 and 0.20 mg dm^-3 EBR for 10 d. EBR, especially at concentration 0.05 mg dm^-3, alleviated growth suppression caused by NaCl stress, decreased electrolyte leakage, superoxide production and content of malondialdehyde and H₂O₂ in NaCl-treated plants. EBR also increased activities of superoxide dismutase, guaiacol peroxidase, catalase and ascorbate peroxidase and the contents of ascorbic acid and reduced glutathione. Furthermore, we also found that Na⁺, Cl^- contents were decreased, K⁺, Ca²⁺ contents and K⁺/Na⁺, Ca²⁺/Na⁺ ratios were increased in the presence of EBR under salt stress.

Glutathione-S-transferases (GSTs) are ubiquitous enzymes that play a key role in stress tolerance and cellular detoxification. The GST gene GsGST14 selected from the gene expression profiles of Glycine soja under alkaline stress was transformed into alfalfa (Medicago sativa L.). Transgenic alfalfa plants showed 1.73-1.99 times higher GST activity than wild-type plants. Transgenic alfalfa grew well in the presence of 100 mM NaHCO₃, while wild-type plants exhibited chlorosis and stunted growth, even death. There were marked changes in malondialdehyde content and relative membrane permeability caused by alkaline stress in non-transgenic lines compared to transgenic lines. The results indicate that the gene GsGST14 could enhance alkaline resistance in transgenic alfalfa.

Brassinosteroids (BRs) have been proposed to increase the resistance of plants to drought stress. The effect of foliar application of 0.1 μM 24-epibrassinolide (EBR) on chlorophyll (Chl) content, photosystem 2 (PS 2) photochemistry, membrane permeability, lipid peroxidation, relative water content (RWC), proline content, and the antioxidant system in drought-stressed Chorispora bungeana plants was investigated. The results showed that polyethylene glycol (PEG) induced water stress decreased RWC, Chl content and variable to maximum Chl fluorescence ratio (F_v/F_m) less in plants pretreated with EBR than in non-pretreated plants. In addition, lipid peroxidation, measured in terms of malondialdehyde content, membrane permeability and proline content in drought-stressed plants were less increased in EBR pretreated plants, while antioxidative enzyme activities and reduced ascorbate and glutathione contents were more increased in EBR pretreated than in non-pretreated plants. These results suggested that EBR could improve plant growth under drought stress

Proline accumulation and mobilization in roots of 7-d-old seedlings of wheat genotypes varying in sensitivity towards water stress were compared. Water stress was induced by polyethylene glycol (PEG-6000; osmotic potential -1.5 MPa) in the presence of 0.1 mM abscisic acid (ABA), 1 mM calcium chloride, 0.5 mM verapamil (Ca²⁺ channel blocker), 0.5 mM fluridone (inhibitor of ABA biosynthesis). While both the genotypes did not differ in total proline accumulation, rate of proline accumulation and utilization was higher in tolerant genotype C 306 as compared to susceptible genotype HD 2380. The treatment with ABA and CaCl₂ caused further increase in proline accumulation during stress and reduced its mobilization during recovery. The membrane stability and elongation rate of roots was observed to be higher at ABA and calcium treatment in both the genotypes under stress. As was evident from inhibitor studies, the tolerant genotype was more responsive to ABA and the susceptible one to calcium.

Alternative oxidase (AOX) transfers electrons from ubiquinone to oxygen in the respiratory chain of plant mitochondria. It is widely accepted that AOX functions as a mechanism decreasing the formation of reactive oxygen species (ROS) produced during respiratory electron transport. However, there are no experimental data to provide unambiguous proof of this hypothesis. We have studied growth characteristics, ROS content, and stress sensitivity in Arabidopsis transgenic lines with reduced or increased levels of AOX. We demonstrated that AOX-deficient plants grown in soil had an extended reproductive phase. Changes in AOX activity did not affect ROS content or stress sensitivity in the whole plants. However in the suspension culture, cells overexpressing AOX had significantly lower ROS content, whereas the AOX-deficient cells had higher ROS contents compared to the wild-type (WT) cells. Prooxidant treatment led to the increase in ROS content and to the reduction of viability more in the cells overexpressing AOX than in WT and AOX-deficient cells. Thus, we demonstrated that differences in the metabolism of whole plants and cultured cells might affect AOX functioning.

Cymbidium shoot buds grown under Mg²⁺ deficiency without naphthalene acetic acid (NAA) showed knotted appearance. Ultrastructure of the cortical cells showed a progressive disorganization and disintegration of chloroplast membranes. The growth of shoots was resumed with the addition of 10 μM NAA. Specific NO scavenger, cPTIO induced deformation in shoot growth in 80 % of cultures. In longitudinal sections of shoots treated with cPTIO, depositions of densely stained particles in cells were observed. These inhibitory responses of cPTIO were ameliorated by 10 μM NAA. The NO donor, sodium nitroprusside (SNP), treated shoot buds displayed rapid senescence followed by necrosis of leaves. Ultrastructure of cortical cells at this stage revealed the endocytosis of mitochondria along with membrane bound cytoplasmic inclusions in the vacuole. A sharp increase in H₂O₂ generation was observed with a little change in the activity of antioxidant glutathione disulfide (GSSG), suggesting NO mediated oxidative stress. Surprisingly, after 4 weeks these necrotic shoots were converted into a globular, embryo like shoot tip with numerous structures termed here as 'neomorph' in its base. Neomorphs were different from protocorm like bodies both anatomically and morphologically. Ultrastructure of the rhizome tip exhibited numerous amyloplast and round mitochondria. At this stage, the generation of high rate of H₂O₂ was masked by GSSG, and the generation of GSSG was proportional with the concentrations of SNP, and not observed in the control (without SNP). The neomorphs were further sub-cultured to medium with different concentrations of SNP or cPTIO. After 4 weeks of culture, only the neomorphs sub-cultured on medium with SNP developed into shoots and approximately ten shoots were observed to emerge from the axils of each rhizome. Ultrastructure of cells of regenerating green neomorphs showed different shapes of mitochondria and chloroplasts and presence of active dictyosomes. The obtained shoots subjected to the acclimatization in polyhouse, expressed good growth with 85 % survival. Therefore it is reasonable to suggest that the process of de-differentiation and re-differentiation leading to rhizome formation under the condition of Mg²⁺ deficiency is NO mediated.

The functions of cytosolic heat shock protein AtHsp90.3 in response to heavy metal stress were characterized by using expression of AtHsp90.3 gene in yeast and Arabidopsis thaliana. AtHsp90.3 supported the Saccharomyces cerevisiae Hsp90 knockout strain R0005 growth and maintaining cells membrane integrity under cadmium and arsenic stresses, which was compatible with the components of ScHsc82 machinery. However, constitutive overexpression of AtHsp90.3 in Arabidopsis impaired plant tolerance to Cd stress with lower germination rate and shorter root length, decreased contents of phytochelatins (PCs) and glutathione (GSH), inhibited activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD), and increased content of malondialdehyde (MDA). These results suggested that proper homeostasis of Hsp90 was critical for cellular response and/or tolerance to heavy metal stress in plants.

The effect of soil moisture on gas exchange and growth of an endangered species, Changium smyrnioides, was compared with a non-endangered species, Anthriscus sylvestris. The two species belong to the same family Umbellaceae. With the decrease of soil moisture, the net photosynthetic rate (P_N) and transpiration rate (E) decreased, while water use efficiency (WUE) increased, P_N and WUE of C. smyrnioides were lower than those of A. sylvestris, whereas E was higher than that of A. sylvestris. The biomass, leaf mass ratio (LMR) and leaf area ratio (LAR) of C. smyrnioides were lower than those of A. sylvestris. Under drought, biomass. LMR and LAR of C. smyrnioides decreased more steeply than those of A. sylvestris, whereas specific root length (SRL) of C. smyrnioides was higher, compared to that of A. sylvestris. The present study indicated that C. smyrnioides accumulated less biomass, and directed more biomass to roots than A. sylvestris.

Sugarcane is cultivated in tropical and subtropical regions where cold stress is not very common, but lower yields and reduced industrial quality of the plants are observed when it occurs. In our efforts to enhance cold tolerance in sugarcane, the gene encoding the enzyme isopentenyltransferase (ipt) under control of the cold inducible gene promoter AtCOR15a was transferred via biolistic transformation into sugarcane (Saccharum spp.) cv. RB855536. Semiquantitative RT-PCR using GAPDH encoding glyceraldehyde-3-phosphate dehydrogenase as the normalizer gene showed the increased expression of the ipt gene under cold stress. The detached leaves of genetically modified plants subjected to low temperatures showed visible reduction of leaf senescence in comparison to non-transgenic control plants. Induced overexpression of ipt gene also enhanced cold tolerance of non-acclimated whole plants. After being subjected to freezing temperature, leaf total chlorophyll contents of transgenic plants were up to 31 % higher than in wild type plants. Also, lower malondialdehyde content and electrolyte leakage indicated less damage induced by cold in transgenic plants. Thus, the expression of ipt driven by the stress inducible COR15a promoter did not affect plant growth while providing a greater tolerance to cold stress.

Xylem sap outflow from fine lateral roots (FLRs) isolated from hydroponically grown young maize (Zea mays L.) plants was visualized by local brightening of test solutions contrasted with purified Indian ink particles. Flow into the vessels was indicated by the adsorption of Evans Blue in their walls. The fraction of the FLRs able to exude xylem sap in a mineral medium with 30 mM mannitol decreased with increasing incubation time. This change was strongly retarded, when the FLRs were incubated in a medium containing glucose instead of mannitol. There was a broad range of variation of the osmotic potential of the test solutions (Ψ_so), wherein the fraction of the FLRs showing an initially reversed flow of the xylem sap varied between zero and unity. A median (M) of the osmotic potential of the xylem sap in FLRs (Ψ_sx) was estimated. It represents the value of Ψ_so that was lower than Ψ_sx in half of the roots of a sample before their transfer to the test solutions (Ψ_sxo). M was dependent on the osmotic potential of the medium used for growth or pre-incubation of the FLRs. Its value was not dependent on the molecular size of the osmolytes used to adjust Ψ_so, including dextran 8, which is excluded from cell walls. In all of the studied plants, M was lower than the osmotic potential of the xylem sap collected from the root before isolation of the FLRs. To explain this finding it is assumed that FLRs with Ψ_sxo > M had a higher hydraulic conductivity and a larger volume contributed to the exuded sap than those with Ψ_sx < M.

The present paper reports a protocol for minimum growth conservation of Drosophyllum lusitanicum (L.) Link. in vitro. Double-node cuttings were maintained for 4, 8 and 12 months at 5 or 25 °C in the dark. The effects of sucrose either alone at 5, 20, 30, 40 and 60 g dm^-3 or at 20, 40 and 60 g dm^-3 in combination with 20 g dm^-3 mannitol, on survival and post-storage shoot multiplication efficiency were investigated. The cultures could effectively be conserved under minimum growth at 5 °C for 8 months on Murashige and Skoog's medium supplemented with 60 g dm^-3 sucrose, 20 g dm^-3 mannitol and 0.91 µM zeatin. Following extended conservation, the cultures could be successfully regenerated into new shoots, and they were morphologically similar to those of non-stored controls.

The manipulation of cytokinin contents via Agrobacterium-mediated transformation is an efficient tool for delaying leaf senescence and improving the resistance to environmental stresses. In the present study, cotton transformants harbouring the Agrobacterium tumefaciens isopentenyl transferase (IPT) gene under the control of the promoter of Gossypium hirsutum cysteine proteinase (Ghcysp) were generated. PCR and Southern blot analysis indicated that the foreign DNA fragment was successfully integrated into the cotton genome. The chlorophyll and cytokinin contents, and ROS-scavenging enzymatic activities were significantly increased in transgenic cotton lines, which resulted in a significant delay in leaf senescence. The growth characteristics of transgenic cotton lines resembled the non-transgenic lines except delaying premature senescence and the lint yield and fiber quality of transgenic lines were improved. In addition, the transgenic lines had higher biomasses, IPT transcripts, and endogenous cytokinin contents compared with those of non-transgenic lines under 200 mM NaCl stress.

Barley (Hordeum vulgare L., cv. Hemus) plants were grown in nutrient solution with or without 54 µM Cd²⁺ for 12 d. A treatment with Cd²⁺ inhibited the growth of young barley plants. The main factor limiting plant growth was net assimilation rate, due to decreased photosynthetic rate and accelerated dark respiration rate. One of the reasons for the reduced photosynthetic rate was the lower chlorophyll and carotenoid content. Cd²⁺ decreased water potential and transpiration rate, but relative water content in leaves of the treated plants was not significantly changed.