Experiments were conducted to determine the interactive effects of salinity and certain growth regulators on growth and nitrogen assimilation in maize (Zea mays L. cv. GS-2). 100 mM NaCl inhibited the biomass accumulation, chlorophyll and carotenoid contents in leaves, nitrate content and uptake and nitrate reductase activity. The application of kinetin, ascorbic acid and 10 and 50 µM abscisic acid in the first experiment and 50 and 100 µM abscisic acid in the second experiment induced a substantial increase in the above parameters, the effect was highest with abscisic acid in salinized as well as non-salinized plants.

Two important enzyme in organic acid metabolism, phosphoenolpyruvate carboxylase (PEPC) and NADP-malic enzyme (NADP-ME), show marked diurnal rhythms in their activities during the establishment of the soybean - B. japonicum symbiosis. The pH of the nutrient solution changes in parallel with NADP-ME activity, being maximal during the night periods, whereas activity of PEPC was highest during the day periods. The results from the experiments with stem girdled plants indicated that the activity of root PEPC is modulated to a great extent by the supply of photosynthates from the shoots. It was also established that succinate application in the nutrient solution during inoculation altered significantly the pattern of assayed enzyme activities. Although our experiments did not reveal the precise mechanism of the involvement of root PEPC and NADP-ME in soybean response to inoculation with B. japonicum, they indicated the pattern of their activity during the first 72 h postinoculation which are critical for establishment and functioning of the symbiosis.

Leaves from mature in vitro grown plants of Drosera spathulata Labill. regenerated new plantlets on solid induction medium in light. Especially vascular sheath parenchyma cells located close to basal part of tentacule showed high embryogenic potential. Proembryoids arrising from the tentacule base part were visible by scanning electron microscopy. Their surface cells were linked and covered with thin external, fibrilar network representing an extracellular matrix (ECM). Proembryogenic surface cells were later connected by coarse strands of fibrils. Young protoderm was formed arround globular embryoids and its cells were characterized by "brain-like" surface structure. However, the surface of fully developed protodermal cells was practicaly smooth and cells were stick to each other very tightly in torpedo and cotyledonary shaped embryoids. The presence of ECM was typical only for somatic proembryos and globular embryos. The ECM network was never observed on the surface of heart and torpedo shaped embryos.

Vigna radiata (L.) seedlings (5-d-old) were exposed to different concentrations of NaCl in light and in dark. The content of proline in the shoots increased with an increase in NaCl concentration, in light as well as in dark. But, irrespective of the concentration of NaCl, proline accumulation in the shoots was higher in light than in dark. Pretreatment of seedlings with dichlorophenyl dimethyl urea (DCMU) did not make any significant difference in light promoted stress induced proline accumulation. As DCMU is a potent inhibitor of photosynthetic electron transport, the light reaction of photosynthesis was not responsible for the observed light promotion of stress induced proline accumulation. In another set of experiments, 5-d-old green as well as etiolated seedlings were exposed to NaCl stress in the presence of different concentrations of sucrose. Irrespective of the concentration of sucrose used, proline content in shoots of stressed seedlings was higher in light than in dark. Although, sucrose enhanced NaCl stress induced increase in proline content in dark by about 32 %, this enhancement was not comparable to the 286 % increase in proline content brought about by light. These results showed that certain factors other than photosynthesis play a role in light promotion of stress induced proline accumulation.

Seasonal changes in foliage nitrogen (N) and carbon (C) concentrations and δ¹⁵N and δ¹³C ratios were monitored during a year in Erica arborea, Myrtus communis and Juniperus communis co-occurring at a natural CO₂ spring (elevated [CO₂], about 700 μmol mol^-1) and at a nearby control site (ambient [CO₂], 360 μmol mol^-1) in a Mediterranean environment. Leaf N concentration was lower in elevated [CO₂] than in ambient [CO₂] for M. communis, higher for J. communis, and dependent on the season for E. arborea. Leaf C concentration was negatively affected by atmospheric CO₂ enrichment, regardless of the species. C/N ratio varied concomitantly to N. Leaves in elevated [CO₂] showed lower δ¹³C, and therefore likely lower water use efficiencies than leaves at the control site, regardless of the species, suggesting substantial photosynthetic acclimation under long-term CO₂-enriched atmosphere. Leaves of E. arborea showed lower values of δ¹⁵N under elevated [CO₂], but this was not the case of M. communis and J. communis foliage. The use of the resources and leaf chemical composition are affected by elevated [CO₂], but such an effect varies during the year, and is species-dependent. The seasonal dependency and species specificity suggest that plants are able to exploit different available water and N resources within Mediterranean sites.

Chlorophyll a (Chl a) content and chlorophyllase (Chlase) activity from leaves of wild type (WT) and the ethylene-insensitive mutant (eti 5) of Arabidopsis thaliana (L.) Heynh during temperature stress and plant recovery have been studied. The plants were subjected to temperatures of 4 °C (LT) and 38 °C (HT) for 24 h. Chl a gradually decreased somewhat during stress and in the first day of recovery, especially in HT-treated plants. At the end of the experimental period (1 d stress and 10 d recovery) Chl a content was lower in eti 5 plants than in WT ones. The Chlase in WT was more affected than in eti 5 plants during the temperature treatment and the recovery period.

The relationship between nutrient composition, crop biomass, and glutamate dehydrogenase (GDH) isoenzyme pattern was investigated in soybean (Glycine max) and maize (Zea mays) by monitoring the nutrient induced isomerization of the enzyme from the seedling stage to the mature crop. GDH was extracted from the leaves of the plants, and the isoenzymes were fractionated by isoelectric focusing followed by native polyacrylamide gel electrophoresis. The isomerization V_max values for soybean GDH, similar to maize GDH increased curvilinearly from 200 - 400 μmol mg^-1 min^-1 as the inorganic phosphate nutrient applied to the soil decreased from 50 - 0 mM. In soybean, combinations of N and K, P, or S nutrients induced the acidic and neutral isoenzymes, and gave biomass increases 25 - 50 % higher than the control plant. GDH isoenzymes were suppressed in soybean that received nutrients without N, K, or P and accordingly the biomass was about 30 % lower than the control. Treatment of maize with NPK nutrients increased the GDH V_max values from 138.9 at the vegetative to 256.4 μmol mg^-1 min^-1 at the reproductive phase, and suppressed the basic isoenzymes, but induced both the acidic and neutral isoenzymes thereby inducing seed production (27.0 ± 1.4 g per plant); whereas both the acidic and basic isoenzymes were suppressed in the control maize, and seeds did not develop. Simultaneous induction of the acidic, neutral, and basic isoenzymes of GDH indicated the occurrence of senescence. Therefore in maize and soybean, the induction of the acidic and basic isoenzymes of GDH led to the enhancement of biomass.

Relative nuclear DNA contents in cortex parenchyma cells in root segments of 3- and 7-d-old soybean seedlings grown at 25 °C and in plants grown for 3 d at 25 °C, and then for 4 d at 10 °C, were determined with cytophotometry. Measurements revealed that in each variant the cortex cell nuclei with DNA content between 2C and 8C were in all the examined segments and nuclei with 8C - 16C DNA appeared in higher parts of roots. However, in chilled plant cells the number of 8C - 16C DNA nuclei was very low. Therefore, chilling inhibited endoreplication in comparison with plants grown at 25 °C for 7 d, and even reduced endopolyploidy level as compared to the initial seedlings, i.e. 3-d-old plants. DNA contents in root hairs grown at 25 °C (control) and in root hairs emerged at 10 °C were also determined. In controls 4C - 8C DNA nuclei predominated while in chilled plants an additional population of 2C - 4C DNA appeared. Thus a reduction of DNA synthesis was brought about by low temperature. The occurrence of an intermediate DNA contents besides those with full endoreplication cycles suggests the possibility of differential DNA replication. This suggestion seems to be supported by the lack of ³H-thymidine incorporation into root hair nuclei at the examined developmental stage both in control and chilled root hairs. The same number, but larger, chromocentric lumps in polyploid cortex cell nuclei of higher root zones, in comparison to meristematic nuclei, suggests that endoreduplication process occurred.

A study of the genetic variability of a population of Hypericum brasiliense was made using several isozyme systems as well as an investigation of the morphogenic potential of apical buds from plants at different development stages (juvenile and adult) using in vitro culture. The results from nine isozymes systems showed low polymorphism in the alleles. Apical buds from juvenile plants originated plantlets with apical dominance and fast growth while those from adults led to the development of flower buds.

The interactive effects of salinity stress (40, 80, 120 and 160 mM NaCl) and ascorbic acid (0.6 mM), thiamin (0.3 mM) or sodium salicylate (0.6 mM) were studied in wheat (Triticum aestivum L.). The contents of cellulose, lignin of either shoots or roots, pectin of root and soluble sugars of shoots were lowered with the rise of NaCl concentration. On the other hand, the contents of hemicellulose and soluble sugars of roots, starch and soluble proteins of shoots, proline of either shoots or roots, and amino acids of roots were raised. Also, increasing NaCl concentration in the culture media increased Na⁺ and Ca²⁺ accumulation and gradually lowered K⁺ and Mg²⁺ concentration in different organs of wheat plant. Grain soaking in ascorbic acid, thiamin or sodium salicylate could counteract the adverse effects of NaCl salinity on the seedlings of wheat plant by suppression of salt stress induced accumulation of proline.

Diurnal and seasonal changes of net photosynthetic rate (P_n) and the efficiency of photosystem 2 (F_v/F_m) were measured on two perennial species growing on a soil catena in semi-arid south-east Spain. Stipa tenacissima, a tussock grass, grows on shallow soil at the top of the catena and Retama sphaerocarpa, a leguminous shrub, grows in the valley bottom. A linear relationship was found between light saturated photosynthetic rates (P_max) and diffusive leaf conductance (g_l) in both Retama and Stipa indicating that the intercellular CO₂ concentration (c_i) was maintained constant in both species diurnally. Relatively high values of calculated c_i in Retama cladodes suggested that was not the primary limitation to carbon assimilation. F_v/F_m for the two species when well watered was around 0.8. Although Retama cladodes maintained this value throughout the year, F_v/F_m decreased to a minimum of 0.43 in Stipa leaves, at the end of the dry season. Our data suggest that plants in the Rambla Honda can substantially reduce transpiration without reducing photosynthetic rates to the same extent by closing their stomata, because P_n is reduced primarily by high respiration, decreased mesophyll conductance and by photoinhibition or permanent damage of photosystem 2.

Eleven monosomics in cotton that were obtained in the progenies of three disomic desynaptic plants were cytologically characterized. The transmission of the monosomes in progeny was shown in the 26 monosomic plants. In 23 plants the frequency of monosomics was ranged between 14.29 and 41.67 %. Three monosomics usually occurred in much lower frequencies (from 3.03 to 5.00 %). Various transmission rates indirectly pointed out different monosomes as a specific chromosomes of cotton genome. Three telochromosomes and one isochromosome were isolated from the progenies of the four monosomics. Using translocation test it was recovered that seven monosomes of different monosomics are homologous to one of the chromosomes of six translocation lines of our collection.

Multiple shoot regeneration from the cut plumular ends of embryo axes of chickpea (Cicer arietinum L.) was evaluated on Murashige and Skoog medium having different concentrations of thidiazuron (TDZ) (0.1 to 10.0 mg dm^-3) 6-benzylaminopurine (BAP) (0.5 and 1.0 mg dm^-3), kinetin (0.5 and 1.0 mg dm^-3) or zeatin (2.0 and 4.0 mg dm^-3). TDZ (0.2 mg dm^-3) was found to be the most effective cytokinin as it produced multiple shoots in 100 % of the explants from genotypes C235, ICC5166, ICC12269, ICC4951, ICC11531, BG256 and a local cultivar. Shoots were elongated on growth regulator-free medium, and rooted on growth regulator-free medium containing 1/4 MS salts + full vitamins + 3 % sucrose. Plantlets formed were acclimatized for 12 - 15 d in MS medium with a gradual reduction in sucrose concentration and transferred into pots filled with soil and kept in the field; this resulted in more than 70 % survival. The plants developed normally and produced fertile flowers and set seeds. Low temperatures, maximum 19.0 °C, and minimum 8.2 °C, during the first 15 d of transfer favoured survival on transfer to pots.

The influence of nitrogen deprivation on leaf development and the biomechanics of leaf growth were studied using maize (Zea mays L.) seedlings grown under low irradiance. Although the nitrogen deprivation had no significant effect on photosynthesis, the leaf length, the leaf area, and the total assimilation area of plants decreased. The mature size of the epidermal cells was not altered, while the cells of nitrogen-deprived plants reached their final length closer to the leaf base than the epidermal cells of control plants. Decreases in the length of the growing zone (from 50 to 30 mm) and in the maximum value of relative elemental growth rate (from 0.08 to 0.06 mm mm^-1 h^-1) were observed in the nitrogen deprived plants. The maximal value of growth velocity in the control treatment was higher along the elongation zone, except for the basal 20 mm, where there was no significant difference between the control and the N-deprived plants. The net deposition rates of water and dry matter were also affected by nitrogen deprivation: the values of these features decreased and the spatial position of the maximum of the deposition rates shifted towards the leaf base.

Response of two spring wheat (Triticum aestivum L.) cultivars, salt tolerant SARC-I and salt sensitive Potohar, to different concentrations of NaCl was examined under glasshouse conditions. Eighteen-day-old plants of both the lines grown in sand culture were irrigated with 0 (control), 80, 160 or 240 mM NaCl in full strength Hoagland's nutrient solution. Shoot fresh and dry masses, and leaf area per plant of SARC-I at the vegetative stage, were significantly greater than those of cv. Potohar at higher salt concentrations, however, relative growth rate (RGR) of cv. Potohar was significantly higher than that of SARC-I. SARC-I had higher net photosynthetic rate (P_N), stomatal conductance (g_s) and transpiration rate (E) than cv. Potohar at the vegetative stage, but the cultivars did not differ significantly in water-use efficiency (P_N/E), intrinsic water use efficiency (P_N/g_s), and intercellular/ambient CO₂ concentration ratio. At the grain development stage, SARC-I had significantly higher P_N and g_s in the flag leaf than cv. Potohar under salinity. SARC-I was superior to cv. Potohar with respect to number of grains per spike, number of grains per spikelet, mean grain mass, and grain yield per plant at all NaCl concentrations.

Eryngium foetidum L. plants were regenerated from mature leaf and petiole explants through direct organogenesis without intervening callus phase. From leaf explants, adventitious multiple shoots raised on Murashige and Skoog (MS) medium supplemented with 4.43 μM benzylaminopurine (BAP) and 0.57 μM indole-3-acetic acid (IAA), whereas in petiole explants shoot regeneration occurred at 8.86 μM BAP and 0.57 μM IAAA. 80% of the leaf explants and 44% of petiole explants produced shoots after four weeks of culture. The regenerated plants were rooted on MS medium supplemented with 2.46 μM indole-3-butyric acid and 2.88 μM gibberellic acid. The plants were successfully established in the soil and showed 70.9% survival in the field.

The contents of several photosynthetic metabolites - 3-phosphoglyceric acid (3-PGA), pyruvate, nicotinamide adenine dinucleotide phosphate (NADP) and adenosine triphosphate (ATP) - were determined in leaves of cotton plants (Gossypium hirsutum L. cv. H-777) subjected to waterlogging at vegetative stage, and/or drought at the reproductive stage. In controls, soil moisture contents was kept at field capacity. One day prior to stress, the plant shoots were sprayed with 5 μM aqueous solution of indole-3-acetic acid (IAA), gibberellic acid (GA₃), benzylaminopurine (BAP), abscisic acid, and ethrel. In control plants, various growth regulators reduced contents of 3-PGA and ATP while increased contents of NADP and pyruvate. During waterlogging IAA promoted 3-PGA content, and BAP enhanced pyruvate content. During drought, GA₃ enhanced ATP and 3-PGA contents, while IAA enhanced pyruvate content.

The seasonal dynamics in content and distribution of N-rich compounds between overwintering organs of Calamagrostis epigeios were examined. Samples were taken both from plants grown in natural conditions and in containers with controlled nutrient supply. There were significant changes in content of nitrate, free amino acids and soluble protein in all investigated plant parts during the course of a year. Amino acids showed both the highest maximum and seasonal fluctuation among the all N compounds observed and, therefore, appear to have a central role in N storage. Their content rises in the autumn, remains stable during winter and declines quickly at the beginning of spring. The most abundant amino acids in the end of winter storage period - asparagine, arginine and glutamine - constituted about 90 % of N in fraction of free amino acids. The portion of N stored in soluble proteins, however, was considerably smaller compare to both amino acids and nitrate. The amount of N stored in rhizomes of C. epigeios was smaller than in roots and stubble base before the onset of spring re-growth. This indicates that roots and stubble base are particularly important for winter N storage in this species.

Using the whole plant and model systems, we demonstrate that the aluminum ions (Al³⁺) stimulate phenolic-dependent lipid peroxidation. Lipid peroxidation in barley (Hordeum vulgare L. cv. Donor) roots was 30 % higher under AlCl₃ treatment than without Al. Major decomposition product of lipid peroxidation was 4-hydroxynonenal (4-HNE) but not thiobarbituric acid reactive substances (TBARS), a widely used markers for lipid peroxidation. Similarly, AlCl₃ stimulated lipid peroxidation of soybean liposomes in the presence of chlorogenic acid (CGA) and H₂O₂/horseradish peroxidase system which can oxidize phenolics. Al³⁺ was found to enhance lipid peroxidation induced by oxidized CGA. Intermediates of lignin biosynthesis in plants, including p-coumaric acid, ferulic acid, sinapic acid and coniferyl alcohol, also showed similar effects. These results suggest that Al³⁺ has a potential to induce oxidative stress in plants by stimulating the prooxidant nature of endogenous phenolic compounds.

Seasonal dynamic of total nonstructural saccharides (TNS) and individual saccharides (starch, sucrose, glucose, fructose, fructans) was followed in rhizomes and stem bases of Calamagrostis epigeios (L.) Roth at two types of meadows communities in the South Moravia (Czech Republic): cnidion and molinion alliances, which differ in their water regime. The TNS were formed mainly by fructans and starch, while glucose, sucrose and fructose were low. The amount of TNS in rhizomes and stem bases of plants from wet cnidion site was higher than in plants from drier molinion site. The seasonal trends of all saccharides were similar in the both sites. During growing season (June to October) the main storage sugar was fructan (18 - 21 % of dry biomass). At the beginning of September the content of fructan decreased to 10 - 12 % and simultaneously the content of sucrose increased from 1 to 3 %. This may increase frost resistance. The content of TNS in the stem bases was lower than in the rhizomes. During winter time the stem bases contained 2 to 2.5 % of sucrose. Plant height and aboveground biomass were also higher in molinion site.

Wheat (Triticum aestivum L.) plants were subjected to mild water stress during grain filling at milk (early, medium, and late) and dough (early, soft, hard) stages. The grains harvested from stressed plants were subjected to low temperature stress of 10 °C for 24 h in presence or absence of 1 mM CaCl₂, and embryos were examined for oxidative injury. The embryos of grains water stressed at milk and soft dough stages showed lowest contents of H₂O₂ and malondialdehyde and highest membrane stability index, ascorbic acid content, and activities of catalase, ascorbate peroxidase, and superoxide dismutase as compared to control embryos or water-stressed at other stages. Presence of Ca²⁺ in the medium reduced H₂O₂ and malondialdehyde content and increased ascorbic acid content, and catalase, ascorbate peroxidase and superoxide dismutase activities.

The effect of mercury and cadmium, in the form of HgCl₂ and CdCl₂ respectively, on proline accumulation and two key proline biosynthesizing enzymes, Δ¹-pyrroline-5-carboxylate synthetase (P5CS) and Δ¹-pyrroline-5-carboxylate reductase (P5CR), was investigated in Phaseolus aureus Roxb. and Triticum aestivum L. The 5-d-old seedlings were exposed to 0.05, 0.1, 0.2 or 0.4 mM concentrations of the metals in Hoagland solution for 12 and 36 h. T. aestivum exhibited considerably greater accumulation of proline than P. aureus in response to the metal treatment. Among the two metals, Hg induced greater accumulation of proline than Cd. The activity of P5CS increased significantly in response to the metal treatment, particularly in T. aestivum in which the activity of the enzyme in the control was much higher than that was in P. aureus. The activity of P5CR on the other hand mostly decreased in response to the metal treatment. The study indicated a strong dependence of the metal induced proline accumulation on the constitutive P5CS content of the plants.

Accumulation of two peripheral membrane polypeptides (20 and 28 kDa) in roots of Al-sensitive (cv. Alfor) and Al-resistant (cv. Bavaria) barley cultivars were analysed during Al stress. Both cultivars were subjected to Al concentration ranging from 0 to 150 µM for 24, 48, 72 and 96 h. Accumulation of both polypeptides was determined 24 h after exposure of plants to Al and content of both polypeptides showed only small depedence upon Al concentration and duration of Al treatment. Although, based on root growth test, Bavaria showed significantly greater resistance to Al than Alfor, analysis of 20 and 28 kDa polypeptide pattern has not revealed significant difference between the two cultivars. However, accumulation of 20 and 28 kDa polypeptides in Alfor was selectively induced by Al treatment because different pH of the root media (pH 3.5 to 6.5) or application of other metals (Cu, Co, or Cd) failed to induce these two bands. On the other hand, accumulation of these polypeptides in Bavaria was induced not only by Al, but also by Cd and in a lesser extent by Co treatment.

Four physiologically and phenotypically diversified tobacco (Nicotiana tabacum L. cv. Samsun) plantlet variants had been generated by cultivation on media either lacking or containing sucrose (0 and 3 %, m/v) under two different photon flux densities (PFD), 50 µmol m^-2 s^-1 (LL) and 200 µmol m^-2 s^-1 (HL). Plantlets were transferred into soil without any pre-acclimation and grown either under PFD of 200 µmol m^-2 s^-1 or 700 µmol m^-2 s^-1. Sucrose feeding in vitro resulted in reduced degree and duration of wilting after transfer. The highest readiness for ex vitro acclimation was found in 3 % HL plants, in which changes of photosynthetic apparatus and stress responses were the smallest. On the contrary, the steepest decline of Fv/Fm ratio on the first day after transplantation, doubled chlorophyll content and almost tripled D1/LHC 2 ratio after 7 d of ex vitro growth under 700 µmol m^-2 s^-1 characterized 0 % HL plants, which had suffered chronic photoinhibition in vitro. Remarkably high abscisic acid content at the end of in vitro cultivation and during acclimation as well as increased synthesis of both D1 and LHC 2 proteins even at the end of analyzed acclimation period were found only in 0 % LL plants. Increase of D1/LHC 2 ratio and chlorophyll contents demonstrate that in vitro developed leaves of all plant variants are able to acclimate to new environment. The most surprising result in the whole study is the drop of D1 protein synthesis in all plants on the 3^rd day. Five times decline of photoprotection level of xanthophylls in plants after ex vitro transfer into the same PFD showed stress character of in vitro cultures.

Cadmium-treated pea plants exhibited PEPC and NADP-ME activities, titratable acidity, and malate concentration in the leaves similar to controls. The PEPC activity in the roots of Cd-treated plants decreased by about 40 %, and NADP-ME increased more than twice. The titratable acidity remained similar as in the leaves, but the malate content diminished by about 30 %. The application of 500 g(d.m.) m-3 biomin and a combination of biomin and algae suspensions to Cd-treated plants brought about an increase in the titratable acidity and in the malate concentrations in the leaves and the roots.