The effects of nitrogen applied at increasing levels of 0, 4, 8, 16 and 32 mM N (KNO₃ or NH₄Cl) were studied in faba bean (Vicia faba) nodulated byRhizobium leguminosarum bv.viceae RCR lool. Nitrogenase activity was higher at 4 and 8 mM N than the zero N treatment (control), but 16 and 32 mM N significantly reduced the efficiency of nodule functions. Nitrate reductase activities (NRA) of leaves, stems, roots, nodules and nodule fractions (bacteroid and cytosol) were increased with rising the NO₃ ^- or NH₄ ⁺ levels. NRA decreased in the order of nodules>leaves>stems>roots. Cytosolic NR was markedly higher than that recorded in the bacteroid fractions. Nitrate levels were linearly correlated to NRA of nodules. Accumulation of NO₂ ^- within nodules suggests that NO₂ ^- inhibits nodule's activity after feeding plants with NO₃ ^- or NH₄ ⁺.

An electrophoretic investigation of the glutenin subunits and gliadin components in F₄ progenies between the hexaploid wheat (Triticum aestivum L. cv. Bezostaya 1) and the wild tetraploid wheat (Triticum turgidum var.dicoccoides Körn) is carried out. The possibility of inserting subunits and components of Glu B1, Glu B3 and Gli B1 loci fromT. dicoccoides in F₄ progenies ofT. aestivum is investigated. For this purpose parental forms with different allelic variants in these loci are chosen. It is established cytologically that the chromosomal number of progenies is 42. Genotype classes and the frequency of progenies are analyzed for which we judge by the phenotype manifestation of the allelic variants of the loci investigated. Different frequency of the transfer of subunits and components of Glu B1, Glu B3 and Gli B1 loci fromT. dicoccoides in the hexaploid wheat genome is established and it is connected with the disposition of the loci on chromosomes arms.

The effects of lead and sodium acetate treatment on the lipid composition of leaves, thylakoid membranes and cell debris of spinach were investigated. The concentration of lead in leaves and cell debris was higher than that in thylakoid membranes, probably due to a protection of photosynthetic apparatus. The lead treatment lead to decrease of contents of monogalactosyl diacylglycerols and phospholipids and to increase of the other glycolipids in the thylakoid membranes. There were no statistically significant differences between the total lipids of thylakoid membranes after incubation with lead and sodium acetate, which was an indication that in this case the effect of metal ion was not specific.

Changes in various components of photosynthetic apparatus during the 4 d dark incubation at 25°C of detached control and ultraviolet-B (UV-B) treatedVigna unguiculata L. leaves were examined. The photosynthetic apparatus was more degraded in younger control seedlings and for a longer time UV-B treated seedlings than in the older or for a shorter time UV-B treated seedlings. This was shown by determining the losses in chlorophyll (Chl) and protein contents, variable fluorescence yield, photosystem (PS) 2, PS1 and ribulose-1,5-bisphosphate carboxylase (RuBPC) activities, and photosynthetic¹⁴CO₂ fixation. In contrast, the Car/Chl ratio increased during the dark incubation due to less expressed degradation of Car.

The experiments were carried out with 96-h-old intact maize seedlings and 10 mm long coleoptile segments cut 4 mm below the tip. The electric fields were applied longitudinally along the seedlings. The electric field (15 V) caused inhibition of the elongation growth of intact seedlings which was dependent on both the polarity and the duration of the applied voltage. The growth inhibition was greater when the tip of the shoot was positive relative to the roots. The electric field also caused inhibition of indole-3-acetic acid (IAA) and fusicoccin (FC) induced growth of maize coleoptile segments excised from electrically treated seedlings. IAA-induced growth of coleoptile segments was greater when the tip of the shoot was negative to the roots (not in the case of FC-treated segments and intact seedlings). It was suggested that apart from the changes induced by electric field in transport system of auxin the electric field affected also the activity of plasmalemma proton pump.

In six rice cultivars the relative amounts of 55, 26-28 and 15 kDa polypeptides were mostly lower in plants grown for 15 d under low irradiance than in plants grown under saturating irradiance. This decline in the polypeptides, especially in those related to light-harvesting chlorophyll proteins, was accompanied with a decrease in the whole chain electron transport and the photosystem 2 activity.

Endogenous phytohormone levels and cell structure ofAcer saccharinum embryos were studied during seed development. Mature seeds had high water content (50%) and were able to germinate immediately after fruit abscission. The submicroscopic cell structure was similar to the structure of functionally active cells. Free and conjugated indole-3-acetic acid (IAA), abscisic acid (ABA), zeatin riboside and dihydrozeatin content and gibberellin-like substances (GLS) activity were determined during embryo maturation. Decrease in ABA, free IAA and cytokinin levels was observed at the end of maturation. Mature seeds contained considerable amounts of conjugated IAA and had high GLS activity.

Plastochron index (PI) in two genotypes of cowpea (Vigna unguiculata L. Walp) showed a remarkable sensitivity to water stress. A linear expression PI = 4.6179 + 0.7451 S (r² = 0.93) summarised the degree of sensitivity and predictability of PI to different stress levels (S). PI could be regarded as a stress sensitive trait in cowpea.

K-humates, obtained from oxihumolites, alleviate infection of tobacco with tobacco mosaic virus both in mixture with virus inoculum and by spraying of leaves before inoculation. However, applications of K-humates after inoculation did not influence the virus infectivity.

In summer seasons of 1991 and 1992 the gas exchange and leaf water relations were analysed in two peanut cultivars: drought tolerant cv. GG 2 (DT) and drought sensitive cv. JL 24 (DS). Soil moisture stress was imposed by withholding irrigation at pod development phase. The decrease in photosynthesis (P_N) under stress was associated with a decrease in stomatal conductance (g_s) and relative water content (RWC). The P_N and RWC were significantly higher under stress in DT than DS. On relief of stress the g_s and RWC recovered more quickly in DT than DS. The maintenance of higher RWC (>80 %), g_s and P_N under stress appears to be imparting drought tolerance in peanut.

The selected NaCl tolerant clones ofMorus alba L. cv. MR₂ grow better at higher concentration of NaCl than non-selected clones. With increasing NaCl concentration the Na⁺, Cl^- and proline content increased more and K⁺ and Ca²⁺ content decrease less in selected clones in comparison with non-selected ones.

The study revealed a marked qualitative and quantitative differences in the pattern of expression of three stress-related cucumber (Cucumis sativus L., cv. Laura) isoperoxidases. Activity staining, as well as the protein gel blot (Western blotting) confirmed that the proteins studied are differentially expressed in both male and female sepals, in male but not in female pedicels and in, pistil. By using antibodies specific to three stress-related peroxidases, one serologically related pistil-specific anionic peroxidase was detected. This specific band had never been observed in other flower organs. Differential appearance of the stress-related peroxidase isoenzymes in both male and female flowers demonstrates that these proteins are developmentally regulated, showing an organ-specific expression.

Treatment of vegetative parts of potato plants two weeks before the harvest with 0.2% 2-chloroethylphosphonic acid (CEPA) delayed the sprouting of tubers and increased the resistance of tubers to infections caused byPhytophthora infestans, Erwinia carotovora andFusarium spp. during the storage period. Levels of free, soluble ester- and glycoside-bound phenolic acids and cell wall-bound phenolics were determined in cortical parenchyma of tubers (periderm). The enhancement of phenolic acids in tubers from treated plants was caused primarily by the increase in the contents of free vanillic, caffeic andp-hydroxybenzoic acids and cell wall-bound ferulic, vanillic andp-coumaric acids.

Nodules of faba bean (Vicia faba L. cv. Giza 3) plants grown in pots containing clay-loam soil for 90 d have an active nitrate reductase (NR), while the leaves did not show detectable activity. Spraying the plant with increasing concentrations of Al³⁺ or Cd²⁺ (0-1000 μM) significantly inhibited the nodules NR activity, the decline being more pronounced in Cd²⁺ treatment. The specific activity of glutamate-oxaloacetate transaminase (GOT) and glutamate-pyruvate transaminase (GPT) were more prominent in the 60- than in 90-d-old plants; GOT was always higher than GPT. Furthermore, GOT was more sensitive to Al³⁺ and Cd²⁺ treatments and its activity was significantly decreased when the metal concentration increased. Also, Cd²⁺ proved to be more effective than Al³⁺ in suppressing the GOT activity in the nodules, with less significant effect observed in the leaves. In contrast, GPT was hardly affected by the various metal treatments, particulary in the leaves.

For maximum avoidance of somaclonal variation risks, the commonly used medium for somatic embryogenesis inPhoenix dactylifera has been lowered in growth regulators and activated charcoal. When initially cultured on MS basal medium containing only 150 mg dm^-3 charcoal, 5 mg dm^-3 2,4-dichlorophenoxyacetic acid (2,4-D) and 5 mg dm^-3 benzylaminopurine (BAP), 10 to 20% of shoot-tip explants developed into embryogenic calli. The embryogenic potential has been maintained for over 24 months with no decline. In addition, this medium has been found to be more efficient than conventionaly one containing 3 g dm^-3 charcoal, 100 mg dm^-3 2,4-D and 3 mg dm^-3 2-isopentyladenosine (2IP). Plantlet regeneration was achieved when somatic embryos were subcultured to medium with 0.1 mg dm^-3 2,4-D and 0.5 mg dm^-3 BAP or without growth regulators.

Reserves of twig nitrogen of drought-deciduous species changed seasonally and provided some of the nitrogen required for canopy reconstruction after drought relief. By contrast, in evergreen species, nitrogen mobilization from old leaves and use in expanding leaves occurred simultaneously at the time of leaf exchange and twig nitrogen remained constant

Changes in various components of photosynthetic apparatus during the 4 d dark incubation at 25°C of detached control and ultraviolet-B (UV-B) treatedVigna unguiculata L. leaves were examined. The photosynthetic apparatus was more degraded in younger control seedlings and for a longer time UV-B treated seedlings than in the older or for a shorter time UV-B treated seedlings. This was shown by determining the losses in chlorophyll (Chl) and protein contents, variable fluorescence yield, photosystem (PS) 2, PS1 and ribulose-1,5-bisphosphate carboxylase (RuBPC) activities, and photosynthetic¹⁴CO₂ fixation. In contrast, the Car/Chl ratio increased during the dark incubation due to less expressed degradation of Car.

Changes in glucose-6-phosphate dehydrogenase, ribonucleases activities and chlorophyll content were studied in leaves of plants systemically infected by potato virus Y, necrotic strain (PVY^N). Potato cultivars Jara and Adretta differing in resistance to potato virus Y were used. No statistically significant differences were observed between healthy and infected plants of both cultivars in chlorophyll content. Activity of glucose-6-phosphate dehydrogenase slowly increased in connection with virus multiplication and reached 203.4% of the values of non-infected control in susceptible cv. Jara and 160.4% in the resistant cv. Adretta. Differences between cultivars were significant from 60 d after inoculation (P≤0.05). The activity of ribonucleases quickly increased in the initial period of the experiment and then slowly decreased. Their activities reached 195.6% in susceptible cultivar and 183.5% in the resistant one. Significant differences (P≤0.01) between susceptible and resistant cultivars was found from 18 to 35 d after inoculation. The activities of enzymes corresponded to PVY^N multiplication which was since 40 d considerably higher (P<0.01) in susceptible cultivar in comparison with the resistant one. Thus the activities of studied enzymes could be considered as markers of resistance of potato cultivars to PVY^N multiplication.

The fungal elicitor prepared fromBotrytis cinerea affected sanguinarine alkaloid formation and accumulation in callus cells ofPapaver somniferum L. Ultrastructural changes have been observed in association with the accumulation and secretion of sanguinarine in elicitor-treated cells. Alkaloid content in elicited cells was showed as a electrondense material (osmiophilic aggregations), which occurred on the tonoplast and in freely floating bodies in the vacuole. A 30-times increasing of sanguinarine content was observed in elicitor-treated cultures.

Phaseolus aureus Roxb. was exposed to HgCl₂ and Cd(NO₃)₂ either at the germination stage in concentration 0.5, 5 and 25 μM for 48 and 96 h, or at the seedling stage (5^th day of germination) in concentration 0.5, 5 and 20 μM for 6, 24 and 48 h. The germination and the growth of roots (germination stage treatment) were less in Hg than in Cd treatment. The seedlings (seedling stage treatment) were, however, more susceptible to Cd than Hg. Both root and leaf tissues of the plant treated at the germination stage showed enhanced lipid peroxidation and activities of the antioxidative enzymes (catalase, guaiacol peroxidase and ascorbate peroxidase), except the catalase in leaf in 25 μM Cd treatment. At seedling stage the content of malondialdehyde increased significantly only in the leaf tissue, during 6 h exposure. The activities of all the enzymes exhibited an increasing trend in both the tissue of the seedlings, particularly the leaf, at least after 24 and 48 h, except the catalase whose activity declined in response to Cd. Active involvement of the guaiacol and ascorbate peroxidases, rather than catalase, in scavenging cellular H₂O₂ was indicated. It was concluded that the two metals had little primary damaging effect on membranes.

The C₄ speciesFlaveria trinervia is obviously better adapted to saline environments than the C₃ speciesF. pringlei. Treatment with 100 mM NaCl diminished crop growth rate inF. pringlei by 38% but not inF. trinervia. Under saline conditions, more assimilates were invested in leaf growth inF. trinervia but not inF. pringlei. Electrolyte concentration inF. trinervia in control and salt treated plants is lower than inF. pringlei. Fluorescence data do not indicate a damage of PS 2 charge separation in both species. Whether the C₄ photosynthetic pathway inF. trinervia is responsible for the improved salt tolerance compared toF. pringlei remains an open question.

The medium forin vitro culture of green and SANDOZ herbicides-treatedChenopodium rubrum L. plants contained saccharides and hormones in different concentrations. Five days after sowing, the plants were exposed to non-inductive (15 long days-LD) or inductive (6 short days-SD + 9 LD) photoperiodic conditions. The length of hypocotyl and cotyledon blade were measured and percentage of flowering was scored. Gibberellic acid (GA₃) stimulated hypocotyl growth of green and photobleached plants under SD and inhibited under LD conditions. Indole-3-acetic acid (IAA) slightly stimulated hypocotyl growth of green plants only under LD conditions. Benzylaminopurine (BAP) inhibited hypocotyl growth regardless of photoperiodic regime. The optimal concentration of glucose or saccharose for flowering in green and SANDOZ-treated plants was 5%. In green SAN 9785-treated plants exogenous saccharides compensated lack of photosynthates to bring about full flowering, but SAN 9789-treated plants needed in addition GA₃.

Net photosynthetic rate (P_N), ribulose-1,5-bisphosphate carboxylase (RuBPC) activity, chlorophyll (Chl) content and biomass production were estimated at monthly intervals inChukrasia tabularis, Dolichandrone atrovirens, Eugenia jambolana, Gmelina arborea, Lannea coromandelica, Terminalia arjuna andTerminalia bellerica from September 1990 to August 1991. The leaves of all the seven tree species showed significantly higher P_N during summer than in winter and these rates differed from one species to the other. A positive correlation was found between P_N of different tree species and their Chl content or biomass production. There was no significant correlation between ribulose-1,5-bisphosphate carboxylase activity and P_N when these were expressed on leaf area basis.

The 24 h effect of low (20°C) and high (43°C) temperature on the antioxidant enzyme activities and lipid peroxidation was investigated in intact cells of the cyanobacteriumSynechocystis PCC 6803 grown at 36°C. At low temperature treated cells, the superoxide dismutase, catalase and glutathione peroxidase activities were significantly higher and the protein content lower than in high temperature treated cells. The increase of hydroxyl free radical level and malonyldialdehyde formation, when algal cells were exposed to low temperature, were due to the stimulated production of superoxide radicals O₂ ^- and hydrogen peroxide (H₂O₂).