The treatment ofLemna minor L. plants with Pb(NO₃)₂ for 90 min, 8 and 24 h resulted in intensified deposition of (l,3)-P-glucan (callose) in plants roots. It was localized in the protodermis of the root tip, and in the center of the stele in the region at the proximal part of the root cap and slightly above

An investigation was carried out on chickpea (Cicer arietinum L.) cv. C-235 inoculated withRhizobium sp.Cicer strain cv 4 Az^r. Nodule functioning was monitored at 15 d intervals starting from 45 days after sowing (DAS) and inoculation in order to study nodule development and senescence under natural and stress conditions (dark treatments of 18 and 66 h). Maximum rate of N₂-fixation was observed between 50 - 60 DAS. After this acetylene reducing activity (ARA) fell and it was negligible 75 DAS. This decline in ARA with ageing of plants and nodules was accompanied by a decline in leghemoglobin content and greening of the nodules. When 60 % of the nodule tissue had turned green 75 DAS, a sharp increase in nodule peroxidase activity (3.7 fold) was observed whereas the catalase activity was reduced by 50 % in comparison with the control. The glutathione-reductase and ascorbate-peroxidase activity followed a trend parallel to that in N₂-fixation, but the variation was much smaller. The changes in the total soluble carbohydrates, cytosolic proteins and nitrogen content per se were not expressive. Dark treatments induced premature senescence of the nodules as was evident from the marked decrease in ARA. However, the decline in leghemoglobin content was relatively small as compared to ARA. The changes in cytosolic proteins, total soluble carbohydrates, peroxidase activity, catalase activity, glutathione reductase activity and ascorbate peroxidase activity of nodules under dark-induced nodule senescence were almost parallel to those observed under natural senescence.

The effect of irradiance on the ratio of variable to maximum fluorescence (F_v/F_m) and on the anthocyanin content of chilled (0.5 °C) young maize plants was investigated after returning the plants to a non-chilling temperature (25 °C). Compared to control plants grown throughout at 25 °C in the light, the F_v/F_m hardly changed during chilling or when returned to a non-chilling temperature in the dark, but there was a decrease in this parameter if the plants were shifted to the light after the cold treatment. Similarly, compared to the control plants there was no change in the anthocyanin content either at low temperature or after transfer to 25 °C in the dark. However, there was a sudden increase in the anthocyanin level after returning the plants from dark cold conditions to a non-chilling temperature in the light.

Dry mater, water content, water, osmotic and pressure potentials, content of saccharides and potassium were measured duringin vitro cultivation ofVitis rootstocks. Three cases were compared: a) the micro-cuttings with normal growth; b) micro-cuttings which stop their growth after 15 d of culture, and c) micro-cuttings reactivated by 6 d of continuous darkness.
Major differences were observed in water content and osmotic potential. The stopping of growth was not a specific property of buds, but was probably due to restriction of translocation of saccharides and water in the shoot.

Difluoromethylornithine (DFMO) counteracted several processes that are promoted or inhibited by auxins or inhibitors of polar auxin transport: inhibition of asymmetric gene expression in carrot, stimulation of gametic embryogenesis inBrassica, inhibition of root elongation in tobacco, inhibition of the development of lateral roots in pea and adventitious roots in apple, and inhibition of floral bud formation inArabidopsis

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).

Wheat seedlings were grown hydroponically in absence and presence of 100 mM NaCl for 7 d. Cell membrane permeability to nonelectrolytes and water was determined by the plasmometric method for individual intact cells. NaCl increased membrane permeability to urea, methylurea and ethylurea and decreased permeability to water. Membrane lipid partiality was decreased by NaCl. The effects of NaCl on cell permeability parallel changes in the lipid composition of the plasma membranes induced by NaCl stress suggesting that nonelectrolyte permeability is a useful tool to probe alterations in the lipid matrix of the membrane.

The ontogenetic changes in growth, and the diurnal changes in net photosynthetic rate (P_N) and stomatal conductance were studied in two peanut cultivars of different habit groups. Significant cultivar differences were noticed: the prostrate cv. M 13 was found superior to the erect cv. J 11 in all the parameters studied. Specific leaf mass and the rates of gross photosynthesis and respiration were higher in cv. M 13 than in cv. J 11. In vegetative phase, the maximum P_N was in cv. J 11, but in pod filling phase, it was in cv. M 13. The differences in growth and P_N of the cultivars were significant after the onset of reproductive sink. Therefore, the screening for higher P_N has to be made at the pod-filling phase, and between 09.00 and 10.00 of the day (at optimum temperature).

An influence of some Random Amplified Polymorphic DNA (RAPD) reaction factors on resulting banding pattern and the ability of RAPD technique to detect DNA polymorphism among six economically important pea cultivars was tested. Relatively high level of DNA polymorphism among peas was observed, using polyacrylamide/urea gels and silver staining. Altogether 13 arbitrarily designed primers produced 313 amplification products. In addition 59 polymorphisms were found. These polymorphisms can serve as potential genetic markers. RAPD data were processed using cluster analysis and plotted as dendrogram. Each tested cultivar was clearly distinguished from the others. Moreover,Pisum sativum andP. sativum subsp.arvense cultivars were separated into 2 different clusters, according to their systematic relationships.

Esterase isoenzyme spectra of different organs of seedlings and field-grown plants of fiber flax (Linum usitatissimum L., cv. Belinka) were studied by electrophoresis in polyacrylamide gel for estimating ontogenetic variability of gene expression. Formation of individual isoesterases depended on the type of tissue and the stage of its development. Isoesterases characteristic of exclusively one or some tissues of the same developmental stage were revealed simultaneously with basic esterase isoforms active in all analysed parts of seeds, seedlings and field-grown plants. The revealed changes of esterase isoenzyme spectrum during germination show tissue and time specificity of the endogenous regulation of genes controlling their formation.

The changes in the content of indole-3-acetic acid (IAA) were investigated in the youngest needles ofPinus mugo in the course of year. In newly formed needles, the content of IAA increased, starting from July and reaching its maximum in August to October. The IAA content decreased with a decline in the intensity of apical dominance during dormancy but no changes were observed in budbreak (May and June).

Spectroscopic characterization of phycobiliprotein (PBP) isolated fromSpirulina platensis indicated that it had a molecular formula of C₃₃H₄₀N₄O₆ with molecular ion peak at m/e 586. The PBP was rich in aliphatic and acidic amino acid residues. The specific ultra-violet absorbance, infrared transmittance, specific absorbance coefficient, nuclear magnetic resonance and mass spectral analysis revealed thatS. platensis PBP was composed mainly of C-phycocyanin and allophycocyanin.

Mechanical stress exerted on youngBryonia dioica internodes which resulted in reduced elongation and increased radial expansion induced a rapid and transient increase in specific mRNAs. Hybridizations were performed using ubiquitin, cyclophilin and heat-shock protein cDNAs as probes on RNA extracted at successive time intervals in control and rubbed internodes. Changes in ubiquitin and cyclophilin were rapidly enhanced after mechanical perturbation. Levels of mRNAs reached a maximum 0.5 h and 1.5 h after rubbing and then decreased. The heat shock protein gene was constitutively expressed; it was however slightly stimulated following the rubbing treatment. All the three genes encoded for molecular chaperones and they were regulated in response to environmental stimuli. The role of chaperones was discussed with regard to the plant response to several natural stresses.

The effects of NaCl and polyethylene glycol (PEG) on superoxide dismutase (SOD) and peroxidase (P) activities, lipid peroxidation (LP) and proline content in seeds and leaves of drought tolerant (FC-506 and MS-100) and drought sensitive (MS-612 and MS-13) sugar beet cultivars were examined. After PEG and NaCl treatment in tolerant cultivars both in seeds and leaves SOD activity mainly increased, though P activity increased only in leaves of tolerant cultivars. In drought sensitive cultivars the decrease of SOD and P activity was mostly observed. LP increased in seeds and leaves of all examined cultivars. The proline content increased in the leaves of examined cultivars and was significantly higher in drought tolerant plants. On the other hand, in the seeds only slight increase in proline content was found. The results obtained indicated that drought tolerance could be correlated with high proline content and enzymatic defense against lipid peroxidation.

We describe a rapid and efficient procedure for isolating leaf mesophyll protoplasts fromSaintpaulia ionantha (African violet). Because of the unusual surface properties of the leaf, efficient digestion required bisection of the lamina into abaxial and adaxial halves to expose the mesophyll. Enzymatic digestion occurred during a 3 h incubation with 2% (m/v) driselase in 0.50 M mannitol, yielding 2-3 × 10⁵ protoplasts g^-1 (f.m.), with 70% viability. Protoplasts ranged in size from 50 to 100μm, and were derived from mostly non-photosynthetic mesophyll parenchyma.

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.