Expression of the gene 4 for cytokinin synthesis in two clones of transgenic tobacco plants resulted in slightly higher(ca. 10 - 20 %) levels of endogenous cytokinins -zeatin, zeatin riboside and isopentenyladenosine. This was associated with changes in photosynthetic processes on chloroplast and leaf level. In comparison with nontransformed plantlets a higher degree of grana stacking was found in both clones of transgenic plants which indicated a higher proportion of photosystem 2 lightharvesting complex in thylakoids. This was supported by a decreased chlorophylla/b ratio in the separated grana fraction. The rate of leaf net photosynthetic rate (measured as CO₂ uptake) wasca. 25 % higher in both clones than in nontransformed plants. Also the rates of dark and light respiration, and CO₂ compensation concentration were higher in transgenic plants. On the other hand, parameters of water relations (water, osmotic and pressure potentials, stomatal and cuticular transpiration rates) were not significantly affected in transgenic tobacco plants.

Nitrate content, activities of nitrate reductase and glutamine synthetase, soluble protein content, and proportion of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) protein in total proteins were measured in leaves of Beta vulgaris L. plants affected by nickel, cadmium, and molybdenum in concentrations of 10^-4, 10^-2, and 1 mM. The most harmful effect on the above mentioned parameters had Cd, less harmful Ni, whereas Mo stimulated the investigated parameters. The proportion of RuBPCO protein showed a high tolerance to heavy metals.

Changes in the peroxidase (EC 1.11.1.7) and catalase (EC 1.11.1.6) activities, and total chlorophyll, soluble sugars, and ascorbic acid contents of leek leaves treated with the herbicide 1,10-phenanthroline (Phe) in concentrations 0.5, 2.5, 5.0, 7.5, and 10.0 mM have been determined. Plants treated with Phe were characterised by a higher activity of peroxidase and a lower activity of catalase and lower contents of chlorophyll, soluble sugars, and ascorbic acid as compared to non-treated plants.

Germination of two rice (Oryza sativa L.) cultivars (Ratna and IR 36) in the presence of 10 µM PbCl2 and 10 µM HgCl2 decreased germination percentage, germination index, shoot/root length, tolerance index and dry mass of shoots and roots. Mercury was more toxic than lead. Reduced glutathione (GSH), cysteine (Cys), ascorbic acid, and α-tocopherol alleviated the adverse effects of these metals on plants in the order GSH > Cys > ascorbic acid > α-tocopherol. The effects were more pronounced in tolerant cultivar IR 36 than in the relatively susceptible cultivar Ratna.

The antagonistic effects of some growth regulators [i.e. indol-3-yl-acetic acid (IAA), gibberellic acid (GA₃) or kinetin] on stress imposed by sea water on leaf area, pigment and photosynthetic activity in leaves of broad bean plants at different stages of development were investigated. Seed priming with GA₃ alleviated either partially or completely the effects induced by the two levels of sea water (10 and 25 %) used on leaf area at all experimental stages. However, IAA, GA₃ and kinetin inhibited leaf growth by themselves in almost all measurements. Seed pretreatment with kinetin alleviated the inhibition of pigment production in sea water-irrigated plants. Furthermore, GA₃ or kinetin nullified the deleterious effects imposed by irrigation with sea water particularly the high level (25 %) on photosynthetic¹⁴CO₂ fixation.

French bean (Phaseolus vulgaris L. cv. Contender) plants at five developmental stages (4, 8, 12, 16 and 20 d after sowing) were exposed to one of three treatments: 1 - 25 °C (control), 2 - exposure to chilling at 10 °C only for 2 d prior to sampling, and 3 - long-term exposure to chilling at 10 °C. Short- and long-term chilling decreased plant growth. Higher concentrations of ascorbate and glutathione were found in the chilling-treated plants throughout the different period of growth in comparison with those in the control plants. The activities of superoxide dismutase, ascorbate peroxidase, and glutathione reductase increased in the chilling-treated seedlings while activities of catalase and peroxidase and of β-carotene content decreased in young chilling-treated plants and slightly increased in older ones.

Chickpea (Cicer arietinum L.) cv. C-235 inoculated with Rhizobium sp. (Cicer) strain cv4Az was raised in sand culture under natural conditions with nitrogen-free nutrient solution. 45-d-old plants were treated with 20 and 50 mM KNO3 and sampling made 2 and 6 d after treatment. KNO3 application induced premature nodule senescence. Light microscopic investigations showed that KNO3 treatments resulted in structural degradation of the central bacteroidal tissue. The mass of green nodules increased by 35 % under these treatments. This was accompanied by a rapid decline in leghemoglobin (Lb) content of the nodules being 51 - 67 % lower than in control. The total soluble nodule proteins showed relatively minor changes under KNO3 treatments thus suggesting preferential degradation of Lb. These changes were associated with a rapid decline in N2-fixing activity. However, the decline in total soluble sugars was relatively minor as compared to acetylene reducing activity, thus indicating that sugar deprivation is not the cause of decreased nitrogen fixation ability. Glutathione reductase and ascorbate peroxidase activity showed a 10 - 20 % decrease in comparison with the control. Accumulation of H2O2 and structural degradation of the nodular tissue are considered to be the factors leading to nodule senescence under nitrate treatments.

Changes in ribonucleases (RNases) and glucose-6-phosphate dehydrogenase (G6P DH) activities, their content and subcellular localisation were studied in relation to virus multiplication in susceptible (cv. Samsun) or resistant (transgenic breeding line NCTG 83) tobacco plants infected with the potato virus Y^N (necrotic strain of PVY). Activities of RNases and G6P DH from diseased susceptible tobacco plants were markedly increased during the experimental period and significantly correlated with the multiplication curve of the PVY^N. In contrast, the activities of RNases and G6P DH were not changed after PVY inoculation of resistant breeding line NCTG 83 producing the CP mRNA of PVY. Changes in the content and in the subcellular localisation of RNases and G6P DH isozymes were also determined in mesophyll protoplasts isolated from healthy as well as PVY^N infected plants of both cultivars by differential centrifugation of broken protoplasts on day eight post inoculation (the culmination of multiplication curve of PVY and enhanced activity of both enzymes). The chloroplasts fraction from infected protoplasts showed an enhanced content of RNases (192.4% when compared with that from healthy control ones), and of G6P DH (174.4 %). The cytosol fraction from infected protoplasts contained slightly enhanced levels of G6P DH (117.4 %) and considerably enhanced levels of RNases (141.7 %). No significant differences in the activities, contents and subcellular localisation of RNases and/or G6P DH isozymes were observed in the resistant line NCTG 83. This is in accordance with no detectable contents of PVY.

The Vigna radiata L. plants were grown in greenhouse at moisture content of sand (SMC) of 12.0 ± 0.5 %. At flower bud initiation stage, i.e. 45 - 50 d after sowing, the SMC was decreased to 3.5 ± 0.5 %, and the effects of applied potassium (0, 2.56 and 3.84 mmol dm-3) were studied. During water stress, K-fed plants maintained higher leaf water potential and relative water content (RWC) of leaves and nodules and lower osmotic potential as compared to untreated plants. The proline content was higher in nodules than in leaves showing their difference in degree of stress. A partial recovery was found after re-irrigation. When subjected to drought, carbon was accumulated in the leaves and declined in nodules and roots. K-fed plants showed higher C and N content in stem, roots and nodules than untreated plants. The content of K significantly increased in stem and nodules in K-fed plants, irrespective of SMC. Dry masses of different plant parts were also increased in K-fed plants.

Detached wheat shoots (ear with peduncle and flag leaf) were incubated for 4 d in a solution containing 1 mM RbCl and 1 mM SrCl2 as well as 10, 40 or 160 µM NiCl2 and CoCl2. The phloem of some plants was interrupted by steam-girdling the stem below the ear to distinguish between xylem and phloem transport. The phloem-immobile Sr flowed mainly to the leaf lamina and to the glumes via the xylem. The Sr transport was not sensitive to steam-girdling. In contrast, the phloem-mobile Rb accumulated during the incubation time mainly in the stem and the leaf sheath. The Rb transport to the grains was impaired by steam-girdling as well as by elevated Ni and Co concentrations in the incubation solution indicating that Rb was transported via the phloem to the maturing grains and that this transport was affected by the heavy metals. Ni was removed more efficiently from the xylem in the peduncle than Co (but far less efficiently than Rb). It became evident that the two heavy metals can also be transferred from the xylem to the phloem in the stem of wheat and reach the maturing grains via the phloem.

The inoculation of mycorrhizal maize plants with three isolates of microaerophilic diazotrophic bacteria obtained from the mycelium of arbuscular mycorrhizal fungi associated with three grasses (Arrhenatherum elatius - bacterial isolate ARR, Agropyrum repens - isolate AGR and Poa annua - isolate POA) caused no increase in nitrogen content in plant biomass. The inoculation with bacterial isolate ARR resulted in the decreased plant growth. Bacterial isolate AGR decreased the percentage of the root length colonized by arbuscular mycorrhizal fungus Glomus fistulosum. The inoculation with both mycorrhizal fungus and isolate POA increased significantly the concentration of phosphorus in plant shoots compared to uninoculated control.

An attempt to reduce the production cost on tissue cultured plants, photoautotrophic culture of a high value orchid Dendrobium was established under CO2-enriched conditions. The shoot length and the number of leaves were almost equal in plantlets grown on medium with 2 % sucrose or without sucrose and under normal or enhanced (40 g m-3) CO2 concentration, whereas the fresh and dry masses were higher in cultures grown in sucrose containing media or under CO2 enrichment. Development of roots was observed only on media without sucrose, but CO2 enrichment did not have significant effects on in vitro rootings.

The effects of gibberellic acid (GA3) and N1-(2-chloro-4-pyridyl)-N2 phenylurea (4-PU-30) on maize seedling growth, photosynthetic parameters, and leaf protein composition were investigated. The agents used alone or in combination increased leaf growth and photosynthetic rate of the seedlings. Chlorophyll and total nitrogen contents in leaves as well as the quantity of individual protein fractions increased simultaneously. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of soluble proteins (albumins and globulins) revealed quantitative differences between 4-PU-30-treated plants and the other experimental variants. They differed in polypeptide composition associated with changes in soluble proteins and amino acids. However, GA3 did not induce similar changes in polypeptide composition of soluble proteins.

Plants of Vigna mungo raised from seeds presoaked in salicylic acid (0.0, 0.01, 0.1 and 1.0 mM) and nodulated with the cowpea strain of Rhizobium leguminosarum were analysed 15 and 30 d after sowing. The foliar nitrate and nitrite contents were varying but soluble protein and total nitrogen contents were lower in treated than control plants. Nitrate reductase activity was increased at the two lower concentrations of 0.01 and 0.1 mM but was inhibited at the highest concentration used (1.0 mM). The number of nodules, their leghemoglobin and protein contents and nitrogenase activity of roots were reduced.

Decrease in seed viability and germination rate may be caused by biochemical changes associated with seed ageing. Different biochemical assays were conducted to investigate the changes occurring at the ageing of Bambusa bambos seeds. A reduction in the total content of food reserves such as sugars, proteins and lipids were recorded. Decreased activity of peroxidase, acid phosphatase, alkaline phosphatase were also noticed during accelerated ageing. A substantial increase in total free amino acids and the activity of amylases confirms the degradation of stored biomolecules in seeds during ageing.

Water and K⁺ fluxes were examined in detopped plants ofZea mays L. (cv. White Horse Tooth), which were grown and exuded on half-strength Long Ashton nutrient solution containing the appropriate concentration of Zn²⁺ at 20 °C. In light-grown plants, 100 and 500 μM Zn²⁺ increased both water and K⁺ fluxes in detopped maize plants whereas 1 000 μM Zn²⁺ inhibited both fluxes. In the dark-pretreated plants, 1 000 μM Zn²⁺ in the medium stimulated K⁺ flux. The fluxes of K⁺, Zn²⁺, Ca²⁺ and Mg²⁺ were usually higher in detopped plants than in intact ones. At 1 000 μM Zn²⁺ in the exudation medium, Zn²⁺ concentration was higher in the xylem exudate of dark-pretreated plants than in roots of plants maintained in light. The results are discussed in relation to the influence of Zn²⁺ on the membrane permeability and transport in plants.

Growth and Na⁺, K⁺, Cl^-, proteins, sugars and proline concentrations were measured in three triticale genotypes M2A, DF99 and Asseret grown on nutrient solution with or without 75 mM NaCl. In saline conditions, leaf area of the three triticales was reduced by 50 % and dry to fresh mass ratio increased. Total protein concentration was diminished by 10 %. K⁺ concentration decreased whereas Na⁺ and Cl^- accumulated in roots and shoots of salt-stressed plants. This ion accumulation was greater in roots of Asseret than in roots of the other triticales. Soluble sugar concentration increased in M2A and Asseret and decreased in DF99. Proline concentration increased in M2A and DF99 and decreased in Asseret. Osmotic adjustment was essentially realized by Na⁺ and Cl^- uptake. Non-reducing sugars and proline contributed too, but to a lesser extent.

Cytokinin content in xylem sap was higher in plants grown under local supply of fertilizers as compared to those grown under homogenous distribution of nutrients in soil. The separate assay of cytokinins in xylem exudate from split root system showed that roots, which were in contact with fertilizer mainly contributed to cytokinins transported from roots to shoots.

Investigations were carried out to determine the sites of lead uptake within the frond and the root ofLemna minor. With the sodium rhodizonate four regions favoured in lead uptake were distinguished: the frond region between the base and the node, the basal part of the root, and the regions at the proximal and distal ends of the root cap. For analysis in electron microscope only the root regions were chosen. The highest rate of lead uptake was found in the basal part of the root. Lead was present in the apoplast of this region after 5 min of exposure and was observed in the stelar cells after 30 min of incubation. Lead deposits were detected mostly in the cell walls adjacent to the plasma membrane and in the lumen of several endomembrane compartments - the endoplasmic reticulum (ER), dictyosomal vesicles, nuclear envelope and the vacuoles. Lead induced changes of cell ultrastructure; an increase in the number of membraneous structures, swelling of ER cisternae and distortion of the dictyosomal cisternae were observed after 2 to 6 h of exposure.

Dynamics of CO₂ evolution at low pressure was studied in barley, maize, pea, wheat and pine seedlings using the gas exchange system with laser photoacoustic spectrometer. The CO₂ evolution from plant surfaces to environment increased with decreasing air pressure. Simultaneously the changes in activities of phosphoenolpyruvate carboxylase, glucose-6-phosphate dehydrogenase, glyceraldehyde phosphate dehydrogenase, alcohol-dehydrogenase, isocitrate dehydrogenase, malate dehydrogenase in pea and maize leaves were observed. The response depended on plant species used as well as on air pressure and period of its action

Energetic aspects of the relation between transpiration and respiration during the dark period were evaluated. One-year old seedlings of three trees, one bush and one annual plant were grown in controlled conditions. Experiments were performed under uniform environment during the day and two regimes of air relative humidity (RH) during the night, low (50 - 65 %) and high (95 %). For all investigated plant species the dark transpiration rate (E), the free energy of respiratory substrate, the entropy production and the free energy balance (FEB) of the dark respiration were higher at low than at high RH. E was linearly related to the FEBr ² ranged between 0.63 and 0.90)

The growth retardant paclobutrazol (PBZ) inhibited stem internode growth of in vitro cloned potato plants. The extent of growth inhibition caused by10-9 M PBZ in Murashige and Skoog medium was genotype-specific, varying between 10 - 60% of the stem growth of untreated controls in ten cultivars examined. An increase in percentage of de novo bud regenerating stem internode segments (SIS) as well as in the total number of buds per explant was observed in SIS taken from PBZ pretreated plants. PBZ applied directly into the regenerative media had no stimulatory effect on there generation process. We assume that the enhancing effect of PBZ on regeneration may be attributed to its interaction with cytokinin metabolism.

The physiological responses of alfalfa (Medicago sativa L. cv. Gilboa) to salinity (100 mM NaCl) and some inorganic nutrients (K+, Ca2+ and N as NO3-) were investigated. Salinity caused a substantial reduction in biomass, carbon assimilation rate, stomatal conductance, water use efficiency, leaf area, relative growth rate, NO3- content and nitrate reductase activity, whereas, transpiration rate was slightly affected. Inclusion of K+, Ca2+ and N as NO3- in plant nutrient medium in combination or alone brought about a marked stimulation in control plants and moderated the salinity caused reductions in NaCl treated plants. In addition, plants also exhibited differences in these parameters at two growth stages.

The ultrastructure of chloroplasts in the primary leaf of 10-d-old bean plants (Phaseolus vulgaris L., cv. Cheren Starozagorski) was studied 3, 5, 24, 48, 72 and 168 h after a single treatment with simulated acid rain (pH 2.4, 2.2, 2.0 and 1.8). Different changes in chloroplast structure till full destruction of organelles were traced. A determining factor for these changes was the histological localization of chloroplasts. In the chloroplasts of palisade parenchyma different degrees of expansion of thylakoids (3, 5, and 24 h after the single treatment), and conformational changes of the inner membrane system (48, 72 and 168 h) were observed. The chloroplasts of spongy parenchyma showed a significantly higher degree of structure resistance. The expansion of thylakoids was weak and did not depend on the duration of treatment. The ultrastructural changes of chloroplasts confirmed relative resistance of this species till pH 2.0.

Dry matter production of shoots and roots and the diurnal fluctuation of titratable acidity of single leaves were investigated in the CAM plant Agave attenuata during the first 70 d after germination. The plants were grown either in vermiculite sub-irrigated with a nutrient solution or in in vitro cultures on an inorganic nutrient agar. Two types of culture tube covers were used: either airtight closures or polypropylene caps with membranes permeable to air.
In the earliest ontogenetic phases of development (cotyledon and primary leaf stage), the plants were already able to carry out considerable nocturnal organic acid accumulation. In vitro cultivated plants, from the beginning of their development, were also capable of diurnal acid fluctuation, though of distinctly weaker activity than the pot plants. The mean relative growth rates (RGR) of pot culture plantlets approached a third of perennial herbaceous plants. Plantlets grown in in vitro culture reached only half to the one quarter of the RGR of pot plants. The reduced yield could be attributed to the low CO2 supply in the culture tubes and the less than optimal water and nutrient supply in the agar medium.