The effects of different osmotic stresses (from 0 to -8× 10⁵ Pa) obtained with NaC or polyethylene glycol 6000 solutions on the germination of flax, sesame and onion seeds were investigated. The effect of presoaking with gibberellic acid (GA³) on the germination of the above mentioned seeds was also studied.
It was found that the rate of seed germination and the final germination percentages as well as the amount of water absorbed by the seeds were considerably lowered with the rise of osmotic stress levels whatever the stress agent used, more considerable reduction was obtained under polyethylene glycol 6000 than under NaCl.
Presoaking with gibberellic acid increased the rate and the final germination percentage of osmotically stressed flax and sesame seeds, while those of stressed onion seeds were slightly retarded.

Chloramphenicol has been found to inhibit nitrate reductase activity in black-gram leaves. It inhibitsin vivo nitrate reductase activity up to 50-67%, and the catalytic property of the enzyme up to a maximum of 70-98%. Modulators, such as KNO₃, NADH and HCO₃ could not protect enzyme inhibition by chloramphenicol. It is suggested that the chloramphenicol inhibition is mainly through its effect on the catalytic process of the enzyme.

The radial transport of organic nitrogen compounds was studied in maize seedling roots in relation to the metabolism of uniformly labelled¹⁴C-amino acids (alanine, arginine, dicarboxylic amino acids and their amides) in the cortex zone. Most active metabolism accompanying transport to the stele was observed for¹⁴C-glutamic acid of "primary" amino acids and for¹⁴C-glutamine of "reserve" nitrogen sources. The transport of¹⁴C-asparagine and¹⁴C-arginine to the conducting bundles is accompanied by weak metabolism. A distinguishing feature of nitrogen metabolism in the stele is intensive decarboxylation of glutamic acid, formed in the course of radial transport and metabolism, to gamma-amino butyric acid. This process is assisted by a highly active glutamate decarboxylase present in the conducting bundles.

Sap flow rate and transpiration dynamics were studied in the course of 3 years in a dominant tree species in the floodplain forest,i.e. in the full-grown oak (Quercus robur L.) tree, using the method of trunk heat balance devised by the authors. The investigations were carried out at a period at which regular and marked fluctuation in a relatively high water table usually occurred, culminating in seasonal flooding. High sap flow rate values in the tree were established under conditions of non-limiting water supply in soil (up to 400 kg per day or up to 39 000 kg per vegetation period) and characteristic daily flow curves (rounded with a large amplitude and with the maximum at noon), corresponding to those described theoretically. Relationships were inferred by means of which tree water consumption can be calculated under these conditions on the basis of data measured at meteorological stations. From these equations it follows that the transpiration of the tree canopy amounted to 80% of the potential evapotranspiration. The amount of the used daily tree water reserve was assessed to be 0.4 mm in the seasonal average. The transpiration coefficient reached in climatically distinct years the values of 400 to 700 of the increase in tree dry matter. The area of the so-called effective tree-crown ground plan approximated to the area determined geodetically. The results obtained are useful for both ecophysiological and hydrological studies. Some of the described procedures are convenient for the evaluation of functional tree dimensions and according to them also of the forest stand structure.

Effects of Na₂CO₃ and NaHCO₃ at equal conductivities (2, 4 and 6 S cm^-1) on germination, seedling growth and some metabolites were studied in two cultivars of green gram (Phaseolus aureus Roxb. cv. Varsha and cv. Pusa Baiskhi) in Petri dishes and sand culture. With increasing conductivity both the salts depressed germination, length of shoot and root and their mass. NaHCO₃ was more depressiv than Na₂CO₃. The contents of chlorophyll, RNA, protein and free amino acids were higher and affected to a lesser extent under salt stress in leaves of cv. Varsha than cv. Pusa Baiskhi. Cv. Pusa Baiskhi was generally more susceptible to salt stress than cv. Varsha.

The stomata and their behaviour towards neutral red uptake in a few arid zone plant species under stress conditions have been inve stigated. Variable patterns of accumulation or non-accumulation and retention of this vital dye, by various cells of leaf epidermis have been observed. The neutral red uptake by the cells of the epidermal strip, coalescence of particles and their movement appear to be connected with the open/closed condition of the stomata.

In an experiment with native maize roots depending on different phosphorus concentration in the external solution (0.001 … 50 mM P), the multiphasic character of the kinetics of phosphate uptake has been stated. The single phases are characterized by the different values of K_m and V_max. In the wide range of concentrations the isotherm of the phosphate uptake has five evident phases. The character of kinetics for the uptake of phosphate is analogical to the kinetics of the enzymatic reactions described by the Michaelis-Menten equation. On the other hand the linear dependence for the inactivated root was determined,i.e. the uptake of phosphate versus different phosphorus concentration in the external solution.
The graphic representation of the logarithmic values for the phosphorus taken up versus the different phosphorus concentration in the external solution gives the biphasic course including concentration less than 1.0 mM P and more than 1.0 mM P. Within the framework of the concentration range the following values of V_max, K_m and ϕ_in were calculated under the conditions if the concentration of phosphorus is less than 1.0mMP: V_max = 1.705 μmol P × g^-1h^-1, K_m = 0.057 mM P and ϕ_in = 0.83,i.e. if the concentration of phosphorus is more than 1.0mM P: V_max = 40 μmol P × g^-1 h^-1, K_m = 16.66 mM and ϕ_in = 20.
According to these results, the phosphate concentration in the external solution influences the activity of the transport mechanisms concerning their conformative changes which discretely change their working regime of membrane transport. This is also demonstrated in the change of values V_max, K_m and ϕ_in.

The inhibitive growth-correlative effect of cotyledons of pea seedlings decreases during their ontogenesis till the age of 14 days. This decrease is associated with an increase in the level of endogenous cytokinins on the one hand and a decrease of endogenous IAA on the other. This is in harmony with the fact that the correlative-inhibiting effect of pea cotyledon upon the growth of its axillary bud can be weakened by exogenous cytokinin and amplified by exogenous IAA.

The action of light on protein synthesis was examined in the cabbage seedlings, a system extensively used in the studies of anthocyanin synthesis. Continuous red and far red light have no effect on total protein content while they cause a marked decrease in the level of free amino acids in cabbage seedlings. The rate of protein synthesis, measured as incorporation of radioaetively-labelled amino acids into proteins, is clearly stimulated by light. Phytochrome involvement in the light stimulation of the incorporation is also demonstrated by the red-far red reversibility of the response. The relative effectiveness of continuous red and far red light upon the incorporation of amino acids into proteins is affected by the nature of the system used to study the incorporation process. When excised cotyledons and short period of incorporation were used, continuous far red was more effective than red. However, when whole seedlings and long period of incorporation were used, red and far red were equally effective. Streptomycin causes a 10- 15% decrease in the rate of incorporation of amino acids into proteins of all cellular fractions, except the plastid fraction where a much higher inhibition (30%) was observed.

Macromolecule syntheses, especially incorporation of radioactive labelled precursors into proteins, RNA and DNA were investigated. Some results on the action of phytohormones applied to dormant seeds and on the influence on water stress conditions by interruption of imbibition even before the radicle protrudes, on germination as well as on RNA and DNA synthesis were analysed. Benzylaminopurine and ethylene, applied in combination, could break dormancy of dormant seeds; a process which is correlated with the onset of DNA synthesis. Interruption of the imbibition during the time of onset of DNA synthesis (after 16 h of imbibition) did not impair the germination, and the protein, RNA and DNA syntheses started after reimbibition at that level which was reached at the interruption point. Only after a break in later phases (after 22 h of imbibition) a weak impairment of germination could be observed.

In the present paper we deal with the possibility of morphogenesis induction in callus tissue cultures of some representatives ofMatricaria andAchillea species. Shoot regeneration from calli ofMatricaria chamomilla andM. inodora has been induced by 0.1 mg l^-1 kinetin or by combination of 0.5 mg l^-1 kinetin and 0.5 mg l^-1 NAA added to Murashige-Skoog culture medium. Rhizogenesis took place without any other addition of auxin. In callus tissue cultures ofAchillea ptarmica cultivated on Murashige-Skoog medium with 1 mg l^-1 2,4-D after a year long cultivation the whole plant has been regenerated without any change of nutrient requirements. In callus tissue ofA. nobilis under the same conditions only roots wore regenerated.

Two cultivars ofCicer arietinum L. with contrasting sensitivities to water stress, cv. C 214 (relatively resistant) and cv. 130 (susceptible) were compared for their protein content and soluble nitrogen (sol-N) under water stress. During water stress shoots of the cv. C 214 showed an increase (over the control) in both protein and sol-N content. The total nitrogen (total-N) also increased in the cv. C 214 while remaining almost unaffected in the cv. G 130. Cultivar C 214 shoots recorded lower protein/sol-N ratios. The results have been discussed in relation to resistance to water stress.

Complexes of water soluble proteins (albumins) were investigated in three cultivarsof Phaseolus vulgaris, viz: Yeltruská Saxa, Vainica Saavegra B, and Krupnaya sakharnaya. The first two cultivars exhibit haemagglutinating activity against rabbit erythrocytes, but have different elution profiles on Sephadex G-100. Their individual peaks have a different subunit composition, as revealed by SDS gel electrophoresis, as well as a different immunoelectrophoretic pattern, although proteins I and II of the specificity Veltruská Saxa are present in both cultivars. The cultivar Krupnaya sakharnaya expressively differs from the preceding lectin cultivars; it has no erythroagglutinating activity, its albumin complex has a high-molecular component, absent in the preceding ones, and has no lectin peak in the region of molecular mass of 100 000 to 200 000. Immunoelectrophoresis gave no evidence of protein I and II of the specificity Veltruská Saxa.

Esterase variation in shoot and root systems of ten-days seedlings of spring barley mutant lines was investigated. By an electrofocusing method it was found that some regions of the esterase activity were specific for the first leaf and for the root system of seedlings. Results showed the absence of close relationships between the morphological and esterase variation. Low negative correlations were only obtained for the root system parameters.

Both root and hypocotyl growths of lettuce, tomato, red cabbage and cucumber were inhibited when the seedlings were grown in Petri dishes together with 1 to 6 fruits ofWashingtonia filifera. This inhibition, in the case of lettuce hypocotyl, was not reversed completely even after the addition of 50 mg l^t-1 GAs. Effect ofW. filifera fruits on the light-induced synthesis of anthocyanin in red cabbage seedlings revealed that the presence of one fruit was enough to reduce the production of anthocyanin three times less than that of control. Water-soluble extract of the fruits when subjected to high temperature increased its growth inhibiting ability several times that of the untreated control.

The paper deals with the distribution of alpha and beta-glucosidases in the germinating pollen grains ofPortulaca grandiflora. Both these enzymes are localized in the pollen wall and the cytoplasmic granules. The latter are distributed throughout the pollen cytoplasm, pollen tube and stigma hair. In non-germinating pollen grains, enzymes are concentrated in the pollen wall. Stigma hair sheaths are completely free from enzymes. The functional significance of these enzymes in the hydrolysis of phenolic glycosides and polysaccharides is discussed.

On the basis of earlier data it was suggested that the induction of cytokinin autonomy might be accompanied by disorders in plastid function and a decrease in cytokinin utilization. In the work presented below the formation of chlorophyll and the isozyme patterns of nine enzymes, some of which are known to be localized in plastids, were compared in tobacco callus tissues differing in their hormonal requirements. Tissues either not requiring cytokinin or both auxin and cytokinin for their growth, contained a lower amount of chlorophyll than the cytokinin-and auxin-dependent strain. The number of isozymes of glucose-6-phosphate and NADP-malate dehydrogenase (i.e. enzymes which are known to be located in plastids) was reduced from four in the cytokinin-and auxin-dependent strain to two and one in the two cytokinin-autonomous strains, respectively. The fully habituated tissue contained an additional isozyme of NADP-malate dehydrogenase. The total number of isozymes of the remaining enzymes (NAD-malate dehydrogenase, peroxidase, esterase and a-and β-galactosidase) either was decreased or not changed in the cytokinin autonomous strains. The exception was an additional anodic peroxidase in one strain. The number of these isozymes in tissue habituated with respect to both auxin and cytokinin either remained the same or increased. Tobacco callus strains with altered requirements for growth regulators contained some new isozymes which were not present in any other strain and some isozymes present in other strains were absent. These differences are discussed in relation to the possible role of plastid function disorder associated with habituation.

IAA-oxidase activity increased in the stem as well as in the leaves of plants treated with GA₃, SA and GA₃ + SA during the early stages under inductive and non-inductive photoperiods, the activity being the highest in GA₃ + SA-treated plants. An isoenzyme of IAA-oxidase with Rm 0.15 developed in the stem as well as in the leaves subsequent to 1 or 2 inductive treatments. As this band persisted till the end of the experiment, it may be associated with the initiation as well as development of floral buds. Another band (Rm 0.30) appears to be associated with the phenol (SA) as it developed in the stem as well as in the leaves of SA- and GA₃ + SA-treated plants under both photoperiods. A band with Rm 0.60 developed in the leaves but not in the stem of GA₃-, SA- and GA₃ + SA-treated plants under both photoperiods.

The application of 2,4-dichlorophenoxyacetic acid at a concentration of 1.0 × 10^-3 M toCucumis sativus brings about a decrease in the activity of carbohydrate catabolizing enzymes in the leaves of experimental plants. On the contrary, in CMV infected plants the activity of sucrase, glucokinase, fructokinase, phosphoglucoisomerase and glucose-6-phosphate dehydrogenase are enhanced at the same time. The application of 2,4-D to virus infected plants promotes this effect further, so that the activities of the enzymes investigated are twice as high as those in the control.

In field-grown sugar beet plants (Beta vulgaris L. cv. Dobrovická A), each of66 successive leaves produoed in the course of the vegetation period was different with respect to its photosynthetic capaoity (P_c), life span, duration of leaf area expansion, and longevity after its maximum leaf area (A_max) has developed. The proportionality between the seasonal changes in these characteristics was not the same if the sequential senescence of leaves was taken into account. With aging of individual leaves, P_c increased with the leaf area expansion having attained the peak value between 75% to 100% of A_max The rate of ontogenetic changes in P_c of each leaf was specified by the rate of its growth and development so that even at comparable ages the successive leaves constituted a series of different physiological units.
The seasonal changes in quantum irradiance (PAR) were found to be responsible for differences in the growth characteristics between the successive leaves: Leaf expansion period was related with daily integrals of the incoming PAR (Io), while leaf longevity, after the A_max had been attained, was closely linked with PAR intercepted by the canopy (I). P_c expressed per the total leaf area of the plant was significantly correlated withI, while P_c calculated per unit leaf area of the plant was related toI _o Leaf potential to adapt P_c correspondingly to changes in PAR was greatest during leaf blade expansion; after the leaf had ceased to expand, changes in P_c were independent of differences in leaf irradiance.
The results stress, at least for field conditions, the inadmissibility of the extrapolation of attributes from one leaf to the other ones sequentially senescing on the plant.

N, P, K, Ca, and Mg contents, chlorophyll content, gibberellin-like substance content, photosynthetic and respiration rates, Hill reaction activity, and specific leaf area of different parts of the leaf blade of maize (Zea mays L.) were determined. Parts with highest values of the determined components and processes were marked in the longitudinal and transverse profiles of the leaf blade. The established gradients of substance contents and of the functional activity were related to the growth stage of the leaf.