The scale of salt tolerance of each plant tissue can be characterized by a "critical" concentration of NaCl. At this concentration the endogenous content of free proline rises. A correlation exists between the endogenous Na⁺-concentration and this increase of proline. Calcium cations can enhance the NaCl-tolerance by inhibiting the Na⁺-permeability. Thus, the rise of the proline concentration in this case is produced only by NaCl concentrations higher than the critical concentration. The calcium pretreatment of caryopses during soaking leads to the enhancement of the tolerance under salt stress, too.

Changes in ribosephosphate isomerase and ribosephosphate pyrophosphokinase activities occurring in tobacco leaf tissues infected with the potato virus Y (PVY) were studied at the stage of acute infection. The results obtained have shown that during the entire experimental period the activities of both enzymes were at the end of a dark phase much higher in virus-infected tissues compared with the values found in healthy control plants. The courses of the activity curves of both enzymes were consistent and correlated with the reproduction curve of PVY. The results obtained suggest a direct involvement of both enzymes inde novo biosynthesis of the virus RNAvia the oxidative pentose phosphate pathway.

The effects of salicylate on stomatal resistance (a measure of stomatal opening) were compared with those produced by 2,4-dinitrophenol and abscisic acid. Salicylate and dinitrophenol had the same minimum effective concentration and comparable kinetics, and induced stomatal closure persisting for a long time in the absence of further supply. However, a K and Ca solution prevented the salicylate-induced, but not dinitrophenol-induced, stomatal closure. The effects of salicylate and abscisic acid had very different characteristics. Cytokinins had no relevant effects on the stomatal closure induced by the three compounds. A close correlation was found between stomatal closure and K⁺ leakage from the treated leaves, suggesting that damage to the cell membrane may be involved.

The delay in development of winter wheat plants grown under conditions of Ca deficiency manifested itself also in the time curve of ferredoxin-dependent glutamate synthase activity. Up to the stage of the first leaf the activity increased. Thereafter it gradually decreased similarly as under conditions of complete nutrition, but with a shift of about 7 days as compared with plants given complete nutrition. Increased glutamate synthase activity in Ca-deficient plants may be one of the factors leading to a high glutamate level under these conditions.

The changes in the concentration of free radicals and bound amino acids in developing maize inflorescences and fruits were ascertained. The concentration rises markedly when tissues disintegrate and desiccate. A slight increase in the concentration may be ascribed to the rise of metabolic processes connected with kernel formation.

Transpiration rate, leaf area, the content of nitrogen and saccharides decreased with the decrease in soil moisture content from 90 % to 30 % of full field capacity. Stomatal frequency, fresh and dry matter and the chlorophyll and carotenoid contents of lupine or safflower remained more or less unaffected. After spraying with the antitranspirant (PMA) the saccharide contents were raised. As concern the lipids content and the contents of Ca, Mg and P, treated plants exhibited variable response to both drought stress and spraying with various PMA concentrations.

An attempt is made to characterize the functional activity of the protein moleculo possessing both peroxidase and IAA oxidase activity by comparing the kinetic parameters for the two types of enzyme activity with regard to the following substrates: H₂O₂, benzidine, guaiacol and IAA. The curves expressing the dependence of the enzyme reaction velocity on the concentration of the enzyme or the substrate are different depending on the enzyme extract origin and the type of the substrate. It is established that the K_m of peroxidase for IAA decreases while its K_m for H₂O₂ increases during cell development. Both types of enzyme activity show similar pH and temperature dependence. The presented data show that IAA oxidase activity of the peroxidase develops as extension and differentiation of the root cells proceed. This is one of the possible mechanisms through which peroxidase may participate in the regulation of growth and differentiation of the primary root cells of maize (Zea mays L.)

The effect of 2,4-dichlorophenoxyacetic acid (2,4-D) at low concentrations on cell cycle duration and sister-chromatid exchange (SCE) frequency was studied using meristem root-tip cells ofAllium sativum L. 2,4-D induced a marked prolongation of the cell cycle. At the same time, small but statistically significant increases in SCE frequencies were observed at 5 μM and 15 μM 2,4-D concentrations. The significance of these findings in the evaluation of mutagenic activity of 2,4-D is discussed.

An enzyme extract from apple(Pyrus malus Borb.) seeds which causes the disappearance of free indol-3-ylacetic acid (IAA) requires the presence of oxygen, but is not inhibited by cyanide. Using 1-¹⁴C-IAA it has been demonstrated that the IAA transformation is not accompanied by its decarboxylation. Decarboxylating IAA oxidase is absent during the whole period of apple seed cold stratification. Free IAA has not been detected in dormant apple seeds and in seeds stratified at low temperature. It appears during stratification at 25 °C. Ethyl ester of IAA and indol-3-ylacetyl aspartate have been identified in dormant and after-ripened seeds. Exogenous 1-¹⁴C IAA taken up by apple embryos is converted into conjugates with aspartate and short peptides containing an aspartate moiety.

The extracellular nuclease fromPinus silvestris pollen was isolated and characterized. Molecular sieving produced only one peak of nuclease with apparent molecular mass of about 30 kDaltons, while molecular mass of the enzyme as determined by means of sodium dodecyl sulphate-DNA gel electrophoresis was 25.7 kDaltons or less. The nuclease exhibited one electrophoretic molecular form only.
Specific antiserum against this nuclease was prepared and the nuclease was shown to be immunochemically cross-reactive with extracellular nuclease from Pinus nigra pollen. No immunochemical relationships were observed between pine nuclease and the pollen extracellular nucleases from the angiosperm species,Nicotiana tabacum, Corylus avellana, Alnus incana andBetula pubescens. No cross-reactivity was detected by double diffusion between the pine nuclease and the extracellular proteins from vegetative spores ofEquisetum arvense.

The free proline and chlorophyll contents, and the chlorophyllase, peroxidase and nitrate-reductase activities were determined in sunflower seedlings grown under controlled conditions and submitted to water stress induced by 14 % polyethyleneglycolj (M_r = 4000) or isotonic NaCl solution. Combined free proline content and peroxidase activity may be used for detection of the factor inducing water stress.

Like wet stigmas, the stigmatic secretions of dry stigmas ofEichhornia also have proteins, sugars, amino acids, phenols and fatty acids. No significant difference could be observed in the composition of stigmatic secretions of long and medium styled flowers except that the components were marginally higher in concentration in the former than the latter. The UV absorption profiles of the stigmatic secretions also showed no difference. Stigma surface esterases could be detected in both the stigmas from a very early stage of development.

Free proline and chlorophyll contents, chlorophyllase, peroxidase and nitrate reductase activities were determined in maize seedlings grown under controlled conditions and submitted to water stress induced by 14 % PEG-4000 or NaCl (isotonic). All the parameters studied showed a significant response to the water stress, but the level of free proline and peroxidase activity together may preferentially be used for the diagnosis of osmotic stress or saline-osmotic stress.

A histochemical method for the determination of IAA-oxidase has been used in sections of various aerial parts of winter wheat plants. High IAA-oxidase activity was localized in the cell walls of sclerenchyma near the periphery of the stem, in the vascular bundle sheath of sclerenchyma and in xylem, both in the stem and in the leaf. The cell wall-bound IAA-oxidase activity therefore appeared in lignifying tissues. The staining was very weak or absent in the cell walls of parenchyma tissues and phloem. The positive reaction of the cytosol at the bulbous ends of guard cells and in the leaf primordia is presumed to be due to cytosolic IAA-oxidase. These results are discussed in relation to peroxidase localization and to our previousin vitro studies.

The values of influx (Ji) and efflux (Jo) of phosphates through intact maize roots (primary, seed roots) have confirmed the dependence of the P concentration in nutrient medium on the activity and efficiency of transport mechanism with respect to the accumulation of phosphates (J) by roots. The phosphate accumulation is about 97-99 % of the total uptake. If the P concentration is < 1 mM the efflux is negligible, and Ji <=g Jo. In contrast, if the P concentration is τ 1 mM, the proportion of efflux significantly increases, up to 45 % of the whole influx. The approximation to the conditions of equilibrium of phosphate flows ( Ji = Jo) depends on the P concentration in root cells, the accumulation of phosphates being determined by the relation Ji τ Jo. In the roots growing in P-containing medium the values of efflux are much higher than in the roots lacking P.
The positive effect of Ca²⁺ ions on the accumulation of phosphates is caused by the decreased proportion of efflux. The factors instigating the integrity or non-integrity of the cell structure (Ca²⁺, SDS, EDTA, Sorbitol,etc.) and thus its effectiveness determine the accumulation of phosphates by roots. Analogously, the factors stimulating the ability of accepted phosphate to be metabolized, and their use in the form of organic compounds decrease the proportion of efflux; these activities are shown in the increased efficiency of the phosphate uptake. The presented results show the importance of the integrity of the cell structure, the functioning of membranes and of metabolism efficiency for the accumulation of phosphates by plant roots. The main form of phosphorus transport in xylem exudate is inorganic phosphorus. Its share is from 79 to 82 % of the total amount of transported P. The utilization of P in the roots in the form of organic, slowly motabolizable P compounds (mannose-6-phosphate) and inhibition of acid phosphatase activity effectively restrains P transport over long distances. The correlation of P transport from roots into shoots with phosphatase activity was established (correlation coefficient is 0.74⁺⁺). It can be summarized that long-distance P tran sport is a function of dephosphorylating reactions.

Major differences betwean the determinate (dt₁Dt₂,dt₁dt₂), semideterminate (Dt₁Dt₂), and indeterminate (Dt₁dt₂) near-isogenic lines of glycine max (L.) Merr, mainly appeared after R1 (reproductive) stage. Increases in specific leaf matter (SLM) between Rl and R6 stages showed that determinate lines have higher SLM than semideterminate or indeterminate lines. Soluble protein and starch also accumulated more rapidly in determinate lines. Insoluble protein, ribonucleic acid (RNA), and deoxyribonucleic acid (DNA), reducing saccharides, chlorophyll, and soluble saccharides contents of leaf from determinate lines resembled those of semideterminate and indeterminate lines.