Regenerants from tobacco(Nicotiana tabacum L. cv. White Burley) leaf segments cultivatedin vitro in vessels with solid agar medium under usual conditions (plantlets) grew under very low irradiance (I = 40 μxmol m-2 s-1), very high relative humidity (more than 90%) and decreased CO₂ concentration (c_a) during light period. In comparison with seedlings of a similar number of leaves and similar total leaf area grown in sand and nutrient solution, the plantlets had lower dry mass of shoots and roots per plant and thinner leaves almost without trichomes and epicuticular waxes. Due to a low transpiration rate under high relative humidity the water potential of plantlet leaves was higher than that of seedling leaves and the difference in water potential between leaves and medium was lowei. The rate of water loss from leaves detached from plantlets was considerably faster than that from seedlings under the same conditions (I = 110 μrnol m^-2; s^-1, temperature 30 °C, relative humidity 50 %). Net photosynthetie rates (P_n) of leaves of plantlets and seedlings measured under saturating I, natural ca and the leaf temperature 20 °C were similar, nevertheless the shape of curves relating Pn to c>> indicated some differences in photosynthetie parameters(e.g. saturation of Pn under lower ca> higher CO2 compensation concentration in plantlets than in seedlings). Similarly compensation and saturating I were lower in plantlets than in seedlings. The shape of transpiration curves as well as the expressive linear phases of P_N(ca) and P_N(I) curves of plantlet leaves indicated ineffective stomatal control of gas exchance. These results were confirmed by microscopic observations of stomatal movementsin situ

The effect of methyl jasmonate (JA-Me) applied in concentration 1.0 % in lanolin paste to detached tomato fruits at the mature green, advanced mature green and light red stages on the ethylene production and l-aminocyclopropane-l-carboxylic acid (ACC) content was investigated at different times after treatment. JA-Me stimulated ethylene production in all stages of ripening, but the level of ACC increased or decreased in comparison with control depending on the stage of ripening. Higher level of ACC in JA-Me treated tissue was found in mature green stage and fully ripened tomatoes-treated at advanced green stage; lower one in light red stage - treated at advanced green stage and fully ripened stage - treated at light red stage.

Salt tolerance ofEchinochloa crusgalli was studied using gravel culture with root medium electrical conductivity between 3 to 25 dS m^-1. Salinity depressed germination and shoot yield. A 50 % reduction in shoot yield occurred at 15.9 dS m^-1. The plant was able to maintain its tissue water content and K concentration in the tissue water while Na, Ca and Cl increased and Mg decreased with increasing root zone salinity.

The cultivars of barley and wheat resistant to mildew had a higher level of free zeatin and its derivatives during the whole ontogeny than the susceptible cultivars. The effect of exogenous application of cytokinins on the growth ofErysiphe graminis DC. was different. Kinetin and benzylaminopurine showed only a slight inhibitory effect. Zeatin and its derivatives completely inhibited growth of this fungus.

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 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.

This paper is a sequential analysis of qualitative and quantitative nuclear evolution inSesbania rostrata (Leguminosae) stem nodules. Before infection, the nuclei of the root primordia (nodulation site) cells show a 2G level of DNA. Immediately upon infection, the cells cease their mitotic activity and the nuclei begin synthesizing DNA up to a 32C level after the onset of the infection. The increase in the diameter of the nuclei of the infected cells is concomitant with the rise in the level of DKA. In the final phase of the evolution of these nodules, the nuclei of the infected cells undergo degenerative changes.

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.

Some general data on the genetic control and the possibilities of regulation of developmental paths inDrosophila are furnished. The insights to be gained from this insect will surely have implications that extend far beyond the fruit-fly. For example, in plants, developmental programs for floral organs, implying specific proteins are known. Developmental mutants in which mutate alleles control developmental programs for flowering were also selected in several species (Zea, Pisum, Sorghum, Cucumis, Mercurialis). Chemicals, especially phytohormones interfering with these programs are discussed. The case of sexual differentiation ofMercurialis is discussed in more detail. In this species, sex organs are controlled by sex determination genes and by auxins (male) and cytokinins (female). Flowers of each sex can be characterized by specific mRNA populations. They were evidenced by translationin vitro in a cell-free system of the various kinds of mRNAs [poly(A), non poly(A), polysomes]. The feminisation of genetic males by cytokinins induces the mRNA population of female type. Evidence concerning the implications of cytokinins in protein synthesis before translation level is presented. This is also probably true for auxins, although direct evidence is lacking.

The phenotype appearance ofArabidopsis thaliana hairy roots and crown galls their teratomas and regenerated plants were compared. Several differences were found, which correlate with T-DNA differences between Ti and Ri plasmids.

CAM-like photosynthesis was found in the isoetid aquatic plantsLittorella uniflora andIsoetes lacustris, but not in the isoetid speciesLobelia dortmanna or in the elodeidElodea canadensis. Of the taxa studied, the first three are known to utilize sediment-borne CO₂, whereasElodea is dependent on bicarbonate.

The analysis of the kinetic behaviour of pea L-tryptophan aminotransferase isolated from mitochondrial and cytosolic fraction unambiguously showed the preference of some of its keto acid substrates demonstrated by statistical criteria (R2, SSQ, AIC). An attempt is made to evaluate this result in connection with the availability of the keto acid substrates in different cell compartments.

Acid phosphatase isolated from low altitude grown plants of two high altitude plant species,Selinum vaginatum Clarke andAcer caesium Wall, displayed higher thermostability than that from plants of the same species grown at high altitude. The isozyme composition, however, remained unchanged inSelinum vaginatum. InA. caesium, one of four isozymes, was thermolabile in the samples from high altitude and was lost after 10 min heating of the extracts at 60 °c. In the samples from low altitude, this isozyme was not detected and a band with slightly lower Rf value was present which was thermostable. The described changes in the thermal properties of acid phosphatase reflect an adaptive step towards high temperature acclimation at low altitude.