With the aim to increase citrus fllowering under tropical conditions, two formulations of 2-chloroethyl phosphonic acid (Ethrel and Flordimex), Alar (succinic acid-2, 2-dimethyl hydrazide) and Cycocel (2-chloroethyl-trimethyl ammonium chloride) were applied during the flower induction period (December) to young "Valencia" orange trees at concentrations of 1000, 2500 and 5000 mg l^-1. These treatments effectively increased flowering, mainly at lower concentrations. Treatment using Flordimex at 500 and 1000 mg l^-1 concentrations resulted in flowering increase which is analyzed in this paper.

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

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.

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 photoblastic seeds of two pioneer trees from the tropical rain forest-Cecropia obtusifolia andPiper auritum - require long diurnal periods of red light to germinate. In the field, the establishment of the trees takes place only in light gaps produced by falling trees. Experiments were performed in order to ascertain the relationship between the light requirements of the seeds and the germination control in the field. Results show that phytochrome regulated germination allows the detection of light gaps.

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.