Thein vitro embryoids ofEschscholzia californica do not form normal plantlets in cultures. However, 6-benzylaminopurine and gibberellic acid, when added to the medium, partially alleviate this inhibition. Experiments involving decotylization, and culture of embryoids at different stages, indicated the cardinal role of cotyledons in plumular growth.

The results of experiments conducted with autumn rye and summer wheat on sandy loam soil at the Institute for Cereal Production of the Martin-Luther University, Halle-Wittenberg (G.D.R.) have revealed that an increase in soil moisture improved the plant water balance, width of stomata, shoot growth, tiller density, leaf area and growth rate. Net assimilation rate, however, decreased with the increase in soil moisture above 50 per cent water holding capacity. Increased soil moisture improved contents of nitrogen, potassium and phosphorus only during early stages of growth, but their uptake was not reduoed at maturity. Air conditioning irrigation proved superior in respect to all above mentioned characteristics, except the uptake of potassium, which decreased with air conditioning irrigation at higher soil moisture relations.

Abscisic acid (ABA) had no significant immediate effect on the activities of Photosystems PS 1 (DPIP/Ascorbate → MV) and PS 2 (H2O → K3[Fe(CN)6]), when added during the activity measurements in a final concentration of 10¯4 M to both freshly prepared chloroplasts from primary leaves ofPhaseolus vulgaris L. and chloroplast preparations preincubated with ABA for 22 h. This incubation also did not induce any significant post-effect on PS activities.

Long-term callus cultures of two barley cultivars have been investigated at the cellular level. One slowly growing, root forming callus of the barley cv. Bulgarische Nackte consists of cells the majority of which contain the diploid chromosome number. Contrarily, a fast growing callus of the cv. Elgina having no regeneration potency at all, is highly polyploid and includes more than two thirds of aneuploid cells. Tn this callus strain, a great number of multinucleate cells has been found. Some problems are discussed with respect to the relationships between growth rate, karyological stability and regeneration capacity in long-term callus cultures of cereals.

Response of epidermal diffusive conductance to simultaneous changes in leaf water potential and photon flux density was studied in primary bean leaves. Values of epidermal conductance corresponding to every photon flux density decreased with decreasing leaf water potential below - 6.9 x 10⁵Pa; slight deorease was followed by a rapid one at water potential ranging from - 8.0 to -10.5 x 10⁵ Pa. In the leaves with water potential lower than -10.5 x 10⁵ Pa neither the saturated photon flux density (1200 [xeinstein m^-2s^-1) induced photoactive stomatal opening.
Negative influence of one factor could be partially compensated by positive influence of the other. These results were in good agreement with the considered mechanism of action of leaf water potential and photon flux density on epidermal conductance.

The sensitization of chlorococcal algae by 5-BdU for the purpose of UV-light mutagenesis was studied. The results obtained were compared with our earlier findings on the sensitization of the same algal strains by 5-BU. No shielding effect of the 5-BdU molecules against UV-light was observed. Probably, the uptake of them from the liquid medium did not result in such excess as compared with the treatment by 5-BU, even if the cells were long enough (24 h) exposed to the concentration of 5-BdU. Likewise, neither stimulating nor inhibiting growth effects on the growing cell colonies were observed after treatment with 5-BdU. The sensitization of the algal cells for UV-light effects was effective in all the experiments. An increased damage of the algal cells by UV-light after sensitization was proved in all the parameters recorded. The frequencies of permanent changes of the cells or their colonies were also increased, but their spectrum did not change significantly. A suitable combination of the 5-BdU sensitization of the cells before their influencing by UV-light and the induction of their repair mechanisms by visible light may decrease the frequencies of the lethal or sublethal damage and increase the frequencies of the useful permanent changes in the characteristics of the chlorococcal algae. The results obtained are discussed from the viewpoint of the regulated mutation process in the breeding of algae.

Embryos ofAgrostemma githago seeds blocked by higher temperature are suitable objects for the study of the regulation of gen expression independent of transeriptional processes. Germination of afterripened seeds can be prevented by imbibing at 30°C, whereas at 20°C germination will be completed after 30 h of soaking (BORRISS 1956). In temperature-blocked embryos RNA is synthesized with undiminished intensity, whereas DNA and protein syntheses are remarkably reduced. Equal amounts of poly(A)-RNA (probably mRNA), enriched by affinity chromatography on oligo(dT)-ceIlulose columns, are detected in blocked and activated embryos.
We suggest that in blocked embryos not synthesis itself, but the availability of mRNA to polysomal fraction is reduced. Benzylaminopurine is able to break secondary dormancy ofAgrostemma githago seeds. In benzylaminopurine-treated seeds there is only a slight increase of the incorporation of¹⁴C-L-leu-cine in protein.

Three-leaf pea (Pisum sativum L. cv. 'Alaska') seedlings were oriented horizontally and³²P was applied to leaf-2 for 6 h period, at the end of which the distribution of isotopes in the seedlings was determined. It was found that (i) isotope accumulation in the apices of the vertical and horizontal seedlings remained almost the same; (ii) on decapitation almost all the isotopes in the apex diverted to the roots in the vertical seedlings; (iii) among the horizontal seedlings³²P was retained in the hanging treated leaf and the rest moved to the roots via shoots; (iv) the dry weight of the hanging treated leaf was slightly greater than the above-axis one; (v) the position of buds on the axis had no effect on the initial³²P accumulation in them, however, a trend of greater isotope accumulation was noted in the above-axis basal buds; (vi) geo.stimulation had no effect on the total dry weight of the seedlings; and (vii) in geo-stimulated seedlings decrease in the dry weights of shoots and its concomittant increase in roots was primarily the result of the movement of substances.

The inhibitor-A, isolated from the leaves of a saline soil tolerant plantSuaeda fructicosaFoRsk., is phenolic in nature, inhibits the IAA-induced growth, and is resistant towards higher temperature.

Changes in respiration, activity of cytochrome oxidase and ascorbic oxidase and in BSMV content were investigated on winter wheat plants cv. 'Kaštická osinatka' after application of growth stimulating and growth inhibiting concentrations of 2,4-D. It has been found that the rate of respiration is almost exclusively dependent on the activity of both these terminal oxidases. Consumption of oxygen was regularly increasing with decreasing herbicide concentration and at concentration 10^-7 M was even higher than the control value. Healthy and BSMV inoculated plants treated with 2,4-D differed in ascorbic oxidase activity while activity of cytochrome oxidase was almost the same. In contrast to healthy plants the BSMV inoculated ones were seriously damaged after 2,4-D application. Plants inoculated with BSMV and treated with 2,4-D contained in contrast to those inoculated and not treated with 2,4-D a higher content of virus (124 to 150 %) which was not proportional to herbicide concentration. These results, which were obtained from experiments with plants grown in nutrient solutions supplemented with 2,4-D, indicate that BSMV inoculation induces metabolic changes which cause a loss of selectivity of 2,4-D.

Threadlike particles from mosaic freesia aggregate during and shortly after the purification which is followed by full degradation into insoluble amorphous precipitate. This irreversible process is caused predominantly by host plant proteases. Such degradation can be completely inhibited if the virus complex is purified and stored in the presence of 0.1 mM phenyl-methylsulfonylfluoride. A modified purification method which gives a higher yield and the virua preparation of greater purity is described.

Some diagnostic methods devised for the demonstration of the presence of plum pox virus in plum (Prunus domestica L.) and apricot (Armeniaca vulgarisLam.) leaves were examined. The method of radial diffusion in agar can be recommended as the simplest and the least time consuming method which can be used during the entire vegetation period. In order to obtain antisera, some preparation methods of PPV antigen were verified. The best preparation method was a modification of Van Oosten's method in which HEPES buffer pH 6.7 was used for the homogenization-of leaves from infectedNicotiana clevelandiiGray plants and for the solution of sediments after ultracentrifugation. In this way, antigens with titre up to 1: 2048 and during the immunization of rabbit antisera with titre 1: 512 to 1: 1024 were obtained. After the saturation of antisera according to Uyemoto, the titre of the antisera was 1: 64 to 1: 256. Antisera were used for agar preparation in transparent plastic boxes. 0.2 to 1 g portions of leaf material were homogenized with 0.05 M Tris-HCl buffer pH 7.2, 3% pyrrolidine and 1 % polyvinylpyrrolidone in the ratio of 1: 3 for the determination of PPV in plum and apricot leaves.

A protease activity was detected in rice (Oryza sativa L. cv. Ratna) leaves that hydrolysed hemoglobin more efficiently than bovine serum albumin. The activity was high when the enzyme was extracted and assayed with tris-maleate buffer [tris (hydroxymethyl) methyl amino-maleate] pH 7.0 rather than with water or with citrate-phosphate buffer pH 7.0. The enzyme had a strong dependence on sulfhydryl groups for its activity without which it was inaotive. The pH optimum was 7.0 and the temperature optimum was 40 °C. Protease activity expressed per unit leaf fresh weight (absolute activity) increased only little during senescence of detached rice leaves while the same activity expressed per unit soluble protein content (specific activity) increased by a greater factor (about 5 times) than absolute activity. Total and soluble protein content decreased during the senescence of detached leaves. Benzimidazole (10-3M) and kinetin (0.5xl0-5M) treatment arrested the increase of the protease activity and the deorease in the protein content during detached leaf senescence. It was indicative that protease protein was more stable than the bulk of other proteins in senescing leaves.

¹⁴CO₂ assimilation, RuBP earboxylase and PEP carboxylase activities show cyclic changes during the development of barley leaves. Cyclic changes, but in phase opposition with respect to carboxylating enzymes, are shown by RuBP oxygenase, phosphoglycolate phosphatase, glycolate oxidase and nitrate reductase activities. The oxygenase function of RuBP carboxylase appears to be the primary source of glycolate in young leaves, whereas in old ones glycolate could be supplied from some source in addition to RuBP oxygenase activity.

In the investigated barley cultivar resistant toErysiphe graminis f. sp.hordei Marchal a temporary decrease in water uptake may be observed during the first days following infection in light. No marked differences could be detected in darkness. Starting from the stage of formation of fructification organs the ratio between water uptake in light and in darkness in the resistant cultivar is similar to that of the control, while the opposite is true in the susceptible cultivar where the ratio markedly decreases with the development of powdery mildew. The resistant cultivar responds more rapidly to the pathogen by changes in water uptake than the susceptible one.

Applications of various amounts of GA₃ onto the shoot apex of biennial rosette-plantHyoscyamus niger L., exposed to long days and non vernalized, caused internodes formation and stem elongation. The stem length was proportional to the amount of GA₃ applied. Number and length of developed internodes and the whole length of the shoot were maximal in plants treated with a greater amount of GA₃. In the end, stem elongation stopped and plants formed perchedrosettes without flowering. Hence, gibberellic acid participates in mechanisms of flowering only by indirect effect on stem elongation and not directly on flower formation itself.

During the period of the highest multiplication of TMV in tobacco tissues (on the 6th to l0th daya after inoeulation) the activities of NADP-glyceraldehyde-3-phosphate dehydrogenase, fructose diphosphatase, and phosphoglucoisomerase increase,i.e. the 3-phospho-glycerate is broken down more intensely, being the primer of photosynthesis via glycolysis. Products of this metabolic pathway, which are not employed directly for virus synthesis, are stored during this period as free saccharides and starch. The breaking-down rate of these substances increases during this period as well, as shown by increased activities of amylophosphorylase, phosphoglucomutase and saccharase. The increased aetivity of glucose-6-phosphate dehydrogenase is proportional to the rate of TMV multiplication; its high value (more than twice as with the control) insinuates that the virus reproduction deereases contents of some intermediates of the Calvin cycle (especiaily NADPH and ribulose-l,5-diphosphate) which act as inhibitors of the photosynthetic regulative system.

Stomata on the cotyledons of Morphactin EMD 7301 and EMD 7311 treated seedlings may be anisocytic, anomocytic, paracytic, diacytio, transitional forms and haplocytic. In spite of this diversity, the most frequent type is anisocytic on both surfaces. The stomatal ontogeny may bo perigenous, mesogenous and mesoperigenous. Morphactin EMD 7301 and EMD 7311 increase the size of cotyledons in all concentrations accompanied by an increase in the number of stomata on the adaxial surface in 100, 150, 250 ppm of EMD 7301. The effect of morphactin is promotive to the size of stomata in all concentrations, but it retards the stomatal density and number of epidermal cells. This may be due to an increase in the size of the epidermal cells. The substrates, however, have no effect on the morphology and ontogeny of the stomata; probably they are inherent chracters.

Studies performed on winter rape plants(Brassica nnpus var.oleifera, cv. 'Gór-czański') revealed that cold treatment affected the cell membranes and led to the temporary increase in electrolytic leakage from a tissue. This was followed by the marked decrease of the electrolytic leakage in the course of hardening. Changes in membrane properties were accompanied by the promotion of soluble protein accumulation. Inhibition of protein accumulation by the cycloheximide treatment brought about wilting of plants under cold conditions. Possible role of soluble protein in protection of cells against secondary water stress caused by the coldinduced changes in membrane properties is suggested. Cold-induced changes in the electrophoretic pattern of soluble protein are described and discussed.

The rise in soil salinity level tended to decrease shoot dry weight, and, grain yield per plant and, to some extent, weight of I grain. This effect was usually more pronounced in the presence of CCC. On the other hand, the shoot dry weight was increased by CCC in salinity absence but the reverse at 0.8 % salinization degree. The grain yield per plant was raised by CCC in the presence or absence of salinity, particularly in the latter case. The dry matter accumulation in the shoot system (at earing stage) rather than grain yield tended to be much more affected, whether regarding the negative response to salinity or the positive one to CCC.