The duration of the mitotic cycle and its individual phases was estimated in root meristems of isolated barley embryos and intact barley seedlings by means of pulse labelling with³H-thymidine and construction of labelled mitoses curve. The duration of the whole mitotic cycle in the cell population of root meristems of isolated barley embryos cultivated in the aerated liquid complete medium is 12.2 h. The mitotic cycle time of root meristems of intact barley seedlings, oultived in Petri dishes on wet blotting paper is 9.2 h. Most of root meristem cells belong to the fraction of rapidly proliferating cells, but this fraction exerts a high degree of variability by itself. Pulse treatment by³H-thymidine in our experimental conditions (74 kBq ml^-1 - or 2 μCi ml^-1, exposure 0.5 h) did not induoe any chromosomal aberrations in unlabelled cells and only a very low frequency of chromosomal aberrations in labelled cells. Measuring the cell population kinetics by pulse labelling with³H-thymidine can be used simultaneously with the study of induction of ohromosomal aberrations by mutagens.

Spraying of CCC (500 ppm) on wheat cv. Kalyan Sona-227 averted the adverse effect of soil moisture stress at the anthesis phase, by maintaining a higher level of chlorophyll, nucleic acids and protein content and acidity of the tissues. Treated plants after recovery from moisture stress yield even more than the untreated plants.

The blue-green algaPlectonema boryanum was chosen for a study of the properties of rRNA of procaryotic organisms. The process of rRNA species maturation was studied by labelling RNA with the isotope 32P.23 S and 16 S rRNA molecules each have their own precursors. Molecules with molecular weights of 1.65 X 10⁶ and 1.24xlO⁶ were identified as precursors of23 S rRNA, while the molecules 0.87 X 10⁶; 0.78 X 106 and 0.68 X 10⁶ were found to be precursors of the 16 S rRNA. No common polycistronic precursor could be found.
Experiments done with algae cultivated in light and in the dark confirmed the fact, that the rate of rRNA synthesis is reduced in the dark, without however stopping completely.

The content of bound proline sharply increased in proteins of different organs of young plants of winter rape and winter wheat exposed for 72 h to temperatures from 0 to 2 °C while it decreased only in root tips of wheat plants. Free proline which at 20 °C occurs in all plant organs only in trace amounts, accumulated considerably after 72 h exposure to low temperatures in the above-ground organs and only slightly in the roots. Free proline did not accumulate during the first 24 h at 0 to 2 °C in detached leaves of winter wheat but it was incorporated into newly synthetized proteins in which proline content increased after 6 h incubation to its maximum ( + 11.75% in comparison to control); the content of free glutamate sharply decreased during the first 6 h of incubation and the accumulation of bound glutamate was belated in comparison to that of bound proline. Sucrose infiltrated into detached leaves of winter wheat strongly stimulated proline incorporation into proteins at low temperatures, but it did not influence glutamate incorporation. The results suggest that the main reason for thede novo proline biosynthesis during the first six hours of hardening of the plants is the synthesis of proteins rich in proline; free proline accumulates later predominantly in the above-ground organs as a surplus. The above-ground organs are dehydrated in the course of the hardening process approximately to the same extent both in the light and in the dark, but proline content increases much less in the dark than in tho light.

The activity of L-tryptophan synthase (TS, E.C.4.2.1.20) was comparedin vivo in seedlings of plants high in L-tryptophan (L-trp) (pea and kohlrabi) and low in this amino acid (maize). In maize the TS was studied both in the normal and in the opaque-2 genotype that forms an endosperm richer in essential amino acids. The activity of TS was determined on the basis of the increase in radioactivity of the chromatographically purified L-trp-¹⁴C, synthetized after vacuum infiltration of L-serine-¹⁴C-(U) and ineubation for 24 h. As regards the TS activity in seedlings, maize is comparable to pea and kohlrabi; in contrast to this TS is less active in pea seedlings, which can be attributed to the presence of TS inhibitor (CHEN and BOLL 1969). In ripening maize kernels and leaves adjacent to the ear the TS activity is about 20 times lower than in seedlings. The differences in the activity of TS in the genotypes of maize could not be detected, even at the period of seed ripening. Therefore the differences in L-trp content in the investigated plants cannot be explained by a differing activity of TS. TS is probably not the determining regulator of L-trp level in plants, its activity is relatively high even in plants low in L-trp.

Excised tomato cotyledons subjected to mannitol induced water stress had more total sugars than normal cotyledons during injury but less total sugars than normal cotyledons in the adaptive phase. During water stress injury, protein and UNA synthesis were reduced, activities of beta-fructofuranosidase and phosphofructokinase were reduced but activities of proteases, ribonuclease, hexokinase and glucose-6-phosphate dehydrogenase were increased. Additions of kinetin reversed the water stress effects on enzyme activities. It is concluded that during water stress injury, there was a fundamental reduction in cytokinin activities leading to the selective shift in the enzyme populations.

The rate of synthesis of RNA was studied under salt and water stresses created by the addition of four different salts and polyethylene glycol-6000 (PEG-6000) in excised embryo axis of mung bean using^l4C-uracil. Iso-osmotio concentrations of salts and PEG resulted in differential effect on RNA synthesis. PEG inhibited, whereas salt stimulated incorporation of labelled uracil into RNA. Ionic differences on RNA synthesis were very clear as synthesis of RNA was more affected with sulphate than chloride and with sodium than potassium ions.

Decapitation of the stem in one-week-old pea seedlings below the first node causes a rapid outgrowth of the two cotyledonary buds. One of them soon becomes dominant, while the other one is inhibited, but can be released from inhibition by cutting off the dominant bud. The level of endogenous auxins and cytokinins was determined in dominant and inhibited buds, as well as in released buds at different time intervals after deinhibition. It was found that the inhibited buds contained very little acidic, ether soluble auxins, a high level of tryptophan and also a high level of cytokinins, in comparison with dominant buds. When the inhibited buda were released from inhibition, their auxin content rose, while that of tryptophan and cytokinins decreased, reaching the level found in dominant buds within six days. Specific changes in content of two undetermined auxin-like substances were found in released buds during de-inhibition. These results are discussed in relation to the current views on the regulation of apical dominance.

The effect of some ammonium salts on nitrate reductase (NR) level, onin vivo nitrate reduction and on nitrate content was followed in the presence of nitrate in the medium, under changing experimental conditions, in excisedPisum sativum roots, and their effect was compared with that of KNO₃, Ca(NO₃)₂ and NaNO₃ at 15 mM NO₃^- concentration, i.e. at a concentration which considerably exceeded the level of saturation with nitrate with respect to nitrate reductase. The effect of ammonium salts on NR level is indirect and changes from a positive one to a strongly negative one which is dependent on the time of action of the salt, on the presence of other cations, on pH of the solution of the ammonium salt and on the nature of the anion of the ammonium salt. A positive effect on the enzyme level can be observed in the presence of other cations than NH₄⁺ at suitable concentrations of those ammonium salts, the solutions of which have their pH values in the acid region (i.e. NH₄H₂PO₄, (NH₄)₂SO₄ and NH₄NO₃). However their positive effect is independent of the presence of NH₄⁺ ions, and it is obviously the result of an increased concentration of H⁺ ions. A clear-cut negative effect on NR level can be observed after 24 h in one-salt NH₄NO₃ solution where NH₄⁺ is not balanced with other cations and thus certainly can adversely influence many metabolic processes, and in the solutions containing neutral (pH 6.2) and dibasic ammonium phosphates in which dissolved undissociated ammonia [(NH₃). (H₂O) which can also affect many metabolic processes incl. proteosynthesis] probably has a toxic influence.
Thein vivo nitrate reduction is always depressed in excised pea roots in the presence of ammonium salts in the medium, regardless of the level of nitrate reductase. Under the described conditions, no relationship could be established between the enzyme level and the so-called metabolic NO₃^- pool (i.e. NO₂^- production under anaerobic conditions), nor between NR level and the total nitrate content in the roots.
One-salt solutions of NaNO₃, Ca(NO₃)₂ and KNO₃ exert different effects on the level of nitrate reductase and on the content of NO₃^- in the roots, but the in vivo NO₃^- reduction shows the same trend as NR level in the roots influenced by these salts. Cl^- ions, supplied in NH₄C1, depress both NR level and NO₃^- content in the roots at higher concentrations, but they do not significantly affect the in vivo nitrate reduction in comparison with other ammonium salts. These results indicate that NR level,in vivo nitrate reduction, and nitrate uptake can be regulated in pea roots independently of each other.

The possibility of using a combination of the mutation process with the induction of the repair processes has been studied to increase the mutation frequencies in algal populations after UV-treatment. From this study it follows that the repair process induced by visible light is much more effective than the dark repair processes in the chlorococcal algae used. In these algae, visible light perhaps does not induce only those repair processes which affect their DNA, but probably also some recovery ones which affect their damaged structures and physiological functions. A suitable combination of the sensitization of algal cells by a DNA-base analogue before UV-treatment and the induction of the light repair and recovery processes resulted in a rather high increase of viable mutations in chlorococcal algae. These findings may be useful in the breeding of chlorococcal algae, which have no possibility of hybridization (except somatic).

Polyethylene glycol (PEG-4000) solution in concentration from 7.5 to 200 g 1-¹ rapidly induced water stress of the desirable level in primary leaves of bean plants. At the same water saturation deficit, however, the water potential as well as the osmotic potential were considerably lower in leaves of PEG - treated plants than those in leaves of plants naturally wilting due to a gradual decrease in substrate moisture.

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.

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.

Storage proteins of the seeds (cotyledons) of the South-American speciesPhaseolus caracalla were compared by means of immunoelectrophoretic methods with other representatives of the genusPhaseolus. These proteins most resemble the proteins of the co-called tropical group (i.e. Ph. atropurpureus, Ph. geophilus, Ph. bracteatus, Ph. semierectus) and least the so-called American endemites (Ph. vulgaris, Ph. coccineus, Ph. acutifolius, Ph. lunatus), the main globulin of which is of a completely different specificity. The proteins ofPh. caracalla are less similar to the group of the so-called Asiatic species (Ph. aureus, Ph. calcaratus, Ph. angularis, Ph. aconitifolius, Ph. trilobus) including the analyzed representatives ofVigna sinensis; their main globulin is only partly similar to that ofPh. caracalla. Some considerations on the relationship ofPh. caracalla with the so-called tropical species is presented.

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.

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.