The formation of polysomes in relation to RNA synthesis was investigated in tobacco (Nicotiana tabacum L.) pollen cultivated submersely for a period of 12 h. The percentage of polysomes was estimated by determining the number of ribosomes carrying nascent polypeptides using RNase and 0.8 M KC1 treatment of the ribosomal preparation. This approach showed that the proportion of ribosomes "active" in protein synthesis amounts to about 12 % in dry pollen rising to 46 % within 10 min of imbibition and to 66 % during the period 1-4 h of cultivation. The latter increase is accompanied by a rapid incorporation of uridine-¹⁴C into polysome-as-sociated RNA and is sensitive to actinomycin D.
The rapidly labelled RNA isolated from the ribosomal preparation sedirnented in the range from about 5S to 30S. Longer labelling periods led to a gradual shift of the major peak of this heterogeneous RNA from about 11.5S and 14S to about 7.5S and the development of radioactivity peaks in the position of 18S and 28S RNA. Uridine incorporated both into the active ribosomes and into the subunits of inactive ribosomes at a more or less constant rate during the whole 12-h period of cultivation.
These results present evidence that in addition to the initial combination of the existing ribosomes with the stored mRNA following imbibition, an activation of pollen tube genome and its implication in directing protein synthesis take place during the early phases of pollen tube growth. From the results on kinetics of labelling of ribosomes it appears that in pollen tubes new synthesized ribosomal subunits enter polysomes directly, the entry of 40S subunits being more rapid than that of 60S subunits.

Seed germination studies onTrichodesma amplexicaule were carried out. Seeds show abnormal behaviour of germination which is termed "Chalazal germination". This abnormal behaviour of germination is due to the presence of an obturator at the micropylar end. Seeds showed maximum (60 per cent) germination with 110 min concentrated H₂SO₄ treatment.

Photoperiodic responses of seedlings of long-day plantBrassica campestris L. cv. Ceres were investigated at different ages and varying length of inductive period. It was found that photoperiodie response increased with age. All plants flowered after one inductive cycle beginning with a light-period of 16h, but remained in the vegetative phase when kept under short-days (16h darkness, 8h light).
Both auxins (IAA and NAA) and cytokinins (kinetin and benzyladenine) inhibited flowering when applied to the plumule or via the roots immediately before the inductive photoperiod. This inhibitory effects was confined to bud formation, whereas the rate of leaf initiation remained mostly unchanged. Only high concentrations of growth substances also affected the growth of roots and leaves. These results agree, in general, with the effects of growth substances in the short-day plantChenopodium rubrum.

Epidermal conductances for water vapour transfer(gep), water vapour efflux(E), and net photosynthetic CO² uptake (P _N ) through adaxial and abaxial leaf surfaces were estimated, simultaneously during the development of water stress in primary leaves ofPhaseolus vulgaris L. Hydration level was characterized by water saturation deficit (ΔW _sat ), water potential (Τ _w ), osmotic potential (Τ₈) and pressure potential (Τ_p). The conductance of the abaxial epidermis was consistently greater than that of the adaxial epidermis, but the response of both surfaces to the increase in water stress corresponded: with increasing water stress epidermal conductances slightly increased, reached a plateau and then sharply decreased (at a rate of about 1.10x10^-6 cm s^-1 Pa^-1 and 1.55x10^-6 cm s^-1 Pa^-1 of Τ_w for adaxial and abaxial epidemics, respectively) to very low value. The curves expressing relationship between epidermal conductances and Δ W_sat, Τ_w, Τ_s, as well as Τ_p were of a similar character. E and P_N through adaxial and abaxial surfaces were practically not affected until water stress reached the "critical" value (Τ_w from - 8.2 to - 9.2 x 10⁵ Pa). With further increase in water deficit, however, they sharply decreased. The "critical" value of Τ_w was the same for both leaf surfaces.

The effect of 0.1% Metation E 50 (fenitrothion) and Fosfotion 50 (malathion) on the level of total nitrogen and that of free amino acids was investigated in juvenile and mature leaves of apple seedlings in the course of six days following treatment. Fosfotion affected both nitrogen and amino acid content to a higher degree than Metation. Fosfotion increased the total nitrogen content in all leaves, but Metation induced the change only in the leaves which were at the end of the logarithmic growth phase at the time of treatment. The level of amino acids increased on the whole, with the exception of a temporary decline in the youngest leaves as well. The treatment with both insecticides affected most the content of amides: the greatest decrease of glutamine occurred in young leaves, the highest increase in asparagine content was recorded in both juvenile and mature leaves.

Toluidine blue is known to induce gynogenic haploids in significant numbersin Populus]. Because the efficacy of a chemical in inducing gynogenesis depends largely on its effeot on pollen germination, on pollen tube growth, and on male gamete formation, the effect of toluidine blue (0, 1, 10 and 100 mgl-1) on these processes was studied in treated pistils ofSolatium nigrum (4 X), as well as on cultured pollen grains ofS. nigrum andTrigonella foenumgraecum.
Irrespective of the time of application, toluidine blue (1 and 10 mg I-1) had no effect on pollen germination or pollen tube growth in pistils ofS. nigrum; at 100 mg I-1 it invariably inhibited both the processes. Almost similar responses were elicited by cultured pollen grains. InT. foenum-graecum toluidine blue had no effeot on pollen germination and suppressed tube growth. Gamete formation was inhibited, to various degrees, at all the concentrations tested; at 100 ing I-1 hardly any pollen tube showed gamete formation. Based on our results, and those on other systems, the potentiality of toluidine blue as an inducer of gynogenesis has been analysed.

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.

The virus replication capacity (determined by density gradient centrifugation and spectrophotometric virus assay) and severity of symptoms were compared in ten cucumber(Cucumis sativus L.) cultivars infected by cucumber virus 4. Except the expected resistant susceptible and symptomless virus carrier plants a new paradoxial group of cultivars was found. This group is characterized by low virus reproduction rate but simultaneously associated with severe symptoms and is responsible for difficulties in the virus transmission and purification. It is concluded that the critical evaluation of the resistance against viruses of TMV-group must include symptomatic and quantitative virus assays, as there need not be a direct relationship between virus symptoms and the virus increase.

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.

During their short preparasitic stage, dodder seedlings are able to absorb phosphates, by means of their rudimentary root. The absorbed phosphorus is translocated into the stem of the young parasite and metabolized.

Cytochrome oxidase and ascorbic acid oxidase activities were investigated in rye, wheat, barley and oat plants. The variations in the activity of both enzymes was followed in the course of the initial 28 days of growth, as well as at the phase of milk ripeness, namely in the cytoplasmic and mitochondrial cell fractions of roots, leaves and spikes.
Both enzymes were active in all measurements. Cytochrome oxidase mostly exhibited a higher activity than ascorbio acid oxidase. The activity of the former enzyme was substantially higher in the mitochondrial fraction of leaves, roots and spikes of the four experimental plants in comparison with the cytoplasmic fraction. On the contrary, the ascorbic acid oxidase activity varied in both cell fractions according to the plant species, organ and growth phase.
The variations in the activity of both enzymes exhibited on the whole a course similar to that of the respiration rate. During the first 14 to 21 days of growth the enzyme activities increased up to the maximum. This was thon followed at first by a rapid, later on by a slow decrease. The course of variations in the enzyme activities was, with certain exceptions, alike in all the four plant species investigated.