Phosphate is an effective inhibitor of the phosphohydrolases of wheat embryos (Triticum aestivum L.).In vitro the inhibition was competitive with K₁ = 4.48 × 10^-3 M (1.6 × 10^-3 M P₁, applied as KH₂PO₄).In vivo the inhibition with KH₂PO₄ was relatively low during germination (48 h), but inhibition increased when other P₁-compounds were used. In ungerminated embryos the phosphatase activity comprised three isozymes; the pattern of iaozymes changes during germination, but there was no influence of P₁ in comparison with the control.
Concluding we may state that the activity of phosphohydrolases is regulated by an inhibition mechanism caused by P_i-concentration.

The variation in stomatal activity within the crowns ofAcer campestre, Carpinus betulus andQuercus cerris was measured by vapour exchange porometer on several summer days in an oak-hornbeam forest, in SW Slovakia, Czechoslovakia. Variation resulted from crown position in the forest stand and from leaf position within the canopy. The highest stomatal conductance was in sunlit sun leaves in the upper part of the canopy. Stomatal conductance decreased with increasing depth in the canopy. The steepest decrease was in the upper canopy, in the intermediate zone between fully sunlit and fully shaded leaves, and was caused by the decline in leaf irradiance and in stomatal density. In codominant trees, the conductance in shade leaves at the base of the crown was significantly lower than in the sun leaves at the top of the crown. In a dominant tree,Q. cerris, the differences in stomatal conductance were small and most frequently insignificant. Variation in incident light also determined the diurnal variation of stomatal conductance with respect to crown aspect. Differences between sun leaves on the east and west facing aspects of the overstory crown ofQ. cerris were demonstrated for several days.

Poly(A)⁺RNA is synthesized during the first hours of pollen germination and is rapidly incorporated into polysomal structures. After a 2-h pulse with uracil-¹⁴C, 42% of the transcribed fraction of polysomal RNA is polyadenylated. Following 4 h of germination the amount of the newly-made poly(A)⁺RNA decreases steadily at the rate of about 14% per h, whereas that of rapidly-labelled poly(A)^-RNA continues to grow. Beginning 1 h of cultivation the ratio of poly(A)^-/poly(A)⁺RNA increases exponentially. Similarly as in non-polyadenylated mRNA the main portion of the synthesized polysomal poly(A)⁺RNA sediments at a rate of 4 to 14 S and its mean size decreases slightly with the time of labelling. RNA isolated from nuclei and cell wall containing pollen tube fraction differed from the polysomal one in higher apeoific radioactivity and the polyadenylated RNA exhibited higher size distribution. The comparison of the results with earlier observations suggests the involvement of poly(A)in mRNA translation in pollen tubes.

Four tree, five shrub, and ten herbaceous species growing naturally in an oak-hornbeam forest were used for simultaneous study of the leaf diffusive resistances in the course of several summer days. Absolute minima of the stomatal resistance in the sun tree, the shrub, and the herbaceous species leaves were 1.7 to 6.2 s cm^-1, 6.1 to 10.8 s cm^-1, and 4.8 to 9.7 (17.3 inConvallaria majalis leaves) s cm^-1, respectively. Minimum daily leaf resistances in the course of a day were noted earlier in the morning in sun leaves of large trees than in shade leaves of other species. Stomata were fully opened later in the morning and they began to close sooner in the afternoon in usual shade leaves of the plants in the interior of the forest canopy than those in sun leaves in active surfaces of the canopy (tops of tree crowns). The relatively large differences in leaf resistances found among investigated species may be explained by differences in leaf anatomy (stomata frequency and size) and in ambient leaf or plant environment caused by leaf (plant) position in different vertical layers.

The formation of adventitious buds under the influence of 6BAP has been observed on various aerial organs of culturedPinus silvestris seedlings. The inductive power of this cytokinin was found to depend on the concentration and the physiological age of the explant.

The rooting capacity of leaves isolated from a vegetative clone ofAnagallis arvensis L. exposed to 9 hours of light (75 W m^-2) at 22 °C and 15 hours of dark at 12 °C a day is significant only in F₁ young leaves and not in adult ones. The rooting capacity of the young leaves and of the vegetative shoots is greater in longer photoperiods. The leaves make roots even under weak (14 W m^-2) irradiance. The rooting capacity of the leaves is diminished and even suppressed by exogenous sucrose (14,60 ×10^-3M). This inhibition may be counteracted by IAA (10^-6M). When leaves and shoots are taken from clones under long (16 h) photoperiods, or in constant irradiance, they progressively lose their rooting capacity during the treatment. Rooting capaoity is regained if the clones are returned again to "short day" (9 h) condition.

Globular embryoids were continually produced in anther cultures of tobacco (Nicotiana tabacum L. cv. Samsun) from the pool of resting microspores if the iron-free medium was used. The supplement of iron stopped the development of fresh early embryoids still inducing continual conversion of the resting globular embryoids into torpedo-shaped embryoids, and into haploid plants. Globular embryoids in the anthers responded to the iron supply even after eight months' cultivation on iron-free media. Isolated embryoids showed the same response. Haploid plants were regenerated from the anthers on the minimal medium consisting of agar, sucrose, iron and distilled water. Iron requirements of preglobular, globular and postglobular embryoids are discussed.

Conductance of abaxial epidermis was measured in leaves ofAcer campeatre, Carpinus betulus, Quercus cerris andQ. petraea sample trees growing in an oak-hornbeam forest. Measurements were performed on several summer days during morning and midday hours. Stomata tended to oscillations only inQ. cerris. The occurrence of stomatal oscillations was controlled by environmental conditions,e.g. weather.

Radioactive phosphate was applied to the roots of intact alfalfa plants (Medicago sativa L.) on the 49th day after inoculation withCorynebacterium insidiosum (Me Culloch) Jensen and the³²P contents in different fractions of phosphoric compounds were determined. In inoculated plants, susceptible to bacterial wilt, the inorganio phosphate contents (³²Pinorg) was increased markedly and the³²P bound in organic compounds soluble in acids (³²Porg) decreased as compared with control. In roots of the same plants the³²P contents in phospholipid fraction and DNA were decreased. In tolerant inoculated plants the³²Pinorg increase and³²Porg decrease as compared with those changes in susceptible plants were less expressive. No expressive changes in determined³²P fractions have been proved in resistant plants without any visible disease symptoms.

Net photosynthetic (P_N) and dark respiration (R_D) rate, stomatal (rs') and internal (ri') resistances to carbon dioxide were measured by gas exchange methods on leaves of different ages, expressed in leaf plastochron index units (LPI) for a fast growing poplar cultivar Unal 2. Although the optimal leaf age differs slightly for the different gas exchange parameters, leaf ontogeny is reflected in the same way in these different parameters. MaximalP_N and minimalrs' and ri' values were found at LPI between 6 and 10. Chlorophyll concentrations were lowest at LPI lower than 10 although an increase in two steps was found, when leaf age increases up to maturity.

Levels of ferricyanide reduction, cyclic and non-cyclic photophosphorylation were measured in chloroplasts of two cultivars of pea and a comparison of their P/2e⁺ ratios were made. No differences were observed in cyclic photophosphorylation or ferricyanide reduction but non-cyclic photophosphorylation was lower in chloroplasts from the dwarf than the normal cultivar. Thus the P/2e⁺ ratio of the dwarf was lower than the normal. Dwarf seedlings treated with gibberellic acid (GA₃) had similar rates of cyclic photophosphorylation as the untreated dwarf but non-cyclic photophosphorylation was lower as was ferricyanide reduction. This resulted in P/2e⁺ ratios that were higher in chloroplasts from the GA₃ treated dwarf seedlings than the untreated, and were the same as the untreated normal. Addition of GA₃ directly to the chloroplasts did not alter the activity in any way. Hence gibberellins do not directly affect changes in chloroplastic activity but may conceivably be involved in a feed-back control system.

Extirped barley embryos were pre-cultivated in aerated liquid nutrient solution for 24 h and then cultivated for 6 h in nutrient solution containing either³H-DNA fromBacillus subtilis or³H-thymidine. After this treatment the embryos were thoroughly washed and transferred to the fresh nutrient medium. Samples were fixed at different intervals up to 24 h. Feulgen squashes were made and covered with autoradiographic emulsion. Microautodiagrams of different parts of the embryos (root meristem, shoot apex plus meristem of the third leaf, second leaf meristem, coleoptile, scutelum) were observed. Labelling of the nuclei after the application of both³H-DNA and³H-thymidine was found in the proliferating parts of the embryos but no label was found in the scutelum. The labelling index values were almost similar in different embryo organs after the treatment with³H-DNA and³H-thymidine. Labelling index and the fraction of labelled mitoses at different intervals after the application of the labelled substances were almost similar after treatment with³H-DNA and³H-thymidine, except some variations due to irrelevant differences in the kinetics of the mitotic cycle. No disappearance of the activity of³H-DNA was observed at different intervals after removal from the labelled solutions during cultivation for other 24 h in non-labelled nutrient medium either containing DNA fromBacillus subtilis or without it. The embryos which were immersed into 0.2% NaCl solution with either one of the labelled compounds did not show any initiation of the S phase nor uptake of³H-DNA. All these results demonstrate that the label from³H-DNA is localized in those cell nuclei which were in the S phase during treatment but they do not yet distinguish unambiguously between the adsorbtion of polymerous DNA or its degradation and reutilization of low-molecular weight products.

The major trypsin inhibitor ofVigna sinensis cv. seridó was isolated and shown to be devoid of chymotrypsin inhibiting activity. It has a molecular weight of 9800 as determined by gel electrophoresis and a pI of 5.0. The activity of the inhibitor was decreased by treatment with trinitrobenzenesulfonic acid, suggesting that it isa LYS-X type trypsin inhibitor. Selfassociation of the molecule was demonstrated both in 1% sodium dodecylsulfate and inacidic (pH 2.4) conditions.

The effect of 5-aminouracil on the S phase and mitosis in root meristems of barley embryos cultivated in the liquid nutrient solution was followed. Embryos were cultivated in different concentrations of 5-aminouracil (200 ppm, 400 ppm and 750 ppm) for 48 h. The drug postponed the onset of mitosis. In the lowest concentration used, synchronization was observed even in the presence of 5-aminouracil. In higher concentrations, mitosis was suppressed irregularly with increasing concentration. 5-aminouracil slowed down the rate of DNA synthesis during S phase and prolonged the S phase, as measured by the utilization of [³H] thymidine. The drug does not influence considerably the entry of cells into the S phase. The transition from G₂ to mitosis is delayed in the presence of 5-aminouracil, especially in higher concentrations. After prolonged treatment with 5-aminouracil, all the effects of the drug on the mitotic cycle decrease continuously.

The beet western yellows virus (BWYV) was identified in sugar beet plants with leaf yellowing symptoms. When transmitted toSinapis alba L. the virus isolate caused severe symptoms of yellowing and violetting of the interveinal leaf tissue of this plant. By aphidsMyzus persicae (Sulz.) the virus isolate was transmitted toLactuca sativa L.,Raphanus sativus L. var.radicula Pers.,Baphanus sativus L. ssp.sativus L. ap., and toBrassica oleracea L. var.gemmifera DC. InLactuca sativa plants the virus induces a yellowing along with thickenning and brittleness of leaves and with mild dwarfing of the plants. InBaphanus sativus var.radicula andBaphanus sativus ssp.sativus plants it brings about a yellowing of the leaf margins with a change in consistency as was the case in lettuce, and inBrassica oleracea var.gemmifera it causes violet spots on the lower leaf sides. The transmission was proved in repeated experiments by a backtransmission to beet andSinapis alba and further transmission from beet toSinapis alba. The transmission of the virus isolate toVicia faba L.,Datura stramonium L., andPetunia hybrida hort. was unsuccessful. In the course of transmissions the isolate properties did not change. In its host range the virus resembles the Duffus' strain 3 BWYV, isolated from beet in the U.S.A. This is the first characteristic of an Europian BWYV isolate, as obtained from naturally infected beet plants.

The capability of utilizing 20 amino acids and 2 amides as the sole nitrogen source for growth was studied in two green algae (Chlorophyceae). A comparison was made of the growth rate of algae in a mineral nutrient solution containing nitrate as the nitrogen source, with that in the same solution in which nitrogen in the form of nitrate was substituted by an equivalent nitrogen amount in the form of various amino acids. In addition to this, another series of experiments was carried out in whioh both culture media were supplied with glucose. The results show that both algae utilize a series of amino acids in dependence of their structure (mostly 3-carbon amino acids). The growth rate ofChlorella in the presence of these sources is the same as in nitrate, that ofScenedesmus even much higher. In the cultures containing glucose both algal species exhibit a higher growth rate in the media with the nitrate nitrogen source than in those with amino acids (with the exception of glycine inScenedesmus).

Isolated barley embryos were cultivated in the complete liquid medium for 24 h and then treated with 200 ppm or 750 ppm 5-AU for 2 h, 8 h or 24 h. During the 24 h treatment, MI decreased from 5-12% to 2-5%. After putting the embryos into the fresh medium without 5-AU, the original decrease of MI was followed by slight increase which was manifested only in part of the roots of some experimental variants. The time of the occurrence of MI maxima varied with the duration of treatment and concentration of 5-AU. After treatment with 750 ppm, the increase of MI occurred later but it was more pronounced than after cessation of the treatment with 200 ppm. In the former case, frequencies exceeding the controls appeared 12 h-16 h after treatment and they were manifested especially after treatments of shorter durations (2 h and 8 h). In the latter case, the increase of MI occurred mainly 6 h after cessation of the 24 h treatment. A slight chromosome breaking ability of this drug was found.

Diurnal and seasonal changes of the xylem pressure potential (Ψ_xylem) were investigated in five species during three years. Intraspecific comparison was made on the basis of the mathematically expressed relationship Ψ_xylem of the individual species to Ψ_xylem inCrataegus oxyacantha, which exhibited the highest drought resistance. With increasing water stress the value for Ψ_xylem of the individual species decreases linearly in comparison with that ofC. oxyacantha, namely to -1.02 MPa inLigustrum vulgare, to -1.33 MPa inCornus mas, and to -2.09 MPa inEuonymus verrucosa. At a higher water deficit the value for Ψ_xylem of these species decreases more rapidly than inC. oxyacantha. On the basis of these findings, the relative drought resistance of the species may by evaluated, and from the value of Ψ_xylem forC. oxyacantha Ψ_xylem of the individual species may be derived. By measuring the difference between Ψ_xylem of free- and polyethylene-covered individuals the existence of water redistribution within the shrub individual was confirmed.

Gmelina arborea L. seedling growth and diurnal stomatal opening (as measured by stomatal resistance) were studied at soil matric potential 0, -0.1 and -0.72 × 10^-5 Pa. Leaf area, leaf number, plant height and dry weights of the vegetative parts were significantly reduced as soil matric potential decreased from 0 to -0.72 × 10^-5 Pa. The growth responses followed the same trend as net assimilation rate and relative growth rate. The highest moisture stress induced leaf senescence and leaf fall. Leaf water potential decreased from - 2 × 10^-5 Pa to - 20 × 10^-5 Pa with increasing soil moisture stress. Results indicate that the diurnal stomatal opening is controlled by photon flux density when this species is grown at soil matrio potential 0 Pa. However, with decreasing soil matrio potential (- 0.10 and -0.72 × 10^-5 Pa) the internal plant water deficit appears to oontrol the stomatal opening.

Experiments were conducted with five barley cultivars with the aim of ascertaining the effect of salt stress on grain filling, grain development and bioohemical composition of developing grains. Reduced grain yield under salt stress was found to be due to reduced efficiency per day to fill the grains and consequent more effective days and also due to disturbed starch-sugar balance.

The present paper deals with the effects of osmotic potential of a medium on cell reproduction and elongation of the roots ofVicia faba L. andVicia sativa L. As the osmoticum polyethylene glycol (PEG 4000) in various concentrations ranging from 5 % to 25 % (i.e. fromca.-0.11 up to -1.27 MPa) has been used. The results show that at higher concentrations than 7.5 %, the growth of roots is slowed down and at the concentration of 25 % PEG this decrease in growth rate is as much as 6 fold compared with the control. The mitotic cycle is prolonged, however, only 1.86 times. Thus, the inhibition of root growth is caused mainly by the inhibition of cell elongation. Concerning the effect of high osmotic potential on mitotic cycle it was found that the roots after immersion into 25% PEG are able to overcome this osmotic stress and after 6 h to renew the mitotic activity. The S phase of the cycle is the most sensitive to this factor and even after mitotic activity was renewed it showed a slower rate in comparison with the control.