The xylem pressure potential (Ψ_xylem) of the leaves ofQuercus cerris, Acer campestre andCarpinus betulus was measured under anticyclonic weather types. The autocorrelation analysis revealed the daily course of the Ψ_xylem values approaching the stationary random process. A close statistical relation was found between the results obtained in three successive measurements of the Ψ_xylem (interval 2 h). A close statistical relation also between the value of the base potential (Ψ_b) measured at dawn and the actual values of the Ψ_xylem allowed the prediction of the Ψ_xylem values on the base of the known Ψ_b-values by means of a simple linear regression model.

Growth parameters and esterase isoenzyme patterns were studied in developing cotton fibre. Fibre length and dry weight when plotted against boll age showed four distinct stages; (i) initiation, (ii) elongation, (iii) secondary thickening, and (iv) maturation. Stage specificity and changing intensities of esterase isoenzyme suggested a finely modulated control of gene expression during fibre development.

The influence of growth regulators (GA and IAA) on the genetic effects of sodium azide was studied. Treatments with growth regulators were administered either prior to or after the mutagen. Post-treatments were found to be more effective against mutagen-induced plant growth injury and gave a slightly higher frequency of mutations. M₁ spike sterility however showed a rise following treatments with growth regulators.

Humic acids in a concentration of up to 100 μg ml^-1 affect the activity of choline esterase of pea only weakly during sinapin (choline ester of sinapic acid) hydrolysis. The inhibition is stronger at higher concentrations. A similar course of inhibition with humic acids was also observed during the synthesis of sinapin catalysed with choline acyltransferase present in the same enzyme extract. The organophosphate malathion is a strong inhibitor of both the hydrolysis and the synthesis of sinapin. Thus, for example, at a 3.5 × 10^-5 M concentration it causes 85% inhibition of pea choline esterase. However, in combination with 100 μg of humic acids this inhibition decreases to about 8%. It was observed that humic acids prevent the inhibition of both the hydrolysis and the synthesis of sinapin with malathion even at low concentrations. The interaction of the organophosphate malathion with humic acids seems specific. Humic acids do not affect the inhibition of choline esterase with physostigmine or the inhibition of the hydrolysis and the synthesis of sinapin with chlorocholine chloride, alar and hexamine either. This is also true of the activation of the processes with the K⁺ ions. Humic acids represent competitive inhibitors of choline esterase. Malathion shows an acompetitive - noncompetitive character of the inhibition. The interaction of humic acids with malathion in the roots of the plants may also be assumed in the soil when malathion is applied as an insecticide.

The substituted 5-chlorodiphenylamine-2-carboxylic acid hydrazides and their N-benzylidene derivatives were tested for their antiviral activity against gomphrena mosaic virus in a hypersensitive hostin vitro as well asin vivo. Most of the compounds exhibited potential antiviral activity. These compounds may be useful in controlling viral infections in garden as well as in field crops.

SixteenPisum sativum cultivars were mechanically inoculated with two isolates of PVX. Distinct necrotic local lesions on the inoculated leaves were found in six cultivars 5 to 6 days after inoculation. The best results were obtained with the Meteor and Raman cultivars, 17 to 23 days old.

An isolate of wisteria vein mosaic virus (WVMV) obtained fromWisteria sinensis in Prague resembled in its properties WVMV isolates described in Italy and Holland.Nicotiana megalosiphon is reported as a new host of WVMV. Other known host plants showed reactions similar to those described formerly. The incubation period extended in some hosts up to two or four weeks. Pea plants showed symptoms within five to seven days. Species ofApium, Brassica,Datura and others were not susceptible. TIP of Prague isolate of WVMV was 61 °C, at a dilution 1: 5000 47% of plants were infected, and 48 h > LIV > 28 h. Modal particle length was 743 nm. Massive granular inclusions were seen in pea epidermal cells, usually adhering to nuclei that did not show alterations. No serological relation to turnip mosaic virus could be established.

Sucrose was markedly superior to fructose and glucose in promoting growth of plantlets from immature maize embryos. The elongation of roots is shown to be more sucrose dependent than that of shoots. On the other hand, the exogenous sucrose was less effective than fructose as substrate for carbohydrate catabolism and for the synthesis of alcohol-insoluble compounds at the beginning of embryo cultivation. The absorbed fructose was found to be rapidly converted to sucrose and the level of endogenous sucrose derived from sugar supplied to the medium was higher in fructosethan in sucrose-fed embryos. The preferential utilization of fructose over sucrose, however, declined with the progress of germination which may be related to the decrease in proportion of scutellum in total mass and physiological activity of the embryo.

Two barley chloroplast nuclease fractions were separated by the affinity chromatography and gel electrophoresis. Both were about 2 times more active to RNA than to native DNA and about half as active to denaturated DNA as to native DNA. Both fractions were as active to UV-irradiated (270 J m^-2) native DNA as to intact DNA but their action was inhibited by apurinic sites. The enzyme activities were inhibited by high concentrations of EDTA, NaCl, Mn²⁺, Ca²⁺, Zn²⁺ ions and by N-ethylmaleimide. They do not require Mg²⁺ ions but are stimulated or at higher concentration inhibited by their presence. Both RNase and DNase were active over a wide pH range (5.5-9), the optimum for DNase action in the presence of Mg²⁺ being 6.5, for RNA decomposing activity at pH 8.0. As no mononucleotides were detected in acid soluble form, it seems likely that DNase acts in the endonucleolytic way.

A previously undescribed disease onLupinus hybrids manifesting typical witches broom symptoms occurred spontaneously in a locality in North Bohemia. Broomed shoots appeared only in late summer and resulted from the abnormal proliferation of dormant axillary buds in leaf and fruit axils. The shoots were bushy and their leaves were dark green and not reduced in size. Electron micrographs of ultrathin sections showed the presence of numerous mycoplasma-like organisms (MLO) in diseased but not healthy phloem tissues.

Changes in glutamine synthetase activity located in the cytosol of root nodules were followed in pea (Pisum sativum L.) plants in relation to their nitrogenase activity. The highest glutamine synthetase activity was found in young nodules (15 days after inoculation) and its changes in 17-to 45-day-old plants showed a positive correlation with nitrogenase activity. In contrast to nitrogenase activity, changes in glutamine synthetase activity during the day and night period could not be unequivocally interpreted in terms of diurnal fluctuation.

Using immunochemical methods a comparison was made of a complex of water soluble (albumins) and salt soluble (globulins) seed proteins, especially vicilin and legumin, in selected species of the genusPisum, to determine the degree of their taxonomic relationship.
Within the genusPisum the interspecific differences betweenP. abyssinicum, P. cinereum,P. elatius, P. fulvum, P. sativum, andP. syriacum are much smaller, and thus the taxonomic distances are shorter than is the casee.g. in the genusPhaseolus. In spite of this fact one may state thatPisum sativum, P. elatius andP. syriacum constitute a definite group, whereasP. abys-sinicum, P. cinereum and P.fulvum have longer taxonomic distances.

The contribution deals with the distribution of β-glucuronidase in the germinating pollen grains ofPortulaca grandiflora. In non-germinating pollen grains the enzyme is localized in the pollen wall; the cytoplasmic activity is subdued. With the initiation of germination, the activity of enzyme increases and the positive granules are richly packed in the pollen grains and pollen tubes. The stigma hairs also have such an activity. The functions of the enzyme in the metabolism of germinating pollen grains are discussed.

The leaves of poplar trees (genusPopulus) contain antimiorobial agents. These antibiotic properties are markedly influenced by interspecific and intraspecific hybridizations. Fractionation of the weakly active crude extracts results in more active antibacterial fractions. There are indications that the substances which inhibit antimicrobial effects during the testing procedure remain in the methanol fractions. In addition the results show that the antibacterial agents differ from the antifungal compounds, which both are different from the antiviral substances.

Twenty-four isolates of turnip mosaic virus (TuMV) from spontaneously infectedSisymbriutn loeselii plants were collected in Bohemian localities. Single lesions on leaves ofNicotiana tabacum cv. Samsun served for inoculating petunia plants used as infection sources for twelve host species. In no case were two identical isolates obtained. 15 isolates could be transmitted toVicia faba, a new TuMV host. Almost all isolates infectedPhaseolus vulgaris cv. Prince locally andTrifolium incarnatum systemically. Seven isolates were transmissible toPisum sativum. No substantial differences between isolates were observed with infectedAn aranthus caudatus, Chenopodium quinoa, Datura innoxia andSinapis alba plants. Several isolates could not infectNicotiana glutinosa at all, other isolates caused in it latent systemic infection and some isolates only local infection contrary to normal local and systemic infections ofN. glutinosa. Attempts to transmit one isolate to cereals failed.

Ethanol-soluble and insoluble nitrogen and protease activity in maize seeds during imbibition period of 6 to 60 h at 30 ± 2 °C were determined both in light and in the dark. In light, soluble and insoluble nitrogen in the embryo were similar to that in the dark. But the increase in soluble nitrogen in the endosperm up to 38 h was higher in light than in the dark. Decrease in insoluble nitrogen was correlated with increase in soluble nitrogen, the level always being higher in the dark. Light increased protease activity also in the endosperm. Among various light qualities, red light was most effective in inducing proteolysis, and loss of nitrogen from the endosperm. Further, the growth and organic nitrogen of primary leaves from seedlings raised from light pretreated seeds were better than those from dark pretreated ones.

A study was made of the changes in the content of essential oil and its components (farnesene, (-)-α-bisabolol, (-)-α-bisabololoxide A, (-)-α-bisabololoxide B and spathulenol, α-bisabolonoxide A, chamazulene, cis en-in-dicycloether) and of the number of secretory canals in the receptacles during the beginning of flowering, full flowering and the termination of flowering of camomile anthodia. The total content of the essential oil was highest during the beginning of flowering and lowest during its termination. The proportion of the individual sesquiterpenes in the essential oil underwent changes mostly during the beginning and termination of flowering. The number of secretory canals in the basal and middle anthodial parts increased during the beginning of flowering and the full flowering.

Three days old excised tomato cotyledons were subjected to mannitol induced water stress in the presence of actinomycin D and cycloheximide. Within a few hours, in the presence of actinomycin D but not cycloheximide, water stress induced increase in ribonuclease activities and decrease in beta-fructofuranosidase activities. The water stress action in the presence of actinomycin D was reversible by addition of kinetin. It was postulated that water stress had some immediate fundamental action on the protein synthesis sites at the ribosomes.

Genetically identical mirror-imaged left and rightLemna minor plants were treated using the stereomers of arginine, asparagine and atebrine (mepacrine). In contrast with the stereomers of arginine and asparagine, those of atebrine were found to be isoeffective throughout the dosage range from the ineffective dose to the lethal one. All indices used (rate of reproduction, length of a frond and sensitivity to the treatments) pointed to the absence of any difference between left and right plants. The left or right handedness inLemna cannot be explained bv assuming the existence of any stereochemical difference between left and right plants.

When stem cuttings were put in water the dormancy of the bud was broken. No inhibitory substances could be found in the leaves and no effect of exogenous growth substances could be detected. Dormancy of buds in the present case seems to be the result of the mechanical resistance imposed by the leaf sheath upon the bud.
Gibberellic acid was very effective in promoting root formation in the woody stem cutting ofPanicum maximum and the present results point to a direct effect on root initiation by gibberellic acid.

The effect of various sodium salts at the early developmental stages of wheat cultivars was studied. Germination was not affected by the presence of salts but cv. H-68 was more tolerant than Mexipak during later growth. The roots were more sensitive than the shoots. The salts under study could be divided into two groups. Bicarbonate, carbonate, acetate and citrate were more toxic for growth than sulphate, nitrate, phosphate and chloride of sodium. The individual members of each group did not vary much from one another.

The effect of exogenous supply of a morphactin - chlorflurenol (IT-3456) CME 74050 p at three concentrations of 100, 500, and 1000 ppm (all applied as dispersions in lanolin paste after scraping the epidermis during December, 1976) was studied on two-year-oldMorus alba plants. Almost three months after the treatment of the regulator, along with the normal sievetube elements of the axial system, these elements were recorded in the ray system as well, arranged either vertically or horizontally. In the latter state, they appear to act as a by-pass between the normally formed sieve elements located on either side of the ray. We have termed them 'ray-sieve-tube elements' to distinguish them from the normal elements. Simultaneously, some sieve-tube elements having sieve plates on their lateral walls were also noticed in the axial system. A direct correlation was observed between the multiplicity of induction of both element types and increasing concentration of the regulator.

Cuttings of pea cv. Alaska and ov. Kelwo were both decapitated and disbudded at different time intervals after cutting. Auxin and cytokinin combined in different ratios were applied to the upper part of the decapitated and disbudded cuttings. The effects of different ratios of auxin and cytokinin were not the same when applied at different developmental stages of the root initiation phase. The results seem to demonstrate an interaction between auxin and cytokinin at different ratios throughout the root initiation phase. The effects of combined application of auxin and cytokinin suggest that different stages of the root initiation phase require different levels of auxin and cytokinin. A higher level of auxin and either lower or equal level of cytokinin may be needed only in the early stages. During the subsequent stages a lower level of auxin in combination with a higher level of cytokinin seems to be more conducive.