In the absence of cations, the release of proteins from pollen tubes ofNicotiana tabacum in culture is greatly dependent on boron concentration and inversely related to growth stimulation. The minimum of proteins in the medium occurs at 100 mg 1^- of boric acid, which is the optimum concentration for growth. The shift of boron level to this optimum further increases the proportion of proteins bound to the insoluble pollen tube fraction; on the other hand the amount of soluble proteins is not affected inside pollen tubes, but greatly decreased in the medium.
The loss of proteins into the medium is considerably reduced by oalcium and also at the optimal boron concentration and in the presence of K⁺ and Mg²⁺ ions. The rate of tube elongation, however, is slightly decreased and the duration of pollen growth activity is not extended. The release of proteins is not affected by potassium and is slightly reduced by magnesium.
The possible mechanism of calcium and boron action on protein release is discussed in relation to the exocytotic function of secretory vesicles and it is suggested that boron supports the incorporation of proteins transported to the growing tip into the pollen tube wall structures.

Twenty three isolates of turnip mosaic virus (TuMV) obtained from spontaneously infected plants ofSiaymbrivm loeaelii JUSL. were serologically related, but differed in reactions of eleven host plants. Susceptibility and sensitivity of each host for each TuMV isolate were classified by one of six degrees (0 to 5) respectively. Similarities of isolates (as compared in 253 pairs) were evaluated by means of a computer; for this purpose the source program MINDIF has been elaborated using the universal program language Algol 60. A table of differences between isolates was obtained and distribution of isolate pairs dependent upon the difference values was stated. The fitness of hosts for differentiating TuMV isolates was ascertained quantitatively. No relation of isolate similarity to geographical indices could be established.

Following moderate water stress in the cortical cells of theZea mays primary roots, the condensation of the nuclear chromatin, a higher density of free ribosomes and a reduction of polyribosomes, the reduction of mitochondrial cristae, elongation of ER elements, less compact dictyosomes and inhibited production of the Golgi vesicles were observed. Severe water stress would cause more severe structural damage in the cortical cells. The more differentiated cortical cells showed more expressive ultrastructural damage when compared with the meristematic nonvacuolated cells. Similarly, the cells of the peripheral layers of the cortex suffered more from water deficit than the cells of the layers situated closer to the central cylinder.

Using water culture technique, some experiments have been performed to investigate the effect of 60 days salinization treatments (0.0-100 meq 1^-1 NaCl) on dry weight and on the content of some nutrient elements (Na, K, Ca, Mg, P, N) in castor bean, sunflower and flax plants. In general the content of sodium increased progressively with the rise of salinity level. The relatively low and moderate salinization levels (20 and 40 meq I^-1 NaCl) resulted in a promotion rather than inhibition of the dry weight and in the content of most of the investigated elements in the different organs of the test plants. However with the rise of salinization level from 60 to 100 meq l^-1, the dry weight and the content of these nutrient elements were mostly reduced.

The influence of light, particularly blue and red light, on the cytokinin content of seedlings ofAmaranthus caudatus was studied. Cytokinin content was determined by two different bio-assays (amaranthin accumulation byAmaranthus seedlings and mtrate-reductase activity ofAgrostemma embryos). In both bio-assays similar results were obtained. Oytokinin content is increased, especially by blue light. It is suggested that especially blue light promotes amaranthin accumulation inAmaranthus seedlingsvia the increase of cytokinin content of tissues. The results support our hypothesis on cytokinin action.

The localization was studied of α- and β-galactosidases in frozen sections of Ca-formol fixed root tips using simultaneous azocoupling reaction. In all species studied (Allium cepa,Cucurbita maxima, Lupinus albus, Pisum sativum, Vicia faba, Zea mays) positive results were obtained, the localization being ubiquitous (according to localization typology given here).
InVicia faba andZea mays the isoenzymes of α- and β-galactosidases were revealed by means of acrylamide gel electrophoresis, using authors' modification of Reisfeld method, in whole root tips, particular growth zones and separately in cortex and central cylinder. No differences were observed comparing stele and cortex. Whereas characteristic isoenzyme patterns were found in individual growth zones in maize, no differences appeared in broad bean.
A comparison was made of thein situ localization and of the isoenzyme patterns of α- and β-galactosidases with α- and β-glucosidases. In the case of galactosidases, positive results appear with both α- and β-galactoside. The rising of pH to neutrality leads to considerable decrease in the activity of both galactosidases.

Excised barley embryos were cultivated in a liquid complete medium for 48 h and then 5-fluordeoxyuridine was added. The concentrations of 5-fluordeoxyuridine differed in the range of 6 orders of magnitude (10^-8 to 10^-3 M). All concentrations, except 10^-8 M led to a total inhibition of mitosis during 24 h. 5-fluordeoxyuridine induced chromosomal aberrations of the non-exchange type in all concentrations used. The frequencies of induced breaks increased during the interval of 12 h in whích they were followed and, in samples fixed at later intervals after the beginning of the treatment, there was a tendency to clustering of the induced fragments in some mitotic figures. The most striking feature of the effects oliowed is the relatively small dependence on the concentration used.

A study was made of the changes in the the content of camomile essential oil and its components [(-)-α-bisabolol, (-)-α-bisabololoxide A, (-)-α-bisabololoxide B and spathulenol, and chamazulene] in dependence on the time of day under field conditions. The essential oil, distilled immediately after sampling, was analysed by means of gas chromatography at 3-h intervals in the course of 51 h. A 24-h period rhythm of (-)-α-bisabolol with maximum content in the scotoperiod, was demonstrated in 1976 using periodogram and cosinor tests. The other substances investigated exhibit a rhythm with a 12-h period. The latter test did not reveal any rhythm in the total content of essential oil.

Decapitation induced an additional formation of secondary shoots and anomalous spikes in all the species. The moan numbers of nodes, spikelets per spike, seeds per spikelet and spike, and the mean length of the stem and spike were reduced on secondary shoots of decapitated plants, while the mean and peak numbers of flowers per spikelet and the peak number of seeds per spikelet increased. The increase in the number of flowers per spikelet was the most striking on spike base; the seeds regularly occurred even in spikelets with an expressively increased number of flowers. The post-decapitation changes of the spike could be well expressed quantitatively according to the increased mean number of the flowers per one seed. Morphological ohanges in anomalous spikes of all the wheat species resemble phylogenetic reversions described in literature. Moreover, the peak numbers of flowers and seeds per spikelet were recorded in 52 varieties belonging to 21 wheat species. As compared with the decapitation trial, the greatest variability and the greatest differences between the speoies were also reoorded in the tetraploid group, and the smallest variability and differences between the species in the diploid group. We suppose that the striking morphological differences in post-decapitation spikes take place because the apical dominance was interrupted before differentiation of the recent form had been controlled in meristems on the decapitated stem base. Ancestral forms were morphologically realized with the help of an assimilating part of the decapitated stem.

Sucrose gradient analyses were made on free ribosomes extracted from Azuki bean seedling leaves subjected to mannitol induced water stress. Comparisons were made of the effect of duration of stress and the effect of urea on the free ribosomes. The capacities of the ribosomal fractions to incorporate amino-acids were also studied. Water stress reduced total free ribosomes and proportion of polysomes in the ribosomes as well as the capacity of the ribosomes to incorporate amino-acids into proteins. Polysomes which were broken down by the water stress also appeared to be more susceptible to denaturation and synthesized different proteins than polysomes which remained in the leaves after water stress.

A virus transmissible toChenopodium quinoa was isolated from leaves of sugar beet showing large chlorotic ring spots and line pattern. The virus was serologically unrelated to tobacco necrosis virus and tomato black ring virus or to its beet ringspot strain either. A positive result was obtained with antiserum against tomato bushy stunt virus. Reactions of herbaceous indicators and properties of the virus in crude sap were in accordance with the serological diagnosis. A survey of natural hosts of tomato bushy stunt virus demonstrated recently by the authors is given.

Isoperoxidase B 1 isolated from winter wheat (Triticum aestivum L., cv. Jubilar) seedlings was shown to catalyze ethylene formation from α-keto, γ-methylmercaptobutyric acid (KMBA). In the presence of Mn²⁺, indole-3-acetic acid (IAA), andp-coumaric acid, the kinetics by isoperoxidase B 1 catalyzed conversion of KMBA into ethylene and other products was similar to that of IAA oxidation. The reaction rate was therefore controlled by IAA through its electrondonating properties.
Exogenous IAA induced ethylene formation in the segments of etiolated wheat coleoptiles. IAA-induced ethylene production was enhanced by L-methionine and mitomycin C. Aminoethoxy-analogue of rhizobitoxine, ferulic acid, sodium benzoate, cycloheximide and actinomyoin D exhibited significant inhibitory effects. These data indicate that the overall reaction mechanism in coleoptile segments involves RNA and protein synthesis.
The site of IAA action is not specific; 2,4-dichlorophenoxyacetic, α-naphthylacetic and indole-3-butyric acids, respectively, possessed comparable inductive effect as IAA. Indole-3-propionic acid, indole, L-tryptophan and glucobrassicin had only low inductive efficiency, and moreover indole and L-tryptophan slowed down IAA-induced ethylene formation.

The stomatal density, dimension and conductances to water vapour diffusion of sevenHevea species were studied. It was found that these parameters were significantly different between the species. However, no distinct relationship between stomatal density or dimension and stomatal conductances could be discerned.

Dimethyl sulfoxide present in the agar medium at concentration 0.2 % (v/v) and lower does not inhibit cytokinin-induced betacyanin synthesis in theAmaranthus caudatus seedlings. The activity of kinetin, N⁶-(Δ²-isopentenyl)adenine andtrans- zeatin is the same when these cytokinins are dissolved in either water or dimethyl sulfoxide and incorporated into the medium after autoclaving. A simple method is described which allows the cytokinin activity of slightly water-soluble and thermolabile compounds,e.g. aromatic urea and thiourea derivatives, to be determined in theAmaranthus bioassay.

Sap flow rate (Q_w) and leaf water potential (Ψ_w.leaf) in adult specimens of birch (Betula) and oak (Quercus) were measured under contrasting soil moisture conditions (Ψ_w.sofl). With sufficient soil moisture Q_w reached about 250 cm³h^-1 calculated per unit tree-trunk segment as given by 1 cm length of its circumference. In soil water-stress conditions (when Ψ_w.leaf = = -15 × 10⁵Pa), birch stopped transpiration and wilted. Oak transpired even when Ψ_w.leaf fell below -20 × 10⁵Pa. The relation between Q_w and Ψ_w.leaf was always linear and with various Ψ_w.soil differed in the slopes of regression lines only. Hydraulic conductance (K_wcu) with nonlimiting moisture conditions reached about 6 × 10^-9m³ 10^-5Pa^-1s^-1 and "conductivity" ("k_wa") when calculated per leaf area unit reached about 23 m 10^-5Pa^-1s^-1. K_wcu and "k_wa" were of about one half to nine times greater in birch than in oak. On the basis of relations between Ψ_w.soil at various depths, Ψ_w.leaf and Q_w (resp. K_w) it is possible to assess the maximal rooting depth and the effective depth where the maximum of absorption of roots occurs. It is to be seen that the root system macrostructure substantially participates in the drought avoidance of adult trees in a forest stand.

Cytokinin activity was demonstrated in the Baltic sea waters. This activity was always higher in the near-bottom water, taken from theFucus vesiculosuszone, than in the superficial zone. A cytokinin-like substance showing properties typical of 6-(3-methyl-2-butenylamino)purine (2iP) was also present in extracts from the thallus ofFucus. It was found that exogenously applied cytokinins, in some concentration ranges, markedly increased the number of adventitious branches formed on the cut surface of the thallus fragments. The growth responses of the investigated plant tissues to the different cytokinins varied according to season and kind of cytokinin applied. The possibility of exudation of some cytokinin like substances by the algal cells into the surrounding waters was considered.

Barley plants were grown until day 21 under conditions which were different in relation to photon flux density, carbon dioxide concentration and temperature. Dry weight and leaf area increase from day 7 until day 21, shoot apex development between day 15 and day 47, and yield of each treatment group were considered. Photon flux density was demonstrated to have a greater influence on net assimilation rate (NAR) of young plants than has carbon dioxide enrichment. High temperature treatment seems to influence NAR less than growth and developmental processes. Grain yield of high temperature treated plants was significantly lower than that of the other treatment groups. Significant correlations have been found between growth analysis values of young plants and some yield components of each treatment.

This paper describes a procedure for isolation and preservation of mesophyll cells, adapted toValerianella olitoria. We have tested the best conditions of temperature, pH, enzyme concentration, plasmolysis and the action of several adjuvants, dithioerythritol and mineral nutrients. The method described gives a high yield of viable cells. The ability of isolated cells and cellsin situ to take up methyl-glucose is compared.