Ribonuclease (RNAse) activity was investigated in cotyledons ofChenopodium rubrum plants subjected to various conditions of illumination (photoperiodic induction, continuous light, induction cancelled by interrupting the dark period by a light-break). At the end of the dark period of the single inductive cycles RNAse activity of induced plants was inferior to that of plants grown in continuous light. At the end of the first two cycles the activity was lowest after the interruption of the dark period by light. The investigation of the enzyme in 6h intervals showed rhythmic changes in activity to occur in induced plants. Enzyme activity followed a pattern opposed to this of nucleic acid (NA) synthesis in the cotyledons. In plants from continuous light the enzyme activity did not show any rhythm and in plants having obtained a light-break during the inductive period the rhythm was less distinct than in the induced ones. The period length of the endogenous rhythm of NA synthesis in the cotyledons is about half as long as this of flowering and the peaks of flowering coincide with the throughs of NA synthesis.

The transpiration rate of intact spring barley plants, cv. Profesor Schiemann resistant to powdery mildew was studied separately in light and in darkness. At the first stage of pathogenesis the fungus temporarily reduced the transpiration rate of the host plants in light (E₁). The transpiration rate in darkness (E_d) was not influenced in this period and only in the period of formation of necrotic spotsE_d in the host plants was somewhat higher than that in the control plants.E₁ of the host plants gradually reached the level of the control plants in this period. The fungus considerably reduced the rationE₁/E_d. The differences in this ratio between infected and control plants increased in the susceptible cultivar but were moderated in the course of necrobiosis.

In field experiments, the competition among plants of two distinct wheat genotypes in binary mixtures, and among three genotypes being grown in adjacent rows was investigated. The competition greatly affected the over-ground dry weight, weight of stem and grain per plant. This effect was undercompensatory, the depression in poor competitor was higher than the enhancement of strong competitor for all these characteristics. From final components of grain yield per plant, the number of fertile stems and number of grains per ear were more affected than weight per grain. More expressively than weight of grain on the main-stem ear, the weight of grain per average secondary ear-bearing stem was affected by competition in binary mixture. The enhancement in standard height-a strongly competitive genotype- reached in binary mixture about 10% for this last characteristic in comparison with the value from the pure stand. Some morphological characteristics of plants being in relation with competition for grain yield per plant are discussed in these experiments.

The three plant types ofAmaranthus namely,A. caudatus f.albiflorus, A. caudatus f.caudatus andA. tricolor var.tristis are qualitative short day plants with critical photoperiods 16.0, 15.5 and 15.0 h, respectively. Gibberellins A₃, A₄₊₇ and A₁₃ affect extension growth, leaf differentiation and floral induction differently. Thus, in all the three plant types ofAmaranthus, whereas, GA₃ and G₄₊₇ enhanced extension growth, GA₁₃ was completely ineffective under both, 24- and 8-h photoperiods. None of the three gibberellins could affect the leaf differentiation. In all the three plant types, flowering was promoted by GA₁₃ and not by other gibberellins tried. GA₁₃ caused promotion was manifested in two manners, firstly by lowering the critical dark period requirement in each inductive cycle, and secondly by shortening the total period taken for the initiation of inflorescence primordia under inductive photoperiods. The floral induction by gibberellins inAmaranthus is contrary to the gibberellin-anthesin concept of Chailakhyan. It is suggested that gibberellins other than GA₃ may be playing an important role in floral morphogenesis of short day plants.

The effect of different growth substances on the development of normal and abnormal stomata are presented. Anomocytic, paracytic, anisocytic and stoma with a single subsidiary cell are observed. Abnormal developments like persistent stomatal cells, degeneration of guard cells, unusual thickening, unequal guard cells, single guard cells and size and shape of the pore are noticed in various growth substances. The growth substances also affect the stomatal frequency, stomatal index, epidermal frequency and size of guard and epidermal cells in both the plants. The highest meristematic activity is found in MOR 100 ppm in brinjal and in GA 25 ppm in tomato. The largest size of stomata is found in COL 25 ppm in brinjal and in MH 50 ppm in tomato. The same growth substance responds differently in the two plants.

The participation of the genotype and of organ specifity effect in the quality of morphogenetic response (callogenesis, bud and root formation) of primary maize explants has been investigated. The presence of synthetic auxins - especially 2,4-D at 1 to 5 mg 1^-1 conc. - in cultivation medium was essential for both callus formation and continuous growth of tissue and suspension cultures. Anatomic structure of callus cultures is permanently heterogeneous, their growth is ensured by the action of meristems of the type found in root tips, and by repeated callogenesis from malformed roots. Adventive buds and plants could be regenerated only from cultures of embryonal origin (of one line). The presence or absence of the endosperm gene "opaque" did not influence callogenesis intensity in cultures of isolated embryos; however the morphogenetic response was clearly "line specific".

The study deals with the absorption and translocation of Ca²⁺ by án intact plant of pumpkinCucurbita pepo L. and with the effect of various concentrations of 2,4-dinitrophenol (DNP) on these processes. The absorption of Ca²⁺ was reduced by the application of this inhibitor, but not completely stopped. The translocation of Ca²⁺ into shoots was affected more expressively: it was almost completely inhibited by higher DNP concentrations. The uptake of Rb⁺ is aubstantially more influeneed than that of Ca²⁺: higher inhibitor concentrations caused its complete cessation.

CCC in either absence or presence of salinity slightly and irregularly affected the shoot dry weight, but consistently increased the seed cotton yield. The extent of such positive effect upon yield tended to be larger in the presence rather than in the absence of salinity when using CCC as a seed-soaking medium alone, but the reverse if applied as a spray after seed-soaking.

The rise in soil salinity level tended to decrease shoot dry weight, and, grain yield per plant and, to some extent, weight of I grain. This effect was usually more pronounced in the presence of CCC. On the other hand, the shoot dry weight was increased by CCC in salinity absence but the reverse at 0.8 % salinization degree. The grain yield per plant was raised by CCC in the presence or absence of salinity, particularly in the latter case. The dry matter accumulation in the shoot system (at earing stage) rather than grain yield tended to be much more affected, whether regarding the negative response to salinity or the positive one to CCC.

Chosen species and cultivars(Nicotiana sanderae, N. glutinosa, N. otophora, N. paniculata, N. sylvestris, N. velutina, N. tabacum cv. Samsun, N. tabacum cv. Samsun - a dihaploid line, and an amphidiploid N.sylvestris x N tomentosiformis) were treated with adequate concentration of n-buthylmethane sulphonate. The anthers of M₁ plants were cultured on the medium of NITSCH 1969 plus 0.1 mg IAA/1. Special attention was paid to quantitative characteristics of androgenesis. Androgenesis occurred more often in the treated variants. The conclusions have been confirmed of a heterosis effect of adequate chemomutagen concentration at the diploid level (an increase in the number of androgenic anthers in the treated variants, and a decrease in the mean number of haploids per androgenic anther) in the broad range of the material. We have recorded a high androgenic ability in the amphidiploidN. sylvestris x N. tomentosiformis, and androgenesis inN. velutina for the first time.

The growth of callus tissue cultures and the infectivity of twenty fiveSolanum laciniatum Ait. plants and of sixteenNicotiana tabacum L. cv. Samsun plants were investigated. The plants were obtained from callus tissue cultures derived from stem pieces of the respective plants infected with a mycoplasma-like organism (MLO) evoking potato witches' broom. The tissues were cultivated on synthetic nutrient medium with kinetin and IAA. Allde novo obtainedS. laciniatum plants were healthy. On the contrary twelve of the sixteen reconstituted tobacco plants showed MLO presence.
Summarizing these and previous results, the authors suppose that the most important factor influencing MLO persistence in callus tissues cultivated on the applied nutrient medium may be the callus growth rate and the organogenesis set. Both these conditions are determined by the metabolism of the investigated plant species.

In comparison with primary leaves of French bean plants grown under a photon flux density of 100 μeinstein m-2 s-1 (LP), leaves grown under 400 μeinstein m-2 s-1 (HP) were thicker (contained 82 to 104% more dry matter per blade area), had 44 to 48% higher stomatal frequency, 18 to 26% more chlorophyll (a + b) per leaf area unit and 31 to 42% less chlorophyll (a + b) per dry matter unit, 41% higher photosynthetic and 38% higher transpiration rates at light saturation, 33% higher stomatal conductance and 40% higher Photosystem 2 (H2O → K3[Fe(CN)6]) activity of isolated chloroplasts. There were no significant differences in the Photosystem 1 (TMPD/Ascorbate → MV) activity per unit amount of chlorophyll. Higher growth irradiance increased the ratio of frequencies of stomata in the upper/lower epidermes.

Water potential of roots was measured by thermocouple psyohometers in a series of two or more plants ofCynodon dactylon (L.)Pers. interconnected by overground stolons and thus forming one s.c. polycormon. Root water potential was lowest (most negative) in the oldest "mother" plant and increased in younger individua to highest walues in the youngest "doughter" plants. This gradient of root water potential was found although the "mother" plants continued to be watered while watering all daughter plants had been stopped one week before the water potential was measured. Thus the whole polycormon consisting of a series of interconnected individua behaves as one hydrodynamic system where all individual root systems act as if being parts of one sole root system.

The distribution of endogenous gibberellin-like substances in individual organs ofZea mays L., cv. CE 250, plants was investigated during the transition from the vegetative to the generative phase of development. The gradient of the content of gibberellin-like substances and photosynthetic activity in leaf segments was followed in different parts of the Jeaves, as well as the changes in the content of gibberellin-like substances in leaf segments during an exposure in the light and in the dark. The gradient of the content of endogenous gibberellin-liko substances in the leaves, in the stem and in the spike is interpreted in terms of possible relationship of these compounds to the regulation of sink - source.

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.

Conditions for the mechanical transmission of some woody viruses to herbaceous hosts were studied. Viruses from naturally-infected spindle tree (Euonymus europaea) and maple (Acer pseudoplatanus) leaves were mechanically transmitted by the homogenate prepared by using charcoal and celite to beans (Phaseolus vulqaris cv. Kocovska and Perlicka). The transmission of Euonymus mosaic virus and maple leaf perforation by nucleic acids prepared from naturally infected woody plants was also successful.

The analyses for the content of endogenous gibberollins and auxins in leaves and adjacent stem internodia of intactBryophyllum crenatum plants revealed that the level of gibberellins increases in tho direction from the apex to the stem base, whereas in the case of auxins the trend in the increase is tho reverse. This corresponds to the results of morphological experiments, according to which the apical stem part appears as affected by phytohormones of an inhibitory character, the basal part as affected by stimulatory ones.

CO₂ absorption (PAT) and transpiration (E) rates, and leaf diffusion resistance (r_i) were individually studied in all leaves of tobacco plants (Nicotiana tabacum L. cv. Wisconsin 38) before flowering. Differences between old, middle age and young leaves were in all characteristics studied and found statistically significant. In all three leaf age groups E was closely correlated to r_i. No similar correlation was discovered between P_N and r_i. The highest ratiosP _N /E in young and middle age leaves indicate that the increase of the internal resistance to photosynthesis with leaf age was more rapid than that of r_i.

In this report, B₉ treatment had no effect on the growing of rosette biennialScrophularia vernalis L.; it inhibited or slowed stem elongation. Applications of GA₃ to B₉ treated plants produced a significant increase of stem elongation, in relation to GA₃ treated plants. Plants treated with only GA3 failed to flower; otherwise, the flowering of vernalized plants was not altered by GA₃. Thus, B₉ effect on flowering was tested by using GA₃. B₉ by itself induced flowering, it increased inflorescence formation in vernalized plants without altering stem growth pattern in the most of cases. The induction or the stimulation of flowering brought about by B₉ was not reversed by GA₃; we may thus hypothesize that flowering by B₉ oannot be traced back to gibberellin biosynthesis.

In contradiction to Paulet's (1965) data, we found that kinetin/IAA strongly affected organogenesis in callus tissue derived from the stem ofNicotiana glauca Grah. plants both in primary expiants and in subcultured calli. The effect of these substances was higher in the subcultured calli derived from mycoplasma-infected plants. Evidence of the absence of the infectious agent in de novo-formed plants in subcultured calli was given by grafting and by the electron micrograph.

The changes of kernel nitrogen (N), phosphorus (P) and dry weight (DW) were determined during the time period from 10 days after anthesis till maturity in three spring barley strains. The plants were cultivated under field conditions in Gatersleben (German D.R.) and Kroměříž (Czechoslovakia). The course of N, P and DW changes was described by Richard's comprehensive growth function dW/dt = aW^m + bW, where W is the amount of N, P or dry matter per kernel, a, b, m are coefficients. The integral of this function was used and several parameters calculated. There was a remarkable synchrony between N or P and total dry matter accumulation in the kernels. Thus, the N or P concentration per unit kernel dry weight was relatively constant during the investigated period and with few exceptions corresponded to 80% to 100% of the final value. However, considerable differences between strains, years or places of cultivation were found.

Alcohol dehydrogenase was prepared from 2-day germinating maize and 3-day germinating broad-bean seeds by ammonium sulphate fractionation of sodium phosphate extracts, chromatography onDEAE cellulose and Sephadex G-200. The activity of the broad beanADH amounted to182 800 units per mg protein, that of maizeADH 79 000 units per mg protein. Besides oxidation of a series of alcohols at pH optimum in the alkaline region and with KM equalling 10-2M, alcohol dehydrogenases isolated from both plants catalyze the reduction of acetaldehyde, n-propanal, n-butanal, isobutanal and crotonal at pH optimum in the neutral region with KM equalling 10-3M. The inhibition studies using fatty acids and chloride ions revealed that the oxidation of alcohols is inhibited competitively by both types of inhibitors, with inhibition constants of 10-2M and 10-1M, respectively. The inhibition in the presence of acetaldehyde is non-competitive since the inhibitors do not compete with acetaldehyde and do not form an enzyme-NADH-inhibitor complex, yet they obviously react with the enzyme-NAD product only, thus giving rise to an enzyme-NAD-inhibitor complex. These differences in the behaviour of inhibitors may be interpreted in the sense that the binding sites of ethanol and acetaldehyde as substrates for broad bean and maize alcohol dehydrogenases are non equivalent. The nonequivalency discussed in the text.

Changes in the transpiration rate of intact spring barley plants, cv. "Slovensky dunajsky trh", were studied separately in the light and in the dark under controlled temperature and illumination, after the infection withErysiphe graminis DC, during an 8 day period of the development of the fungus. In the first stage of pathogenesis, the fungus diminishes water output from the host plants in the light. An opposite phenomenon can be observed in the dark; water output from infected plants in the dark increases sharply mainly in the stage of advanced fructification. Thus, the fungus considerably diminishes the ratio of water output from the host plants in the light to that in the dark.

In two branched plants ofImpatiens balsamina with intact apex and leaves floral buds are induced only in the branch which is either exposed to 8-h (inductive) photoperiods or receives GA₃ treatment if maintained under 24-h (non-inductive) photoperiods. GA₃ induces floral buds on the treated branch even if the leaves on that branch are removed, showing that while leaves are essential for photoperception, these are not neoessary for GA₃ to cause induction. The effect of the inductive photoperiods or GA₃ treatments to a branch is not transmitted to the other branch which is treated with water and is maintained under non-inductive photoperiods even when the latter is defoliated but is transmitted if the apioal or both the apical and axillary buds on the branch receiving inductive photoperiods or GA₃ treatment are excised. It, therefore, appears that the existence of strong sinks in the form of axillary and apical buds on the treated branch prevents the transmission of photoperiodic as well as GA₃ effects to the other branch in this plant.

This work is a study on the presence of free and bound (mainly proteins) amino acids at the levels of both the individual plants and the producers of a phryganic ecosystem. Therefore the amount of free and bound amino acids (both quantitatively and qualitatively) is determined during two seasons. As far as the producers (green plants) at the ecosystem level are concerned, the amount of free and bound amino acids was determined for both the above ground (stems, leaves) and the below ground (roots) parts during an annual period. On the basis of the above mentioned measurements it was found that, in a year, 17 and 4 g.m~²of bound and free amino acids are produced, respectively. A percentage of about 50% of this quantity remains in the plants, as their annual growth, and the rest returns to the soil because of the litter and root turnover. The model of their flow in the ecosystem was formed considering also data from plant physiology.

Zn²⁺ ions slightly enhance at low concentrations (0.01 μg ml^-1) the activity of tryptophan synthase obtained from the shoots of 14-day-old pea seedlings (Pisum sativum L.). On the contrary, high concentrations of Zn²⁺ (10 μg ml^-l) exert an inhibitory effect. The direct Zn²⁺ activation of tryptophan synthase, establishedin vitro with a partially purified enzyme preparation, is relatively low and obviously is not decisive from the point of view of tryptophan biosynthesis of the enzyme and thus they are participating in thein vivo experiments.

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.

Kinetin at a concentration from 3.10^-6 M to 1.10^-3 M was applied to the plumule ofChenopodium rubrum plants during photoperiodic induction. Different levels of induction were compared (one and three short days). The higher concentrations of kinetin applied to induced plants inhibited flower formation. The rate of leaf initiation was increased under these treatments. Lower concentrations of kinetin (from 3.10^-6 M to 1.10^-5 M) usually promoted lateral bud formation and flowering. The step-wise application of kinetin revealed that the inhibitory effect on flowering had been restricted to the inductive period.
The effects of kinetin, benzyladenine and trans-zeatin were compared in plants partially induced by two short days. High concentrations always inhibited flowering. Benzyladenine was the most effective in this respect.
Root removal diminished the inhibitory effects of cytokinins on flowering as was stated with benzyladenine.
It is assumed that endogenous cytokinins play a role in the regulation of organogenetic activity of the stem apical meristem. Depending on the photoperiodic conditions, they presumably exert their activity by maintaining the vegetative functions of the apex.

The fruit pitting symptoms on cherries, plums and prunes were investigated from the standpoint of their etiology. Tomato bushy stunt virus (TBSV) was isolated from pitted fruits of these plants and from their leaves and identified by means of biological and serological methods. Both isolates reacted with antisera againstPetunia and artichoke strain of this virus. In addition, the etiology of pseudopox disease of plum and that of cherry detrimental canker is discussed.