The cytokinin-autonomous strain (A_s) of tobacco callus differs from the original cytokinin-dependent strain (D) and from the cytokinin- and auxin-autonomous strain (A₄) by a significantly lower activity of glucose-6-phosphate dehydrogenase (G-6-PDH). Changes in the total G-6-PDH activity were associated with differences in the number of G-6-PDH isozymes. The A_s strain contained only one isozyme, four isozymes were found in D and A₄ strains.

In Jerusalem artichoke tuber,in situ RNA synthesis along vegetative cycle shows two maximums. The first one appears during tuberization and installation of dormancy and a growth inhibition is sufficient to bring it about. The second reveals breaking of dormancy and precedes germination.

Callus tissue cultures were established from stems of tobacco plants (N. glaucaGrah.) both healthy and mycoplasma (potato witches' broom disease) infected on a modified nutrient medium (with a lower content of mineral salts) according toMurashige andSkoog (1962) in the presence of 2,4-D (1 mg l^-1) as a growth regulator. No differences were observed in the growth and development of both tissues. Organogenesis appeared on a nutrient medium (Petrůet al. 1972) supplemented with kinetin (0.64 mg or 2.56 mg l^-1) and IAA (2 or 4 mg l^-1). Callus derived from mycoplasma diseased plants started to form numerous buds after three months whereas organogenesis in callus from healthy controls appeared only after six months. We suppose that the reason of this difference is the fact that an expressively higher content of 2,4-D was found in the calli from healthy plants in comparison with the corresponding tissue from mycoplasma diseased ones. Reconstituted plants were isolated, rooted and transferred in the soil. The infectivity of these plants was assayed by grafting their stem tips on tomato plants which indicate very reliably and sensitively this mycoplasma disease. 31 reconstituted plants were obtained in the whole from calli isolated from mycoplasma infected plants and all of them were healthy.
It was established that mycoplasma failed in the presence of 2,4-Din vitro. Stem pieces from diseased plants in which mycoplasma presence was proved, lose their infectivity after 4 weeks of cultivation on nutrient medium with this growth regulator. On the contrary 2,4-D which spreads and acts especially through phloem (Smithet al. 1947) does not kill mycoplasmain vivo even in doses evoking strong symptoms of 2,4-D effect on experimental plants.

Cytogenetic effects of different concentrations of 2,4-D on suspension cultures ofVicia hajastanaGrossh. andHaplopappus gracilis(Nutt.) Gray were studied using a simple, chemically defined medium. InVicia, the frequency of dicentric chromosomes showed a negative association with the 2,4-D concentration. In both the species, the frequencies of anaphase bridges were negatively associated, while those of the diploid cells showed a positive association with the 2,4-D concentration in the culture medium. A decrease in the frequency of diploid cells was observed in the cultures transferred to a lower concentration of 2,4-D. This decrease was transient inVicia, while inH. gracilis a new equilibrium at a lower level was established. Both endoreduplication and selection appear to be involved in the achievement of the lower equilibrium inH. gracilis, although selection appears to be the major factor.

In squashes of broad bean and sunflower root tips, the staining with aluminium lake of nuclear fast red led to reliable results, comparable-otherwise-with the use of acetoorcein and similar procedures: the nucleus and ohromosomes are brightly red, the cytoplasm weakly pink.

The construction of the track for automatic, continuous horizontal transporting of the sensor which measures radiation with controlled velocity at various heights above the ground in a plant stand has been described.

The absorption of nitrate and the activity of nitrate reductase were much lower in Ca-deficient plants ofCururbita pepo L., cv. 'Kveta' than in normal plants grown in complete nutrient solution for a period of 8 days. After the addition of nitrate to the nutrient medium, nitrate reductase activity in the roots of NO₃-deficient plants sharply rose during the first 6 h and then remained constant during the following 6 h; the content of endogenous NO₃^- rose slowly and continuously. These processes were depressed in (Ca, NO₃)-deficient plants independently of the addition of Ca²⁺ to the medium in the variant with NO₃^-. Thus it seems that the whole nitrogen metabolism,i.e. both NO₃^- absorption and the synthesis of nitrate reductase, is impaired in Ca-deficient plants.

The mutual relationship between the water potential (γ _w ), its components, namely the osmotic potential (γ _s ) and the pressure potential (γ _p ), and the water saturation deficit (ΔW _sat ) were determined in the leaves of different insertion levels. During the water stress development in kale plants induced by decreasing soil moisture theγ _w decreased, parallely in all the leaves but the same decrease ofγ _q was accompanied by the highest decrease of theγ _p , probably due to the accumulation of osmotically active solutes, and the lowest decrease ofγ _p in the upper leaves and with the lowest decrease ofγ _s and the highest decrease ofγ _p in the lower leaves. Also the corresponding values of the ΔW _sat were always lower in the upper than in the middle and lower leaves. Thus the upper leaves wilted at more negative values ofγ _w than the other leaves. On the contrary, during the wilting of the cut off leaves the relationship betweenγ _w and ΔW _sat in the upper, middle and lower leaves was practically the same. The very slightly higher decrease ofγ _s in the upper leaves in comparison with the other leaves was compensated by a lower deerease of theirγ _p .
These changes in the ratios ofγ _w ,γ _s ,γ _p and ΔW _sat with the leaf insertion levels enabled the preference of the upper leaves in retaining the necessary water supply during the wilting of plantsin situ.

The elongation of pine seedlings (Pinus silvestris L.) is associated with nutation movements. Trajectories of these growth oscillations were recorded by film technique in horizontal and vertical projection during a three day period of growth. On the basis of these data the parameters of elongation and nutation oscillations,i.e. rate, amplitudes and frequency of oscillations, were calculated and their changes during plant development compared. Oscillation trajectories are circular or elliptic spirals the amplitudes of which are increasing with the age of hypocotyl from 1.5 mm to 7.5 mm. The frequencies of nutations are decreasing during the growth from 0.5 to 0.2 rev. h^-1. On the other hand, the growth rate of hypocotyl increased from values near to 10^-3 mm h^-1 at the beginning of the experiment to 4×10^-1 mm h^-1 recorded at the end of the third day. The zone of nutation curvature was slightly transferred from the middle of the hypocotyl toward the apex and its location has not been identical with that of elongation. This indicates that the system controlling nutation oscillations need not be identical with that controlling direction of elongation. At a certain stage of development behaviour of the decapitated pine hypocotyl is analogical to that of the root without the centre of georeception. A possibility of analogy of the system controlling direction of hypocotyl growth and of the system proposed for geotropical control of root growth is discussed.

The suitability was evaluated of MNNG as a mutagen inducing increased frequencies of mutations in the cell populations of three strains of chlorococcal algae for the purposes of selection. MNNG has proved to be highly toxic to those algae as it produces severe physiological responses of the affected cells. The mutagenic effect of MNNG was relatively small in comparison with the recorded toxic effect. From these results it has been concluded that in reverse to NEU, MNNG can hardly be applied with such good an effect in the mutation breeding of chlorococcal algae that are suitable for mass cultivation.

Barley seeds were treated for 3 h at 25°C with 240 mM ethyl methanesulphonate (EMS), washed for 18 h, treated with various concentrations of unbuffered sodium azide (pH 6.7-7.3) for 3 h at 25°C, re-dried to 30% water content and either sown immediately or stored at 25°C for 12 days and then sown. The synergistic action of sodium azide post-treatment has been demonstrated only for the EMS-induced M₁ germination reduction, while the EMS-induced M₁ sterility and the yield of M₂ chlorophyll mutants were unaffected. The "storage" recovery from EMS-induced mutagenic effects was insensitive to sodium azide post-treatment. The 12 day-seed storage at 25°C brought about an improvement of M₁ germination, M₁ survival, M₁ fertility and a decrease in the amount of M₂ mutants, regardless of whether sodium azide post-treatment was applied or not.

Various quantitative anatomical characteristics were measured in the potato tuber by the using of integration methods. There were found the gradients showing the dependence of the changes on the distance from the surface of the tuber.

Changes in the metabolic pathway linked up directly with respiratory pathways were followed inN. tabacum L. cv. 'Samsun' plants inoculated with potato Y virus. The consumption of oxygen in infected tissues before the occurrence of visible symptoms (up to the sixth day) was lower than in control plants, then it started to rise and the tenth day after inoculation it reached 116% of the control. It was established that two main respiratory chains were involved, from which the glutathion-ascorbate system was responsible for the total respiration rate during the entire period of investigation.
The other respiratory system,i.e. NADPH-glyoxalate-glycolate, is not related directly to the respiration rate, but, it is probably linked up with the changing content of NADPH. The results obtained with catalase and peroxidase show that these enzymes are not directly linked up with changing glycollate oxidase activity but that they cooperate. While at the beginning their activities are mutually compensated, at the later period of enhanced glycollate oxidase activity and increase in the activities of both these enzymes occurs which then remove the originating excessive toxic H₂O₂.

Humus substances synthesis was investigated in the course of birch wood decomposition by a brown-rot fungusPiptoporus betulinus. With progressing decomposition of wood by brown rot the proportion of high molecular weight humic acids is gradually increased at the expense of fulvic acids, the amount of which is proportionally lowered. The high molecular weight humus constituents are not accumulated in wood decomposed by a laccase producing white-rot fungi despite the availability of suitable phenolic substrates; the low molecular weight fraction of fulvic acids is permanently higher than the fraction of humic acids. The function of laccase in lignin degradation and in biosynthesis of humic acids is problematic.

Most of the peroxidase activity of strawberry petiole is obtained from ionic treatment and pectinase-cullulase digestion of the cell-walls: two ionically-and three covalently- bound isoperoxidases were separated by starch gel electrophoresis. A technique is described for preparing an active IAA-oxidase extract. Final oxidation products of indoleacetic and indoleacrylic aeids appear to be the most effective IAA-oxidase promoters.

Methyl methanesulphonate (MMS), applied on barley seeds, inhibits the seed respiration and thein vitro activity of cytochrome-oxidase and catalase, whereas doubles the activity of total dehydrogenases and has no influence on the activity of peroxidase.
Storage of MMS-treated seeds for 10 days at 30% seed water content, thus under conditions favouring the recovery from the MMS-induced toxic and genetic effects, resulted in an enhancement of the cytochrome oxidase and catalase activity, which reached or exceeded the activity of the control. The activity of peroxidase, although increasing during storage, did not attain the value of the control and the activity of total dehydrogenases remained two times higher as compared to the control.

The culture filtrates of the rhizosphere fungi of broad bean (Vicia faba L.) and cotton (Gossypium barbadense L.) were analysed for the presence of plant growth substances of auxin and gibberellins nature. Bioassay test and chromatographic analysis indicated that these fungi, each synthesized different auxins in their culture medium. These auxins were indole compounds. Similarly the rhizosphere fungi produced in their culture medium some gibberellins and gibberellin-like substances.

Isoenzyme pattern of peroxidase, polyphenol oxidase and catalase at different intervals during germination and in different plant parts during early development of 'C-306' and 'Hira' cultivars, representing tall and dwarf wheats, respectively were investigated. The number of isoenzymic components of the three enzymes increased progressively with the concomitant increase in the stage of germination. The isoenzymic patterns, in general, were more clear and better developed during the later stages of germination. Different tissues or organs of the wheat plant possessed specific isoenzymic pattern of these enzymes. Differences between cultivars were observed both in the number and relative intensity of the various isoenzymic fractions.

No proportional changes in the photosynthetic rate,P, (measured as the dry weight increments in leaf discs) as related to the specific leaf weight,SLW (i.e. leaf dry weight per unit leaf area) were found because of different variation inP andSLW, respectively, with the age and insertion level of individual sugar beet leaves as well as with the age of the whole plant.

Neither the incubation of the flower scapes of garlic (Allium sativum L.) in tetracycline solution nor the extirpation of the bulblets from the inflorescences led to the development of fertile binuclear pollen. Higher tetracycline concentrations than 125 mg per litre showed a clearly phytotoxic effect. The removal of the bulblets from the inflorescences improved the survival of flowers but it enabled only the initial stages of seed development. The seeds obtained were defective and not able to germinate. The hypothesis on infectious nature of the factors causing sterility in garlic is discussed.

Populations ofScenedesmus quadricauda grown in a continuous chemostatic regime and synchronized by light and dark intervals were exposed to continuous illumination. The effect of light on synthetic and reproduction processes during the time of the omitted dark period and in the subsequent cell cycle was studied. In general, the sequence of cellular processes and their mutual coupling remain the same as in the darkened population. Synthetic processes and photosynthetic activity are depressed during the period of protoplast fission also in the light. The synchronizing effect of the dark period in chlorococcal algae consists in reducing the developmental variability in the population. The developmental state of daughter cells at the end of the dark interval varies in the span of two (as a rule) or four (at maximum) genomic cycles, while at the end of the light period this variability comprises up to eight genomic states. The more advanced autospores start the next cycle with a greater lag.

The endodermal cells of the maize roots are linked to each other via plasmodesmata mainly localized at the proximity of the Casparian band on the anticlinal walls. In this part of the walls was noticed the absence of the suberin lamella in the thickening endodermal cells.

Pollination induced dissolution of nucellar cells at the micropylar end forming a passage for pollen tube entry even when the pollen tubes are in the stylar region.

Virus origin of lilac ringspot and chlorotic ringspot of lilac was identified serologically by means of double gel diffusion method. The former of these diseases is due to Arabis mosaic virus, the latter to a mixture of Arabis mosaic virus and cherry leaf roll virus. The occurrence of these viruses has been detected for the first time in Czechoslovakia.