The application of 10^-3 g 1^-1 of 2,4 dichlorophenoxyacetic acid, 2-methyl-4-chlorophenoxyacetic acid, 3-amino-1,2,4-triazole and 6-chloro-2-ethylamino-4-isopropyl-amino-1,3,5-triazine toNicotiana tabacum cv. 'Samsun' plants inoculated with tobacco mosaic virus results in an increase in the content of this virus in the tissues. When whole plants are used, TMV content increases by 20% after herbicide application; when leaf dises are used, the amount of the virus can be doubled by the herbicide in comparison with control untreated inoculated discs. The results clearly show that the used non-selective herbicides act as stimulators of virus biosynthesis, probably via enhanced pentose phosphate cycle activity which enables an enhanced formation of viral RNA.

Free nucleotides of the primary root of maize were extracted with 5% HClO₄ and separated on a column of Dowex 1×8 ion exchanger in HCOO^- cycle. A two-step elution gradient (HCOOH, HCOOHNH₄) was used for the elution of the nucleotides. The incorporation of³²P into the nucleotides was followed at different time intervals and also in young and more mature root tissues. The nucleotides AMP, GMP, ADP, GDP, and ATP were identified. Labelled phosphorus was found in ATP after 30 s, in ADP after 3 min, and in AMP after 5 min incubation of the roots. More mature roots (18 days) contained higher amounts of AMP than the young ones (3 days).

The activity and localization of alcohol (AD), lactic (LD), malic (MD), isocitric (ICD) and succinic (SD) dehydrogenase, resp. was histochemically determined in shoot apices of plants in the vegetative condition during transition to flowering and at the reproductive state. The enzymes were determined in freehand sections, as well as in shoot apices incubatedin toto according toNachlaset al. (1958) using Nitro-BT. The characteristic localization of the enzymes depending on the ontogenic stage of the shoot apex is described. Different parts, layers and cell groups of the apex showed differences in enzyme activity. SD could not be detected in shoot apices. The histochemical findings are discussed in relation to former results obtained from a biochemical investigation of respiration in the same material.

If one cotyledon is removed from decapitated pea seedlings and the remaining one is treated with the cytokinin BA, then a complete correlation reversal occurs in numerous cases: instead of the bud belonging to the removed cotyledon, the bud belonging to the remaining cotyledon starts to grow. However, if GA is applied to the remaining cotyledon together with BA, then the number of these correlation reversals sharply drops. This in respect to cytokinin morphogenetically (correlatively) contradictory effect could play a significant role in apical dominance in plants.

The enzyme xylonase was used to isolate the protoplasts from the leaves ofCalendula officinalis L.,Gazania splendensMoore,Tithonia rotundifoliaBlake,Zinnia elegansJacq- and from the petals ofDahlia variabilis(Willd.) Desf. The recovery of spherical undamaged protoplasts differed. The same method did not lead to the isolation of the protoplasts from callus cultures derived fromCalendula, Gazania andTithonia leaves respectively.

The exposure of maize plants to drought led in most cases to a decrease in both the total and free water percentages, but to an increase in cell sap concentration, bound water percentage and bound water/free water ratio, comparing with the case of normal water supply. The employment of any of the studied treatments at either the normal or low soil moisture levels led throughout the period of time preceding the milky stage to a decrease in the free water percentage in maize leaves, but to the reverse effect with respect to both the bound water percentage and the bound water/free water ratio. The determinations of water fractions in leaves (free, bound water % and the ratio between them) before or at the tasseling stage appeared to be more reliable, compared with osmotic pressure determinations, as indication for the effective use of a given treatment in increasing the drought resistance of maize plants.

A technique is described for the establishment of infectious axenic callus cultures originated from stems of tobacco plants suffering from a mycoplasma disease, potato witches' broom. When stem pieces from a diseased tobacco plant (Nicotiana glaucaGrah.) are culture on a modified nutrient medium according toMurashige andSkoog (1962) with added kinetin (0.64 mg or 2.56 mg 1 000 ml^-1) and IAA (2 mg or 4 mg 1 000 ml^-1), the pathogen persists and spreads in the newly formed callus tissue. The presence of the pathogen was proved by implantation of callus slices into stems of tomato plants which indicate the disease very reliably. Reconstituted tobacco plants too recovered the infectious agent of potato witches' broom; 27 plants from the 35 reconstituted plants were diseased. Similar results were obtained with Crimean yellows. Calli were cultured and subcultured from 1 to 18 monthsin vitro and some infectious cultures are maintained and their investigation goes on. We suppose that kinetin plays a very important role for infectivity preservation in callus cultures.

The differences between leaves of different age according to their descending insertion level (starting from the youngest, 18th leaf) were compared with the changes occurring during the corresponding period of ontogenesis of the 18th unshaded leaf using the gas exchange [net photosynthetic CO₂ uptake (P _N ), water vapour efflux (E)] of the adaxial and abaxial surfaces of tobacco leaves as an example. Experimental elimination of the influence of shading during the involved period of ontogenesis of the 18th leaf manifested itself by a relatively slower decrease inP _N and by fluctuation of theE values at approximately the same level. Thus the differences between leaves of different insertion levels cannot be exclusively ascribed to the effect of their ontogenetic age.

Initially closed stomata in isolated leaf epidermal peelings ofCalotropis procera, Prosopis cineraria andTephrosia purpurea, opened when incubated in distilled water in light or in darkness. Water-induced open stomata closed down on incubation in abscisic acid (0.01 ppm) solution within half an hour. Sodium chloride induced the opening of stomatal aperture. NaCl-induced open stomata also completely closed down when incubated in abscisic acid solution, but open again when transferred to NaCl.

The effect of gametocides FW-450, maleic hydrazide and Dalapone on the course of microsporogenesis, gametogenesis and starch synthesis in pollen grains of winter rye ev. 'Esto' was investigated. Solutions containing various concentrations of tested substances were applied on leaves in amount of 2.5 ml and 5.0 ml per plant at the beginning, at the full and at the end of shooting. The effect of gametocides was detectable already in the phase of microspore formation when a decrease of anther weight, pollen grain size and starch content in grains and an increase of the number of microspores with nonfinished development were observed. The manner and the extent of injuries were dependent on the applied substance, its concentration and on period of its application.

Vicia faba plants cv. 'Erfordia' were treated with single application of CCC at 250 mg l^-1, 7 days before extraction. Such a concentration resulted in a 10.4, 14, 5 and 3.3 fold, respectively, increase in the levels of endogenous IAA, ABA, gibberellins and cytokinins relative to the controls. The results obtained indicate that a single application of CCC at a low concentration was sufficient to enhance the endogenous growth hormones in the treated plants. The results were obtained using GLC analyses for IAA, ABA and cytokinins, and the lettuce hypocotyl and soybean callus bioassay for gibberellins and cytokinins, respectively.

Humate (10 mg l^-1) supplemented to streptomycin solutions (0.1 and 1 mM) stimulates growth of germinating wheat and barley grains and of apical cuttings ofCrassula portulacea after 24 h treatment. It does not, however, prevent formation of albinic leaves. Albinism induced by the streptomycin alone and by streptomycin in presence of humate is irreversible and can be removed neither by an iron salt nor by a chelate added to the nutrition solution or applied on the leaves. Cells of plants treated with streptomycin and humate are larger than those of plants treated with the streptomycin alone. The same is true for plastids which in both cases are colourless and much smaller than chloroplasts of control plants. These plastids in a living or a fixed state have reduced ability to uptake stains. The albinic leaves are anatomically similar to chlorotic leaves of virus infected plants.

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 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.

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.

Oscillation movements of primary roots of pea seedlings were investigated after low- and high-energy irradiation (10^-2 and 10⁶ W m^-2) which was applied continuously and in pulses at intervals of 3 and 30 min. Oscillation amplitudes of control roots grown in darkness were lower (1 mm) than those of irradiated ones recorded in our previous experiments. The elongation rate of roots grown under scattered and low-energy irradiation as well as their mean oscillation amplitude (2.6 mm) and frequency (8 h) correspond to the standard values recorded in previous experiments. The same effects on root growth and oscillations had scattered electronic flash irradiation.
Side-irradiation did not influence the oscillation movements of growing roots. Their frequency and oscillation amplitudes were not changed. Their longitudal axis was, however, deflected 2.75° from the vertical one due to the negative phototropic response of the root.
The growth oscillations may be, according to present results, interpreted as consequences of tropic growth controlling system. External factors, like irradiation, may influence oscillation parameters,i.e. their amplitudes and after application of side-irradiation also the direction of longitudinal axis of oscillation spirals. The resultant trajectory is composed from movements which resulted from geotropic and phototropic responses of the roots.

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.