The contents of NADP⁺, NADPH, changes in the activity of glucose-6-phosphate dehydrogenase and some questions relating to its regulation in leaf tissues of tobacco plants infected with PVY were studied. The content of NADP⁺ and the total sum of pyridine nucleotides decreased after inoculation to 15 % and 30 %, respectively, whereas the content of NADPH increased up to the threefold control value. The contents of NADP⁺, NADPH and Σ(NADPH + NADP⁺) linearly correlated with the reproduction curve of PVY. The value of the reduction charge RC and the value of the ratio NADPH/NADP⁺ sharply increased after inoculation up to tenfold and eighteenfold values, respectively, of the healthy control.
The activity of glucose-6-phosphate dehydrogenase was markedly increased in virus-infected tissues during the entire experimental period both in crude homogenate and after its partial purification when compared with the values found in healthy control plants. The time courses of the activity curves of both crude and partially purified enzymes were coincident and correlated with the reproduction curve of PVY. The results indicate the involvement of coarse regulation of the activity of the enzyme by its content without the involvement of fine regulation by the ratio NADPH/NADP⁺ and RC.

Gibberellins A₃ and A₁₃ cause floral induction inImpatiens balsamina, a qualitative short day plant, under non-inductive 24-h photoperiods (continuous illumination). However, the influence of the two inductive factors,i.e. gibberellins and short days (8-h photoperiods) on the peroxidase enzyme system is different. The total peroxidase activity decreases under both inductive and non-inductive photoperiods, with or without gibberellin treatment. The electrophoretic pattern of isoperoxidases changes only in response to gibberellin treatment. Under 24-h photoperiods, treatment with gibberellins A₃ and A₁₃ causes the appearance in the stem of three additional isoenzymes of peroxidase (Rm 0.50, 0.71 and 0.76). These bands do not appear in the leaves, which are non-essential for gibberellin-caused floral induction in this plant. Under 8-h photoperiods also, gibberellins induce the appearance of new isoenzyme bandsi.e. two in the stem (Rm 0.50 and 0.76) and one in the leaves (Rm 0.05). These may be correlated with the synergistic increase in the number of floral buds in these plants in response to simultaneous exposure to two inductive factors.

InArabidopsis thaliana the relative measure of Darwinian fitness - the adaptive values of the two homozygotes related to the reference heterozygous genotype in one locus system were estimated on the original and on three changed genetic backgrounds. It was stated that the change of the genetic background with different gene-modifiers of the pleiotropic effect of a given gene on fitness may be important for the existence of mutations in populations, especially if we take into consideration not only the selection pressure against the homozygotes but also a certain real percentage of outcrossing. Special attention is paid to statistical elaboration of the experimental data.

A binary vector system inA. tumefaciens for the introduction of foreign genes into the plant genome was developed. The first component is the Ri plasmid and the second component is a small vector plasmid, replicating inAgrobacterium, which carries the 25 bp terminal sequence of the Ti plasmid, theNos gene as the selectable marker and neighbouring sequences of the Ti plasmid. Functions necessary for integration are providedin trans by the virulence region of the Ri plasmid. Transformed cells are selected on the basis of hairy root tumor proliferation and agropine synthesis. They also showNos activity coded by the gene on the small part of Ti T-DNA.

On the basis of proportionality between flow and its conjugated force a mathematical model for volume, current and osmotic flows was designed and a method for the experimental measurement of flows, the transbarrier (trans-segmental) potential and the rate of flow was devised.
The results obtained experimentally as well as using the mathematical model indicate that the plant root is differentiated not only according to localization, but also according to the conductivity, permeability and selectivity of these tissues.

XAD-4 resin was used to isolate cytokinins present in Baltic sea water. Four compounds were tentatively identified as 6-(3-methylbut-2-enylamino) purine and zeatin, and their ribosides.

Populations ofAllium montanum from 6 localities in Czechoslovakia show a certain variability, but no correlation between their mutual affinity and geological substrate, climate or altitude above sea level.

When the wheat germ cytokinin-binding protein (CBF-1) is isolated from excised wheat embryos only one group of polypeptides near 54 000 is observed as opposed to three polypeptide groups reported for CBF-1 from commercially milled wheat germ. The other two lower molecular mass polypeptide groups previously reported are probably proteolytic degradation products of the 54 000 species resulting from excessive heat or physical damage during milling. The CBF-1 polypeptide accumulates rapidly in the embryo after 20 days post-anthesis. A larger set of polypeptides near 66 000 - 68 000 appears during embryo development and also reacts with anti-CBF-1 serum. These polypeptides are also observed upon immunoprecipitation of 20-day embryo polyadenylated RNA translation products although the data are not definitive enough to prove a precursor relationship to the CBF-1 54 000 polypeptide. The new findings are discussed in regard to previous characterizations of CBF-1.

³H-labelled zeatin riboside (ZR) was applied to pod walls of intactLupinus luteus L. plants. Metabolites present in mature, dry seeds were zeatin nucleotide (ZNT), zeatin riboside (ZR) and zeatin (Z), zeatin O-glucosides and lupinic acid (LA), and the corresponding dihydro-derivatives of the cytokinins listed. Endogenous cytokinins were rapidly metabolised in germinating seeds. In seeds labelled with [³H]ZR for 90 min following a 2 h period of imbibition in water, ZR was actively converted to ZNT and dihydro-ZNT but the prevailing CTK was Z in cotyledons and ZR in embryo axes (EA); later LA and dihydro-LA, and O-glucoside metabolites accumulated. When [³H] zeatin was introduced into imbibing seeds, it was converted to dihydro-ZNT, ZNT, dihydro-ZR, ZR and dihydro-Z; in EA of the Z-labelled seeds, dihydro-ZR and ZR were the main cytokinins. After incubation of the Z-labelled seeds for 6 h in water, the ratios of dihydro-ZNT: ZNT and dihydro-ZR: ZR were, respectively, 20: 1 and 3.4: 1 in EA, and 3.5: 1 and 1.4: 1 in cotyledons.

Buckwheat cotyledons were induced to form callus tissuein vitro, in which shoots or roots could be regenerated, by changing the hormonal composition of the medium. The effect of gibberellic acid (GA₃) was studied in these processes. Addition of GA₃ to cell division medium during the first 5 days after inoculation did not interfere either with the induction of cell division, or with the subsequent organogenesis. However, GA₃ had a very pronounced effect on organogenesis when added immediately upon the transfer of expiants to organ induction medium. While root initiation was accelerated and root number increased, bud induction was inhibited. An initial GA₃ treatment had a long-lasting effect on bud induction and the tissue recovered from inhibition only in the fifth subculture.

Chromosomal variability in callus culture ofAsparagus racemosus was comparatively higher in the presence of 2,4-D than of NAA. The frequency of polyploid cells was enhanced with the increase in the concentration of 2,4-D or with the addition of coconut water. Gradual polyploidization with increasing age of the callus has been recorded.

Endogenous concentrations of indol-3-ylacetic acid (IAA) in auxin-autotrophio crown gall tissue cultures are presented in relation to culture growth rate and to tissue IAA levels in auxin-dependent cultures maintained on IAA as auxin source. Cellular levels of synthetic auxins absorbed from culture media were monitored in auxin-dependent cell cultures exhibiting selectivity in growth response to exogenous auxins. The results are used in modelling culture growth patterns and changes in intracellular auxin content.

Germination and seedling growth of rice was studied in NaCl and PEG 6000 solutions having osmotic potentials -0.2, -0.4, -0.6 and -0.8 MPa.
At isoosmotic concentrations, the NaCl proved more harmful to germination, seedling growth, per cent moisture content of seedling organs as well as mobilization of food matter from seed to the growing seedlings. This fact suggested that in rice, at least in the early stage, a specific ion effect rather than osmotic effect is the prime cause of salt injury. Compared to susceptible cultivar, the tolerant one was less inhibited by salinity.

Treatment of etiolated and excisedCucurbita cotyledons with exogenous cytokinin (benzyladenine) in darkness or light results in a marked stimulation of Rubisco activity, content of enzyme protein, and incorporation of labelled precursors into it, indicating cytokinin-stimulatedde novo synthesis of the enzyme. Cell-free translations of RNA in the wheat germ andE. coli systems show an increase in both large and small subunit mRNA amounts relative to the increase of total RNA under the influence of the phytohormone and light. This increase in the level of translatable RNA is confirmed by RNA hybridization with the Rubisco large subunit gene of spinach. In addition, our results demonstrating additive effects of benzyladenine and light in cotyledon and chloroplast development suggest that the two factors co-act independently in the causal sequence of Rubisco gene expression. The data are discussed in a general view of cytokinin action in gene expression steps.

The auxin transport inhibitor TIBA strongly influences meristem structure and activity in the unistratose gemmaling ofRiella. The gradient of cell cycle duration, essential for normal morphogenesis, is abolished and the cell cycle is reversibly arrested during exposure to light. At the same time starch accumulation in the light is inhibited. Possibly, these effects are the consequencc of the inactivation of sulfhydryl-containing proteins by TIBA.

Leaf expiants from vegetative plants of the short-day plantStreptocarpus nobilis (C. B. Clarke) developed flower budsin vitro when cultured in 8 h photoperiods. Tn non-inductive photoperiods only vegetative buds were formed.In vitro photoinduction was demonstrated by giving the expiants short-day (SD) cycles and then transferring them to non-inductive photoperiods for expression of flowering. On medium containing 6-benzylaminopurine (BAP) organogenesis was initiated during the photoinductive treatments. Photoinduction of leaf tissue without adventitious bud development was obtained on medium without BAP. The photoinductive state of the leaf tissue was fairly stable, being expressed after 2-3 weeks in non-inductive photoperiods when adventitious buds were formed. The quantitativein vitro flowering response to the endogenous floral stimuli, resulting from photoinduction, could provide the basis of a bioassay for presumptive flower inducing chemicals.

A specific, high affinity, IAA binding site was demonstrated in both a cytosolic fraction, and in isolated nuclei, fromNicotiana tabacum cv. Wisconsin No. 38 cells grown in suspension culture. The amount of the binding site detected in both these fractions changed during the culture cycle according to a strict pattern. The molecular mass of the binding site was estimated by gel filtration to be approximately 175 000 and it appears to be a protein. When partially purified by affinity chromatography and allowed to pre-incubate with IAA, the site had a significant stimulatory effect on total RNA synthesis, as measured by a cell-free assay system. Unpurified extracts had no such effects. The system behaves rather like the steroid hormone-receptor system in animals.

A range of endogenous cytokinins have been identified inDatura crown-gall tissue by GC-MS. Incorporation of [³H]adenine into zeatin riboside, zeatin and its nucleotide(s) is also shown. Metabolism studies usingcis- andtrans-isomers of zeatin riboside indicate that interconversion of the two isomers does not occur in this tissue. Data on the identity of major endogenous cytokinins in a genetic tumour line of tobacco is also provided.

The influence of different organs on flowering of photoperiod- or temperature-dependent plants and of neutral plants is described. Special attention is given to the influence of roots which generally inhibit flowering. High or low temperatures applied to the roots ofChenopodium polyspermum, a quantitative short day plant, induce flowering. Vernalizing treatment of roots ofCichorium intybus suppresses the inhibition of flowering arising from the tissues immediately underlying the terminal bud. Other plants such as coniferous trees can flower more intensively if the growth of their roots is reduced. After a short presentation of the very complex situation concerning the regulation of floweringvia the presently known hormones, the methodological limitations of our understanding of the precise hormone mechanism of flowering will be discussed. One example of an immunologica 1 approach to localize endogenous hormones inside tissues is given, using abscisic acid.