Influx and efflux of inorganic phosphate was determined in freshly cut and "aged" slices of sweet potato tubers, in the presence or absence of abscisic acid. Slices aged in the phytohormone took up considerably less phosphate than did the control slices. No difference in the rates of uptake of phosphate by the fresh tissue was observed. Kinetics of uptake of the aged untreated slices, proved to be bi-phasic. This was not the case for the treated slices. Neither the treated nor the untreated uptake curves for the fresh slices were bi-phasic. Efflux of phosphate from the slices aged in abscisic acid was greater than from the untreated slices. The results strongly suggest an effect of abscisic acid on the cell membrane.

Regeneration abilities of buds on shoot segment explants isolated from adult trees of oak (Quercus robur), aspen (Populus tremula), black locust (Robinia pseudacacia), Japan pagoda tree (Sophora japonica), and English walnut (Ailanthus glandulosa) were studied during the growing season. Optimum BAP concentrations for the regeneration of oak bud meristems were dependent on the date of sampling. Axillary shoots could be induced from winter and summer buds of oak and aspen on Dustan and Short media supplemented with activated charcoal and BAP at concentrations from 0.5 to 2 mg 1^-1. More intensive rooting of segments of newly formed shoots was observed on MS medium diluted to one half and supplemented with 2 % sucrose and 0.2 mg 1^-1 of IBA.Populus tremula formed longer axillary shoots on DS media supplemented with 0.5 mg 1^-1 of BAP and 1 mg 1^-1 of GA₃.
Regeneration capacities of black locust, Japan pagoda tree, and English walnut were higher. In addition to the induction of multiple shoots from buds, shoots could also be obtained from calluses formed on basal segment parts. Asparagine and glutamine at a concentration of 25 mg 1^-1 stimulated the percentage of differentiated stems on callus surface. Inhibitory effects of substances which accumulated in buds in the second half of the growing season could be reduced by means of pulse treatments in 50 mg 1^-1 BAP solutions or using short-term dipping into 0.1 % AgNO₃ solution.

Organogenic callus cultures ofPapaver somniferum L. were studied with the aim of describing the morphology of the callus and observing the changes occurring during differentiation and induction of organogenesis. The morphology of the cells and the formation of meristemoid areas were studied on a light microscopic level. Histological evidence showed that from the inner meristematic centres, protracheal elements are differentiated, from the surface meristematic centres meristemoids are formed and therefrom green leaf-like organoids.

Actinomycetes were isolated from the upper 1 - 3 cm of the soil layer in a well-developed forest and in an adjacent clearcut area where Douglas-fir [Pseudotsuga menziesii (MIRB.) Franco] regeneration had been impaired for two decades. The population density in the clearcut area was two times as high as that in the forested area. The percentage of actinomycetes that inhibited seed germination of the test plants was significantly higher in isolates obtained from the clearcut area than in those obtained from the forested area, and isolates from the clearcut showed five times the phytotoxic effect of those from the forest. Some actinomycete isolates, 4 % from the clearcut and 2.6 % from the forest, significantly reduced in vitro growth of two common ectomycorrhizal fungi of Douglas-fir,Laccaria laccata andHebeloma ovstuliniforme. Two actinomycete isolates from the clearcut reduced fungal growth by 40 % and 73 %. Reduction of the nutrient in the growth medium did not affect the antifungal activity of the actinomycetes. The data support the idea that, along with other factors, phytotoxic and antifungal actinomycetes may suppress natural regeneration or establishment of planted seedlings - either directly or. indirectly - through inhibition of seed germination or of mycorrhizal fungi.

In the long-term cultivated callus cultures ofMatricaria recutita L. the identical concentration changes in the biosynthesis of glutathione, glutamate, aspartate, total thiols and proteins were detected within the subculture. The level of oxidized glutathione during the growth of callus culture was low with the highest value 10.66 nmol g^-1 on the 13th day of subculture. The ratio GSH/GSSG which significantly influences the redox processes in a cell, and the activity of glutathione reductase increased from the 8th day. Ascorbate formation was detected on the 17th day, although no relation between the ascorbate synthesis and the concentration of glutathione and glutathione reductase was found.

Continuous treatment with spermidine or 1-aminocyclopropane-1-carboxylic acid stimulated ethylene production and ethylene-forming enzyme activity and accelerated chlorophyll breakdown in detached tobacco leaves. The treatments also induced the production of eleven major acidic pathogenesis-related proteins, which were also produced during the hypersensitive reaction to tobacco necrosis virus. A delay between the onset of the stimulated ethylene increase and the detection of PR-proteins was found; ethylene production was stimulated after a few hours of treatment, whereas one, three and all the eleven PR-proteins were detected by polyacrylamide gel electrophoresis of fluid extracts after 2, 4 and 6 days of treatments, respectively. The possible causal relationship between stimulation of ethylene production and PR-protein accumulation is discussed.

The growth of primordia of marginal buds (marginals) which differentiate on leaf margins is correlatively inhibited on intactBryophyllum crenatum plants. Following leaf isolation, the marginals are released from this correlative inhibition, which process is accompanied within 2 to 10 h after leaf isolation with a decrease in the content of endogenous IAA in the leaf blade. This decrease can be enhanced by transversal cutting of the leaf blade into three parts which also results in enhanced subsequent growth of the marginals. The growth which follows after the release of the marginals from correlative inhibition is accompanied in cut leaf blades with an increased content of endogenous IAA in the period from 12 h to 7 d after leaf isolation when compared with uncut leaf blades. The highest content of endogenous IAA was recorded in the middle section, and the lowest IAA content in the basal section of the leaf blade.

Allelopathic interactions between plants and other organisms have been recognized by scientists worldwide because they offer alternative uses in agriculture, such as decreasing our reliance on synthetic herbicides, insecticides, and nematicides for disease and insect control. The recognition of the role that allelopathy can have in producing optimum crop yields is of fundamental importance. Despite much optimism and some progress in unravelling the complexities of biochemical interactions between species, a firm foundation for the scientific rationale of the existence and function of the allelopathic phenomenon has not been developed. Allelopathic chemicals are primarily secondary products of plant metabolism which have been an enigma to plant scientists; however, they undergo a variety of reactions with plant, insect and animal species that inhibit or stimulate their growth and development. Examples of some allelochemicals and their basis of molecular and biological action are shown: interaction between the unicorn plant (Proboscidea louisianica L.) and cotton (Gossypium hirsutum L.); diterpenoid alkaloids (fromDelphinium ajacis L.) as allelochemicals; substances that occur in wheat (Tritcum aestivum) and wheat soil that cause autotoxic effects; alfalfa (Medicago sativa L.) root saponins as allelochemicals; humic acids from wheat soil as allelochemicals; and structure-function of flavonols serving as allelochemicals in chloroplast-mediated electron transport and phosphorylation. This paper concludes with a discussion of some frontier areas of research in allelopathy.

Lead was detected and located in definite regions of thePopulus adventitious roots with the light microscope. Incubations of 24, 48, and 72 h in solutions of Pb(NO₃)₂ resulted in clear sequences of microscopic images. Interpretation of these images allows the construction of a scheme for lead transport pathways in roots.

Changes in macromolecule syntheses, especially RNA synthesis, and the energy providing system were investigated in seeds ofAgrostemma githago aged for different periods. In embryos of aged seeds all macromolecule syntheses start later and reach a lower level than young ones. It was found that the synthesis of rRNA in embryos of aged seeds is reduced whereas the synthesis of poly (A⁺) RNA in relation to the total RNA synthesis is highly increased as well as the amount of this RNA species with long poly (A) chains. The results are discussed in connection with the decreased protein synthesis and the reduced ATP content and ATP formation ability in embryos during the long time storage of seeds.

The inheritance of the gliadin spectra in F₂ hybrids between cultivars hexaploid wheat Bezostaya 1 and Bisel has been investigated. The results from the electrophoretic examination and analysis of the gliadin spectra reveal that the components 1,2,3,11 and 15 from the Bezostaya 1 spectrum and 1,2, 3, 7,11 and 15 from the Bisel spectrum are controlled by allelic variants of one gliadin coding locus in 1D chromosome.

Protein complex patterns of cloves and esterase isoenzyme patterns of apical buds of cloves were studied with Czechoslovak virus-free cultivars ofAllium sativum L. and the wild speciesA. longicuspis Regel, Similarly, four clones-regenerants obtained using explant culture techniques from A.sativum L. cv. Bzenecký paličák (two somaclones and two clones derived from plants regenerated from meristem cultures treatedin vitro with colchicine) differing in their ploidy, morphology, and yields were studied. Immunophoreograms of protein complexes of theA. sativum L. cultivars under investigation differed from one another in the number and mobility of protein fractions in both the cathodic and anodic regions and thus these cultivars can be distinguished. On the basis of esterase isoenzyme patterns, the Czechoslovak cultivars of A. sativum L. can be arranged into three groups - bolting winter cultivars with broad leaves, non-bolting winter cultivars with broad leaves, and non-bolting spring cultivars with narrow leaves. All the clones-regenerants showed the same protein complex and esterase isoenzyme patterns as their original cultivar.A. longicuspis Regel markedly differed in its protein complex and esterase isoenzyme patterns from all the other genotypes studied.Received May 17, 1989: accepted January 5,1990

Embryogenic callus which has maintained its embryogenic ability on media without growth regulators for three years has been induced at the base of shoots of a genotype with CMS propagated for a long timein vitro by transferring the shoots onto media richer in inorganic and organic components. The effect of two basal media (MS and PG₀) on the intensity and completeness of the proliferation of somatic embryos was examined with different combinations of growth regulators. Pollen fertility was evaluated in 87 plants regenerated from somatic embryos. Cytoplasmic male sterility was conserved in all of them.

Phenolic content and IAA-oxidase (IAA-o) activity have been assayed in cells and medium of tobacco crown gall suspension culture in several stages of culture cycle. The highest content of total phenolics in the cells were found prior to cell division and in the middle stage of intensive growth. The beginning of intensive growth is accompanied by temporary reduction in phenolic level in the cells as well as their intensive secretion to the medium. In the second part of the culture cycle, when the phenolic production was weaker, the majority of these compounds were maintained in the cells.
The highest activity of IAA-o in the cells was detected in the middle stage of intensive growth, simultaneously with high phenolic content; following it a considerable decrease of IAA-o activity is correlated with maximum of chlorogenic acid (ChA) content (at reduced amount of total phenolics). IAA-o activity increased again at the end of the stage of intensive growth when the level of phenolics was low including ChA. These data suggest that IAA-o in relation to phenolic level determines cell growth in the culture.
In the culture medium - fairly distinct negative correlation between IAA-o activity and phenolic content suggests that the latter participates in enzyme activity regulation. During intensive growth IAA-o activity is strongly inhibited.
The results prove that phenolic level. IAA-o activity and auxin level are closely correlated and may constitute essential elements of a mechanism of regulation crown gall cell growth in culture.

A simple equipment was developed to cultivate young cereal plants under enhanced CO₂ concentration. Cultivation system permits growing of about 40 barley seedlings for about 2 to 3 weeks. The system consists of two identical growth chambers (volume about 30 dm³), gas conditioning circuit and measuring circuit with an infra-red CO₂ analyser. Capabilities of the whole equipment were tested by growing barley plants under 330 and 1000 cm³ (CO₂)m^-3 and in combination with high or low nitrate level.

Haploid tobacco plants (cv. Samsun) form inflorescences with a larger number of flowers than diploid plants. Leaves of haploid plants were shown to have lower free IAA level (by 40 %), higher peroxidase (by 160 %) and IAA-oxidase (by 70 %) activities and produce less ethylene (by 25 %) than leaves of corresponding diploid plants. The increase of peroxidase activity in haploids was due to the increase in the activity of the cathodic isozyme which is known to have high IAA-oxidase activity. It is proposed that higher peroxidase/IAA-oxidase activity in haploid plants may take part in IAA catabolism, at least duringin vitro culture of haploid explants. Lowered IAA level and ethylene production may then be directly correlated with a larger number of flower buds; as a higher IAA level is generally considered to act as a background inhibitor of flowering.

Chlorophyll deficient plantlets were obtained after the treatment of sugar cane callus cells with 3-azido-l,2-propanediol (AG) and sodium azide with approximately the same frequency. Both mutagenic agents postponed the regeneration of plantlets from calli, the total number of regenerated plantlets following the AG treatment being, however, higher than after the sodium azide treatment and control.

Evidence for the existence of a neutral inhibitor specific for auxin has been in the literature for 45 years. The inhibitor is demonstrable by its effect in causing positive curvature of theAvena coleoptile. The growth of the mesocotyl of oat and corn seedlings in darkness and its inhibition by light are determined by the neutral inhibitor as is the phototropic response of the sunflower stem. Production of the inhibitor is promoted by red and fluorescent light. Irradiance at 730 nm promotes auxin production while irradiance at 660 nm promotes production of the inhibitor. The positive curvature induced by 2,3,5-triiodobenzoic acid can be used to quantify the neutral inhibitor. Since the benzoic acid is more effective than iodoacetate in reacting with the sulfhydryl of cysteine, a sulfhydryl group is indicated to bo one reaction site for auxin and to be the basis of polar transport.

In pea, maize and tomato plants a hitherto undescribed L-tryptophan dehydrogenase activity (TDH) has been detected. This enzyme catalyzes the reversible formation of indolepyruvic acid (IPyA) from L-tryptophan (L-trp). TDH and L-glutamate dehydrogenase (GDH), related enzymes in their mode of action, could be separated by gel chromatography. Enzymatic activity of TDH was sustained by both pyridine coenzymes NAD/NADP. With pea TDH the coenzyme NAD displays, at optimum pH 8.5 and at room temperature, only about 40-70 % of the activity of NADP. The amination of IPyA is catalysed more actively than the deamination of L-trp. L-trp/IPyA, L-glu/ketoglutarate, L-ala/pyruvate reacted as dehydrogenase substrates; L-phe/ phenylpyruvate, D-trp and D-phe did not react with pea enzyme extracts. A considerable similarity between the active centres of TDH and GDH has been found using inhibitors: absence of heavy metals, presence of a carbonyl group, indispensibility of bivalent ions for the enzyme activity. Pea TDH and GDH were distinctly inhibited by sodium azide. For the activity of TDH the presence of SH groups is less important than for GDH. The TDH activity in the investigated plants was lower than the GDH activity. The possible role of TDH in the regulation of the IPyA pool is discussed.Doc. RNDr. PhMr. M. Kutáček died on 28 November, 1989. The final form for print was prepared by dr. Ivana Machdckovd of the same Institute, who will also answer the reprint requests. Received June 6, 1990; accepted October 10, 1990

Effects of 2,3,5-triiodobenzoic acid (TIBA) and age of etiolated pea epicotyl segments on the indol-3-ylacetic acid (IAA) stimulated transport of¹⁴C-abscisic acid (ABA) was studied. In spite of a slight decrease of IAA transport after the application of TIBA, the IAA stimulation of¹⁴C-ABA transport did not change. In segments excised from epicotyls of different age,³H-IAA transport was identical and the induction of prolongation growth by IAA in segments from the upper part of the epicotyl was observed. The IAA ap{ie226-01}ation to the growing segments was connected with intensive attraction of¹⁴C-ABA to the site {ie226-02}AA application, while the application of IAA to the older segments was growth ineffective ana no stimulation of¹⁴C-ABA transport by IAA was observed.

Subeellular localization of the enzymes which phosphorylate hexoses was studied in photosynthesizing tobacco leaves by means of differential centrifugation and centrifugation in sucrose gradient. More than 80 % of the total hexokinase activity of leaf tissues were found to be associated with the particulate fraction of mitochondria; however, the ratio of the particulate hexokinase fraction to the soluble fraction was influenced by the extraction medium applied. The particulate hexokinases showed a high affinity to glucose (Km = 26.8 μM) and a relatively low affinity to fructose (Km = 17.6 mM). They had a broad pH optimum, because 81 % of the phosphorylating activity obtained for glucose and 75 % of the activity obtained for fructose occurred in pH range from 7.9 to 9.1 (Tris-HCl buffer). The hexokinases were Mg2+ dependent with the highest activity occurring at equimolar Mg2+ and ATP concentrations. Their activity was enhanced by KC1, NaCl, and (NH4)2SO4 at 30 to 120 mM concentrations.