Glucose, fructose, sucrose, maltose, and lactose stimulated photoheterotrophic growth ofNostoc linckia (Roth.)Born. as well as its heterocyst frequency, chlorophyll and protein contents, ammoniacal nitrogen uptake and nitrogenase activities. Glucose, fructose and sucrose also supported slow chemoheterotrophic growth. α-ketoglutarate, pyruvate, ribose, succinate, acetate, sorbose and formate were inhibitory.

The content of spinach-leaf cells was compartmented by differential centrifugation. Three fractions were obtained,i.e. chloroplasts, pellet of remaining organelles sedimenting at 97 000g and cytosol. Enzyme activities of L-tryptophan aminotransferase (TAT) as well as L-tryptophan dehydrogenase (TDH) were demonstrated in all cell fractions. The highest activities of both enzymes were found in the pellet of organelles followed by the enzyme activities in the chloroplasts. The cytosol had the lowest enzyme activities. Chloroplasts are characterized by a relatively higher TDH activity, organelles sedimenting at 97 000g were marked by a relatively higher TAT activity. In all fractions both pyridine nucleotide coenzymes catalyzed the TDH activity. Ca²⁺ in a concentration of 0.8 minol l^-1 increased markedly the TDH activity in both directions of its activity.

The mechanisms by which exogenously applied plant growth regulators act to express those genes that are selectively involved in cell and tissue differentiation are not at all well comprehended. However, the ontogenetic sequences of events that enable receptor or target cells to be activated and to undergo dedifferentiation and redifferentiation, can often be followed experimentally and can lead to a better understanding of the causal relations and control mechanisms in coordinated cell growth and development.
Cytokinins, applied either in an agar medium or as high-concentration, short-duration pulses to expiants or as high-concentration, intermittent sprays to intact plants, induce switches in the normal developmental pattern of cells of certain explanted tissues. Examples of cells that are particularly receptive are the subsidiary cells of stomatal complexes and the differentiating cells of very young presumptive leaf primordia, that is before the latter have become irreversibly determined as leaves.

Several examples of transmission of rapid signals within plants are described. Most of these signals may be inhibited by pretreating plants with LiCl, with inhibitors of ionic permeability, or with substances interfering with Ca²⁺. Accordingly, they are dependent on ionic changes. LiCl also prevents or delays the onset of flowering in long-day plants. In addition isolated organs or tissues most often do not react to an external stimulus as do similar organs or tissues within an intact plant. All these facts lead to the conclusion that plants are highly integrated organisms. Any change in the ionic equilibrium occurring in one part of these organisms has rapid consequences in other parts. This hypothesis may be applied to the floral process: after perception of the appropriate environmental conditions, the leaves modify the orientation of meristem differentiation by promoting the redistribution of ions (especially Ca²⁺, which has a "second messenger" function).

Flower bud formation was studied in thin-layer tissue expiants of epidermis plus subepidermal cortex from the inflorescence ramifications ofNicotiana tabacum cv. Samsun. With appropriate hormone concentrations of BA and NAA expiants from flowerv and fruitbearing stalks regenerate flower buds only, while those from the internodes of the inflorescence ramifications produce generative as well as vegetative buds. In both types of expiants the number of buds formed depend mainly on the hormone concentrations but, in addition, the age of stalks and internodes from which expiants are taken also affects bud formation. Both ABA and JA inhibit flower bud formation in expiants of flower stalks. JA was shown to particularly inhibit bud initiation.

6-benzylaminopurine (BAP), β-indolylbutyric acid (IBA), phenylacetic acid (PAA) and a triazine herbicide (TH) affected the development of vascular bundles both in coleoptiles and the last intemodium below the ear of wheat plants. These substances were applied before the conductive tissues in the organs investigated were fully differentiated, the degree of their effect being dependent not only on the concentration, but also on the developmental stage of the plants and on cultivation conditions. In coleoptiles the area of vascular bundles was increased especially in the dark. In the stalk, BAP, PAA, IBA and IBA + TH increased the area of phloem. BAP also stimulated the activity of parenchymatous cells of xylem. TH had the same effect only on xylem, which became evident by an increase in vascular bundle area, but not in that of phloem. These anatomical aberrations were confirmed by cytological analysis which revealed that the stimulatory effect of the substances investigated consisted in activation both of companion cells of phloem and parenchymatous cells of xylem, whose function is analogous. As a result, both types of cells contained numerous organelles characteristic of meristematic cells, which suggests protein synthesis and an active transport of substances.

The radiotracer technique is described for transport and metabolic studies in latex producing bark. This technique provided further evidence that carbohydrates are supplied to latex vessels as sucrose and that sucrose is readily used for rubber synthesis. Bark treatment with ethylene resulting in latex flow stimulation is shown to activate within a few hours sucrose and water transport into the latex vessels. The available knowledge suggests an implication of an energy-dependent process of proton excretion which could explain the earlier observed ethylene induced alkalization of latex cytosol enhancing invertase and sucrose utilization.
An increase of tapping intensity decreases the level of latex sucrose and changes its distribution pattern in drained bark. There is a clonal difference in the early response to exploitation. Bark excision by conventional tapping inhibits downward sucrose translocation, the inhibition being proportional to the surface of consumed bark above the tapping cut. Seasonal variation in the level of latex sucrose is related to variations in sunshine duration and sucrose concentration rises during the process of refoliation. The results stress the importance of sucrose supply to latex vessels for latex producing potentialities and indicate an association of low sucrose availability in latex vessels with premature latex vessel degeneration and bark dryness.

Lemna gibba G3 is an ideal system for studying the chemical control of flowering in a photoperiodic plant due to its small size and aquatic growth habit which allow substances to be taken up continuously and rapidly distributed throughout the plant. Each of the known plant growth regulators has been tested onL. gibba G3 and only the gibberellins appear to be important for flowering, although they are not the limiting factor for flowering on short days. Salicylic acid (SA) and ferricyanide will both induce flowering inL. gibba G3 with ferricyanide being most effective on short days where flowering is daylength limited and SA most effective where flowering is limited by factors other than daylength. The ferricyanide action is probably due to HCN and it may act during photoperception or photoinduction. SA is most effective when reversing the inhibition caused by various parameters including copper and agar, and its effect is always strongly daylength dependent. It is postulated that SA may interact with the flowering stimulus to promote flowering and thus that SA acts at some point following photoinduction and the formation of the flowering stimulus.

Agrobacterium tumefaciens C58M (a nopaline strain) was used for induction of crown gall tumors inCentaurium umbellatum Gilib. The formation of tumors is very rare. After elimination of bacteria the tumor tissues grow in the light on R3B medium without growth regulators. They are positive in nopaline synthase.

An improved system of plant cultivation at stable and specific levels of polyethyleneglycol (PEG, mol. mass 1400-1600) - induced water stress has been described. To set up this system a perforated tubular glass vessel containing soil to support seedling growth was wrapped externally first with a layer of macroporous silica gel-G and then with three layers of a dialysis membrane of a lower exclusion limit (2000 mol. mass). Effects of 8 days of PEG - induced stress have been studied on uptake and translocation of N and P and growth of barley (Hordeum vulgare L. cv. KN 16) seedlings. Some of the noteworthy improvements of the system were exelusion of PEG from the plant consequent upon use of silica gel-membrane combination, shorter time (2 days) for the soil-plant-air continuum to attain steady state, and stability of the plant water potential over a period of a few days.

The addition of Na₂EDTA to a minimal medium (agar, sucrose) deprived of cations produces no morphoregulatory effect. This effect is induced only by the addition of iron. Traces of iron present in the agar are sufficient for the development of globular embryoid into a complete plant. The traces of iron in distilled water and sucrose (p. a.) are insufficient for the morphoregulation. The marked difference between the necessary limiting amount of chelate and necessary limiting amount of iron in non-modified media is explained by the presence of other cations, which saturate and thereby inactivate a greater part of Na₂EDTA. It is recommended to decrease the amount of iron and leave the commonly used amount of chelate in the prepared media. Simultaneously with optimal morphoregulatory effect in androgenesis and somatic embryogenesis, vitality of tissue culture will be lengthened and ageing as well as necrosis of the cultures be decreased.

This paper deals with some morphological and histological changes observed during regular intervals inMatricaria inodora L. tissue cultures derived from leaf expiants. The expiants were cultivated on Murashige-Skoog's culture medium supplemented with 1.0 mg 1^-1 2,4-dichlorophenoxyacetic acid. The callus formation started about a week after isolation. During the second week the meristematic centers were differentiated from which root and shoot apices were later formed. During long term cultivation under the same culture conditions the inhibition of development of shoot apices took place. Only roots of unorganized growth have been regenerated. The influence of culture conditions on morphogenetic potential is discussed.

Water-stress for 10d at different developmental stages, affected relative water content and leaf water potential of plants. Subsequent rewatering removed these effects. Water stress lowered the contents of chlorophyll, protein, RNA and the activity of catalase, while it increased free proline accumulation and activities of protease, RNase and peroxidase. An overall improvement in biochemical parameters was achieved as soon as the stress was withdrawn by watering and this was reflected in subsequent developmental stages. Water-stress at the reproductive stages induced similar changes as in the vegetative stage but the removal of stress could not improve these parameters to the same extent as at the vegetative stage. In consequence, stress applied at the vegetative stage augmented yield parameters but when applied at the reproductive stage it significantly reduced the yield.

Growth, dark transpiration rate (DTR) as well as water saturation deficit (WSD) of 30 single plants of 8 alfalfa genotypes growing in experimental field of 50 × 10 cm spacing, in four cuts at early bud stage, were studied. The growth and WSD of genotypes examined were significantly different, the differences in DTR were not significant. The growth of alfalfa plants was in negative correlation with both DTR which reflects non-effective water loss and WSD. Significant negative correlation established between plant growth and its variability shows that fodder productivity in alfalfa genotypes was dependent on growth variability of individual plants. Positive correlations established between WSD or DTR and the growth variability show some of the causes of growth variability.

Influence of high intensive flashes on the yield of free radicals in intact seeds and excised embryonic axis, endosperm, and seed coat, and its resulting effect on seedling growth, total biomass production and phosphorus metabolism in wheat (Triticum aeativum), vetch (Vicia sativa L.) and onion (Allium cepa L.) was studied. Free radicals (f.r.) were formed mainly in seed coat and not in the endosperm. Vetch seeds after irradiation had 20.76 X 10¹³ f.r. g^-1 dry intact seed and 17.30 X 10¹³ f.r. g^-1 dry seed coat. Excised seed coats exposed to irradiation also yielded 17.28 × 10¹³ f.r. g^-1 dry matter. High irradiance "white light" flashes induced more f.r. than a monochromatic one of the same photon content. Red (650 nm), farred (750 nm) and even infra-red (1100 nm) radiation did not initiated f.r. formation but resulted in their decay in samples irradiated earlier by "white", blue and green parts of the spectrum. Blue irradiation of seeds led to the decrease in the length of shoots and roots in comparison to "white", green and red irradiation but their biomass increased faster than in the seedlings obtained from non-irradiated or irradiated with "white" and green radiation. The quantity of total acid soluble phosphorus followed a sequence with respect to wavelength of radiation: 436 nm > 650 nm> > 540 nm > non-irradiated > 300-800 nm. Quantity of inorganic phosphorus remained unaffected by different spectral character of radiation. The quantity of organic acid soluble nucleic phosphorus and acid insoluble polyphosphates was higher in samples irradiated with red beams (650 ± 6 nm).

There was a slow and gradual rise in the deoxyribonucleolytic activity of both excised and attached first leaf of ragi (Eleusine coracana Gaertn. cv. PR 202) during senescence. The decline in DNA content is correlated with the rise in deoxyribonucleolytic activity; but both DNA and deoxyribonucleolytic enzyme were photo-insensitive and did not respond to the application of senescence retardants - benzimidazole and gibberellic acid. Increase in deoxyribonucleolytic activity in excised leaves was not affected by actinomycin D; it was, however, wholly or partially prevented by cycloheximide. The effect of the translation inhibitor depended on the time of application. The enzyme activity seems to have no specific relation with the process of senescence.

The contents of reducing sugars, proteins and ascorbic acid and the activities of protease, peroxidase, catalase, indole acetic acid oxidase, ascorbic acid oxidase, succinic dehydrogenase and the rate of respiration were investigated in regenerating and non-regenerating parts ofClerodendrum viscosum Vent. root cuttings. All the above variables have registered higher in the regenerating parts, particularly at the distal end where roots appear, than in the non-regenerating parts of root cuttings. The contents of metabolites and the activities of enzymes in the presence of endogenous cytokinins at the proximal end and auxins at the distal end, were compared and discussed in relation to the initiation of shoots and roots at two ends of root cuttings. In general it was concluded that interacting hormonal and nutritional factors must be appropriate to initiate shoots or roots in the root cuttings.

Contents of individual carotenoids in the fruits of Ramillete cultivar ofCapsicum annuum L. changed during ripening of recently harvested fruits or fruits stored 15 d in a dark and cool room. β-carotene and β-cryptoxanthin contents rose to a maximum and then declined, while the contents of other earotenoids rose to a rather steady level. Capsanthin was the main carotenoid which together with capsorubin were responsihle for the ripening colour.

The sensitivity of stomata to water stress increased during ontogeny of primary bean leaves growing under constant environmental conditions: the decrease in both adaxial and abaxial epidermal conductances was induced by slightly more negative values of leaf water potential in young than in mature and especially old leaves. However, these differences were less expressive than the differences mentioned in the literature for leaves of different insertion level, where adaptations to microclimatic conditions in different canopy layers in addition to ontogeny may occur.

During high altitude acclimatization the highest number of amino acids were found in temperateArtemisia species (A. vestita) and the lowest one in tropical species (A. scoparia). The amount of free amino acids in temperateArtemisia species was higher when this was grown at 3600 m altitude. InA. scoparia, A. vulnaris andA. parviflora, the higher amount of individual amino acids was ascertained in plants grown at lower altitudes.
InA. vestita, the nitrogen contents per unit dry matter was lower in plants grown at high altitude. In the other three species, the contents were significantly higher in the leaves of plants grown at a higher altitude. The nitrogen contents per unit leaf dry matter determined during active growth of plants were minimum inA. parviflora and maximum inA. vestita. With progressing plant senescence the concentration of nitrogen decreased in all species studied.

Sugar-beet invertase preparation was found to be highly temperature-dependent in its activity (T_opt = 40 °C), to be decreased by bivalent metal salts (especially CaCl₂ and MgCl₂ and relatively unaffected by heavy metal cations from the end of the periodic table. Inhibitors of SH groups, such as iodoacetamide andp-chloromercuribenzoate, were highly inhibitory while ouabain was a medium-strength inhibitor, with 2,4-dinitrophenol having no effect. The intracellular pH of 7.3, corresponding to the optimum for invertase (at 7.2) could be substantially decreased (to 5.8) by exposure of cells of whole sugar-beet roots to carbon dioxide in aqueous solution.

Long-term effects of glycinebetaine on water use efficiency (WUE), dry matter production and net photosynthetic rate have been studied. Applied glycinebetaine enhanced the WUE and the grain yield of wheat.

The rates of maintenance and growth components of leaf dark respiration of a C₃ plant (Phaseolus vulgaris L.) and C₄ plant (Zea mays L.) as affected by temperature were studied using the McCree concept. Respiration rates were measured by means of infrared gas analysis in a closed gas exchange system. In both C₃ and C₄ species R_D and R_m increased with temperature in the temperature range (15-62 °C) studied. R_G depended on temperature with an optimum near the temperature optimum of gross photosynthetic rate, P_g. Significant correlation between R_D and R_M and between R_G and P_G was found.