The bean first internode bioassay ofMeudt andBennett (Physiol. Plant.44: 422-428, 1978) is based on the curvature of bean internode sections after unilateral application of test material near to their base. The test was also used for estimation of biological activity of brassinosteroids which enhance the effect of auxin. Sensitivity of the assay to both IAA and 24-epibrassinolide was increased 1000 and 100 times, respectively, when internode sections were incubated in morphologically inversed position. Under these conditions test material was applied to the young auxin-sensitive morphologically apical internode tissues and auxin was basipetally translocated to the zone of curvature. Using this bioassay as little as 10 fmol of IAA and 1 pmol of 24-epibrassinolide can be estimated.

Pharbitis nil, strain Kidachi and Violet, were grown at 20° C under continuous light in various cases of different sizes, containing the nutrient solution or tap water. Kidachi initiated flowers when seedlings were cultured in small cases containing nutrient solution but did not flower in large cases. The application of NAA, kinetin, ABA or 5-chlorobenzoiec acidvia roots in large cases caused flowering, Floral initiation was always accompanied by the suppression of root elongation. The promotion of root elongation by aeration inhibited flowering. Root cutting inhibited flowering. On the other hand, Kidachi did not flower in tap water irrespective of vessel size. Violet did not flower in the nutrient solution even in small vessels, but initiated floral buds in tap water irrespective of vessel size, though the plants grown in large cases developed very long roots. In both types of flowering, cotyledons are necessary to induce flowering and the removal of cotyledons before the 16th day after the start of culture in Kidachi and before the 12th day in Violet completely inhibited flowering. GA₃ promoted stem elongation without preventing flowering of Kidachi.

Black currant reversion disease causes serious problems in some cultivars of black and red currant. Investigating ultrathin sections prepared from overground parts of diseased red currant plants cv. Heinemann's rote spätlesse, we observed consistently local cell wall disintegration of tracheids in vascular bundles. We have observed these changes in red currant plants showing reversion symptoms during the vegetation period from March to June. The observed phenomenoni.e. cell wall disintegration of tracheids might be utilized as an auxiliary diagnostic criterion m ident ification of red currant reversion disease in the cultivar Heinemann.

In five-day-old etiolated pea seedlings an increase in IAA content and in L-tryptophan aminotransferase (TAT) and L-tryptophan dehydrogenase (TDH) activities in the apical part of the epicotyl was found 12 h after root excision, which was followed by a decrease up to 48 h. In ten-day-old seedlings a continuous decrease in IAA, TAT and TDH levels in the apical part of the epicotyl was recorded up to 48 h after root excision. This indicates a growth-correlative effect of the root becoming evident in dependence on plant ontogenesis in changes of IAA content and activities of the above enzymes catalysing IAA synthesis.

The work concerns the senescence of isolated young leaves of oats (Avena sativa) floated on water or solutions. Senescence is rapid in darkness but slow in white light; the effect of light is not due to photosynthesis, but is paralleled by stomatal opening. Closure of the stomata by osmotic or chemical means makes senescence in light proceed as fast as in darkness, while opening the stomata in darkness by cytokinins, fusicoccin,etc., delays senescence to rates typical of light. The osmotic closure in light is mediated by abscisic acid, and since this also accumulates in darkness it appears as a major factor controlling senescence. Efflux of ions into the solution; indicating increased permeability, occurs almost in parallel with senescence. Senescence in light is accelerated by 1-aminocyclopropane-l-carboxylic acid (ACC) and inhibited by cobalt, silver or aminoethoxyvinyl glycine (AVG) which interfere with ethylene production or action; however, ethylene's role is unclear because some reagents, including kinetin, that delay senescence, actually increase ethylene production. At the endogenous level, therefore, ethylene may not be a limiting factor. Finally, a new ethylene-generating system is described in which the dehydrogenation of linoleic acid is coupled through manganese to the oxidation of ACC; it is probably activein vivo.

Evidence is presented to support the generalization that gibberellin A₁ is the main 'gibberellin hormone' that is activeper se in the control of elongation growth in higher plants. The evidence is based on a combination of chemical and genetic studies using single gene mutants of maize, pea and rice.

Two selected strains ofSilene armeria L. were used: S_1-2 (GA-line, not induced to flowering by GA₃ in SD of 8 h) and S_2-1 (GA+ line which reacts to GA₃ with flowering in non-inductive photoperiod). Moreover S_1-2 and S_2-1 differ in their critical daylength 14.5 and 8.0 h, respectively. Changes in the mitotic index and DNA content of cells in the various zones of the apical meristem during GA₃ treatment were described. At the start of the experiment, the functioning of the apex was characterized by a predominance of G₁ phase in the two strains. Therefore S_2-1 differed by a higher mitotic activity specially in the central zone. In S_1-2, GA₃ acted mainly on the rib-meristem cells, which resulted in stem elongation. Lack of response in the cells of the central zone explains why GA₃ fails to induce flowering in this strain. In S_2-1, GA₃ acted mainly on the central zone where a gradual increase in mitotic acitivity and in the percentages of nuclei at the (S + G₂) level was recorded. This stimulation brought the meristems into the prefloral stage. The differences between the two strains are discussed according to the status of control meristems. The reactions induced by GA₃ were compared with the pattern of changes during induction, in LD.

The inhibitor of microsomal monooxygenase activities 9-hydroxyellipticine markedly inhibited the frequency of embryonic and chlorophyll mutations induced by the metabolism-requiring mutagen dimethylnitrosamine (DMN) in a higher plantArabidopsis thaliana, but had no effect on the frequency of mutations induced by the direct-acting mutagen N-methyl-N-nitrosourea (MNU). The presence of thiol containing compounds thiourea and cysteine before and during DMN or MNU treatment resulted in a decline of mutation frequency as compared to treatment with either nitroso compound alone. In contrast, the mutagenicity of DMN and. MNU was not altered in the presence of two other thiol compounds, thiouracil and glutathion and by six naturally occurring phenolic acids: ellagic. vanillic, cinnamic, coumaric, caffeic and ferulic acids.

IAA synthesis proceeding by indol-3-ylpyruvate (IPyA) pathway seems to be regulated in two steps. In the first the L-trp conversion into IPyA is reduced by a low affinity of L-trp to the unspecific aminotransferase, by competition of L-trp with some aminoacids (e.g. L-asp) and indoles (e.g. indol-3-ylacetylaspartate). Simultaneously, a specific L-trp-dehydrogenase in dependence on the NAD(P)/NAD(P)H ratio regulates by its reversible effect the level of IPyA, connecting photosynthesis with growth. A second more "delicate" regulation of IAA level is carried out by the indol-3-ylacetaldehyde system. In pea plants two indol-3-ylacetaldehyde oxidases with pH optima 4.5 and 7.0 were found. The oxidases are differentially inhibited by an excess of IAA, different indoles as indol-3-ylacetylaspartate and aminoacids as L-asp. GA₃ and kinetin stimulate the conversion of indol-3-ylacetaldehyde to IAA.

The possibility that some of the variation in callus cultures involves epigenetic changes is examined in cultures established from the hypoootyls and roots ofEuphorbia heterophylla. It is shown that the responses of the cultures are affected by the light regimes under which they are grown and that in the dark and under short photoperiods, there are differences between the two types of culture with respect to pigmentation, auxin requirement, capacity to regenerate buds and roots and in certain isozyme patterns, whereas the two cultures are similar from the first passage under continuous light. However, these differences are only maintained for 2-3 passages, after which the root callus becomes similar to the hypoc otyl callus. Evidence is presented that these differences between cultures are epigenetic. Callus cultures established from the apical meristems of shoots and roots ofE. hetero phylla show similar differences to those observed between hypocotyl and root cultures and these differences are also lost after 3 passages. These results indicate that the cells of apical meristems are not totally uncommitted, but are determined as 'shoot' and 'root' meristem colls, respectively. The practical importance of a better understanding of epigenetic effects in plant cells is strassed.

Curves relating net photosynthetic rate to irradiance [P(I) curve relation] were estimated and analysed inMercurialis perennis L. plants stemming from three forest (spruce, beech and ash) stands with different tree leaf canopy development and different light regime.
The saturating irradiance (I_s) reached the highest values in plants of all three stands in spring (spruce forest: 438 W m^-2, beech forest: 440 W m^-2 and ash forest: 367 W m^-2), it declined sharply in the middle of the growing season (283, 285 and 297 W m^-2, respectively) and this I_s level persisted until autumn. A pronounced dynamics in plants from spruce and beech forests made itself manifest also in the adaptation (I_a) and compensating (I_c) irradiances, respectively. After a sudden decline in summer, values in autumn were close to those of the vernal season.
The most pronounced parameter, which optimally expressed the adaptation ofMercurialis perennis to various light conditions, was the photosynthetic efficiency (α) calculated as the slope of the linear part of the curve relating net photosynthetic rate to irradiance.
At the time of the highest P_{N sat.} value in course of the growing season (August) (spruce forest: 100, beech forest: 98.7 and ash forest: 85.8 μg CO₂ m^-2 s^-1), R_D was in its minimum; in autumn P_{N sat.} reached the lowest values which corresponded to the most intensive R_D.
It was found thatMercurialis perennis plants stemming from forest stands with different light conditions did not make use equally of the altering light conditions in the course of the growing season. By the underlying analysis of P(I) curves this rhizomatous perennial herb (geophyte) may be characterized as a shade tolerant species.

A possible involvement of the alternative oxidase pathway in proton translocation was investigated. Net H⁺ efflux- and elongation-rates were simultaneously and continuously measured by means of a pH-stat and an angular position transducer. Disulfiram, an inhibitor of the alternative path, reduces the IAA- and Fusicoccin-induced as well as endogenous proton secretion and growth. Fusicoccin-induced H⁺ secretion is very sensitive to reduced oxygen concentration values far apart from the K_m of cytochrome oxidase. The sensitivity of non stimulated proton secretion to reduction of oxygen concentration depends on the age of plant material. It is proposed that more than one system is responsible for proton translocation across the plasmalemma. One of them has a high sensitivity to reduced oxygen concentration which is within the same range of the high K_m value of the alternative oxidase.

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.

The current status of our knowledge of auxin effects on floral induction is summarized. The most general effect is inhibition, although the concentration of synthetic auxins added to. plants tends to be too high for us to be certain that the inhibitory effects are truly physiological. Studies of endogenous levels of auxin have focused almost entirely on IAA-like bioassay activity. Chemical identifications of endogenous IAA are needed and feasible. In addition, a search for-other auxins involved in vegetative to floral transitions, their chemical identification, and measurement of their changing levels in the plant are urgently needed.

Inhibition of root growth was observed inChenopodium rubrum under photoperiodic conditions inducing flowering. That this inhibition is mediated by the cotyledons was shown directly by the effect of their excision, which changes the responsiveness of the roots to photoperiodic treatment. On the other hand, decapitation did not lead to such an effect. Some evidence is put forward suggesting that changes in IAA may be involved in these correlations. The existence of two different mechanisms of photoperiodic action in flowering and in root growth is proposed to explain these differences.

A low reproducibility of some characteristics in the life cycle of the volvocal algaChlamydomonas geitleri was observed in repeated experiments. The sets of the cultures were very similar in the number of the studied characteristics, but some of them differed significantly in one or several characteristics whereas the others agreed in a whole set. This is documented by the growth in a nitrogenless medium, the formation of zygotes, and their maturation and germination. The results of a small representative set of experiments were treated by an analysis of variance. Some possible explanations are discussed.

Recurrent exposures (17 administrations in 37 days) to the direct-acting mutagens N-methyl-N-nitrosourea and N-ethyl-N-nitrosourea and a chronic exposure (38 days) to the metabolism-requiring mutagen dimethylnitrosamine markedly increased the frequency of somatic mutations in a double heterozygous chlorophyll mutant ofNicotiana tabacum, whereas exposure to N-methyl-N'-nitro-N-nitrosoguanidine was ineffective.

The roles of the different cytokinin structures are discussed in relation to our knowledge of their biological activities, endogenous occurrence and metabolism.

When tissues ofCatharanthus roseus A6 crown gall were incubated on medium supplemented with 50 (μM N6-isopentenyladenine (i⁶Ade), endogenous i⁶Ade, N6-isopentenyladenosine (i⁶A) and i⁶A nucleotide (i⁶AXP) increased to. 6, 5 and 12 nmol g^-1, respectively, during 100 h. Whereas i⁶Ade and i⁶AXP increased rapidly during the initial 4 h and then remained relatively constant, the level of i⁶A continued to increase to 25 nmol g^-1 by 16 h and then decreased; Ribosylzeatin (io⁶A) and its nucleotide (io⁶AXP) remained constant at 1.5 and 1.7 nmol g^-1, respectively. Upon transfer to cytokininless medium, i⁶Ade and i⁶AXP declined rapidly but i⁶A increased to 10 nmol g^-1 after 4 h and then declined. Again, io⁶A and io⁶AXP were unchanged. Prolonged incubation of crown gall tissue on i⁶Ade completely inhibited growth. By contrast, nonrtransformed, autonomous tissue lines fromCalycanthus fertilis andActinidia chinensis Xarguta continued to proliferate on this medium. TheActinidia Une was shown to metabolize i⁶Ade to zeatin and to accumulate this cytokinin to levels in excess of 70 nmol g^-1.

In short-day plantChenopodium rubrum the photoperiodic requirement for flowering increases from one short day at the age of four days to two or three short days at the age of five to seven days. The photoperiodic requirement decreases again to one short day between the 10th and 12th day of cultivation. This feature, together with endogenous circadian rhythmicity of flowering, enabled us to test the effects of PGRs under different morphogenetic patterns. Representative PGR effects on flowering are quoted.

Nitrate consumption, nitrite production and nitrite loss were followed in the"in vitro" nitrate reductase (NR) assay mixtures with pea root extracts, and nitrite production in the "in vitro" NR assay was compared with anaerobic nitrite production in the "in vivo" assay with pea root segments. NR activity could not be reliably determined on the basis of nitrate consumption using three methods of NO₃-determination (salicylate, cadmium, enzymatic). NR activity based on nitrite determination was slightly underestimated due to nitrite loss (less than 10% with pea root extracts) in the assay mixture. Nitrite production in the "in vivo" NR assay under optimum conditions closely resembled nitrite production in the "in vitro" NR assay and thus reflected NR level in the tissue.

The seed protein patterns of 12Arachis species were compared by polyacrylamide gel electrophoresis (PAGE), similarities between patterns were measured by the Jaccard index. Results obtained confirm the close relationships established between members of the genus on morphological grounds and support the more recent classification schemes.A. villosa andA. correntina could well be regarded as distinct species on grounds of protein differences whileA. macedoi andA. villosulicarpa (although members of the same section, Extranervosae) show considerable differentiation of their protein patterns. Surprisingly, the formA. ×batizogaea showed less similarity in protein pattern to those of its parental species than might have been expected. The principle value of seed protein pattern data appears to be in distinguishing species within sections.

Salinity caused a consistent reduction in the growth of cowpea plants and water content in their leaves. The total as well as the pigment fractions, except carotenoids, exhibited lower values than those of control plants at almost all salinity levels. With the rise of salinization, the total nitrogen and potassium contents in the leaves were decreased but the sodium content was increased and phosphorus content was not significantly affected as compared with the controls.
The application of IAA to salt-treated plants increased the water content in the leaves but it had no effect on the number of leaves and the stem length. The pigment contents in the leaves were either promoted or inhibited with the application of IAA, depending upon the level of salinization. The application of IAA to plants irrigated with water of the highest salinity level was effective in increasing the potassium content in the leaves as compared with the control, but it had no effect on the other mineral elements.