Zeitschrift für Pflanzenphysiologie最新文献

The effects of brassinosteroid, of twelve related sterols and of three sterols on maize root growth and on H₊ secretion were investigated. A number of steroids stimulated root segment elongation and H₊ secretion as brassinosteroid does. Defined structural requirements were found for the effect on growth; on the contrary, all the steroids tested, among which stigmasterol, cholesterol and ergosterol, were active on H₊ secretion. Cholesterol stimulated K₊ uptake and dark CO₂ fixation, two processes generally associated with the activity of the H⁺ pump.

The influence of ammonium on the development patterns of proteolytic enzymes and glutamine synthetase was examined during the germination and early seedling growth of mung bean. Protease and carboxypeptidase activities in the cotyledons of seedlings grown on water increased 15-fold and 7-fold, respectively over a 5-day germination period. The provision of 10 mM NH₄⁺ to the seedlings decreased the enzyme activities by 30% in the cotyledons. A similar decrease in both protease and carboxypeptidase was observed with the hypocotyl of NH4 grown seedlings as compared to water control. Germination was accompanied by a marked decline in leucine aminopeptidase activity, and NH₄⁺ did not appear to have a significant effect on the development pattern of this enzyme. A comparison of glutamine synthetase activity on day 5 between control and NH₄⁺ showed that the enzyme level was repressed by 50%, 30%, and 25% in root, hypocotyl, and cotyledon, respectively, due to NH₄⁺ treatment.

The increase in the proteolytic activities were concurrent with a decrease in the protein content of cotyledon and hypocotyl tissues, whereas the proteolytic activities in the root decreased as the protein content declined during development. There was a progressive accumulation of soluble amino acids in the cotyledons of NH₄⁺ grown seedlings with relatively less accumulation in the hypocotyl. The reverse occurred for the seedlings grown on water. These results suggest that exogenously supplied NH₄⁺ during the germination of mung bean seeds slows down protein hydrolysis and the synthesis of glutamine synthetase.

There is no significant difference between the ATPase present in the Hevea tonoplast of freshly isolated vacuoles and of lyophilized tonoplast vesicles (same k_m value for MgATP^2-, same pH-dependence, same effect of inhibitors, same effect of ionophores and protonophores).

It is suggested that the components of the protonmotive force regulate the activity of the tonoplast H⁺-translocating ATPase. The consequences of such effects may be very important in the regulation of events linked to the compartmentation of solutes inside the plant cell.

During early germination of unicellular spores, separation between molecular processes induced by hydration or by photoinduction was possible. There was an extensive adenosine incorporation into low molecular mass, poly(A) rich RNA composed of 30 to 60 nucleotides during the pre-photoinduction phase immediately after hydration. It was followed by gradual increase in the rate of cytoplasmic rRNA synthesis. Photoinduction by 2 short red irradiations given shortly after the preinduction phase caused an immediate 2 fold increase in the rate of ³H-adenosine incorporation into this low molecular mass RNA followed by a heavy shift to the production of rRNAs starting 10h after photoinduction. An increase in mRNA template activity was observed in a cell free translation system 16h after photoinduction: A 30,000d protein and 48,000d protein were preferentially synthesized. Still, the rate and pattern of ³⁵S-methionine incorporation in vivo remained unchanged during the first two days after photoinduction. Then methionine incorporation rapidly rose to four times the rate of the blue light (non photoinduced) control. The delay of over a day between the photoinduced appearance of new mRNAs and in vivo increase of protein synthesis suggests that.there are separate transcriptional and translational controls during Pteris spore germination.

The temperature response of biological systems (Q₁₀) is described in terms of the physical model of dissipative structures of thermodynamically open systems, which are far away from thermal equilibrium. The theory is shown to be consistent with experimental results on physiological temperature responses of cucumber seedlings.

Free amino acids, total methylated onium compounds (TMOC) and total nitrogen were investigated in young and old leaves of 22 mangrove species from Northern Queensland (Australia). Total nitrogen ranged between 0.35 to 2.5% of dry matter depending on leaf age and species. The soluble nitrogen compounds accounted only in a few cases for more than 10% of the total nitrogen. High proline accumulation was observed in only three species: Aegialitis annulata (28.5 mol · m^-3 plant water), Xylocarpus granatum (76.0 mol · m^-3 pw) and Xylocarpus mekongensis (56.7 mol · m^-3 pw). The latter two species contained also hydroxyproline as a major component of the amino acid fraction. GABA, GLU, ASP and ALA were the most frequently occurring amino acids in the other species. Avicennia eucalyptifolia, Avicennia marina, Hibiscus tiliaceus and Heritiera littoralis accumulated high concentrations of TMOC (up to 107 mol · m^-3 plant water), while Acanthus ilicifolius stored both TMOC and PRO.

The occurrence of organic solutes in mangroves is discussed in comparison to herbaceous halophytes.

Both 6-(2,3,4-trihydroxy-3-methylbutylamino)purine and N-(purin-6-yl)glycine were metabolised slowly when applied to developing fruits of Lupinus albus. Biological activity which co-chromatographed with glucosylzeatin, ribosylzeatin and zeatin was detected in the developing seeds. As the recovered radioactivity did not co-elute with glucosylzeatin or zeatin it would appear as if the applied oxidation products of zeatin were not incorporated readily into free cytokinins. These compounds may however, play an important role in the inactivation, or the regulation of endogenous cytokinin levels in fruits and seeds.

Spring and summer treatments like pruning, defoliation, disbudding and shoot bending greatly affect the depth and the development of bud dormancy in the following winter period. Correlations between plant parts are thus among the factors that control onset and course of dormancy and through which the behaviour of the plant in given winter climates could be modified.

Imposition of water stress either through waterlogging or droughting leads to changes in endogenous ethylene level in both Kalanchoe daigremontana, a CAM-plant, and Caltha polypetala, a hydrophyte. These changes consist of an initial sharp rise followed by a decrease in the level of ethylene. In Kalanchoe and in droughted Caltha the ethylene levels appear to be related to the degree of stress imposed. No such relationship has been observed with waterlogged Caltha.