Zeitschrift für Pflanzenphysiologie最新文献

Net H⁺-transport was continuously monitored by means of a computer assisted pH stat. Application of cycloheximide leads rapidly to a transient proton influx, followed by a periode of uncomplete recovery. This occurs even when net H⁺-efflux is stimulated before with indolacetic acid or dilute concentrations of the fungal toxin fusicoccin. The uncomplete recovery of proton secretion is unaffected by repeated treatment with CHI but it is markedly reduced by sulfhydril-blockers. The inhibition of proton secretion induced by sulfhydril-blockers is only reversed transiently by dithioerythritol. The results give no clear evidence for the existence of different pumps or a different mode of action between auxin and fusicoccin in their stimulation of net H⁺-transport.

In Eremosphaera glycolate is synthesized and can either be excreted or metabolized by the cells. All the enzymes required for the conversion of glycolate to glycerate are present in this organism. In contrast to higher plants and also to some other algae the enzymes of glycolate metabolism are located exclusively in the mitochondria. Oxidation of glycolate is catalyzed by a dehydrogenase which also has a high affinity for D-lactate. Glycolate as well as D-lactate supplied in the culture medium can be taken up and metabolized by the whole cells. The metabolism of both substrates causes an increase in respiration activity. With D-lactate the oxygen consumption is much higher than with glycolate.

Microbody fractions not contaminated by mitochondria, plastids, or protein bodies were isolated from sunflower cotyledons during the transition of the cotyledonary microbody population from glyoxysomal to leaf peroxisomal function. In these microbody fractions, specific enzyme activities could be determined based on microbody protein content. The amount of microbody protein per cotyledon was estimated from the specific and total activities of isocitrate lyase and glycolate oxidase. This can be considered to be a relative measure of the size of the cotyledonary microbody population (number of microbodies per cotyledon). The amount of microbody protein per cotyledon remained constant over most of the transition period, declining only during the final stage. This result suggests that there is no pronounced and selective degradation of glyoxysomes during the transition in cotyledonary microbody function.

Serotonin (5-HT) was measured by HPLC with electrochemical detection in walnuts (Juglans regia) during ontogeny and germination.

Whereas 5-HT levels in catkins were low and did not increase during maturation, they increased in seed buds. The embryo reached highest amounts of 5-HT mainly during the final development of the seeds. Extremely high concentrations of 5-HT (1.6 mg g^-1) were observed in the seed coat. In the seeds the 5-HT content remained stable during their storage over a period of at least one year.

The level of 5-HT in the cotyledons doubled during germination in two months. In the shoots the apical buds contained as much 5-HT as the seed coat whereas the 5-HT concentration in the roots was extremely low. Besides the possibility that 5-HT is not more than an end product of tryptophan metabolism its high concentration in seed coats and apical buds suggest a function in the defense against other plants or pests.

Autotrophically grown Chlorella vulgaris cells show a low rate of hexose and amino acid uptake. After pretreatment with glucose or glucose analogues the rate of uptake of hexoses and of six amino acids (catalyzed by one hexose- and two amino acid transport systems) is increased one hundred-fold or more. Induced cells possess at least two additional membrane proteins, which are detectable after radiolabelling. Their apparent molecular weight on SDS gels increases with increasing acrylamide concentration and possibly correct values were estimated by extrapolation to be about 65,000. The putative hexose transport protein does not seem to be N-glycosylated.

The proteins were enriched approximately 30fold starting from a partly purified membrane fraction and following a purification procedure worked out for E. coli lac-permease (Newman et al., 1981, J. Biol. Chem. 256, 11, 804). The purified extract from induced cells contained a protein which was detected as diffuse band after silver staining; this protein was absent from the extract of non-induced cells. The stained band corresponded to the radiolabelled proteins described above.

NADP-malate dehydrogenase (NADP-MDH) is normally activated in the light and inactivated in the dark in plant leaves, including the C₄ species maize. In the present study, leaf discs of maize were taken from illuminated plants and the state of activation of the enzyme followed in darkness under various conditions. After 30 min of incubation of the leaf discs in the dark, NADP-MDH was largely inactivated, but during the next hour of incubation in the dark the enzyme was reactivated. Bubbling air into the solution containing the leaf discs or addition of 100 μM Antimycin A prevented the reactivation of the enzyme in the dark. It is concluded that leaf discs of maize in solution in the dark become deficient in O₂ due to respiration and that the depletion of O₂ leads to activation of NADP-MDH.