Biochemie und Physiologie der Pflanzen最新文献

The levels of endogenous ABA were measured by ELISA in embryogenic cells, nonembryogenic cells and somatic embryos of carrot. Embryogenic cells were estimated to contain a 67.2 times higher level of ABA than non-embryogenic cells, and a 2.5 times higher level than somatic embryos. The correlation between the endogenous level of ABA and embryogenic competence of carrot cultured cells is discussed.

Development of glutamate dehydrogenase (GDH) and glutamine synthetase (GS) activity, as well as growth, were studied in dark-grown suspension cultures of Atropa belladonna initiated from root callus. The nutrient media contained NaNO₃ (15 mM) or NH₄NO₃ (7.5 mM). In order to study the effect of early precursors of tropane alkaloids, the cultures were supplemented with proline or ornithine (2.5 mM) during the rapid growth phase on day 10. Growth was accelerated by NH₄NO₃ (days 0-13), but higher fresh and dry weights were obtained at the end of the growth period (day 30) with NaNO₃. Ornithine temporarily retarded growth in NaNO₃ (days 13, 16). GDH and GS were assayed on days 9, 13 and 16. Considerable GS levels were found in all cultures. However, GS activity in NaNO₃ was markedly higher than in NH₄NO₃. In contrast, GDH activity was distinctly higher in NH₄NO₃ than in NaNO₃. Proline and ornithine were effectively metabolized by the suspension cultures, and only transitional accumulation of these amino acids in the cells was observed after amino acid supplementation. GDH and GS were hardly affected by proline, whereas ornithine enhanced GDH activity in the NaNO₃-grown cultures and decreased GS in both nutrient media.

Protein stabilities can be influenced by interactions with low molecular weight compounds. Using glucose-6-phosphate dehydrogenase as a model protein in this context, we found that it was stabilized by low concentrations (below 5 mM) of inorganic phosphate or sulfate. The pyridine nucleotide NADP (one of the substrates in the enzyme reaction) already protected glucose-6phosphate dehydrogenase activity at concentrations below 0.2 mM, whereas NAD was not effective. An excellent stabilization of glucose-6-phosphate dehydrogenase was achieved by the simultaneous addition of NADP and inorganic phosphate. Interactions of various ligands with different binding sites of the same enzyme can affect the susceptibility to proteolysis in a complex manner. Metabolic changes might influence selectively the catabolism of proteins in vivo by altering such interactions.

Storage patterns of soluble sugars, starch, lipids and fatty acids were investigated in leaves, stems and roots of Euphorbia acanthothamnos and Phlomis fruticosa throughout a year. Winter leaves of both species contained higher amounts of lipids than summer leaves. Leaf soluble sugar content showed two peaks (winter and summer) in P. fruticosa and a winter peak in E. acanthothamnos. Starch was mainly accumulated in young expanding winter- and summer-leaves and depleted twice over the year, during the cold winter and the drought summer, respectively. Considering stems and roots, storage substances exhibited identical fluctuations, i.e. the maximum values of lipids being recorded during winter and those of starch during spring. The molar quotient (MQ) of polyunsaturated to saturated fatty acids was low, mainly due to the high percentage of palmitic acid in all tissues of both examined species. Nevertheless, roots exhibited a different fatty acid composition than the above ground parts of the plants. The energy content of storage substances (ECS) was mainly contributed by lipids and the minimum values in both species were recorded during drought. On the basis of seasonal variation of ECS, dimorphic phrygana can be situated between mediterranean evergreen sclerophylls and central european evergreen conifers. It was presumed that in the case of dimorphic phrygana, summer seems to be a dormant period, whereas winter the investive period.