Biochemie und Physiologie der Pflanzen最新文献

Acetohydroxyacid synthase (EC 4.1.3.18) has been extracted from cell suspension cultures of Isatis tinctoria (Cruciferae) and Ruta graveolens (Rutaceae). A combination of salt precipitation, gel filtration and ion exchange chromatography was used for partial purification. The apparent molecular masses of AHAS were M_r 82,000 and 85,000 for Isatis and Ruta, respectively. FAD was an absolute requirement for AHAS activity. The apparent K_m values of Isatis-AHAS are the following ones: FAD 6,3 × 10⁻⁶ M; TPP 6,3 × 10⁻⁶ M; pyruvate 7 × 10⁻³, and 6 × 10⁻³ M (for Ruta-AHAS).

Branched-chain amino acids and chlorsulfuron are feedback inhibitors for Isatis-AHAS but acetohydroxyacid synthase from Ruta is not sensitive to valine, leucine and isoleucine.

Soluble starch synthase from spinach leaves can use ADPG and UDPG for chain elongation in the presence of an appropriate primer (glycogen, amylopectin). Whereas calcium ions alone or in combination with calmodulin (CaM) insignificantly reduce the biosynthesis of starch, ATP causes a substantial decrease in activity. EDTA and ADP on the other hand promote the incorporation of glucose. Using CaM-Sepharose-4B, a protein kinase (molecular weight 68 kD) could be isolated. This protein kinase is able to eliminate the ATP-induced inhibition in a calcium-CaM dependent way in the presence of Mg⁺⁺. The enhancement of the starch synthase activity by the protein kinase is Ca⁺⁺ and CaM specific. The optimum is observed at 5 mM ca⁺⁺ and 1.45 · 10^-7 mM CaM. The Ca-CaM dependence of protein kinase was proven by CaM antagonists (fluphenazine, trifluoperazine and calmidazolium at 5 · w^-5 M). Fluoride on the other hand enhanced the starch synthesis via the inhibition of a protein phosphatase. The phosphorylation of starch synthase was demonstrated by the incorporation of ³²P after application of ³²P-γ-ATP in the presence of the protein kinase.

Study of the role of H₂O₂ on senescence and photobleaching of chlorophyll revealed that pretreatment with H₂O₂ enhanced the loss of chlorophyll and protein in Hydrilla verticillata (L.f.) Royle and Ottelia alismoides (L.) Pers. leaves, more markedly so in the light than in the dark. Endogenous H₂O₂ and free phenol contents significantly increased during senescence, the effect being larger in light than in darkness. DCP (2,4-dichlorophenol, a monophenol) greatly accelerated the loss of chlorophyll and protein in the light while catechol (a diphenol) significantly retarded them. However, both these phenols retarded the loss of these components in the dark. Both peroxidase and chlorophyll oxidase activity greatly increased in light over dark treatment. The activity of superoxide dismutase and catalase declined more markedly in light than in darkness in either species. The possible involvement of oxygen free radicals and light-induced phenol peroxidase - H₂O₂ system in the photobleaching of chlorophyll and senescence development in the two submerged angiosperms has been suggested.

Cell suspension cultures of C. majus L. — obtained from callus — were characterized on growth and on accumulation of isoquinoline alkaloids. The liquid batch cultures consisted of coarse cell aggregates; their fresh volume becames triple each 14 days after subcultures. Cell cultures were found to produce relatively large amounts of isoquinoline alkaloids; sanguinarine is accumulated as main alkaloid and also released into the medium.

The fungus isolated from diseased tissues of pearl millet leaves was identified as Curvularia lunata. A toxin, isolated from 14 day old culture filtrate of C. lunata, was partially purified by ammonium sulfate fractionation followed by gel filtration through Sephadex G-100. The toxin was heat stable and soluble in water and acetate buffer at pH 5.5 to 6.0. Toxin was found to be most active at pH 5.5. The partially purified toxin showed some degree of host specificity. Different host varieties were screened for disease resistance. Toxin also affected cell permeability of susceptible host tissues.