Jan A. De Greef

STIMULATION OF INDOLE-3-ACETIC ACID PRODUCTION IN RHIZOBIUM BY FLAVONOIDS

Flavonoids activate nod gene expression in Rhizobium resulting in the synthesis of Nod signals which trigger organogenesis in the host plant. This paper shows that nod‐inducers also stimulate the production of the phytohormone IAA (indole‐3‐acetic acid).

Duroquinone-stimulated NADH oxidase and b type cytochromes in the plasma membrane of cauliflower and mung beans☆

Microsomal membrane preparations of cauliflower inflorescences and mung bean hypocotyls possess duroquinone (DQ)-stimulated NADH oxidase activities at rates of 1–10 nmol NADH · min− · mg−. These redox reaction are associated with the endoplasmic reticulum (ER) and the plasma membrane (PM) as shown by the distributions of marker enzymes in sucrose gradients. The NADH oxidase thus partially cosediments with a specific blue light (or ascorbate) reducible b type cytochrome of the PM. Cauliflower membranes are further purified by means of an aqueous polymer two phase method. The NADH oxidase in this presumptive PM fraction is to some extent stimulated by Triton X-100 and insensitive to KCN (1 mM) or quinacrine (0.4 mM). Kinetics for DQ stimulation showed a biphasic saturation curve. These membranes also have a high FeCN reduction capacity induced by NADH but insensitive to DQ. No evidence could be found in the present study for the involvement of the specific b type cytochrome in the NADH dehydrogenase system.

b-Type Cytochromes, Light- and NADH-Dependent Oxido-Reductase Activities in Plant Plasma Membranes

Blue light induces many important biological phenomena in plants and microorganisms (Senger, 1980, 1984a; Senger and Briggs, 1981; Senger and Schmidt, 1986). The characterization of the sequence of events from the photoperception to the final respons is the ultimate aim in the area of photobiological research. These responses are often extensively described at the macrophysiological level but the molecular perception mechanism(s) remain obscure. In higher plant phototropism it seems justified to propose an alteration in membrane properties (Firn, 1986). The basic discussion centers obviously around the primary reactions as a consequence of the photochemical reaction of the receptor. Changes in transmembrane ion gradients are considered as an early step in the reaction chain and occur by alterations in the existing electrochemical potential differences (Evans, 1985). According to chemiosmotic principles, changes in plasma membrane ATPase activity are directly or indirectly responsible for ion exchange (Serrano, 1985). Another system also working as a proton pump is provided by an electron transfer chain. The latter system is well described for mitochondria and chloroplasts but now increasing evidence supports the presence of a proton translocating redox mechanism in the plasma membrane (Crane et al., 1985; Moller and Lin, 1986). It is precisely the aim of this symposium to discuss the possible involvement of these systems in membrane transport and growth phenomena. Several contributions will describe the various oxidoreductases located on the plasma membrane.

Senescence of oat leaves : changes in the free sterol composition and enzyme activities of the plasma membrane

Abstract Plasma membrane fractions were prepared from young (10-day-old), mature (17-day-old) and senescent (10 + 7-day-old) oat leaves ( Avena sativa L.) through aqueous two-phase partitioning and analyzed for their free sterol composition. Continued leaf growth resulted in a strong increase in overall sterol content from 40 nmol · mg −1 lipid to about 120 nmol · mg −1 lipid (1.5% and 5% by wt. of total lipids respectively). This increase could be completely ascribed to increased cholesterol and stigmasterol concentrations. Kinetic parameters of vanadate-sensitive ATPase and NADH-FeCN reductase activities did not change significantly with leaf maturation. The sterol concentration increased to a lesser extent (4.2% and 4.4% by weight) in the plasma membrane of 10-day-old leaf segments that were cut and kept in light or dark for 7 more days. However, the increase in this case was completely due to a raise in Δ 7 -avenasterol and 28-isofucosterol concentrations. The K m and V max values for the ATPase activity decreased significantly in these membranes. The characteristics of the FeCN 2 reductase and of glucan synthetase II activity were apparently not affected. The effect of senescence on sterol biosynthesis and on plasma membrane enzyme activities is discussed.

Plasma Membrane Cytochrome Components: Midpoint Redoxpotentials, Light- and NADH Mediated Reductions

The thorough characterization of PM redox components is highly dependent on the method for isolation and purity of the membranes. The purity and cytochrome content of PM fractions from several plant species, obtained by aqueous two phase partitioning, was investigated. Preparations are generally enriched in vanadate-sensitive ATPase activity (PM marker) and show strongly decreased (6 to 50 fold) levels of NADH-CCR activity (presumptive ER marker). The remaining activity might originate from specific PM redox constituents. Variable amounts of latent IDPase activity (Golgi marker) were detected. PM preparations oxidize NADH (in piesenye of duroquinone and KCN) at rates between 9 and 40 nmol NADH.min−1.mg−1 protein. Triton X-100 stimulation indicates the presence of tightly sealed right-side out PM vesicles.

T-DNA Controlled and Plant Specific Metabolism in Agrobacterium tumefaciens Transformed Tobacco and Soybean Tissues

SummaryThe endogenous IAA and cytokinin levels measured in Agrobacterium tumefaciens transformed tobacco and soybean tissues were correlated with the onc-T-DNA genes and their functional effect on tumor growth and morphology