Control of Seed Respiration and Growth in Vicia faba by Oxygen and Temperature: No Evidence for an Oxygen Diffusion Barrier.

The rate of dry matter accumulation by seeds of Vicia faba L. cv. Minica increases with temperature in the range of 16 to 26 degrees C. The duration of dry matter accumulation decreases with temperature, resulting in a decrease of final seed dry weight. In this study we test the hypothesis that a diffusion barrier for O(2), located in the seed coat, inhibits seed respiration and growth. The rate of O(2) uptake of intact seeds and of excised embryos and seed coats (separated seeds) was measured in air and buffer at 16, 20, and/or 26 degrees C at various O(2) concentrations and developmental stages. Oxygen uptake rates of intact seeds in buffer were only 9 to 15% of those in air. In buffer, the respiration rate of intact seeds decreased at a pO(2) below air saturation (21 kilopascals), whereas separated seeds showed a decline of O(2) uptake only below 80% of air saturation. In air, embryo excision had no effect on the sensitivity of seed respiration to pO(2), at both 20 and 26 degrees C. In air at 20 degrees C, separated and intact seeds showed similar rates of O(2) uptake. Oxygen uptake by intact seeds, both halfway and beyond the linear growth phase, showed a temperature coefficient Q(10) of 2.3 and was insensitive to pO(2) in the range of 80 to 100% of ambient. These results indicate that V. faba seed respiration in air is not limited by the diffusion of O(2) into the seed.

The occurrence of free and bound cytokinins in plasmodia of Plasmodiophora brassicae isolated from tissue cultures of clubroots.

Plasmodia have been isolated from Brassica campestris tissue infected with Plasmodiophora brassicae. Cytokinins were extracted from plasmodia and from the remaining host cytoplasm. Fractions were separated in a butanol soluble fraction containing free cytokinins and a water soluble fraction containing bound forms, presumably glucose-6-phosphate derivatives of zeatin and zeatin riboside. The butanol fraction was analysed by high pressure liquid chromatography (HPLC). The different glucosides were determined after treatment of the water fraction with ß-glucosidase.Plasmodia contained zeatin riboside and its glucose derivative (175 and 1600 ng/g dry weight, respectively). Host cytoplasm contained zeatin riboside (132 ng/g dry weight) and small amounts of the glucose-6-phosphate derivatives of zeatin and zeatin riboside. The results suggest that plasmodia synthesize cytokinins which are released into the host cytoplasm inducing host cell division.

The effect of acetylcholine on growth and on growth inhibition by CCC in wheat seedlings.

The inhibition of the growth of wheat seedlings by 2-chloroethyltrimethylammonium chloride (CCC) was strongly reduced by root application of acetylcholine (Ach). Ach was applied after uptake of CCC by the roots or by the leaves. Ach also stimulated growth of non-CCC-treated seedlings up to 30% when applied to the roots. Growth stimulation appeared to be dependent on pH of the medium and most effective at pH 4.5 and 6. At pH 7.5 Ach did not promote growth of wheat seedlings.