Field and pot experiments showed that the P demand of wheat is highest in early stages of growth (up to 1.67 μg P per cm2 root surface and day). The needed orthophosphate ions H2PO4− and HPO42‐move from soil to the root by diffusion. This process is controlled by the concentration gradient of the diffusible phosphate and the effective diffusion coefficient according to Pick's first law. Root excretions (rhizodeposition) are able to affect both characteristics. The water soluble portion of rhizodeposition contains more than 50% of up to 8 different sugars, 10–40% carboxylic acids and 10–15 amino acids and amides. The composition varies in dependence on the age of the root parts and on nutrition (Zea mays L., Brassica napus L., Pisum sativum L.). Diffusion experiments using small soil blocks showed that 50–75% of the root exudates were decomposed by respiration within 3 days. The rest was largely chemically converted. Originally present sugars disappeared. Due to the biosynthesis of different organic acids from the individual sugars the mobilisation of Ca3(PO4)2 by Pantoea agglomerans increased when the sugar mixture was derived from the rhizodeposition of P deficient plants with more pentoses instead of glucose and fructose (mainly effect of anions). In the rhizosphere therefore a mixture of rhizodeposition and its conversion products exists which affects the binding of phosphorus in soil and the P transport to the root. This should be considered both for the development of new soil extractants and for modelling the P supply to plants.
Etodolac, 1,8-diethyl-1,3,4,9-tetrahydropyrano[3,4-b]indole-1-acetic acid, a clinically effective analgesic and antiinflammatory agent, has been resolved via a chromatographic separation of its diastereoisomeric esters with (-)-borneol. The effects of the enantiomers were studied in vitro on prostaglandin synthetase and on adjuvant-induced arthritis in rats. The biochemical and pharmacological results show that virtually all of the effects of etodolac are due to the (+) enantiomer.
Abstract. Biological dinitrogen fixation by legume-rhizobia symbiosis is very important both from the economic and from the ecological point of view. Theoretically, the reduction of the N2-molecule to ammonia requires at least 16 ATP and 1.5 mg C per mg N fixed (N~x). These values are difficult to determine in situ as this necessitates the determination of that part of root respiration which drives N2-fixation. New approaches to such determinations and the results obtained are described. The values vary, depending on the plant species studied, the developmental stage of the plants and the genetic variability of macro-(and micro-?) symbionts. The values range between 1.5 and 4 nag C/mg N~x. In some species (e.g. Viciafaba L. cv. Fribo), the apparent CO2 assimilation is enhanced in order to meet this high energy need. In others (e.g. Pisum sativum L. cv. Grapis), root growth is restricted. Physiological criteria are discussed which allow an early diagnosis of the energetic efficiency of various eombinations of macroand microsymbionts as a basis for a selection in plant breeding. Key words. N2-fixation, nitrogenase; carbon and energy demand of nitrogen fixation; leguminous plants.Biological dinitrogen fixation is a process of great economic importance world-wide, since many legumes are grown as crop plants. These plants can be cultivated almost without mineral nitrogen fertilizers. In the last decades, remarkable progress has been made in nitrogen fixation research, especially in the genetic analysis of the symbiosis involved 15. The reduction of nitrogen in root nodules means a great energy loss for the plants, since N2-reduction is coupled with a considerable hydrolysis of ATP and a consumption of reducing equivalents. There has been much debate as to whether assimilate supply to the nodules limits nitrogen fixation and plant growth, or whether the plants can compensate from this demand by enhanced photosynthesis 32. Situations were observed experimentally where nitrogen fixation was limited by the assimilate supply to the nodules 29. The present paper analyses the carbon demand resulting from nitrogen fixation under various conditions, and investigates the effects on the carbon balance of the host plants. Furthermore, possible methods will be shown to identify such assimilate deficiencies by means of simple indicators. The findings could give valuable information to plant breeders for overcoming deficiencies in the plant-Rhizobium symbiosis.
Theoretical considerations on the carbon demand of N 2-fixati0nIn dinitrogen fixation, the reduction of molecular nitrogen to ammonia is catalyzed by the enzyme nitrogenase. In leguminous plants this process takes place in the bacteroids in root nodules. A simplified outline of the process is given in figure 1.The enzYme complex nitrogenase consists of two parts 9. Molecular nitrogen is bound to a Mo-cofactor. Reducing equivalents come (in most cases) from ferredoxin, and are transported via the enzyme complex, finally reducing nitrogen to ammonia. The electron flux is couple...
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