Nitrogen Fixation in Peanut Nodules during Dark Periods and Detopped Conditions with Special Reference to Lipid Bodies

Abstract

The peanut plant (Arachis hypogaea L.), unlike other known legumes, can sustain nitrogen fixation when prolonged periods of darkness or detopping curtail the supply of photosynthate to the nodule. This ability to withstand photosynthate stress is attributed to the presence of lipid bodies in infected nodule cells. In both dark-treated and detopped plants, the lipid bodies show a gradual decrease in numbers, suggesting their utilization as a source of energy and carbon for nitrogen fixation. Lipolytic activity can be localized in the lipid bodies, and the existence of ,Boxidation pathway and glyoxylate cycle is shown by the release of 14C02 from 14C lineoleoyl coenzyme A by the nodule homogenate.Symbiotic association of leguminous plants and the soil microbe Rhizobium results in the formation of root nodules where rhizobia fix atmospheric nitrogen. Carbon compounds derived from the host plant are essential for the reduction of N2 and for the assimilation of the fixed nitrogenous products (7). In symbiotic N2 fixing systems, blockage in the import of photosynthate availability drastically affects N2 fixation (5, 6, 12. 14, 23, 29) as measured by ARA2 (10). Diurnal variation in N2 fixation activity due to the dark period of night has been reported in various legumes (16,19 Such blockage in photosynthate supply could be induced experimentally by keeping the plants in dark or by detopping the aerial part. This paper deals with the results of such experiments supplemented by cytological and radioisotope tracer studies. MATERIALS AND METHODS Plants and BacteriaSeeds of peanut (Arachis hypogaea L. var Jumbo virginia) and cowpea (Vigna unguiculata L. var California blackeye) were obtained from W. Atlee Burpee Co. Warminster, PA. The seeds were planted in pots (6 inch standard) containing vermiculite, and the seedlings were inoculated with a broth culture of Bradyrhizobium sp. 32H 1 provided by the Nitragin Co. Ltd, Milwaukee, WI. The potted plants were kept in an environment chamber with approximately 700 ,tmol m-2 s-1 PPFD under day/night conditions of 16 h/8 h, 27°C/22°C, and 70%/50% RH and were irrigated with nitrogen-free nutrient solution according to Elfolk (8). Well-nodulated healthy plants were used for dark treatment and detopping at 45 d after inoculation. The plants were kept in the dark for 96 h, during which samples were taken at 0,3,6,12,24, 48, 72, and 96 h. Detopping was achieved by cutting the stem 10 cm above ground, and the root system was sampled at 0, 24, 48, 72, and 96 h.

Early stages of nodulation in roots of Oxytropis arctobia (Leguminosae) induced by the arctic rhizobial strain N31

“…While in association, some of them reveal an impression of being partially used up (arrow) as the remaining portion is shaped following the contour of the membrane of the infection thread. The very rare occurrence of lipid bodies in the mature infected cells of the symbiotic zone is also an indication that the lipid bodies are consumed during growth and development of the infected cells: thus, they may have no direct relationship to the nitrogen-fixing activity, contrary to the recent findings for peanut nodules (Bal et al 1989;Siddique & Bal 1991), where lipid bodies persist all through the different developing stages.…”

Shoot Pruning and Impact on Functional Equilibrium Between Shoots and Roots in Simultaneous Agroforestry Systems

“…The results from studies with peanut (Arachis hypogaea L.) could be validated for a perennial legume such as Arachis pintoi Krapov & W.C. Gregory. Siddique & Bal (1990) found that peanut, unlike other known grain legumes, can sustain N-fixation when prolonged periods of darkness or de-topping curtail supply of photosynthate to the nodule. This ability to withstand photosynthate stress is attributed to the presence of lipid bodies in infected nodule cells.…”

“…The original rates of N-fixation were attained after one week's growth. Siddique & Bal (1990) reported that the rate of N 2 fixation decreased at night and under shady conditions during the day. Thus, any shading and/or defoliation which diminish photosynthate supply can also limit the fixation of nitrogen.…”

Symbiotic nitrogen‐fixing root nodules of Lathyrus maritimus (L.) Bigel (beach pea) from Newfoundland shore lines with special reference to oleosomes (lipid bodies)

“…Absence or scarcity of oleosomes from mature nitrogen-fixing symbiotic zones may indicate the lack of any role in the nitrogen fixation process. Oleosomes have been implicated in supplying supplementary energy source for nitrogen fixation in peanut nodules (Bal et al 1989;Jayaram & Bal 1991;Siddique & Bal 1991, 1992. In peanut nodules, oleosomes are present at a metabolic equilibrium level in the infected cells at all stages of growth and maturation (Jayaram & Bal 1991).…”

“…They are known to occur in nodules of arctic legumes (Newcomb & Wood 1980), where their function is not clearly understood. Oleosomes are also present in peanut nodules (Bal, Hameed & Jayaram 1989), where they are thought to be a supplementary source of carbon and energy for maintenance of nitrogen-fixation activity (Siddique & Bal 1991, 1992. In beach pea nodules, oleosomes are found in large numbers as in other arctic legume nodules, and in this investigation, an attempt has been made to localize oleosomes histochemically and determine their pattern of distribution in the nodule tissue with a view to clarifying their role.…”