Differentiation of nitrogen-fixing nodules of Sesbania rostrata with special reference to oleosomes (lipid bodies)

Denduluri, Srinivas (1994) Differentiation of nitrogen-fixing nodules of Sesbania rostrata with special reference to oleosomes (lipid bodies). Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Development and differentiation in the early stages of nitrogen-fixing stem and root nodules was studied in Sesbania rostrafca. Correlated light and electron microscopic observations have revealed that the bacterium Azorhizobium caulinodans IRG 46, which nodulates Sesbania possibly enters the host through fissures encircling the secondary roots or the root initials present on the stems. Root hair infection threads could not be seen, although root hair growth inhibition was induced by the bacteria. The bacteria passed through the intercellular space before producing infection thread-like invaginations in the target cells, where they were released. -- One of the striking features of the early stages of differentiation in the infected cell is the occurrence of oleosomes (lipid bodies) in both root and stem nodules. Even more remarkable is the size of the oleosomes in the stem nodule cells, which are in some cases eight times larger than those in the root oleosome ( 0.5 - 1.0 μm in diameter) population. This increased size is thought to be due to the oversupply of photosynthate from the chlorophyllous cortex of the stem nodule. The photosynthate is possibly stored in triacylglycerol form within oleosomes for short term use. The oleosomes disappear in both root and stem nodules after maturation of the infected cells. In both nodules maturation leads to multiple occupancy of bacteroids within peribacteroid membranes, which proliferate during nodule maturation. -- Lipolytic activity could be localised in the infected zone of the nodule by the Nile Blue dyeing method. Catalase activity was determined by spectrophotometry of the bacteroid and the host cytosol fractions, the latter showing higher activity. Catalase was localized in vesicles budding off the perisymbiotic membrane by the DAB reaction. -- Total lipid estimation by the gravimetric method indicated that the seeds have a higher total lipid content than the stem and root nodules. Gas chromatographic analyses of the lipids from the isolated oleosomes indicate that the dominant unsaturated fatty acids are C14:1, C16:1 in the stem nodule, whereas C18:1, C18:2 are dominant in the root nodule and seeds. Among saturated fatty acids C16:0 and C18:0 in the stem nodule, and C16:0 in the root nodule and the seed are dominant respectively. -- In Sesbania nodules the oleosomes seem to be used up for the growth and development of the infected cells; they are not involved in nitrogen fixation per se.

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