No abstract

High-performance liquid chromatography (HPLC) with fluorescence detection was used to study thiol metabolism in legume nodules. Glutathione (GSH) was the major non-protein thiol in all indeterminate nodules examined, as well as in the determinate nodules of cowpea (Vigna unguiculata), whereas homoglutathione (hGSH) predominated in soybean (Glycine max), bean (Phaseolus vulgaris), and mungbean (Vigna radiata) nodules. All nodules had greater thiol concentrations than the leaves and roots of the same plants because of active thiol synthesis in nodule tissue. The correlation between thiol tripeptides and the activities of glutathione synthetase (GSHS) and homoglutathione synthetase (hGSHS) in the nodules of eight legumes, and the contrasting thiol contents and activities in alfalfa (Medicago sativa) leaves (98% hGSH, 100% hGSHS) and nodules (72% GSH, 80% GSHS) indicated that the distribution of GSH and hGSH is determined by specific synthetases. Thiol contents and synthesis decreased with both natural and induced nodule senescence, and were also reduced in the senescent zone of indeterminate nodules. Thiols and GSHS were especially abundant in the meristematic and infected zones of pea (Pisum sativum) nodules. Thiols and ␥-glutamylcysteinyl synthetase were also more abundant in the infected zone of bean nodules, but hGSHS was predominant in the cortex. Isolation of full-length cDNA sequences coding for ␥-glutamylcysteinyl synthetase from legume nodules revealed that they are highly homologous to those from other higher plants.The tripeptide glutathione (GSH; ␥Glu-Cys-Gly) is the major non-protein thiol in most animals, plants, and prokaryotes (Meister and Anderson, 1983; Hausladen and Alscher, 1993; Rennenberg, 1997). In plants, GSH is a versatile antioxidant that can directly scavenge activated oxygen species and participate in the ascorbate-GSH cycle for peroxide removal in the chloroplasts. It is also involved in many other vital functions of plants, including the transport and storage of sulfur, the synthesis of proteins and DNA, tolerance to abiotic and biotic stress, and the detoxification of xenobiotics, air pollutants, and heavy metals (Hausladen and