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Source: From Kumar, V. et al., Plant Soil, 59, 3-8, 1981.

Source: From Kumar, V. et al., Plant Soil, 59, 3-8, 1981.

of sulfoquinovosyl diacylglycerol is still under investigation; in particular, the sulfur precursor for the formation of the sulfoquinovose is not known, though from recent observations it is evident that sulfite is the likely candidate (58).

Cysteine is the precursor for the tripeptide glutathione (yGluCysGly; GSH), a thiol compound that is of great importance in plant functioning (32,59,60,61). Glutathione synthesis proceeds in a two-step reaction. First, y-glutamylcysteine is synthesized from cysteine and glutamate in an ATP-dependent reaction catalyzed by y-glutamylcysteine synthetase (Equation 7.1). Second, glutathione is formed in an ATP-dependent reaction from y-glutamylcysteine and glycine (in glutathione homologs, P-alanine or serine) catalyzed by glutathione synthetase (Equation 7.2):

Cys + Glu + ATP-,, , ,.-—-> vGluCys + ADP + Pi (7i)

J y-glutamylcysteine synthetase ' J \ f . i J

vGluCys + Gly + ATP ——--—-> yGluCysGly + ADP + Pi (7 2)

glutathione synthetase

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