Effect of hydrogen peroxide on degradation of cell wall associated proteins in growing bean hypocotyls
1995
The possible involvement of active oxygen species and an apoplastic endopeptidase (EP) in the digestion of cell wall proteins was studied in extracellular fluid (EF) from hypocotyls of Phaseolus vulgaris at different stages of elongation. EF proteins underwent significant changes in polypeptide pattern during hypocotyl growth, which were characterized by increases in 35, 39, 40 and 50 kDa peptides and appearance of 61, 70 and 75 kDa peptides at the exponential growth phase. EFs also contain endopeptidase [Gomez et al. (1994) Agriscientia 11:3]. Autolysis experiments without or with purified EP revealed that many cell wall polypeptides are liable to degradation by the protease. Besides, EF polypeptides increased their susceptibility to EP during hypocotyl elongation. The 50 and 40 kDa polypeptides were poorly degraded when extracted from hypocotyls in active growth, but greatly hydrolyzed when extracted from fully elongated tissues, suggesting that in the course of growth proteins underwent modifications that rendered them more prone to proteolytic attack. These modifications seemed to involve active oxygen species, as indicated by: (a) H2O2 level rised when protein susceptibility to EP increased; and (b) EF proteins from growing hypocotyls (comparatively less susceptible to EP) treated with H2O2 were rapidly degraded by the protease.
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