Pith autolysis in plants. IV. The activity of polygalacturonase and cellulase during drought stress induced pith autolysis
1993
Huberman, M. | Pressman, E. | Jaffe, M.J.
The water potential, amount of pith autolysis and activities of apoplastic cellulase and polygalacturonase of tomato stems were measured during 24 h of drought stress (DS) and for 24 h following reirrigation. During DS the water potential dropped from -5.5 to -10.4 bars and rose to -8.3 bars soon after reirrigation. Drought stress induced considerable pith autolysis, more of which occurred after reirrigation. Pretreatment with mechanical perturbation (MP) of the stems or application of exogenous ethephon on the buds hardened the tomato plants against DS-induced pith autolysis. Drought stress caused an increase in apoplastic polygalacturonase and an even greater increase in apoplastic cellulase. Reirrigation caused a large transient increase in the former and a decrease in the latter. The apoplastic reducing sugar content (as galacturonic acid) of the stem rose in parallel with the activity of the enzymes. Both DS and MP caused an increase in ethylene evolution, although the former was significantly greater than the latter. However, when MP preceded DS, the amount of ethylene produced was significantly less than DS alone induced. Pretreatment with either MP or exogenous ethephon inhibited the increase in apoplastic cellulytic enzymes. It is concluded that DS induces ethylene evolution from the tomato stem, causing an increase in the stem apoplastic cellulytic enzymes, which in turn start the autolysis of the pith cell walls. Pretreatment with MP or ethephon, each of which induces ethylene evolution, hardens the stem so that it does not produce more ethylene during DS, and thus becomes resistant to DS-induced pith autolysis.
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