Ribonuclease activity of stressed tomato leaflets

Homogenates of leaflets of desiccated tomato plants show increased ribonuclease activity compared to homogenates of turgid controls. Much of this increase is independent of changes in translocation to and from the leaflet. Interruption of translocation through living cells by detachment of leaflets or steam damage to the petiolules produces increased ribonuclease activity, but this activity is increased further when excised leaflets are allowed to wilt. Increases in ribonuclease often parallel or precede increases in the soluble nitrogen content. Further increases in activity occur when excised leaves become yellow. Exposure of leaflets to CO(2)-free air has little effect on activity at low-light intensity (120 ft-c). These results suggest that water stress directly affected ribonuclease activity at the cellular level.