Activation and de novo synthesis of ribonuclease following mechanical damage to leaves of Solanum tuberosum L.

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Abstract
The pattern of changes in RNase activity in damaged potato leaves incubated in the presence of [14C]leucine followed closely that of leaves incubated in the absence of the radioisotope, but the levels of activity during time course experiments were consistently lower. Contributions of other nucleolytic enzymes to the increased capacity of damaged leaves to hydrolyse RNA were slight. Two peaks of RNase activity were isolated from leaves that had been damaged for 24 h. One of these peaks represented a form of the enzyme that occurred in undamaged leaves and which increased markedly in activity on damage. The second peak represented a novel form of the enzyme which still possessed appreciable radioactivity after further extensive purification. It is suggested that a component of this peak was due to de novo synthesis of enzyme. Several additional new peaks of RNase activity were resolved from homogenates of leaves which had been damaged for 48 h. None of these peaks contained a significant amount of radioactivity when final purification was attained. It was concluded that although some de novo synthesis of RNase may occur during the first 24 h following mechanical damage the majority of increased enzyme activity up to that point and thereafter is due to activation of pre-formed enzyme.