The relationship between proteolytic activity and loss of soluble protein in rice leaves from anthesis through senescence

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Abstract
The relationship between proteinase activity and loss of soluble protein from leaves was examined in the top four leaves on the main stems of rice from anthesis through senescence. During the period of rapid loss of soluble protein in the early and middle stages of senescence, changes in the proteinase activity were relatively small in these leaves: the activity slightly increased or fluctuated to some extent. However, the activity increased remarkably in all four leaves in the last stage of senescence although only a small amount of soluble protein had remained in these leaves. Rice plants were cultured with different amounts of nitrogen application and changes in proteinase activity in the third leaves from flag leaves were followed during senescence. The changes in the activity in the leaves were small during the period of rapid loss of soluble protein regardless of the status of nitrogen nutrition. These results indicate that proteinase activity is not necessarily correlated with the rate of protein loss from leaves during senescence of rice leaves.