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Articles

Senescence of Rice Leaves ¹

VII. PROLINE ACCUMULATION IN SENESCING EXCISED LEAVES

Department of Agronomy, National Taiwan University, Taipei, Taiwan, Republic of China

Proline content increased greatly in detached rice (Oryza sativa cv. Taichung Native 1) leaves during senescence. There was a slight but significant increase in proline level after one day of incubation, and, subsequently, proline accumulated relatively rapidly. By 4 days after excision, the level of proline had increased 30- to 50-fold, which is similar to the level seen in the water-stressed detached rice leaves. It is unlikely that the proline accumulation in detached leaves is to be derived solely from protein hydrolysis, since the addition of L-glutamic acid increased the proline level during senescence. The proline analog, 3,4-dehydroproline, did not affect the level of proline during senescence. It seems that accumulation of proline may, at least in part, result from an increased rate of synthesis, possibly due to a disruption of the normal feedback inhibition of proline synthesis. Potassium cyanide and 2,4-dinitrophenol strongly inhibited proline accumulation, indicating that some energy compound(s) may participate in proline accumulation during senescence of excised rice leaves.

¹ Supported by research grant to C. H. Kao from the National Science Council of the Republic of China.