Senescence of Rice Leaves

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.