Senescence of Rice Leaves VI. Comparative Study of the Metabolic Changes of Senescing Turgid and Water-Stressed Excised leaves

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Some metabolic changes of senescing turgid and water-stressed excised rice leaves were compared under incubation in the dark. The decrease of the chlorophyll and protein level and the increase of the α-amino nitrogen were faster in the water-stressed leaves than in the turgid leaves during the first two or three days of incubation. How-ever, the changes in levels of chlorophyll, protein and α-amino nitrogen were later retarded by water stress. The rate of decline in soluble sugar was more rapid in the turgid than in the water-stressed leaves. In turgid leaves, there was a slight but significant increase in the proline content in the first day of incubation; subsequently, proline accumulated relatively rapidly, yet at a slower rate than in the stressed leaves. The activity of acid inorganic pyrophosphatase increased, but that of alkaline inorganic pyrophosphatase decreased during the senescence of both turgid and water-stressed leaves. The enzyme activities are, therefore, due to two separate enzyme proteins. Water stress enhanced the increase of acid inorganic pyrophosphatase activity only during the first two days; it retarded the decrease of alkaline inorganic pyrophosphatase activity at later stage of incubation. It is concluded that water stress does not accelerate all the metabolic changes associated with the senescence of excised leaves.
日本植物生理学会の論文