離體玉米葉片在老化過程中的一些分解代謝

Metabolism of Detached, Senescing Corn Leaves: Some Events About the Disassembly

在照光下生長八天的玉米幼苗，切取第一片葉，分別懸浮於水或1×10-5 M BA（N6-benzyladenine）內，並放置於28°C黑暗下。在此條件下，懸浮於水的對照組葉片，在第二天之後，其葉綠素、蛋白質與核糖核酸就開始顯著減少。BA處理組則延緩上述各種症狀的顯現。因懸浮於水的對照組的葉片會增加蛋白分解酶（protease）及核糖核酸分解酶（RNase）的活性。離體葉片先在照光下以35S-methionine標誌5小時，再如上述的方法將葉片分別懸浮於水或BA，由結果得知懸浮於BA溶液的葉片蛋白質放射性之活性比對照組高出許多。因此可推測BA可抑制葉片在正常老化情況下蛋白質分解酶活性的增加。在老化過程中，葉片的呼吸率會增加；而且在老化之末期，acid phosphatase的活性會劇增，但細胞壁的組成分，半纖維素I、II及纖維素則沒有任何顯著的減少。

First leaves of 8-day-old, light grown corn seedlings were cut and then were floated in water or 1 × 10-5 M N6-benzyladenine (BA) solution at 28°C in the dark. Under these conditions, the leaf segments in water showed a significant lose chlorophyll, protein and RNA after 2 days. Treatment with BA delayed the appearance of these symptoms. Protease and RNase activities of segments floated in water were seen to increase. If leaf segments were preincubated with 35S-methionine for five hours under light shortly after cut and then transfered to the treatments described above, the segments floated in BA solution had more radioactivity in the protein fraction than the segments floated in water. We concluded that BA can supress the increase of proteolytic activity normally associated with senescence. During senescence the respiration rate of leaf segments increased. Acid phosphatase activity increased strongly during the late stages of senescence of leaf segments. The contents of hemicellulose I, II and cellulose of the cell wall did not decrease significantly.