Gidrol X, Lin W S, Dégousée N, Yip S F, Kush A
Institute of Molecular and Cell Biology, National University of Singapore.
Eur J Biochem. 1994 Aug 15;224(1):21-8. doi: 10.1111/j.1432-1033.1994.tb19990.x.
Seed germination is an important developmental switch when quiescent seed cells initiate oxidative phosphorylation for further development and differentiation. During early imbibition of soybean seeds (Glycine max L. cv. Weber), a superoxide dismutase (SOD) activity peak was observed, in embryonic axes, after 6 h imbibition. Peroxidase activities, including catalase, were significantly increased after 12 h inhibition and during germination phase III. Catalase was the most efficient enzyme in catabolizing H2O2 in embryonic axes. When stored at 42 degrees C and 100% relative humidity, seeds were stressed and lost their viability in a time-dependent manner. A significant increase in the Cu, Zn-superoxide-dismutase activity, and to a lesser extent, Mn superoxide dismutase activity was observed during germination in low-viability (stressed) seeds as compared to high-viability (unstressed) seeds. Northern blot analysis confirmed that superoxide dismutase induction resulted from an accumulation of its transcripts in response to the production of O2-. The induction of catalase did not occur in low-viability seeds, resulting in dramatic accumulation of H2O2. Using capillary electrophoresis, HPLC and NMR we found that the endogenous cytokinin, zeatin riboside, was present in large quantities in the high-viability seeds, but it was oxidized into adenine in the low-viability seeds. In vitro superoxide anion could also oxidize the cytokinin. Zeatin riboside, but not adenine, was found to act as a scavenger of superoxide anions and may help to maintain seed viability by detoxifying reactive oxygen species. Germination of stressed seeds was partially restored by the addition of exogenous cytokinin (zeatin riboside). Protection against oxidative stress by cytokinin seemed to be a general phenomenon, as Escherichia coli cells were also protected against superoxide stress in the presence of cytokinin.
种子萌发是一个重要的发育转变过程，此时静止的种子细胞启动氧化磷酸化以进行进一步的发育和分化。在大豆种子（Glycine max L. cv. Weber）早期吸水过程中，在吸胀6小时后，胚轴中观察到超氧化物歧化酶（SOD）活性峰值。包括过氧化氢酶在内的过氧化物酶活性在抑制12小时后和萌发第三阶段显著增加。过氧化氢酶是胚轴中分解过氧化氢最有效的酶。当种子在42摄氏度和100%相对湿度下储存时，会受到胁迫并随时间推移丧失活力。与高活力（未受胁迫）种子相比，在低活力（受胁迫）种子萌发过程中观察到铜锌超氧化物歧化酶活性显著增加，锰超氧化物歧化酶活性增加程度较小。Northern印迹分析证实，超氧化物歧化酶的诱导是由于其转录本响应O2-的产生而积累。过氧化氢酶在低活力种子中未被诱导，导致过氧化氢大量积累。使用毛细管电泳、HPLC和NMR，我们发现内源性细胞分裂素玉米素核苷在高活力种子中大量存在，但在低活力种子中被氧化成腺嘌呤。体外超氧阴离子也能氧化细胞分裂素。发现玉米素核苷而非腺嘌呤可作为超氧阴离子的清除剂，并可能通过清除活性氧来帮助维持种子活力。添加外源细胞分裂素（玉米素核苷）可部分恢复受胁迫种子的萌发。细胞分裂素对氧化应激的保护似乎是一种普遍现象，因为在细胞分裂素存在的情况下，大肠杆菌细胞也受到超氧应激的保护。
