Williamson J D, Scandalios J G
Department of Genetics, North Carolina State University, Raleigh 27695-7614.
Plant J. 1992 May;2(3):351-8. doi: 10.1111/j.1365-313x.1992.00351.x.
Many fungi of the genus Cercospora produce a light-induced, photoactivated polyketide toxin called cercosporin. In the presence of light an excited form (triplet state) of the toxin molecule is produced which, depending on the reducing potential of the environment, reacts with molecular oxygen to produce singlet oxygen and/or superoxide radicals. In this paper a system is presented for analysis of antioxidant defense gene response using purified cercosporin under conditions demonstrated to favor superoxide formation. Under the assay conditions employed, changes in total catalase activity, as well as individual isozyme protein levels generally mirrored the changes observed in corresponding steady-state RNA levels in response to applied cercosporin. In contrast, while transcript accumulation for most maize superoxide dismutases increased dramatically, both total superoxide dismutase activity and individual isozyme protein levels remained constant in all toxin treatments. In one case, the analyses indicated that there are two distinct transcripts that hybridize with a gene-specific probe for Sod3. These two transcripts responded differentially to applied toxin (levels of the larger transcript increased while the smaller decreased), whereas corresponding steady-state levels for the SOD-3 isozyme proteins remained constant. This suggests that protein turnover might play a role in the response of these SODs to activated oxygen species.
尾孢菌属的许多真菌会产生一种光诱导、光活化的聚酮类毒素，称为尾孢菌素。在光照条件下，会产生毒素分子的激发态（三重态），根据环境的还原电位，它会与分子氧反应生成单线态氧和/或超氧自由基。本文介绍了一种系统，用于在已证明有利于超氧形成的条件下，使用纯化的尾孢菌素分析抗氧化防御基因反应。在所采用的测定条件下，总过氧化氢酶活性的变化以及各个同工酶蛋白水平通常反映了在施加尾孢菌素后相应稳态RNA水平中观察到的变化。相比之下，虽然大多数玉米超氧化物歧化酶的转录本积累显著增加，但在所有毒素处理中，总超氧化物歧化酶活性和各个同工酶蛋白水平均保持不变。在一个案例中，分析表明有两个不同的转录本与Sod3的基因特异性探针杂交。这两个转录本对施加的毒素反应不同（较大转录本的水平增加而较小转录本的水平降低），而SOD-3同工酶蛋白的相应稳态水平保持不变。这表明蛋白质周转可能在这些超氧化物歧化酶对活性氧的反应中起作用。
