Synthesis of the photorespiratory key enzyme serine: glyoxylate aminotransferase in C. reinhardtii is modulated by the light regime and cytokinin
2006
Tian, Bao-jing | Wang, Yong | Zhu, Ye-rong | Lü, Xian-yu | Huang, Kaiyao | Shao, Ning | Beck, Christoph F.
Serine:glyoxylate aminotransferase (SGAT) is a key enzyme of photorespiration. Changes in SGAT transcript levels and in enzyme activity following shifts from light to dark or dark to light and after cultivation in media supplemented with 6-benzyladenine (6-BA), a synthetic cytokinin, were analysed in the green alga Chlamydomonas reinhardtii. Cells grown in darkness had higher transcript levels than those grown in the light and transcript levels decreased upon transfer of cultures from dark to light; in contrast, they increased upon shift from light to dark. However, higher enzyme activities were detected in light-grown vs. dark-grown cells, which could be correlated with an elevated photorespiratory activity of the light-grown cultures. Application of the synthetic cytokinin into the medium promoted both the accumulation of SGAT mRNA and enhanced SGAT enzyme activity. Under these conditions an accelerated multiplication of cells as well as higher final cell densities were observed. However, the synthetic cytokinin did not affect chlorophyll content, which is different from cytokinin effects observed in higher plants. The presence of cytokinin-like activities in C. reinhardtii was confirmed using high-performance liquid chromatography. One of these activities was identified by mass-spectroscopy to be zeatin riboside.
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