Cheng W. H., Im K. H., Chourey P. S.
Program in Plant Molecular and Cellular Biology (W.-H.C., P.S.C.), Departments of Plant Pathology (K.H.I., P.S.C.) and Agronomy (P.S.C.), University of Florida and United States Department of Agriculture-Agricultural Research Service (P.S.C.), Gainesville, Florida 32611-0680.
Plant Physiol. 1996 Aug;111(4):1021-1029. doi: 10.1104/pp.111.4.1021.
Immunohistological analyses for sucrose phosphate synthase (SPS) show that the protein is localized in both bundle-sheath cells (BS) and mesophyll cells (M) in maize (Zea mays) leaves. In young leaves, SPS protein was predominantly in the BS, whereas mature leaves showed nearly equal levels of signal in both BS and M. A cell-type-specific response was also seen in light and dark treatments. Dark treatments led to reduced signal in M; however, little or no change was detected in BS. We suggest that SPS in BS is engaged in sucrose biosynthesis by both photoassimilatory and starch turnover reactions in maize leaves. In addition, we suggest that the enzyme in BS may play a major role in the early biosynthesis of sucrose in young leaves. These cell-specific changes in expression in situ were in agreement with the estimates of extractable enzyme activity from isolated BS and M of mature leaves (R. Ohsugi, S.C. Huber [1987] Plant Physiol 84: 1096-1101). In contrast, western blot analyses did not show any significant changes in the levels of SPS protein in either young or mature leaves subsequent to similar dark treatments. It is interesting that the northern blot analyses indicate that the steady-state levels of SPS transcripts were markedly reduced after dark treatments of > 12 h. Overall, our results indicate that Sps gene expression in maize leaf is modulated at multiple levels of controls by both developmental and environmental factors.
对蔗糖磷酸合酶（SPS）的免疫组织学分析表明，该蛋白定位于玉米（Zea mays）叶片的维管束鞘细胞（BS）和叶肉细胞（M）中。在幼叶中，SPS蛋白主要存在于维管束鞘细胞中，而成熟叶片在维管束鞘细胞和叶肉细胞中的信号水平几乎相等。在光照和黑暗处理中也观察到了细胞类型特异性反应。黑暗处理导致叶肉细胞中的信号减少；然而，在维管束鞘细胞中未检测到明显变化或没有变化。我们认为，玉米叶片中维管束鞘细胞中的SPS通过光同化和淀粉周转反应参与蔗糖生物合成。此外，我们认为维管束鞘细胞中的该酶可能在幼叶蔗糖的早期生物合成中起主要作用。这些原位表达的细胞特异性变化与从成熟叶片分离的维管束鞘细胞和叶肉细胞中可提取酶活性的估计结果一致（R. Ohsugi，S.C. Huber [1987] Plant Physiol 84: 1096 - 1101）。相比之下，蛋白质印迹分析未显示在类似黑暗处理后幼叶或成熟叶片中SPS蛋白水平有任何显著变化。有趣的是，Northern印迹分析表明，黑暗处理超过12小时后，SPS转录本的稳态水平显著降低。总体而言，我们的结果表明，玉米叶片中Sps基因的表达受到发育和环境因素在多个控制水平上的调节。
