Roth R., Hall L. N., Brutnell T. P., Langdale J. A.
Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, United Kingdom.
Plant Cell. 1996 May;8(5):915-927. doi: 10.1105/tpc.8.5.915.
Within the maize leaf primordium, coordinated cell division and differentiation patterns result in the development of two morphologically and biochemically distinct photosynthetic cell types, the bundle sheath and the mesophyll. The bundle sheath defective2-mutable1 (bsd2-m1) mutation specifically disrupts C4 differentiation in bundle sheath cells in that the levels of bundle sheath cell-specific photosynthetic enzymes are reduced and the bundle sheath chloroplast structure is aberrant. In contrast, mesophyll cell-specific enzymes accumulate to normal levels, and the mesophyll cell chloroplast structure is not perturbed. Throughout mutant leaf development, the large and small subunits of ribulose bisphosphate carboxylase are absent; however, both rbcL and RbcS transcripts accumulate. Moreover, chloroplast-encoded rbcL transcripts accumulate ectopically in mesophyll cells. Although the bundle sheath cell chloroplast structure deteriorates rapidly when plants are exposed to light, this deterioration is most likely a secondary effect resulting from cell-specific photooxidative damage. Therefore, we propose that the Bsd2 gene plays a direct role in the post-transcriptional control of rbcL transcript accumulation and/or translation, both in bundle sheath and mesophyll cells, and an indirect role in the maintenance of bundle sheath cell chloroplast structure.
在玉米叶原基中，协调的细胞分裂和分化模式导致了两种形态和生化特性不同的光合细胞类型的发育，即维管束鞘细胞和叶肉细胞。束鞘缺陷2-可变1（bsd2-m1）突变特异性地破坏了维管束鞘细胞中的C4分化，因为维管束鞘细胞特异性光合酶的水平降低，且维管束鞘叶绿体结构异常。相比之下，叶肉细胞特异性酶积累到正常水平，且叶肉细胞叶绿体结构未受干扰。在整个突变叶发育过程中，1,5-二磷酸核酮糖羧化酶的大亚基和小亚基均不存在；然而，rbcL和RbcS转录本均有积累。此外，叶绿体编码的rbcL转录本在叶肉细胞中异位积累。尽管当植物暴露于光照下时，维管束鞘细胞叶绿体结构会迅速恶化，但这种恶化很可能是细胞特异性光氧化损伤导致的次级效应。因此，我们提出，Bsd2基因在维管束鞘细胞和叶肉细胞中对rbcL转录本积累和/或翻译的转录后控制中起直接作用，并在维持维管束鞘细胞叶绿体结构中起间接作用。
