Prina A R, Arias M C, Lainez V, Landau A, Maldonado S
Instituto de Genética Ewald A. Favret, CICVyA CNIA INTA CC 25, B1712 WAA Castelar, Buenos Aires, Argentina.
Theor Appl Genet. 2003 Nov;107(8):1410-8. doi: 10.1007/s00122-003-1391-0. Epub 2003 Aug 15.
Cytoplasmic line 2 (CL2) has been previously reported as a cytoplasmically inherited chlorophyll-deficient mutant selected from a chloroplast-mutator genotype of barley. It was characterized by a localized effect on the upper part of the first-leaf blade. At emergence the CL2 seedlings-phenotype varied from a grainy light green to an albino color. They gradually greened during the following days, starting from the base of the blade and extending to cover most of its surface when it was fully grown. The present results, from both light microscopy and transmission electron microscopy (TEM), confirmed the previously described positional and time-dependent expression of the CL2 syndrome along the first-leaf blade. During the first days after emergence, light microscopy showed a normally developed chloroplast at the middle part of the CL2 first-leaf blade, meanwhile at the tip only small plastids were observed. TEM showed that the shapes and the internal structure of the small plastids were abnormal, presenting features of proplastids, amyloplasts and/or senescent gerontoplasts. Besides, they lack plastid ribosomes, contrasting with what was observed inside chloroplasts from normal tips, which presented abundant ribosomes. Phenotypic observations and spectrophotometric analysis of seedlings produced by mother plants that had been grown under different temperatures indicated that higher temperatures during seed formation were negatively associated with pigment content in CL2 seedlings. In contrast, higher temperatures during the growth of CL2 seedlings have been associated with increased pigment content. Aqueous solution with kanamycin and streptomycin, which are antibiotics known to interfere with plastid gene translation, were used for imbibition of wild-type and CL2 seeds. Antibiotic treatments differentially reduced the chlorophyll content in the upper part of the first-leaf blade in CL2, but not in wild-type seedlings. These results suggest that in the wild-type, plastid-gene proteins which are necessary for chloroplast development and chlorophyll synthesis in the upper part of the first-leaf blade are usually synthesized during embryogenesis. However, under certain circumstances, in CL2 seedlings, they would be synthesized after germination. In addition, a shortening of the sheath has been observed in association with pigment decrease suggesting the existence of plastid factors affecting the expression of some nuclear genes. We consider the CL2 mutant a unique experimental material useful to study biological phenomena and external factors regulating plastid, and nuclear gene expression during embryogenesis and early seedling development.
细胞质系2（CL2）先前已被报道为从大麦叶绿体突变体基因型中筛选出的一种细胞质遗传的叶绿素缺乏突变体。它的特征是对第一片叶片上部有局部影响。在出土时，CL2幼苗的表型从粒状浅绿色到白化颜色不等。在接下来的几天里，它们逐渐变绿，从叶片基部开始，在叶片完全长成时扩展到覆盖其大部分表面。目前来自光学显微镜和透射电子显微镜（TEM）的结果证实了先前描述的CL2综合征沿第一片叶片的位置和时间依赖性表达。在出土后的头几天，光学显微镜显示CL2第一片叶片中部有正常发育的叶绿体，而在叶尖仅观察到小的质体。TEM显示小质体的形状和内部结构异常，呈现前质体、造粉体和/或衰老质体的特征。此外，它们缺乏质体核糖体，这与正常叶尖叶绿体内部观察到的情况形成对比，正常叶尖叶绿体有丰富的核糖体。对在不同温度下生长的母本植物产生的幼苗进行表型观察和分光光度分析表明，种子形成期间较高的温度与CL2幼苗中的色素含量呈负相关。相反，CL2幼苗生长期间较高的温度与色素含量增加有关。已知会干扰质体基因翻译的抗生素卡那霉素和链霉素的水溶液用于野生型和CL2种子的浸种。抗生素处理不同程度地降低了CL2第一片叶片上部的叶绿素含量，但对野生型幼苗没有影响。这些结果表明，在野生型中，第一片叶片上部叶绿体发育和叶绿素合成所需的质体基因蛋白通常在胚胎发生期间合成。然而，在某些情况下，在CL2幼苗中，它们会在萌发后合成。此外，观察到叶鞘缩短与色素减少有关，这表明存在影响一些核基因表达的质体因子。我们认为CL2突变体是研究胚胎发生和幼苗早期发育过程中调节质体和核基因表达的生物学现象及外部因素的独特实验材料。
