Reversibility of Functional Transformation of Microbodies

1.在萌发的脂肪幼苗中，微体在功能上从乙氧基体转化为叶片过氧化体，在衰老过程中从叶片过氧体转化为乙氧体。免疫细胞化学研究表明，绿化期乙氧基体可以直接转换为叶片过氧体，衰老过程中叶片过氧体再次直接转化为乙氧体。为了明确微体转化的调控机制，获得了由柠檬酸合成酶(GCS)和β-葡萄糖苷酶(GUS)的N-末端区域组成的融合蛋白的转基因拟南芥植株，并用免疫学和免疫细胞化学方法对其定位和加工进行了研究。融合蛋白被运送到功能不同的微体中，如乙氧基体、叶片过氧化物体和非特化微体，并随后进行加工。这些观察结果表明，GCS的转运是由其α…介导的。更多的微末端前序列，运输系统在所有植物微体中都起作用。因此，乙氧基体和叶片过氧化物体不太可能具有不同的靶向机制。羟丙酮酸还原酶属于叶片过氧化物体专一性酶，在绿色化过程中积累在微体中。两种不同的羟丙酮酸还原酶(HPR1和HPR2)在南瓜中表达。HPR的cDNA和基因组DNA克隆强烈表明HPR1和HPR2是通过选择性剪接产生的。两种不同的羟丙酸还原酶HPR1和HPR2分别定位于微体和胞浆中，提示微体的转变可能是通过选择性剪接来调节的。对乙氧基体膜上的两种蛋白质进行了纯化和鉴定，其分子量分别为31 kDa和28 kDa。前者是一种新的抗坏血酸过氧化物酶。结果表明，这些膜蛋白在微体从乙氧体向叶过氧化体转变的过程中逐渐减少，大的保留在叶片的过氧体中，而在微体转变完成后在叶片的过氧体中没有发现小的膜蛋白。结果清楚地表明，糖氧体中的膜蛋白在微体转变过程中发生了显著变化，基质中的酶也是如此。较少

1. In germinating fatty seedlings, microbodies are functionally transformed to leaf peroxisomes from glyoxysomes, and during greening to glyoxysomes from leaf peroxisomes during senesecence.Immunocytochemical studies have shown that glyoxysomes can exchange directly into leaf peroxisomes during greening and leaf peroxisomes are once again converted directly to glyoxysomes during senescence. To crarify the regulation underlying the microbody tranformation, transgenic Arabidopsis plants that expressed a fusion protein composed of the N-terminal region of and glyoxysomal citrate synthase (gCS) and beta-glucuromidase (GUS), were generated and their localization and processing were characterized by immunological and immunocytochemical methods. The fusion protein was transported into functionally different microbodies, such as glyoxysomes, leaf peroxisomes and unspecialized microbodies and was subsequently processed. These observations indicated that the transport of gCS is mediated by its a … More minoterminal presequence and that the transport system is functional in all plant microbodies. Therefore, it is unlikely that glyoxysomes and leaf peroxisomes possess different targeting machineries.2. Hydroxpyruvate reductase belongs to leaf-peroxisome specific enzymes and is accumulated in microbodies during greening. Two different hydroxypyruvate redutase (HPR1 and HPR2) are expressed in pumpkin. cDNA and genomic DNA cloning for HPR strongly suggests that HPR1 and HPR2 are produced by alternative splicing. Two different hydroxypryuvate reductase, HPR1 and HPR2, are shown to be localized in microbodies and in the cytosol respectively, suggesting the possibility that the microbody transition may be regulated by alternative splicing.3. Two proteins in glyoxysomal membranes with molecular masses of 31kDa and 28kDa were purified and characterized. The former was shown to be a novel ascorbate peroxidase. It was found that the amounts of these membrance proteins decreased during the microbody transition from glyoxysomes to leaf peroxisomes and that the large one was retained in leaf peroxisomes, whereas the small one could not be found in leaf peroxisomes after completion of the microbody transition. The results clearly showed that membrane proteins in glyoxysomes change dramatically during the microbody transition, as do the enzymes in the matrix. Less