Li X X, Franceschi V R
Program in Genetics and Cell Biology, Washington State University, Pullman 99164-4230.
Eur J Cell Biol. 1990 Feb;51(1):9-16.
Calcium oxalate formation in Lemna minor L. occurs in structurally specialized cells called crystal idioblasts. Cytochemical and immunocytochemical protocols were employed to study the distribution of peroxisomes and the enzymes glycolate oxidase, glycine decarboxylase and ribulose 1,5-bisphosphate carboxylase-oxygenase (RuBisCO) in relation to synthesis of oxalate used for Ca oxalate formation. These enzymes are necessary for photorespiratory glycolate synthesis and metabolism. Using catalase cytochemistry, microbodies were found to exist in crystal idioblasts but were smaller and fewer than those found in mesophyll cells. Glycolate oxidase, which can oxidize glycolate to oxalate via glyoxylate, could not be found in microbodies of crystal idioblasts at any stage of development. This enzyme increased in amount in microbodies of mesophyll cells as they matured and could even be found in dense amorphous inclusions of mature cell peroxisomes. Glycine decarboxylase and RuBisCO could also be detected in increasing amount in mesophyll cells as they matured but could not be detected in idioblasts or were just detectable. Thus, Lemna idioblasts lack the machinery for synthesis of oxalate from glycolate. Based on these results and other available information, two general models for the generation and accumulation of oxalate used for Ca oxalate formation in crystal idioblasts are proposed. The biochemical specialization of crystal idioblasts indicated by this study is also discussed with respect to differentiation of cellular structure and function.
浮萍（Lemna minor L.）中草酸钙的形成发生在结构特殊的细胞中，即晶体异细胞。采用细胞化学和免疫细胞化学方法，研究过氧化物酶体以及乙醇酸氧化酶、甘氨酸脱羧酶和1,5-二磷酸核酮糖羧化酶加氧酶（RuBisCO）的分布与用于草酸钙形成的草酸合成之间的关系。这些酶是光呼吸乙醇酸合成和代谢所必需的。通过过氧化氢酶细胞化学方法发现，晶体异细胞中存在微体，但比叶肉细胞中的微体更小且数量更少。在晶体异细胞发育的任何阶段，微体中均未发现能将乙醇酸通过乙醛酸氧化为草酸的乙醇酸氧化酶。随着叶肉细胞成熟，该酶在叶肉细胞微体中的含量增加，甚至在成熟细胞过氧化物酶体的致密无定形内含物中也能发现。随着叶肉细胞成熟，甘氨酸脱羧酶和RuBisCO在叶肉细胞中的含量也逐渐增加，但在异细胞中未检测到或仅可检测到少量。因此，浮萍异细胞缺乏从乙醇酸合成草酸的机制。基于这些结果和其他现有信息，提出了两种用于解释晶体异细胞中草酸钙形成所涉及的草酸生成和积累的一般模型。本研究表明的晶体异细胞的生化特化也结合细胞结构和功能的分化进行了讨论。
