Cronshaw J, Esau K
J Cell Biol. 1968 Aug;38(2):292-303. doi: 10.1083/jcb.38.2.292.
During maturation of sieve elements in Cucurbita maxima Duchesne, the P-protein bodies (slime bodies) usually disperse in the tonoplast-free cell. In some sieve elements the P-protein bodies fail to disperse. The occurrence of dispersal or nondispersal of P-protein bodies can be related to the position of the sieve elements in the stem or petiole. In the sieve elements within the vascular bundle the bodies normally disperse; in the extrafascicular sieve elements the bodies often fail to disperse. Extrafascicular sieve elements showing partial dispersal also occur. The appearance of the sieve plate in fixed material is related to the degree of dispersal or nondispersal of the P-protein bodies. In sieve elements in which complete dispersal occurs the sieve plate usually has a substantial deposit of callose, and the sieve-plate pores are filled with P protein. In sieve elements containing nondispersing P-protein bodies the sieve plate bears little or no callose, and its pores usually are essentially "open." The dispersed P-protein components may aggregate into loosely organized "strands," which sometimes extend vertically through the cell and continue through the sieve-plate pores; but they may be oriented otherwise in the cell, even transversely.
在南瓜（Cucurbita maxima Duchesne）筛管分子成熟过程中，P蛋白体（黏液体）通常在无液泡膜的细胞中分散。在一些筛管分子中，P蛋白体未能分散。P蛋白体分散或未分散的情况可能与筛管分子在茎或叶柄中的位置有关。在维管束内的筛管分子中，这些体通常会分散；在束外筛管分子中，这些体常常未能分散。也会出现部分分散的束外筛管分子。固定材料中筛板的外观与P蛋白体的分散或未分散程度有关。在完全分散的筛管分子中，筛板通常有大量胼胝质沉积，筛板孔充满P蛋白。在含有未分散P蛋白体的筛管分子中，筛板几乎没有或没有胼胝质，其孔通常基本“开放”。分散的P蛋白成分可能聚集成松散组织的“链”，有时垂直穿过细胞并继续穿过筛板孔；但它们在细胞中可能以其他方式排列，甚至是横向排列。
