Ting J T, Wu S S, Ratnayake C, Huang A H
Department of Botany and Plant Sciences, University of California, Riverside 92521, USA.
Plant J. 1998 Dec;16(5):541-51. doi: 10.1046/j.1365-313x.1998.00325.x.
In Brassica anthers during microsporogenesis, the tapetum cells contain two abundant lipid-rich organelles, the tapetosomes possessing oleosins and triacylglycerols (TAGs), and the elaioplasts having unique polypeptides and neutral esters. B. campestris, for its simplicity of possessing only the AA genome and one predominant oleosin of 45 kDa, was studied. In the developing anthers, the lipids and proteins of the tapetosomes and elaioplasts were concomitantly accumulated but selectively degraded or retained. Upon incubation of isolated tapetosomes in a pH-5 medium, the predominant 45 kDa oleosin underwent selective enzymatic proteolysis to a 37 kDa fragment, which was not further hydrolyzed upon prolonged incubation. The unreacted 45 kDa oleosin was retained in the organelles, whereas the 37 kDa fragment was released to the exterior. The fragment would become the predominant 37 kDa polypeptide in the pollen coat. Isolated tapetosomes did not undergo hydrolysis of the TAGs upon incubation in media of diverse pHs. An alkaline lipase in the soluble fraction of the anther extract was presumed to be the enzyme that would hydrolyze the tapetosome TAGs, which disappeared in the anthers during development. The tapetum elaioplasts contained several unique polypeptides of 31-36 kDa. The gene encoding a 32 kDa polypeptide was cloned, and its deduced amino acid sequence was homologous to those of two proteins known to be present on the surface of fibrils in chromoplasts. Upon incubation of isolated elaioplasts in media of diverse pHs, the organelle polypeptides were degraded completely and most rapidly at pH 5, whereas the neutral esters remained unchanged; these neutral esters would become the major lipid components of the pollen coat. The findings show that the constituents of the two major tapetum organelles underwent very different paths of degradation, or modification, and transfer to the pollen surface.
在芸苔属植物花药的小孢子发生过程中，绒毡层细胞含有两种丰富的富含脂质的细胞器，即含有油质蛋白和三酰甘油（TAGs）的油质体，以及具有独特多肽和中性酯的造油体。由于白菜型油菜基因组简单，仅拥有AA基因组和一种主要的45 kDa油质蛋白，因此对其进行了研究。在发育中的花药中，油质体和造油体的脂质和蛋白质同时积累，但会被选择性地降解或保留。将分离的油质体在pH值为5的培养基中孵育时，主要的45 kDa油质蛋白会被选择性地酶解为37 kDa的片段，长时间孵育后该片段不会进一步水解。未反应的45 kDa油质蛋白保留在细胞器中，而37 kDa的片段则释放到外部。该片段将成为花粉壁中主要的37 kDa多肽。分离的油质体在不同pH值的培养基中孵育时，TAGs不会发生水解。花药提取物可溶部分中的一种碱性脂肪酶被认为是水解油质体TAGs的酶，这些TAGs在花药发育过程中消失。绒毡层造油体含有几种31 - 36 kDa的独特多肽。克隆了编码32 kDa多肽的基因，其推导的氨基酸序列与已知存在于有色体原纤维表面的两种蛋白质的序列同源。将分离的造油体在不同pH值的培养基中孵育时，细胞器多肽在pH值为5时完全且最快速地降解，而中性酯保持不变；这些中性酯将成为花粉壁的主要脂质成分。研究结果表明，两种主要绒毡层细胞器的成分经历了非常不同的降解、修饰途径，并转移到花粉表面。
