Section of Plant Biology, Division of Biological Sciences, Cornell University, Ithaca, New York 14853-5908.
Plant Physiol. 1992 Jun;99(2):643-51. doi: 10.1104/pp.99.2.643.
Phloem import and unloading in perfused bean (Phaseolus vulgaris L.) seed coats were investigated using steady-state labeling. Though photosynthate import and unloading were significantly reduced by perfusion, measurements of photosynthate fluxes in perfused seed coats proved useful for the study of unloading mechanisms in vivo. Phloem import was stimulated by lowered seed coat cell turgor, as demonstrated by an increase in tracer and sucrose import to seed coats perfused with high concentrations of an osmoticum. The partitioning of photosynthates between retention in the seed coat and release to the perfusion solution also was turgor sensitive; increases in seed coat cell turgor stimulated photosynthate release to the apoplast at the expense of photosynthate retention within the seed coat. There was no evidence of a turgor-sensitive sucrose uptake mechanism in perfused seed coats. Thus, the turgor sensitivity of photosynthate partitioning within perfused seed coats was consistent with a turgor-sensitive efflux control mechanism. Measurements of tracer equilibration and sugar partitioning in perfused seed coats provided strong evidence for symplastic phloem unloading in seed coats.
我们采用稳态标记法研究了灌流菜豆（Phaseolus vulgaris L.）种皮中的韧皮部物质输入和卸出。尽管光合作用产物的输入和卸出在灌流后显著减少，但对灌流种皮中光合作用产物流的测量对于体内卸出机制的研究仍然很有用。降低种皮细胞膨压可刺激韧皮部物质输入，这可通过用高浓度渗透压物质灌流时示踪剂和蔗糖输入到种皮的增加来证明。光合作用产物在种皮中保留和释放到灌流溶液之间的分配也对膨压敏感；种皮细胞膨压增加会刺激光合作用产物向质外体释放，而牺牲种皮中光合作用产物的保留。在灌流种皮中没有发现对膨压敏感的蔗糖摄取机制。因此，灌流种皮中光合作用产物分配的膨压敏感性与膨压敏感的外排控制机制一致。示踪剂平衡和灌流种皮中糖分配的测量为种皮中存在共质体韧皮部卸出提供了有力证据。
