Biology Department, Carleton University Ottawa, K1S 5B6, Ontario, Canada.
Planta. 1976 Jan;129(3):265-9. doi: 10.1007/BF00398269.
Young leaves of Cucurbita pepo L. were examined by whole-leaf autoradiography and serial paradermal sections were examined by light microscopy to determine whether commencement of sugar export depends upon the minor vein phloem achieving structural maturity. Maturation of these veins develops progressively from the largest toward the smallest elements with the minor veins in the distal region of the leaf maturing before those in the proximal region. Commencement of sugar export is coincident with maturation of the abaxial phloem of the minor veins delimiting the areoles. The abaxial phloem elements of the larger minor veins, which are probably capable of vein loading too but border only relatively few areoles, mature before export starts. The adaxial phloem surrounding the areoles and the xylem elements, mature in advance of the abaxial phloem and well before the beginning of sugar export. It is therefore considered unlikely that structural development alone directly governs the initiation of export. The results suggest that some other rate controlling step is involved.
对南瓜的嫩叶进行全叶放射自显影，对连续的平行表皮切片进行光镜检查，以确定糖的输出是否取决于小叶脉韧皮部达到结构成熟。这些叶脉的成熟是从最大的元素向最小的元素逐渐发展的，叶片远端的小叶脉比叶片近端的小叶脉先成熟。糖的输出开始与界定叶窝的小叶脉背侧韧皮部的成熟同时发生。较大的小叶脉的背侧韧皮部元素可能也有叶脉装载的能力，但只与相对较少的叶窝相邻，在出口开始之前就成熟了。围绕叶窝的韧皮部和木质部元素，在背侧韧皮部成熟之前，以及在糖输出开始之前就已经成熟了。因此，结构发育本身不太可能直接控制输出的启动。结果表明，可能涉及到其他一些控制步骤。
