Outlaw W H, Fisher D B, Christy A L
Department of Botany, University of Georgia, Athens, Georgia 30602.
Plant Physiol. 1975 Apr;55(4):704-11. doi: 10.1104/pp.55.4.704.
Leaflets of Vicia faba L. were pulse labeled with (14)CO(2) and the kinetics of (14)C-sucrose redistribution among individual tissues was followed. Sucrose specific activity in the whole leaf peaked about 15 minutes after labeling and declined with a half-time of about 80 minutes. In one experiment, leaflet discs taken at various times during the (12)CO(2) chase were quick frozen, freeze-substituted, and embedded in plastic. The tissue was sectioned paradermally and sections of palisade parenchyma, of spongy parenchyma, and of spongy parenchyma that contained veins were collected. Water extracts from these sections were assayed for sucrose specific activity. Sucrose specific activity in the palisade parenchyma was higher than that of the spongy parenchyma and reached a maximum in both tissues 9 to 15 minutes after labeling. Sucrose specific activity initially declined rapidly in the palisade parenchyma followed by a period during which little or no loss occurred. Sucrose specific activity in sections containing veins peaked at 15 minutes with a maximum value substantially higher than either mesophyll tissue, indicating that recently synthesized sucrose was preferentially exported from the mesophyll. Decline of activity in these sections containing veins continued for the remainder of the experiment. Sucrose specific activity in lower epidermal peels peaked several minutes after that of the whole leaflet and remained lower. Sucrose specific activity in upper epidermal peels was variable (probably due to contamination), but the limited data suggest that the sucrose specific activity there reached somewhat higher values than those of the lower epidermis. The experiments indicate that each leaf tissue contains a kinetically identifiable sucrose pool (which we refer to as "histological compartmentation"), and that further compartmentation may occur at the intracellular level. A simulation of leaf sucrose compartmentation is presented.
用(14)CO(2)对蚕豆叶片进行脉冲标记，并追踪(14)C - 蔗糖在各个组织间重新分配的动力学过程。标记后约15分钟，全叶中蔗糖的比活性达到峰值，随后以约80分钟的半衰期下降。在一项实验中，在(12)CO(2)追踪过程中的不同时间采集叶圆片，迅速冷冻、冷冻置换并包埋于塑料中。将组织进行平周切片，收集栅栏薄壁组织、海绵薄壁组织以及含有叶脉的海绵薄壁组织的切片。对这些切片的水提取物进行蔗糖比活性测定。栅栏薄壁组织中的蔗糖比活性高于海绵薄壁组织，且在标记后9至15分钟时，两种组织中的蔗糖比活性均达到最大值。栅栏薄壁组织中蔗糖比活性最初迅速下降，随后有一段很少或没有损失的时期。含有叶脉的切片中蔗糖比活性在15分钟时达到峰值，最大值显著高于任何一种叶肉组织，这表明新合成的蔗糖优先从叶肉输出。在实验的剩余时间里，这些含有叶脉的切片中的活性持续下降。下表皮的蔗糖比活性在整个小叶比活性达到峰值几分钟后达到峰值，且保持较低水平。上表皮的蔗糖比活性变化不定（可能是由于污染），但有限的数据表明，那里的蔗糖比活性达到的值略高于下表皮。这些实验表明，每个叶片组织都含有一个动力学上可识别的蔗糖库（我们称之为“组织学区室化”），并且在细胞内水平可能会发生进一步的区室化。本文给出了叶片蔗糖区室化的模拟情况。
