Botany Department, University of Michigan, Ann Arbor, Michigan 48109.
Plant Physiol. 1983 May;72(1):182-5. doi: 10.1104/pp.72.1.182.
Excised soybean (Glycine max [L.] Merrill) cv Anoka leaf discs tend to remain green even after the corresponding intact leaves have turned yello on fruiting plants. We have found that explants which include a leaf along with a stem segment (below the node) and one or more pods (maintained on distilled H(2)O) show similar but accelerated leaf yellowing and abscission compared with intact plants. In podded explants excised at pre-podfill, the leaves begin to yellow after 16 days, whereas those excised at late podfill begin to yellow after only 6 days. Although stomatal resistances remain low during the first light period after excision, they subsequently increase to levels above those in leaves of intact plants. Explants taken at mid to late podfill with one or more pods per node behave like intact plants in that pod load does not affect the time lag to leaf yellowing. Explant leaf yellowing and abscission are delayed by removal of the pods or seeds or by incubation in complete mineral nutrient solution or in 4.6 micromolar zeatin. Like chorophyll breakdown, protein loss is accelerated in the explants, but minerals or especially zeatin can retard the loss. Pods on explants show rates and patterns of color change (green to yellow to brown) similar to those of pods on intact plants. These changes start earlier in explants on water than in intact plants, but they can be delayed by adding zeatin. Seed dry weight increased in explants, almost as much as in intact plants. Explants appear to be good analogs of the corresponding parts of the intact plant, and they should prove useful for analyzing pod development and mechanisms of foliar senescence. Moreover, our data suggest that the flux of minerals and cytokinin from the roots could influence foliar senescence in soybeans, but increased stomatal resistance does not seem to cause foliar senescence.
切除的大豆（Glycine max [L.] Merrill）cv Anoka 叶片即使在对应的完整叶片在结果植物上变黄后也往往保持绿色。我们发现，包括叶片以及茎段（节点以下）和一个或多个豆荚（保持在蒸馏水中）的外植体与完整植物相比表现出相似但加速的叶片黄化和脱落。在预豆荚填充时切除的带荚外植体，叶片在 16 天后开始变黄，而在晚期豆荚填充时切除的叶片仅在 6 天后开始变黄。尽管在切除后的第一个光照期内气孔阻力保持较低，但随后增加到高于完整植物叶片的水平。在中期到晚期豆荚填充时带有一个或多个节间荚的外植体的行为与完整植物相似，因为荚的负荷不会影响叶片变黄的时间滞后。通过去除荚或种子、或在完全矿物质营养溶液或 4.6 微摩尔玉米素中孵育，可以延迟外植体叶片黄化和脱落。与叶绿素分解一样，蛋白质损失在外植体中加速，但矿物质或特别是玉米素可以减缓损失。外植体上的荚显示出与完整植物上的荚相似的颜色变化（绿色到黄色到棕色）的速率和模式。这些变化在外植体上的水比在完整植物上更早开始，但添加玉米素可以延迟它们。外植体上的种子干重增加，几乎与完整植物一样多。外植体似乎是完整植物相应部分的良好模拟物，它们应该有助于分析豆荚发育和叶片衰老的机制。此外，我们的数据表明，矿物质和细胞分裂素从根部的通量可能会影响大豆的叶片衰老，但增加的气孔阻力似乎不会导致叶片衰老。
