Brock T G, Kaufman P B
Department of Biology, University of Michigan, Ann Arbor 48109, USA.
Plant Physiol. 1988;88(1):10-2. doi: 10.1104/pp.88.1.10.
Starch in pulvinus amyloplasts of barley (Hordeum vulgare cv Larker) disappears when 45-day-old, light-grown plants are given 5 days of continuous darkness. The effect of this loss on the pulvinus graviresponse was evaluated by following changes in the kinetics of response during the 5-day dark period. Over 5 days of dark pretreatment, the lag to initial graviresponse and the subsequent half-time to maximum steady state bending rate increased significantly while the maximum bending rate did not change. The change in response to applied indoleacetic acid (100 micromolar) plus gibberellic acid (10 micromolar) without gravistimulation, under identical dark pretreatments, was used as a model system for the response component of gravitropism. Dark pretreatment did not change the lag to initial response following hormone application to vertical pulvini, but both the maximum bending rate and the half-time to the maximum rate were significantly reduced. Also, after dark pretreatment, significant bending responses following hormone application were observed in vertical segments with or without added sucrose, while gravistimulation produced a response only if segments were given sucrose. These results indicate that starch-filled amyloplasts are required for the graviresponse of barley pulvini and suggest that they function in the stimulus perception and signal transduction components of gravitropism.
当对生长45天、处于光照下的大麦（大麦品种Larker）植株进行5天连续黑暗处理时，叶枕淀粉质体中的淀粉会消失。通过跟踪5天黑暗处理期间响应动力学的变化，评估了这种淀粉损失对叶枕重力响应的影响。在5天的黑暗预处理过程中，初始重力响应的延迟以及随后达到最大稳态弯曲速率的半衰期显著增加，而最大弯曲速率没有变化。在相同的黑暗预处理条件下，对施加吲哚乙酸（100微摩尔）加赤霉素（10微摩尔）且无重力刺激的响应变化，被用作向重力性响应成分的模型系统。黑暗预处理并未改变激素施加到垂直叶枕后初始响应的延迟，但最大弯曲速率和达到最大速率的半衰期均显著降低。此外，黑暗预处理后，在添加或不添加蔗糖情况下，垂直切段在施加激素后均观察到显著的弯曲响应，而只有在切段添加蔗糖时重力刺激才会产生响应。这些结果表明，淀粉填充的淀粉质体是大麦叶枕重力响应所必需的，并表明它们在向重力性的刺激感知和信号转导成分中发挥作用。
