Physiological Studies on Pea Tendrils. II. The Role of Light and ATP in Contact Coiling

Abstract

Incubated light excised pea (Pisum sativum L.) tendrils coil more than dark incubated ones. This light effect, which displays spectral responses characteristic of chlorophyll-mediated mechanisms, is increased by at least 8 hr. of prior dark incubation of plants from which the tendrils were derived. Considerable evidence indicates a major role of ATP in coiling; for example, inhibitors of ATP production decrease contact coiling. Exogenous ATP increases curvature in the dark, whereas exogenous adenosine, AMP and ADP are practically without effect. This ATP effect can be reversed by the addition of sucrose to the bathing solution. Tendrils of plants placed in the dark overnight have lower ATP levels than those held in the light. One half hour after stimulation, the endogenous ATP level of tendrils on plants kept in the light decreased fourfold; in the same period, the endogenous inorganic phosphate level increased markedly, indicating high ATPase activity. Curvature is proportional to the logarithm of the molarity of applied ATP between 10-4 and 10-2 [image], whereas elongation responses occur only at higher dosages. Endogenous ATP maybe involved as an energy sourve in coiling, especially in the initial phase, which involves contraction of the tendril. The existence of a higher plant analog of actomysin is supported.