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

Excised pea (Pisum sativum L.) tendrils incubated in the light coil more than those incubated in the dark. This light effect, which displays spectral responses characteristic of chlorophyll-mediated mechanisms, is increased by at least 8 hours 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. The 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 adenosine triphosphatase activity.Curvature is proportional to the logarithm of the molarity of applied ATP between 10(-4) and 10(-2)m, whereas elongation responds only to the higher dosages. It is inferred that endogenous ATP is involved as an energy source in coiling, especially in the initial phase, which involves contraction of the tendril. The existence of a higher plant analog of actomyosin, suggested by others, is supported.