Physiological Studies on Pea Tendrils

Abstract

When excised tendrils of pea (Pisum sativum L. cv Alaska) are mechanically perturbed there is an immediate and transient increase in callose deposition in the sieve cells. Mechanical perturbation (MP) results in a coiling response in light-grown tendrils and in dark-adapted tendrils, provided, in the latter case, that they receive adequate illumination within a limited period of time after MP. In nonperturbed tendrils the number of callose deposits decreases to some minimum with increasing time in the dark, and their ability to coil in the dark in response to MP diminishes with time in the dark. The transient increase of callose deposition due to MP, however, occurs whether or not tendrils are dark adapted, and whether they receive light or are retained in the dark after MP. This indicates that if callose is directly involved in tendril coiling, then it exerts its effect on the sensory perception of the mechanical stimulus. In the present investigation, there is never tendril coiling without the transient increase in callose, and the time after MP at which the peak of callose deposition occurs precedes the time of the peak amount of coiling.

An inhibitor of callose formation, 2-deoxy-d-glucose (DDG), is equally effective at inhibiting tendril coiling and MP-induced callose deposition, indicating, within the limitations of the specificity of DDG, that callose deposition may be required in order for the coiling response to occur. Alternatively, DDG may prevent the availability of some other factor necessary for tendril coiling.