Photophysiology of Turion Germination in Spirodela polyrhiza (L.) SCHLEIDEN. VII. Action of Jasmonic acid

Abstract

Germination of photoblastic light-grown as well as dark-grown turions of Spirodela polyrhiza (L.)SCHLEIDEN, strain SJ, was stimulated by jasmonic acid QA) and its methylester QA-Me). Dose-response-curves for non-dormant turions were bell-shaped with an optimal concentration of about 3 · 10 -5 M in both compounds applied in darkness. Higher concentrations of JA and JA-Me decreased the induced germination response. Exogenously applied Ca 2+ is required for the effect of JA as known for the phytochrome-mediated response, too. Signal-transduction chains, induced either by red light pulses or by application of JA or JA-Me, are not identical but different in the following features: (i) kinetic parameters, (ii) threshold values of the calcium requirement, and (iii) frequent JA-induced formation of two daughter fronds simultaneously. Furthermore, we did not find any indication for a phytochrome - JA interaction. JA also induced germination of dormant turions. However, the kinetics of this germination response differed significantly from the kinetics of red light-induced germination in after-ripened turions. JA treatment of dormant turions resulted in a transient increase of respiration. The endogenous level of JA equivalents was determined by radioimmunoassay in dormant and after-ripened turions. Contrary to the experience of the application experiments, the level of JA equivalents was higher in dormant than in after-ripened turions.