Jasmonic acid affects dormancy and sugar catabolism in germinating apple embryos

Embryos isolated from dormant seeds of apple (Malus domestica Borb., cv. Antonowka) were cultured in darkness in the presence of jasmonic acid (JA, 20 μM) for 7 d in parallel to control non-treated ones. Soluble sugars were quantified and some sugar-catabolysing enzyme activities were determined in axes and in cotyledons of the embryos during the culture. JA treatment stimulated growth of the axis and sucrose hydrolysis in this organ. In contrast, JA inhibited the growth of isolated cotyledons. In intact embryos, JA treatment inhibited the growth of the lower cotyledon (being in contact with wet medium) thus alleviating the growth asymmetry of cotyledons. In both cotyledons JA stimulated hydrolysis of sucrose during the period preceding growth. The effect persisted in the upper cotyledon for the whole experimental period, whereas in the lower one the treatment provoked a sharp rise in soluble sugar levels observed relatively late during the experiment. The later effect correlated with the stimulation of isocitrate lyase activity in the lower cotyledon by JA. The results suggest the induction of the gluconeogenetic pathway by JA in the lower cotyledon of cultured dormant apple embryos. They also provide evidence for the site of JA action in the regulatory complex controlling embryonic dormancy in apple.