Alterations of the ethylene pathway in germinating thermoinhibited chick-pea seeds caused by the inhibition of polyamine biosynthesis

Abstract

The alterations in the ethylene biosynthetic pathway provoked by cyclohexylamine (CHA) and/or methylglyoxal-bis(guanylhydrazone) (MGBG), inhibitors of the polyamine synthesis, have been studied in thermoinhibited seeds (delayed germination by supraoptimal temperatures) of the chick-pea ( Cicer arietinum). CHA and/or MGBG stimulated ethylene synthesis both at 25°C (control) and at 30°C (temperature at which thermoinhibition is induced, and reversed by both inhibitors). Moreover, both inhibitors caused: (1) an increase in ACC-synthase (EC 4.4.1.14) and free ACC; (2) a stimulation of in vivo ACC-oxidase; and (3) a stimulation of (malonyl)-1-aminocyclopropane-1-carboxylic acid synthesis at 25°C (since the supraoptimal temperatures had no effect). Compared with the control, both supraoptimal temperatures lead to a decrease the AdoMet-decarboxylase (AdoMetDC) (EC 4.1.1.50) activity. This was not affected by CHA. However, MGBG induced an increase of this activity at 25°C and at 30°C, which diminished strongly up to 35°C. The fact that the inhibition of spermidine and spermine synthesis by CHA and/or MGBG provoked an induction of the enzyme of ethylene biosynthesis and a concomitant increase in ethylene production and a reversion of thermoinhibition in chick-pea seeds suggests that the ethylene and polyamine pathways compete during germination, placing polyamines in the possible role of an endogenous germination regulator possibly by modulating ethylene biosynthesis.