The effects of paclobutrazol, abscisic acid, and gibberellin on germination and early growth in silver, red, and hybrid maple

Silver maple (Acer saccharinum L.) seeds were used to examine the mechanisms regulating recalcitrant seed germination aiming towards the development of a biochemical method to temporarily inhibit germination without refrigeration. Treatment of fresh silver maple seeds with the cytochrome P450 inhibitor paclobutrazol delayed germination and reduced root and shoot extension. The inhibitory effect of paclobutrazol plus abscisic acid (ABA) on the shoots of silver maple could not be overcome by a brief treatment with gibberellic acid A3 (GA3). Red maple seeds (Acer rubrum L.) were almost completely inhibited by the treatment with paclobutrazol alone, and this inhibition could not be overcome by a brief treatment with GA3. In the red × silver hybrid, root growth was little affected by paclobutrazol plus ABA; however, shoot growth was markedly inhibited by paclobutrazol, and this inhibition was sharply increased by the combination with ABA but partially alleviated by GA3. Treating fresh silver maple seeds with paclobutrazol for 12 h followed by storage under ideal germination conditions, in the presence of 1 mM ABA, completely prevented germination for 1 week. Root extension was completely restored by the continuous provision of GA3 along with the ABA.