Distinct ethylene- and tissue-specific regulation of beta-1,3-glucanases and chitinases during pea seed germination

The expression of beta-1,3-glucanase (beta Glu) and chitinase (Chn) was inv estigated in the testa, cotyledons, and embryonic axis of germinating Pisum sativum L. cv. 'Espresso generoso' seeds. High concentrations of beta Glu and Chn activity were found in the embryonic axis. Treatment with ethylene alone or in combination with the inhibitor of ethylene action 2,5-norbornad iene showed that an early, 4-fold induction of beta Glu activity in the emb ryonic axis during the first 20 h after the start of imbibition is ethylene -independent. This initial increase was followed by a later 4-fold ethylene -dependent induction in the embryonic axis starting at 50 h, which is after the onset of ethylene evolution and after completion of radicle emergence. The beta Glu activity in cotyledons increased gradually throughout germina tion and was ethylene-independent. In contrast, the ethylene-independent Ch n activity increased slightly after the onset of radical emergence in the e mbryonic axis and remained at a constant low level in cotyledons. Immunoina ctivation assays and immunoblot analyses suggest that early beta Glu activi ty in the embryonic axis is due to a 54-kDa antigen, whereas late induction is due to a 34.5-kDa antigen, which is likely to be the ethylene-inducible class I beta Glu G2 described for immature pea pods. Increases in Chn in t he embryonic axis were correlated with a 26-kDa antigen, whereas amounts of the additional 32- and 20-kDa antigens remained roughly constant. Thus, et hylene-dependent and ethylene-independent pathways regulate beta Glu and Ch n during pea seed germination. The pattern of regulation differs from that of leaves and immature pods, and from that described for germinating tobacc o seeds. The functional significance of this regulation and its underlying mechanisms are discussed.