In the present study, it was clearly shown that MeJA inhibited maize seed germination and root elongation (Fig. 1a,b). The inhibition of root elongation could result from inhibited α-amylase activity, limited ethylene production or changes in both parameters. Our results showed that α-amylase activity decreased with increasing the concentration of MeJA (Fig. 2). α-amylase is a key enzyme in cereal seed germination. It degrades the insoluble starch granules to soluble glucose moieties which translocate towards the embryonic axis. Thus, it can be deduced that the reduced germination percentage and root elongation could be the result of limited production of substrate for respiration and consequently limited energy production. Limited energy production, in turn, results in lower activity of plasma membrane proton-pumping ATPase (H+-ATPase) and lower acidification of the cell wall and depolarization and lower ΔpH conditions. Ion absorption will decrease sharply and cell wall loosening will be retarded which consequently results in limited root elongation (Canellas et al., 2002). The above conclusion is further supported by the native-PAGE showing α-amylase activity in polyacrylamide gel (Fig.3a). In this respect our finding was similar to results of other researchers (Bialecka and Kepczynski, 2003a). The reduction of the α-amylase band intensity correlated negatively with MeJA concentrations applied (Fig. 3b). Consequently, it can be proposed that the reduction of germination percentage and decreased root elongation of maize seeds treated with different concentrations of MeJA was due to decreased α-amylase activity as a result of the reduction in α-amylase production in degrading starch reservoirs in the endosperm. The reduction of α-amylase activity due to its limited production could be the consequence of the inhibition of gibberellin
In our study, ethylene production decreased with increasing MeJA concentrations (Fig. 4). Thus, lower germination percentage due to MeJA treatment can be attributed to lower production of ethylene. It is known that MeJA and ABA are able to inhibit the conversion of ACC to ethylene, and this inhibitory effect increased with increasing the concentration of both growth regulators (Bailly et al., 1992).
In conclusion, our data showed that decreased α-amylase activity and/or concentration as well as reduced ethylene production plays significant roles in the physiological and biochemical processes underlying inhibited seed germination and root elongation in maize under conditions of increased MeJA concentrations.