Endo-?-mannanase isoforms are present in the endosperm and embryo of tomato seeds, but are not essentially linked to the completion of germination

Abstract

A current hypothesis is that endo-β-mannanase activity in the endosperm cap of tomato (Lycopersicon esculentum Mill. cv. Moneymaker) seeds is induced by gibberellin (GA) and weakens the endosperm cap thus permitting radicle protrusion. We have tested this hypothesis. In isolated parts, the expression of endo-β-mannanase in the endosperm after germination is induced by GAs, but the expression of endo-β-mannanase in the endosperm cap prior to radicle protrusion is not induced by GAs. Also, abscisic acid (ABA) is incapable of inhibiting endo-β-mannanase activity in the endosperm cap, even though it strongly inhibits germination. However, ABA does inhibit enzyme activity in the endosperm and embryo after germination. There are several isoforms in the endosperm cap and embryo prior to radicle protrusion that are tissue-specific. Tissue prints showed that enzyme activity in the embryo spreads from the radicle tip to the cotyledons with time after the start of imbibition. The isoform and developmental patterns of enzyme activity on tissueprints are unaffected when seeds are incubated in ABA, even though germination is inhibited. We conclude that the presence of endo-β-mannanase activity in the endosperm cap is not in itself sufficient to permit tomato seeds to complete germination.