β‐1,3‐Glucanase gene expression in low‐hydrated seeds as a mechanism for dormancy release during tobacco after‐ripening

Abstract

Summary: An air‐dry developmental state with low‐hydrated tissues is a characteristic of most plant seeds. Seed dormancy is an intrinsic block of germination and can be released during after‐ripening, that is air‐dry storage of mature seeds. Both seed‐covering layers, testa and endosperm, cause the coat‐imposed dormancy of tobacco (Nicotiana tabacum). After‐ripening and over‐expression of class I β‐1,3‐glucanase (β Glu I) confer maternal effects on testa rupture and dormancy release. Very little is known about the molecular mechanisms of after‐ripening and whether gene expression is possible in low‐hydrated seeds. Transient, low‐level β Glu I transcription and translation was detected during tobacco seed after‐ripening. 1 H NMR 2D micro‐imaging showed uneven distribution of proton mobility in seeds. β Glu I gene expression is associated spatially with the inner testa and temporally with the promotion of testa rupture. Local elevation in moisture content seems to permit local, low‐level β Glu I gene transcription and translation in the maternal tissues of air‐dry, low‐hydrated seeds. De novo gene expression is therefore proposed to be a novel molecular mechanism for the release of coat‐imposed dormancy during oilseed after‐ripening.