Internal anatomy of individual tomato seeds: relationship to abscisic acidand germination physiology

Tomato seeds that have been dried, imbibed and redried (primed) develop int ernal free space between the embryo and endosperm. Seeds of the ABA-deficie nt sitiens (sit(w)) tomato mutant can exhibit internal free space at the co mpletion of seed development even without priming. Both primed and sit(w) s eeds germinate more rapidly than untreated wild-type seeds. To determine wh ether internal anatomy predicts germination physiology, individual sitw and primed wildtype seeds were sorted into three categories based upon the ext ent of internal free space observed nondestructively using X-radiography. C ategory 3 (C3, extensive free space present) sit(w) seeds completed germina tion more rapidly than all other seed categories and genotypes in water, in abscisic acid (ABA) or under far-red illumination. The force necessary to puncture the endosperm caps (and testa) of C3 sit(w) seeds was less, and th e percentage of nuclei in C3 sit(w) radicle tips in the G(2) stage of the c ell cycle was greater than for all other seed categories. Wild-type seeds e xhibited free space following long-term priming, but germination was still prevented by far-red light and ABA, and endosperm cap strength and nuclear DNA contents were not altered. Endo-beta-mannanase activity of individual e ndosperm caps was not consistently related to their resistance to puncture. While internal free space is diagnostic for primed tomato seeds and occurs in a fraction of sitw seeds, it is not predictive of many aspects of germi nation physiology.