Study on seed coat morphology and histochemistry in three anthocyaninless mutants in tomato (Lycopersicon esculentum Mill.) in relation to their enhanced germination

The morphology and histochemistry of seed coat in three tomato mutants anthocyaninless of Hoffmann (ah), anthocyanin without (aw) and baby lea syndrome (bls) were studied in relation to their enhanced germination observed under optimal and stress conditions. The study was performed on a set of isogenic/near isogenic lines differing in these genes. It was found that wild type seeds possessed longer hairs than ah and bls mutant seeds. The aw seeds were a dark yellowish-beige colour, while wild type ones were light beige. No differences in seed coat composition were detected between the anthocyanin-containing and the anthocyaninless lines in terms of the presence or absence of polysaccharides, lipids and lignin. Differences in seed coat staining between the wild type line and ah, aw and bls mutants were identified using the Nitroso reaction and after staining with Vanillin-HCl. The inner epidermal testa layer of the three anthocyaninless genotypes stained yellow, indicating the absence of condensed tannins, and brownish red in the wild type, indicating the presence of this compound. Condensed tannins are known to contribute to the rigidity of cell structure. The absence of condensed tannins in the testa inner epidermal layer of the three mutants may therefore the main seed coat characteristic that contributes to increased seed coat permeability. The increased permeability is a prerequisite for more rapid water uptake that subsequently leads to the more rapid germination of mutant seeds.