Physicochemical basis for hardseededness in mung bean (Vigna radiata (L.) Wilczek)

Hard seeds ranged from 0 to 3.8% in four varieties and four seed lots of mung bean from commercial sources. Uncooked normal and hard seeds were indistinguishable although, after boiling for 30 min, the hard seeds remained uncooked and were hard, brownish, and wrinkled. The hardness and seed coat thickness of hard seeds were twice those of normal seeds. Hard and normal seeds had similar chemical proximate composition except for fiber content, which was 9-25% greater in the hard seeds. The seed coats of hard seeds had 12% higher fiber content, 7 times more lignin, and 23% higher silica than the normal. The amino acid composition and pectic substances content of the two types of mung bean were similar. Histochemical analysis and scanning electron microscopy revealed a more rigid and highly structured palisade layer in the hard seed than in the normal seeds