LIGNIN AND HYDROXYCINNAMIC ACIDS IN WALLS OF BROWN MIDRIB MUTANTS OF SORGHUM, PEARL-MILLET AND MAIZE STEMS

The characteristics of walls from stems of brown-midrib (bmr) mutants from Sorghum bicolor (L) Moench bmr6 and bmr18 (watery- to milky-grain stage), Pennisetum americanum (L) Leeke KS81-1089 (soft-dough stage) and Zea mays L bm3 (early-dent stage) with respect to the types of lin kages of hydroxycinnamic acids to wall polymers and to structural feat ures of their lignins were investigated. The lignin content of all mut ants, determined using the acid detergent lignin procedure, was signif icantly lower than that of their normal counterparts. There was, howev er, no significant differences in total lignin contents between bmr an d normal lines as determined by the acetyl bromide procedure or the su m of the acid-insoluble (Klason) lignin and acid-soluble lignin. It is suggested that this behaviour could be explained if bmr mutants are c haracterised by higher amounts of lignin with a lower degree of polyme risation than normal lines. The lowered SIV ratio and lowered total yi eld of alkaline nitrobenzene oxidation products in lignin from bmr mut ants was confirmed. No etherified p-coumaric acid was found in any sam ple tested, except the normal line of pearl millet. The concentration of etherified ferulic acid, which is probably involved in ester-ether bridges between lignin and polysaccharides, was lower in bmr mutants t han in the normal plants. The low content of ferulic acid bridges in b mr mutants may contribute to the elevated digestibilities of their ste ms.