Free and bound indole-acetic acid is low in the endosperm of the maize mutantdefective endosperm-B18

The maize mutant defective endosperm-B18 (de (*)-B18), which is recessive to its wildtype, accumulates substantially less dry matter in the endosperm than its normal counterpart. Both free and bound indole-acetic acid (IAA) content has been measured at 5 different developmental stages. In endosperm tissue, the level of IAA is at least 15 times lower in the mutantde (*) -B18 than in the wildtype. The situation found in the diploid tissues is somewhat different: in the mature embryo the level of total IAA is lower in the mutant than in the wildtype, while in 4-day old seedlings the level of total IAA is, to some degree, similar in both genotypes. Naphthalene-acetic acid (NAA), a stable synthetic auxin which mimics IAA in its biochemical effects, is able to normalize the seed weight of the mutant when applied to developing grains. The results favor the conclusion that in maize endosperm the mutationde (*) -B18 is involved in IAA metabolism.