Dynamics of accumulation of lysine and tryptophan, and kernel modification in opaque2, opaque16, and double mutant (opaque2/opaque16) genotypes during kernel development in maize.

Recessive opaque2 (o2) and opaque16 (o16) genes enhance lysine and tryptophan in maize kernels. Though few o2, o16-, and o2o16-based maize genotypes have been developed, the transition of quality attributes and seed morphology through different stages of kernel development has not been studied yet. To understand the role of o2 and o16 genes in the regulation of essential amino acids and kernel opaqueness in maize, we analyzed the accumulation pattern of lysine and tryptophan, and the occurrence of opaqueness in the developing kernels at 15, 30, and 45 days after pollination (DAP) among a set of o2-, o16-, and o2o16-based inbreds. Genotypes with o2o16 possessed significantly higher lysine (0.64%) and tryptophan (0.25%) over o2 (lysine, 0.48%; tryptophan, 0.18%) and o16 (lysine, 0.46%; tryptophan, 0.17%) alone across kernel development stages. A decreasing trend of amino acid accumulation in o2-, o16-, and o2o16-based genotypes was observed through 15-, 30-, and 45-DAP. Kernel opaqueness also showed a similar decreasing trend among o2-, o16-, and o2o16-based inbreds during kernel development. A positive association was observed between lysine and tryptophan (r = 0.95), tryptophan and opaqueness (r = 0.60), and lysine and opaqueness (r = 0.60) across DAPs. Hard endosperm in wild types and o16 genotypes was due to compact starch-granule structures packed with more proteinaceous matrix compared to o2 and o2o16. This is the first report on nutritional quality and opaqueness at different stages of kernel development in o2-, o16-, and o2o16-based genotypes.