Factors Underlying Genotypic Differences in Kernel Set in Maize Subjected to Water Deficit and Shade at Flowering.

In maize, yield in drought environments has been improved by selecting for genotypes with better ability to sustain floral growth and development during stress.  The available evidence suggests that sensitivity to drought at this stage is regulated by response to kernel carbohydrate supply, and its interaction with abscisic acid (ABA).  However, the underlying basis of genotypic differences in this response is not known.  To gain improved understanding of these differences, the levels of carbohydrates and ABA, and gene expression, were compared in a set of maize hybrids with contrasting anthesis silking interval (ASI) and yield under water deficit at flowering.  In controlled greenhouse trials, these hybrids were subjected to pre-pollination water deficit and shade.  In water stressed plants, ear-tip ABA and ABA metabolite levels increased similarly in all lines, but sucrose levels were decreased more in susceptible than tolerant lines.  Transcript expression was analyzed in pre-pollination ear tips of stress and control plants of susceptible and tolerant hybrids using a transcript profiling system for 30,000 genes.  The expression profiles in ear tips showed that the susceptible lines had relatively higher transcript levels for stress genes (dehydrins, ethylene metabolism, and stress transcription factors) whereas tolerant lines had higher levels of growth-associated genes.  These studies support the idea that better yield performance is related to maintenance of growth-related processes in the face of stress rather than ability to have a high expression of stress-stabilizing gene-products.