IDENTIFYING FAVORABLE RESPONSES TO DROUGHT STRESS IN DIVERSE GENOTYPES OF MAIZE (ZEA MAYS L.)
Solliday, Amanda J
Of the many potential abiotic stresses, insufficient water supply is the major limiting physiological constraint for crop production in many regions of the world. Because yield is a product of many phenotypic components, plant breeders experience difficulties when selecting lines for higher yield under drought conditions. The use of other measurable traits, such as reproductive timing or concentrations of stress hormones, can reveal information regarding changes in plant behavior during low water availability. The purpose of this project is to further decipher the signaling behind the drought response of maize and identify which physiological responses might characterize drought-resistant genotypes. Eight tropical inbred maize genotypes, previously shown to have varying behavior under drought conditions, were surveyed for physiological response during water stress. Water stress was imposed once plants reached the flowering period. During a ten-day treatment period, transpiration, ear growth and silk length were calculated daily for each plant. Upon tissue harvest (after ten days of treatment), ear size and leaf water potential were measured. Leaf and ear tissue sampled in the greenhouse were analyzed for non-structural carbohydrates, abscisic acid (ABA), cytokinin, and invertase. Physiological differences in genotypic response to water stress were apparent. Of the eight lines examined, the P1 genotype appeared to respond best to low water availability. Under water stress, P1 maintained low ear and leaf ABA concentrations, higher sucrose levels in the leaves, more starch in the ear tissue, and exhibited little change in ovary invertase activity. When comparing measured traits among all genotypes, leaf and ear ABA was negatively correlated with reproductive growth. Leaf carbohydrate levels were positively correlated with ear growth, and negatively associated with ABA levels in the leaves and ears. In general, cytokinin levels in the ear tissue increased under water stress. Invertase activity decreased in water-stressed ear tissue compared to control plants, and cell wall invertase activity was higher than soluble invertase. Carbohydrate partitioning appears to be an important indicator of reproductive growth under water stress, and identifying the differences in invertase behavior and their relationship to yield performance in several genotypes would be a crucial next step in assessing drought tolerance.
Dr. Tim Setter, Dr. Margaret Smith
maize; drought; invertase; abscisic acid; cytokinin; carbohydrate partitioning
Dissertation or Thesis