Balancing of hormonal biosynthesis and catabolism pathways, a strategy to ameliorate the negative effects of heat stress on reproductive growth.

In pea (Pisum sativum L.), moderate heat stress during early flowering/fruit set increased seed/ovule abortion, and concomitantly produced fruits with reduced ovary (pericarp) length, and fewer seeds at maturity. Plant hormonal networks coordinate seed and pericarp growth and development. To determine if these hormonal networks are modulated in response to heat stress, we analyzed the gene expression patterns and associated these patterns with precursors, and bioactive and inactive metabolites of the auxin, gibberellin (GA), abscisic acid (ABA), and ethylene biosynthesis/catabolism pathways in young developing seeds and pericarps of non-stressed and 4-day heat-stressed fruits. Our data suggest that within the developing seeds heat stress decreased bioactive GA levels reducing GA growth-related processes, and that increased ethylene levels may have promoted this inhibitory response. In contrast, heat stress increased auxin biosynthesis gene expression and auxin levels in the seeds and pericarps, and seed ABA levels, both effects can increase seed sink strength. We hypothesize that seeds with higher auxin- and ABA-induced sink strength and adequate bioactive GA levels will set and continue to grow, while the seeds with lower sink strength (low auxin, ABA, and GA levels) will become more sensitive to heat stress-induced ethylene leading to ovule/seed abortion.