Stress Hormone Levels Associated with Drought Tolerance vs. Sensitivity in Sunflower (Helianthus annuus L.)

Abstract

Six inbred lines (B59, B67, B71, R432, R419, and HAR4) of sunflower (Helianthus annuus L.) were evaluated in field and laboratory experiments under drought vs. irrigation. In field studies, relative seed yield per hectare and oil yield per hectare were reduced under drought in B59, B67, and R419, but not in R432, B71, or HAR4. In lab studies, germination percentage was reduced under 200 and 400 mM mannitol treatment (which simulates drought) for B59 and under 400 mM mannitol for R432, B71, and HAR4. B59 and B71 were used as typical drought-sensitive and drought-tolerant lines, respectively, for subsequent experiments. Levels of the phytohormones jasmonates (JAs), abscisic acid (ABA), and ABA catabolites were evaluated in dry and germinated seeds from B59 and B71 parent plants grown under drought and irrigation. For dry seeds from plants grown under drought, ABA was the major compound accumulated in B71, whereas 12-OH-JA was the major compound in B59. Germinated seeds of both lines, compared to dry seeds, showed increased 12-oxophytodienoic (OPDA) and decreased ABA. Our results indicate that soil moisture conditions under which parent plants grow affect hormonal content of seeds produced, and JAs and ABA levels during germination are variable. F3 seedling families obtained by crossing R432 (drought-tolerant) and A59 (drought-sensitive) lines were assayed for germination percentage and endogenous levels of salicylic acid (SA), JA, and ABA following drought treatment (400 mM mannitol). Germination percentage showed a typical segregation pattern of quantitative inheritance to drought tolerance in the phenological stage of seedling. Levels of SA and ABA under drought compared to control condition increased in F3 tolerant families but decreased in F3 sensitive families. JA levels changed under drought condition, but the direction of change was not consistent within tolerant or sensitive families. Our results provide important information for strategies to maintain or increase yield of sunflower crops under drought conditions.