|Tuttle, Keiko - Washington State University|
|Schramm, Elizabeth - Washington State University|
|Takebayashi, Yumiko - Advance Science Institute, Riken|
|Seo, Mitsunori - Advance Science Institute, Riken|
Submitted to: Seed Science Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2015
Publication Date: 6/1/2015
Citation: Tuttle, K.M., Martinez, S., Schramm, E.C., Takebayashi, Y., Seo, M., Steber, C.M. 2015. Grain dormancy loss is associated with changes in ABA and GA sensitivity and hormone accumulation in bread wheat, Triticum aestivum (L.). Seed Science Research. 25(2):179-193.
Interpretive Summary: Susceptible wheat cultivars have problems with preharvest sprouting, germination on the mother plant, when mature grain is exposed to cool and rainy conditions before harvest. This study shows that preharvest sprouting susceptibility is associated with differences in hormone sensitivity. Preharvest sprouting tolerance is associated with low sensitivity to the germination stimulating hormone, GA (gibberellin). Preharvest sprouting susceptibility is associated with low sensitivity to the dormancy-promoting (germination-inhibiting) hormone ABA. GA sensitivity increases and ABA sensitivity is lost as wheat grains lose dormancy through cold stratification or dry after-ripening. Sprouting tolerant lines generally lose dormancy more slowly that susceptible lines, making them more prone to emergence problems upon sowing. However, some preharvest sprouting tolerant lines lose dormancy faster, suggesting that there is room to improve selection for this trait in breeding programs.
Technical Abstract: Knowledge about the hormonal control of seed dormancy and dormancy loss is essential in wheat, because low seed dormancy at maturity is associated with the problem of preharvest sprouting (PHS) when rain occurs before harvest. Low GA (gibberellin) hormone sensitivity and high ABA (abscisic acid) sensitivity were associated with higher seed dormancy and PHS tolerance in three wheat cultivars. In two PHS tolerant cultivars, seeds were very dormant at maturity, and insensitive to GA-stimulation of germination. PHS susceptible seeds were more GA sensitive and less ABA sensitivity at maturity. As seed dormancy was lost through dry after-ripening or cold stratification, seeds first gained GA sensitivity and then lost sensitivity to ABA-inhibition of germination. These changes in GA and ABA sensitivity can serve as landmarks defining stages of dormancy loss that cannot be discerned without hormone. These dormancy stages can be used to compare different cultivars, seed lots, and studies. Changes in hormone levels associated with different dormancy loss stages were examined in imbibing seeds. Long after-ripened seeds had significantly lower embryonic ABA levels, whereas seeds that had lost little dormancy through after-ripening showed no decrease in ABA, but a significant decrease in JA-Ile (jasmonic acid-Ile) hormone. Aleurones from imbibing after-ripened seeds showed a significant increase in GA1 and auxin (IAA) levels. Seed dormancy loss through cold imbibition also led to decreased endogenous ABA levels, suggesting that reduced ABA signaling is a general mechanism triggering dormancy loss.