Changes in plant hormone contents in Japanese apricot flower buds during prolonged chilling exposure

摘要

Bud endodormancy is an important factor affecting the blooming date and subsequent the fruit production of deciduous fruit trees. However, the underlying physiological mechanism remains uncharacterized. To elucidate the physiological changes occurringduring endodormancy release, we investigated the relationship between endodormancy depth and plant hormone contents in Japanese apricot flower buds. Comprehensive plant hormone analyses revealed that the abscisic acid (ABA) contents in flower buds fromlow-chill and high-chill cultivars decreased as the season progressed, with lower levels in low-chill 'Ellching' than in high-chill 'Nanko'. The abundance of ABA catabolites (i.e., dehydrophaseic acid and ABA glucosyl ester) increased in 'Nanko' flower buds during an artificial chilling treatment, but remained relatively low in 'Ellching' flower buds. Our results suggest that genotype-dependent control of ABA metabolism is associated with the timing of endodormancy release and blooming. The abundance offree and conjugated forms of indoleacetic acid decreased and cytokinin contents increased in response to a prolonged exposure to cold conditions. However, we did not observe considerable differences between the two genotypes or a relationship between hormone level changes and endodormancy depth. The indoleacetic acid and cytokinin contents increased just before blooming, suggesting that these hormones are related to flower development rather than endodormancy release.