Abscisic acid promotes flowering and enhances LcAP1 expression in Litchi chinensis Sonn.

In order to investigate the role of abscisic acid in litchi flowering, litchi trees were treated with exogenous ABA before or when panicle primordia emerged. The results showed that ABA spraying when panicle primordia emerged reduced the number of leaves per panicle, enhanced the number of axillary panicles per panicle and the ratio of axillary panicles to total nodes per panicle. When trees were treated with ABA before panicle primordia emerged, the number of flowers per panicle in the ABA-treated trees was higher than that of the control. The ABA biosynthesis inhibitor naproxen reduced the percentage of flowering terminal shoots and number of flowers in one panicle, and suppressed the litchi homologue gene (LcAP1). To confirm whether the enhanced AP1 expression depended on H2O2, NO and calcium, the effect of ABA was compared with that of ABA plus NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl3-oxide (PTIO), or the H2O2 trapper dimethylthiourea (DMTU), the calcium chelator glycol-bis (β-amino ethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA) and calcium channel blocker LaCl3. The results showed that ABA enhanced AP1 expression, but the inductive effects were suppressed by DMTU, EGTA and LaCl3 but not PTIO, suggesting that ABA promotion of LcAP1 expression may be H2O2 and calcium dependent but not NO dependent.