Abstract:

Using diphenylboric acid 2-amino ethyl ester（DPBA），a flavonol fluorescent dye，and a laser scanning confocal microscope（LSCM），we found that an increase of flavonol fluorescence appeared in the guard cells of the abaxial epidermis of detached leaves of apple（Malus ´ domestica Korkh.‘Fuji’），especially around the nucleus，after 5-ALA pretreatment for 2–4 h. 5-ALA pretreatment also inhibited ABA-induced stomatal closure，which was inseparably related to the reduction of the reaction oxygen species（ROS）accumulation. Coincidently，pretreatment of quercetin or kaempferol，two kinds of natural flavonols，also inhibited stomatal closure induced by ABA，and meanwhile decreased ROS content in the guard cells of apple leaves. Furthermore，the exogenous flavonols eliminated the effect of H₂O₂ that induced stomatal closure in apple leaves. Together with these above，it can be deduced that 5-ALA-induced stomatal opening is associated with its up-regulation of flavonol levels in guard cells，which then eliminates ROS levels. Therefore，flavonols are involved in stomatal regulation induced by 5-ALA in apple leaves.

Key words: apple, ABA, 5-ALA, flavonol, stomatal aperture, guard cell