[Effects of exogenous abscisic acid (ABA) on growth and physiological characteristics of Machilus yunnanensis seedlings under drought stress].

In this study, the effects of exogenous abscisic acid (ABA) on the growth and physiolo-gical characteristics of Machilus yunnanensis seedlings were examined under well water supply conditions (70%-75% field capacity, FC) and different drought stress conditions, i.e., light drought stress (50%-55% FC) and severe drought stress (30%-35% FC), respectively. The results showed that drought stress reduced leaf relative water content, plant height, and total biomass of seedlings significantly decreased, as well as net photosynthetic rate and maximal photochemistry efficiency (F/F), but enhanced root/shoot and malondialdehyde contents (MDA). Exogenous ABA improved the adaptability of seedlings under drought stress, especially under severe drought stress, with leaf relative water content being improved 21.0%. Plant height and biomass allocation were improved by exogenous ABA under drought, while root/shoot was improved by 1.1 times compared with the well watered plants. The accumulation of MDA was decreased, the activities of CAT and SOD were significantly increased, and the proline content was increased 6.7 times by exogenous ABA under drought. Exogenous ABA application alleviated the negative effect of drought on photosynthetic organs, reduced the decrease of net photosynthetic rate and stomatal conductance under drought, and enhanced F/F value. The results suggested that exogenous ABA treatment could enhance the resistance of M. yunnanensis to drought stress.