Mechanism Of Exogenous ABA For Improving Drought Resistance Of Tobacco Seedlings Under Drought Conditions

Seedlings of tobacco "Longjiang911", as an main referential in this study, spraying the leaf respectively with10,25,40μmol·L-1ABA, we measured series of physiological and biochemical parameters such as malonaldehyde (MDA), the chlorophyll content; catalase (CAT) and the activity of ascorbic acid peroxidase (APX); chlorophyll fluorescence parameters, component of xanthophyll cycle (PRI) to study the mechanism of exogenous ABA on drought resistance of tobacco seedlings under different drought stress on preliminary discussion, the research results are as follows:1、Drought stress significantly inhibited the chlorophyll content and relative water content (RWC), and increased the malondialdehyde (MDA), relative conductivity, the activity of ascorbic acid peroxidase (APX) and catalase (CAT). However, application of25μmol·L-1ABA alleviated such inhibition caused by drought, low concentration(25μ mol·L-1) ABA treatment alleviated the increased of H2O2. relative conductivity and MDA content of tobacco seedlings, which indicated that suitable concentration of ABA solution has the ability to protect the environmental stability of tobacco leaf cells Seeding, Furthermore, exogenous ABA alleviated the damages caused by the drought stress.2、Drought stress could decrease the maximum photochemical efficiency (Fv/Fm) and potential activities of PS Ⅱ (Fv/Fo), which is indicated that drought stress could induced the obvious photoinhibition, with the extension of drought stress, drought stress decreased the active reaction centers (ψo), increased the PSII primary electron acceptor (QA), which indicated that drought stress may blocked the photosynthetic electron transport chain, decreased the primary photochemical reaction of the maximum yield, reducted the electron transport flux per reaction center, increased the dissipated energy flux per reaction center, so the drought stress changes the PS II reaction center of each treated tobacco seedlings, however, exogenous ABA alleviated the damages to the various parameters of the plant photosystem Ⅱ caused by the drought stress, which is showed that exogenous ABA can enhance the drought tolerance of tobacco seedlings.3、Drought stress could decrease the quantum yield of PSⅡ (ΦPS Ⅱ), electron transportr rate, photochemical quenching, photochemical reflectance index(ETR). In contrary, non-photochemical quenching (NPQ), were increased under drought condition, which is indicated that drought stress make the PS II of tobacco seedlings reaction center inactivation, in order to defend against such damage, plant seedlings enhances the xanthophyll cycle to dissipate excess energy, application of exogenous ABA alleviated the descending trend of FV/Fm, ΦPS Ⅱ and ETR, increased the non-photochemical quenching, and decreased the photochemical reflectance index, which indicate that exogenous ABA could protect the tobacco seedling to dissipat the excess excitation energy through the xanthophyll cycle under drought stress, Furthermore, exogenous ABA improved the drought resistance of tobacco seedlings to some extent.