The influence of ABA on the photosynthesis of the rare and endangered Emmenopterys henryi under salt stress

Emmenopterys henryi Oliv., a monotypic genus in family Rubiaceae with high scientific and application value, is currently endangered. Adaptability of E. henryi to environment is important for its cultivation, management, and application. In this paper, the effect of abscisic acid (ABA) on the photosynthesis of E. henryi under salt stress was discussed. Results showed that 0.3 % (m/v) NaCl led to reduction of net photosynthetic rate (PN), instantaneous carboxylation efficiency (ICE), and Rubisco activity but the increase of intercellular CO2 concentration (ci), which were remarkable relieved by ABA pretreatment. NaCl also induced reduction of the maximal efficiency of PS II photochemistry (Fv/Fm), the photochemical quenching (qP), the non-photochemical quenching (NPQ), the actual PS II efficiency [Y(II)], the regulated-energy dissipation [Y(NPQ)], whereas the increase of the unregulated energy dissipation [Y(NO)]. ABA application remarkably mitigated the depression of Fv/Fm, qP, Y(II) and the increase of Y(NO), but further promoted NPQ and Y(NPQ) in E. henryi due to high salinity. In addition, decrease of chlorophyll content, accumulation of MDA, and ion leakage in E. henryi due to high salinity were significantly alleviated by ABA pretreatment. Fluridone, an inhibitor of endogenous ABA synthesis, partially or completely reversed ABA mediated effects. These results suggested that ABA might improve the photosynthesis of E. henryi under salt stress via allocating more energy to photochemical reactions, or/and mitigating the decrease of Rubisco activity, or/and protecting photosynthetic apparatus by reinforcement of heat dissipation and alleviating oxidative damage.