The impact of salicylic acid and silicon on chlorophyll a fluorescence in mung bean under salt stress

The ameliorative effect of salicilic (SA) and silicon (Si) on photosystem II (PSII) activity of mung bean plant under salt stress (control, 3, 6, and 9 dS/m) was studied by chlorophyll a fluorescence measurement. Results showed that Na+ accumulation decreased, but K+ accumulation increased in mung bean (Vigna radiata (L.) Wilczek) leaves by application of Si and especially SA, leading to improvement in PSII activity under salinity. Initial fluorescence (F0) and energy necessary for the closure of all reaction centres (Sm) were increased with increasing salt levels. Exogenous foliar application of SA and Si decreased initial fluorescence (F0) and increased photosynthesis relative vitality (PI). Maximum fluorescence (Fm), variable fluorescence (Fv), the activity of the water-splitting complex on the donor side of the PSII (proportional to Fv/F0) and the average redox state of QA in the time span from 0 to Tfm (Sm/Tfm) were also enhanced by foliar application of SA. Exogenous application of SA improved maximum quantum efficiency of PSII (Fv/Fm) and performance index (PI) under both saline and non-saline conditions. Increasing in the size of the plastoquinone pool (Area) was much greater for SA than that for Si treated plants. It was concluded that foliar application of Si and SA in particular could play a key role in salt stress tolerance of mung bean plants.