Abstract

In this study, 24-epibrassinolide (EBR), an active brassinosteroid, was exogenously applied to investigate photosynthetic performance of salt-stressed eggplant (Solanum melongena L.). EBR, especially 100 nM, dramatically alleviated growth suppression caused by salt stress. Similarly, the application of 100 nM EBR, the most effective concentration, for salt-stressed plants significantly increased chlorophyll concentration, net photosynthetic rate (P_n), stomatal conductance (g_s) and intercellular CO₂ concentration (C_i). In addition, maximal quantum efficiency of photosystem II (PSII) photochemistry (F_v/F_m), PSII maximum efficiency (F_v´/F_m´),photochemical quenching coefficient (qP), PSII operating efficiency (ΦPSII) and the fractions of light absorbed which is utilized in PSII photochemistry were also increased, while nonphotochemical quenching (NPQ) was reduced. However, higher concentrations (200 and 400 nM) of EBR reduced its effects or even caused a further reduction of photosynthetic capacity as compared to plants that received high salinity treatment alone. Furthermore, the changes in P_n at varying levels of EBR under salt condition were not accompanied by a significant corresponding change in C_i, suggesting that g_s was not the sole factor for EBR-induced changes in photosynthesis. Results obtained here demonstrate that EBR application could improve photosynthesis and alleviate the detrimental effects of salt stress on plant growth.

Key words: Chlorophyll fluorescence, eggplant, 24-epibrassinolide, photosynthetic gas exchange, salt stress, thermal energy dissipation.

Abbreviation

BR, Brassinosteroid; Ci, intercellular CO2  concentration; EBR, 24-epibrassinolide; Fo, minimal fluorescence at the dark-adapted state; Fo΄, minimal fluorescence at the light-adapted state; Fm, maximal fluorescence at the dark-adapted state; Fm΄, maximal fluorescence at the light-adapted state; Fs, steady-state level fluorescence; Fv, variable fluorescence at the dark-adapted state; Fv/Fm, maximum quantum yield of PSII photochemistry; Fv´/Fm´, PSII maximum efficiency; gs, stomatal conductance; NPQ, nonphotochemical quenching; Pn, net photosynthetic rate; ΦPSII, PSII operating efficiency; qP, photochemical quenching coefficient; Tr, transpiration rate.