Abstract
Background Abiotic stress, such as salinity, affects the photosynthetic apparatus of plants. It is reported that the
use of selenium nanoparticles (Se NPs), and biochemical compounds such as chitosan (CS) increase the tolerance of
plants to stress conditions. Therefore, this study aimed to elucidate the potential of Se NPs, CS, and their composite
(CS+Se NPs) in improving the photosynthetic apparatus of C. sinensis under salt stress in greenhouse conditions. The
grafted seedlings of C. sinensis cv. Valencia after adapting to the greenhouse condition, were imposed with 0, 50, and
100 mM NaCl. After two weeks, the plants were foliar sprayed with distilled water (control), CS (0.1% w/v), Se NPs (20
mg L−1
), and CS+Se NPs (10 and 20 mg L−1
). Three months after treatment, the levels of photosynthetic pigments,
leaf gas exchange, and chlorophyll fluorescence in the treated plants were evaluated.
Results Under salinity stress, total chlorophyll, carotenoid, and SPAD values decreased by 31%, 48%, and 28%
respectively, and Fv/Fm also decreased compared to the control, while the ratio of absorption flux (ABS), dissipated
energy flux (DI0) and maximal trapping rate of PSII (TR0) to RC (a measure of PSII apparent antenna size) were
increased. Under moderate (50 mM NaCl) and intense (100 mM NaCl) salinity stress, the application of CS+Se NPs
significantly increased the levels of photosynthetic pigments and the Fv/Fm value compared to plants treated with
distilled water.
Conclusions It may be inferred that foliar treatment with CS+Se NPs can sustain the photosynthetic ability of C.
sinensis under salinity stress and minimize its deleterious effects on photosynthesis.