Chlorophyll a Fluorescence: an effective tool for quick screening of salinity tolerance in Pearl Millet (Pennisetum glaucum L.)

Abstract Chlorophyll a fluorescence (CF) is an effective tool to measure the photosynthetic efficiency, functional capacity and structural stability of photosystem-II and the overall health status of plants in normal or stress environment. The present study was designed to investigate the response of PSII through CF in pearl millet (Pennisetum glaucum L.) grown under saline stress (200 mM NaCl). In first round, eighteen varieties were screened for salinity tolerance at vegetative stage. The relative rate of reduction in biomass, pigments, Na+ and K+ indicated YBS-93, YBS-94 and YDR-8-1 varieties as tolerant and the YBS-98, YCMP-19 and YCMP-34 varieties as salt sensitive varieties. While the chlorophyll-a fluorescence transient analysis, raw OJIP induction curves, Fo and Fm normalised curves exhibited that substantial variation in CF occurred at the O, J, I and P steps in salt sensitive varieties. The comprehensive investigation of JIP test attributes proposed that salinity stress triggered photoinhibition of PSII via disturbance in absorption of light from reaction centres (ABS), low electron transport and photochemical fluxes (ETo, ψ0 & ɸEo) and increased dissipation fluxes (DIo & ɸDo). However, increased dissipation energy (DIO/RC) under salinity stress acts as a preventative control to protect PSII from photooxidative damage in the thylakoid membrane. While photoinhibition of PSII resulted in decrease in quantum yield of PSII (Fv/Fm) and performance index (Pi) under salinity stress. These findings provided important understanding of the salinity tolerance in pearl millet and have opened avenues to further explore the molecular signalling pathways involved in salinity tolerance.