Fig. 4
a The Fv/Fm (maximum potential quantum efficiency of PSII), (b) Fq′/Fm′ (quantum yield of PSII), (c) qL (fraction of open PSII centers), (d) NPQ (non-photochemical quenching) and (e) rapid light-response curves of ETR (electron transport rate) in leaves of tomato after 42 h exposure to control, cold, drought and combined stress conditions. The Fq′/Fm′, qL and NPQ were measured at a PPFD of 285 μmol m− 2 s− 1, which was close to the growth PPFD of 300 μmol m− 2 s− 1. The data represents mean values ± SD (n = 4). Different letters indicate significant difference at P < 0.05. For ETR, the different letters were marked for light levels of 190, 285, 420, 630 and 822 μmol m− 2 s− 1