[Effects of salicylic acid on chlorophyll fluorescence and xanthophyll cycle in cucumber leaves under high temperature and strong light].

In this study, cucumber leaves were under high temperature and strong light stress after two days of spraying with 50 to approximately 400 micromol x L(-1) salicylic acid (SA) solution. The measurements showed that SA pretreatment could inhibit the decrease of intrinsic photochemical efficiency (Fv/ /Fm), quantum yield of PSII(phiPSII), maximum fluorescence value (Fm), and photochemical quenching (qP) by 16.1% to approximately 30.2%, 11.9% to approximately 33.0%, 7.2% to approximately 41.0% and 27.2% to approximately 160.8%, respectively, and promote the increase of non-photochemical quenching (NPQ) by 13.1% to approximately 62.9%, but had little effect on initial fluorescence value (Fo). SA pretreatment could also inhibit the decrease of xanthophyll cycle pool in cucumber leaves, and increase the de-epoxidation extent of xanthophyll cycle (A + Z)/(V + A + Z),which was 29.5% and 24.6% higher than control, respectively. It was suggested that SA could protect the photosynthetic apparatus of cucumber leaves under high temperature and strong light through promoting non-radiative energy dissipation.