Long-Term Chilling of Young Tomato Plants under Low Light. IV. Differential Responses of Chlorophyll Fluorescence Quenching Coefficients in Lycopersicon Species of Different Chilling Sensitivity
Temperature dependences of chlorophyll fluorescence quenching coefficients were studied in the cultivated tomato (Lycopersicon esculentum) and three lines of the chilling-tolerant L.peruvianum from different altitudes, i.e. LA 1373 (20 m a.s.l.), LA 2157 (1,650 m a.s.l.) and LA 385 (2,400 m a.s.l.). At actinic light intensity near light saturation of photosynthesis (370 μE m−2 s7minus;1), photochemical quenching (qP) increased with increasing temperature between 5 and 30°C. The temperature, at which qP reached the numerical value 0.5 [T (qP=0.5)] decreased by 2.5–4.5°C after a chilling treatment of 14 days at 10°C in L. peruvianum, indicating acclimation of the photosynthetic dark reactions in this species. The final T (qP=0.5) attained after chilling could be arranged in the order L.esculentum>LA 1373>LA 2157>LA 385. The fast relaxing non-photochemical quenching (qN) component (qf, consisting mainly of energy-dependent quenching, qE) exhibited minima near the optimum temperature for photosynthesis. These minima shifted to lower temperatures upon chilling in L. peruvianum. Photoinhibitory quenching (ql) was unaffected by chilling in the high altitude lines, but-increased strongly in LA 1373 and L. esculentum. Under low actinic light (40 μE m−2 s−1), temperature dependences of qP and qN were nearly identical in L. esculentum and LA 385 and revealed abrupt changes at approx. 8°C. It is concluded that qP and ql, measured after defined chilling treatments, are valuable screening parameters for chilling tolerance in early growth stages of Lycopersicon plants.