Long-term effects of temperature shifts on xanthophyll cycle and photoinhibition in spinach (Spinacia oleracea)

Abstract

The present study tested with spinach (Spinacia oleracea L.), whether leaves are capable of long-term acclimative responses of carotenoids when warm-grown (20°C) plants were subjected to a regime of low temperature (1–6°C) and excess light (250 mol m^–2 s^–1). About 17 days after the temperature shift, leaves of the third leaf pair were compared with the respective leaves of warm-grown control plants. The cold-treated leaves exhibited reduced susceptibility to photoinhibition (at 4°C) and considerably faster kinetics of ‘recovery’ (at 20°C), as determined by changes in the ratio of dark-adapted variable to maximum chlorophyll fluorescence, F_V/F_M. The temperature shift induced marked changes in the composition of photosynthetic pigments. In particular, the pool of xanthophyll cycle pigments, viola-, anthera- and zeaxanthin, based on chlorophyll a+b, was enlarged by about 50%. The proportion of xanthophyll cycle pigments referred to the sum of carotenoids increased by about 25% and, in excessive light, a larger fraction of violaxanthin became deepoxidized. Overall, in respect of carotenoid composition and xanthophyll cycle activity, leaves that had been acclimated by temperature shift were very similar to leaves acclimated by growth in the field during autumn and winter. The data show that in spinach leaves, photoprotective mechanisms can be induced by temperature shift without requirement for development and growth at low temperature.