Moderate photoinhibition of PSII and oxidation of P700 contribute to chilling tolerance of tropical tree species in subtropics of China.

Abstract

In the subtropics, a few tropical tree species are distributed and planted for ornamental and horticultural purposes; however, the photosynthesis of these species can be impaired by chilling. This study aimed to understand how these species respond to chilling. Light-dependent and CO₂ assimilation reactions of six tropical tree species from geographically diverse areas, but grown at a lower subtropical site in China, were monitored during a chilling (≤ 10°C). Chilling induced stomatal and nonstomatal effects and moderate photoinhibition of PSII, with severe effect in Ixora chinensis. Woodfordia fruticosa was little affected by chilling, with negligible reduction of photosynthesis and PSII activity, higher cyclic electron flow (CEF), and oxidation state of P700 (P700⁺). Photoinhibition of PSII thus reduced electron flow to P700, while active CEF reduced oxidative damage of PSI and maintained photosynthesis during chilling. Studied parameters revealed that coupling between light-dependent and CO₂ assimilation reactions was enhanced under chilling.