Fig. 10: Summary of how S. viridis responds to high light or high temperature.

Light blue boxes denote changes that may lead to the reduced photosynthetic capacities; light green boxes denote changes that may be adaptive for high light or high temperature acclimation. M: mesophyll chloroplasts; BS, bundle sheath chloroplasts. High-light-treated leaves had over-accumulated starch and increased chloroplast crowdedness, which may hinder PSII repair and result in photoinhibition. Starch accumulation may also inhibit photosynthesis through feedback regulation. Increased plastoglobuli (PG) formation in high-light-treated leaves may affect thylakoid composition and function. Under high temperature, mesophyll chloroplasts had swollen grana and bundle sheath chloroplasts had some different responses. Heat-induced photorespiration and PG formation could further reduce photosynthesis. Meanwhile, high light and high temperature also induce adaptive responses for acclimation. Under high light, the induced photoprotection, down-regulated light reaction, and increased water-use efficiency through abscisic acid (ABA) can help S. viridis acclimate to excess light. Under high temperature, the induced cyclic electron flow (CEF) and Rubisco activase (RCA-α) can protect photosynthesis from heat stress. The induced heat shock transcription factors (HSFs) and heat shock proteins (HSPs) are adaptive responses to both high light and high temperature, although the induction was much quicker under high temperature than under high light.