Winter and summer leaves of Cistus incanus: differences in leaf morphofunctional traits, photosynthetic energy partitioning, and poly(ADP-ribose) polymerase (PARP) activity

Leaf anatomy, photosynthetic performance, and the role of poly(ADP-ribosyl)ation in maintaining genomic stability inwinter and summer leaves of Cistus incanus L. were investigated to evaluate the strategies allowing this species to grow in aMediterranean climate. Measurements on summer leaves (SL) were conducted at midday and on the following morning to assessthe reversibility of changes induced by high temperatures and irradiances reached at midday. Winter leaves (WL) were thickerwith a lower leaf density and higher intercellular spaces compared with SL, which showed reduced net photosynthesis (Pn) anda decrease in Rubisco activity. Compared with WL, SL showed a higher thermal dissipation (FNPQ) in compensating for thereduced Pn. This allowed minimization of ROS production (low FNO) and hence prevented photo-oxidative damage. In SL,poly(ADP-ribose) polymerase (PARP) activity was down-regulated, probably allowing leaves to become tolerant to high temperaturesand irradiances. SL are also characterised by chloroplasts occupying larger cell volume and well exposed to intercellularspaces. This may well favour better liquid-phase CO2 diffusion towards carboxylation sites, contributing to reducing the negativeinfluence of high leaf density and the low percentage of intercellular spaces on photosynthesis.