Isoprene emission in the monocot Arundineae tribe in relation to functional and structural organization of the photosynthetic apparatus

Several plant species emit isoprene, a compound able to protect plants against high temperatures and oxidative stresses, and to affect the oxidative capacity of the atmosphere. The emission of isoprene in monocots is much less investigated than in dicots. We explored the emission of isoprene among members of the Poaceae tribe Arundineae, and its potential impact on plant performance. Our results confirm, also in monocots, the existence of a significant correlation between photosynthesis and isoprene emission and further suggest that isoprene inversely correlates to habitat xericity in unstressed Arundineae. Isoprene emission capacity developed rapidly in unfolding leaves, implying some developmental differences in the control of this biosynthetic pathway with respect to dicots. Among Arundineae, marked species-specific differences in several parameters related to plant productivity (photosynthesis, carbon lost as isoprene, water use efficiency, biomass and chloroplast ulrastructure) were observed. Isoprene presence improved structural organization of thylakoid membrane system and decreased the heat dissipation at physiological temperature. Our results demonstrate that, as in dicots, also in monocots isoprene could contribute to improve photosynthesis performance, although this was not necessarily reflected in higher yields, at least in unstressed conditions