Effect of Photon Flux Density and Exogenous Sucrose on the Photosynthetic Performance during <i>In Vitro</i> Culture of <i>Castanea sativa</i>

Abstract

The low photon flux density (PFD) under in vitro conditions and sucrose added to the culture medium negatively limits the photochemical activity and photoprotective mechanisms of microshoots. In this work we hypothesize that decreasing sucrose in the culture medium in combination with increasing irradiance, could improve the photosynthesis and consequently the in vitro growth. We evaluated the effect of exogenous sucrose (30 and 5 g&middot;L -1 , HS and LS, respectively), under different PFD (50 and 150 μmol photons m -2 &middot;s -1 , LL and HL, respectively) on the photosynthetic performance and growth of Castanea sativa microshoots. Decreasing sucrose negatively affected the physiological attributes evaluated. Only chloroplast ultrastructure was improved by LS; however this did not lead to an improved in photosynthesis or growth. HL HS produced an increase in photosynthetic activity and chlorophyll contents, reaching under these conditions a higher proliferation rate and biomass production. Additionally, the photochemical activity (electron transport rate and non-photochemical quenching) was improved by HL. Thus, our results suggest that, at least for C. sativa HL is beneficial during the in vitro culture, improving photosynthetic performance as well as growth, but this is only possible in the presence of moderate concentrations of sucrose added to the culture medium.