Influence of in vitro growth conditions on the photosynthesis and survival of Castanea sativa plantlets during ex vitro transfer

Adequate in vitro micro-environments are crucial to induce life compatible leaf development. Key morphological and physiological traits are needed to allow ex vitro survival. We study, how in vitro light and ventilation affect physiological performance and survival of ex vitro Castanea sativa plantlets. In vitro treatments consisted of two irradiances of 50 and 150 µmol m⁻² s⁻¹in ventilated vessels (VL₅₀and VL₁₅₀, respectively), compared to traditional cultures at 50 µmol m⁻² s⁻¹in non-ventilated vessels (NVL₅₀). After the exposure to each condition a photoinhibitory treatment (PhT) was also applied to study whether the above in vitro conditions exerted photoprotection and facilitated the recovery of C. sativa during sudden ex vitro transfer. During rooting, a decrease in net photosynthesis (Psat), electron transport rate (ETRII) and maximal efficiency of PSII (F ᵥ /F ₘ) were observed. Transpiration rates (E) decreased, concomitantly with a rise in water use efficiency (WUE), mainly in microplants originating from ventilated treatments (V). Throughout this stage, the PhT was lethal for all in vitro treatments. During acclimation, the number and leaf size increased principally in plantlets originating from V treatments. These microplants were also able to recover their ETR and F ᵥ /F ₘ . Initially, the PhT produced a drastic drop in Fᵥ/Fₘof plantlets in all treatments however they did show a tendency to recover. Transferring plantlets to the greenhouse produced a decrease in the Psat in all treatments; however, over time Psat increased reaching values of 3.2 and 5.3 μmol CO₂m⁻² s⁻¹in microplants originating from VL₅₀and VL₁₅₀, respectively. Transpiration rate were similar in all treatments and remained at levels of about 0.9 mmol H₂O m⁻² s⁻¹; thus, WUE increased significantly, reaching values of almost 3.8 µmol CO₂/mmol H₂O in microplants originating from VL₁₅₀. After the PhT, all of the plantlet’s recovery capacity increased concomitantly with their dynamic heat dissipation and their de-epoxidation capacity. Our results suggest that managing in vitro conditions can improve plantlets photosynthetic performance in early stages after ex vitro transfer, playing a key role in the ameliorating the transfer stress.