Influence of CO2 and sucrose on photosynthesis and transpiration of Actinidia deliciosa explants cultured in vitro.

Explants of Actinidia deliciosa Chev. Liang and Ferguson var. Hayward were cultured in controlled CO2 atmospheres in the presence of different sucrose concentrations. Organogenesis was measured after 45 days in explants from the different assays, and quantification of photosynthesis, transpiration, chlorophylls, RUBISCO and total soluble protein content was performed in leaves from the different treatments. The best results were those of explants cultured at 600 &mgr;mol CO2 mol-1 on 20 g l-1 of sucrose for the first 20 days and then transferred to sucrose-free medium until the end of the culture period. Increasing CO2 to 2000 &mgr;mol CO2 mol-1 in the atmosphere of the culture vessel reduced all the parameters studied. Photosynthesis of autotrophically developed explants trebled that of the reference heterotrophic explants, as there was an apparent inverse relationship between photosynthesis and transpiration. Photosynthesis was saturated at 300 &mgr;mol m-2 s-1 PPFD and 600 &mgr;mol CO2 mol-1. Chlorophylls and RUBISCO presented differences between treatments, mainly between different CO2 concentrations, with the highest values in autotrophically cultured explants. Explants grown at 2000 &mgr;mol CO2 mol-1 showed the lowest RUBISCO/Prots ratio, probably due to negative adaptation of RUBISCO to long-term high CO2. In short, explants grown in a controlled microenvironment, with increased CO2 and under autotrophic conditions, developed wholly functional photosynthetic apparatus well prepared to be transferred to ex vitro conditions, which has many advantages in micropropagation.