In vitro photoautotrophic acclimatization, direct transplantation and ex vitro adaptation of rubber tree (Hevea brasiliensis)

Abstract

We investigated the effect of carbon dioxide (CO2)-ambient (350 µmol CO2 mol−1) and CO2-enriched (1500 µmol CO2 mol−1) conditions of in vitro photoautotrophic system on two cultivars, ‘RRIM600’ and ‘RRIT413’ of rubber tree (Hevea brasiliensis) in an acclimatization process of 45 days. Survival percentage of in vitro rubber tree plantlets derived from somatic embryos under ambient CO2 was better than those under CO2-enriched conditions, especially in cv. ‘RRIT413’. Subsequently, the survival rate of ex vitro transplanted plantlets was similar to the in vitro plantlets and abnormal morphological characters such as light-green leaves (SPAD), small leaves in cv. ‘RRIT413’ acclimatized under CO2-enriched conditions were demonstrated 30 days after the plantlets were transferred into the soil. Maximum quantum yield of PSII, photon yield of PSII, stomatal conductance and transpiration rate in cv. ‘RRIT413’ acclimatized under CO2-enriched conditions were sharply declined by 39.0, 50.6, 47.1 and 45.8%, respectively as compared to those acclimatized under ambient CO2 conditions. In contrast, the in vitro acclimatized plantlets of cv. ‘RRIM600’ were un-responsive under both ambient- and enriched-CO2 conditions. In conclusion, genotypic dependent in response to CO2 enriched conditions in in-vitro acclimatization of rubber tree plantlets was evidently demonstrated as a key result to regulate plant growth and development in ex vitro environments. Interestingly, soluble sugar contents (sucrose, glucose and fructose) were increased after transplanting the plantlets of cv. ‘RRIM600’ acclimatized under CO2-enriched condition into the soil and thus, can be considered as an adaptive indicator of ex vitro adaptation.