Stability and activity of Rubisco in chestnut plantlets transferred to ex vitro conditions under elevated CO2

Heterotrophic plantlets obtained by in vitro propagation are biochemically different compared to autotrophic plantlets. When heterotrophic plantlets are transferred to ex vitro conditions, higher irradiance levels are generally applied. Irradiance levels higher than those used in vitro lead to oxidative stress symptoms that can be counteracted by CO2 concentrations above normal. We analyzed the stability and activity of Rubisco and leaf-soluble sugars and starch contents in chestnut plantlets transferred from in vitro to ex vitro conditions under four treatments obtained by associating two irradiances of 150 (low light, LL) and 300 (high light, HL) mu mol m(-2) s(-1), respectively three and six times in vitro irradiance, with two CO2 levels of 350 (low CO2, LCO2) and 700 (high CO2, HCO2) mu l l(-1). In in vitro plantlets it was possible to immunodetect apparent products of degradation of Rubisco large subunit (LSU). In ex vitro plantlets, these degradation products were no longer detected except under LL associated with LCO2. The decrease in soluble sugars and starch in plantlets under HL HCO2 gave an indication of a faster acquisition of autotrophic characteristics. However, under the same treatment, a down-regulation of Rubisco activity was observed. From the results taken as a whole, two aspects seem to be confirmed: HL HCO2 is more efficient in inducing an autotrophic behavior in chestnut ex vitro plantlets; actively growing systems as ex vitro plantlets reflect the down-regulation of Rubisco by HCO2 without accumulation of carbohydrates.