Whole-plant growth and N allocation in transgenic rice plants with decreased content of ribulose-1,5-bisphosphate carboxylase under different CO₂ partial pressures

Abstract

Growth of transgenic rice (Oryza sativa L.) with an antisense gene to the small subunit of Rubisco was analysed under 36 and 100 Pa CO₂ during a 14-h photoperiod (1000 mol quanta m^–2 s^–1). Two lines of the antisense plants were used; one with 65% wild-type Rubisco and the other with 40% wild-type Rubisco. The plants were grown hydroponically for 70 d. The final biomass of the antisense plants grown in 36 Pa CO₂ was much smaller than that of the wild-type plant. However, several compen-sation phenomena were found in the antisense plants. Increased biomass allocation to leaf blades and preferential N investment in leaf blades were observed. Leaf senescence was also delayed. Elevated CO₂ levels up to 100 Pa caused the antisense plants to achieve a size similar to that of the wild-type plant. However, although the antisense plant with 65% wild-type Rubisco was selected as a plant with optimal Rubisco content for CO₂ -saturated photosynthesis, its final biomass was not greater than that of the wild-type plant. This may have been caused by a relatively strong Rubisco-antisense effect during the early stage of growth (21–42 d). N-use efficiency for growth after d 42 was greater in the selected antisense plant. Thus, improvement of N-use efficiency at the level of a single leaf did not necessarily lead to greater production of biomass at the whole-plant level.