Response of rice to p(CO2) enrichment: the relationship between photosynthesis and nitrogen metabolism

• Published in: Journal of crop improvement Vol. 13; no. 1-2; pp. 31 - 53
• Main Authors: Seneweera, S, Makino, A, Mae, T, Basra, A.S
• Format: Journal Article
• Language: English
• Published: Taylor & Francis Group 01.01.2005
• Subjects: carbon dioxide; downregulation; elevated atmospheric gases; Elevated p(CO; enzyme activity; gene expression; messenger RNA; nitrogen; nitrogen metabolism; Oryza sativa; photosynthesis; plant nutrition; ribulose-bisphosphate carboxylase; rice; Rubisco
• ISSN: 1542-7528; 1542-7536
• DOI: 10.1300/J411v13n01_03

Rice (Oryza sativa L.) is grown in many different agro-ecological zones and it assimilates CO 2 directly through C 3 photosynthesis. At current CO 2 partial pressure [p(CO 2 )], rice is not photosynthetically saturated but immediately after exposure to 100 p(CO 2 ), photosynthetic rates are increased by 48 percent on an average. However, this increase is not sustained during prolonged exposure and is associated with reduced amounts of ribulose-1-5-bisphospate carboxylase/oxygenase (Rubisco) content and its maximum potential activity (V cmax ). Rubisco content and V cmax were reduced by 33 and 22%, respectively, at elevated p(CO 2 ) and this has an additive effect on leaf photosynthesis. Activation state of the Rubisco is also decreased by elevated p(CO 2 ) but no deactivation of Rubisco occurs in rbc S antisense rice with 40% wild type Rubisco suggesting that deactivation is an optimize response. Large amounts of Rubisco (about 80-90%) is synthesized prior to full expansion of leaf when sugar accumulation is minimal. After the leaf has fully expanded, very little Rubisco (about 10-20%) is synthesized and a large amount of sugar accumulates during this period. Therefore, it is unlikely that downregulation of Rubisco at elevated p(CO 2 ) is caused by decreasing the mRNA transcripts for Rubisco small subunit (rbcS) and Rubisco large subunit (rbcL) through soluble sugars. It is more likely that elevated p(CO 2 ) mediated decline in Rubisco is due to rapid degradation of protein and lower nitrogen (N) allocation to Rubisco due to reduced N afflux. Leaf N content was reduced by 16% in plants grown at elevated p(CO 2 ) though leaf N to Rubisco ratio remained consistently unchanged regardless of growth p(CO 2 ) suggesting that N assimilation, distribution and remobilization at the whole plant level is tightly controlled at elevated p(CO 2 ). Further, changes in N and C metabolisms at elevated p(CO 2 ) are likely to reduce the critical N concentration by 30% at elevated p(CO 2 ).