Adaptation of pea to elevated atmospheric CO2: Rubisco, phosphoenolpyruvate carboxylase and chloroplast phosphate translocator at different levels of nitrogen and phosphorus nutrition
Resource allocation in high CO2 was studied with respect to plant nutrition. Pea (Pisum sativum) was grown in CO2-enriched air (1000 cm 3 m3 CO2) during the entire vegetative phase, or grown in ambient air (340 cm3 m3 CO2), with different levels of nitrogen or phosphorus supply. Rubisco specific activity, abundance and small subunit transcript levels were unaltered at high N but declined at reduced N depending upon the degree of N deprivation. It is proposed that (a) a threshold value for the N status occurs in pea above which Rubisco is not down-regulated by high CO2 and (b) a high leaf level of soluble carbohydrates is not a sufficient condition to downregulate Rubisco in high CO2. Phosphoenolpyruvate (PEP) carboxylase decreased, and chloroplast phosphate (P)-translocator increased, in high CO2. In contrast to Rubisco, down-regulation of PEP carboxylase was alleviated by low N and enhanced by low P. The increase in the P-translocator was little affected by N but was accentuated by low P. The increase in the P-translocator is considered to be one way of alleviating low P conditions in the chloroplast and thus rebalancing carbon partitioning between starch and soluble carbohydrates and amino acids. It is proposed that acclimation of PEP carboxylase and P-translocator reflects adaptation to metabolic perturbations caused by high CO2.