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 nutr ition. Pea (Pisum sativum) was grown in CO2-enriched air (1000 cm(3) m (-3) CO2) during the entire vegetative phase, or grown in ambient air (340 cm(3) m(-3) CO2), with different levels of nitrogen or phosphorus supply. Rubisco specific activity, abundance and small subunit transc ript levels were unaltered at high N but declined at reduced N dependi ng upon the degree of N deprivation. It is proposed that (a) a thresho ld value for the N status occurs in pea above which Rubisco is not dow n-regulated by high CO2 and (b) a high leaf level of soluble carbohydr ates is not a sufficient condition to down-regulate Rubisco in high CO 2. Phesphoenolpyruvate (PEP) carboxylase decreased, and chloroplast ph osphate (P)-translocator increased, in high CO2. In contrast to Rubisc o, down-regulation of PEP carboxylase was alleviated by low N and enha nced 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 chl oroplast and thus re-balancing carbon partitioning between starch and soluble carbohydrates and amino acids. It is proposed that acclimation of PEP carboxylase and P-translocator reflects adaptation to metaboli c perturbations caused by high CO2.