Photosynthesis-Rubisco relationships in foliage of Pinus sylvestris in response to nitrogen supply and the proposed role of Rubisco and amino acids as nitrogen stores

Relationships between photosynthetic capacity, and needle contents of N, Rubisco and amino acids were investigated in potted Pinus sylvestris L. trees. Three-year-old seedlings of P. sylvestris were grown for 4 years with three nutrient regimes. Concentrations of N, amino acids, amides and Rubisco were measured and expressed on a needle area basis, and the in vivo performances of Rubisco (maximum rate of carboxylation, V^sub cmax^) and of electron transport (maximum light driven electron flux, J^sub max^) were estimated via a biochemically based model of photosynthesis. Needle content of Rubisco-N was at least six times that of amino acid + amide-N and was positively related to N^sub area^. The estimated in vivo specific activity of Rubisco (V^sub cmax^/Rubisco content per unit area) was low and negatively related to N content per unit area (N^sub area^). J^sub max^/Rubisco content was negatively related to N^sub area^, whereas V^sub cmax^/J^sub max^ was unrelated to N^sub area^. Hence, Rubisco content was in excess of the amount required for photosynthesis and this excess was positively related to N^sub area^. These data support the hypothesis that with increasing N^sub area^, Rubisco functions increasingly as a storage protein in addition to its catalytic functions.[PUBLICATION ABSTRACT]