Regulation of Photosynthesis during Leaf Development in RbcS Antisense DNA Mutants of Tobacco

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Abstract
We have previously characterized RbcS antisense DNA mutants of tobacco that have drastic reductions in their content of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; S.R. Rodermel, M.S. Abbott, L. Bogorad [1988] Cell 55: 673–681). In this report we examine the impact of Rubisco loss on photosynthesis during tobacco (Nicotiana tabacum) leaf development. Photosynthetic capacities are depressed in the antisense leaves, but the patterns of change in photosynthetic rates during the development of these leaves are similar to those in wild-type plants: after attaining a maximum in young leaves, photosynthetic capacities undergo a prolonged senescence decline in older leaves. The alterations in photosynthetic capacities in both the wild type and mutant are closely correlated with changes in Rubisco activity and content. During wild-type leaf development, Rubisco accumulation is regulated by coordinate changes in RbcS and rbcL transcript accumulation, whereas in the antisense leaves, Rubisco content is a function of RbcS, but not rbcL, transcript abundance. This indicates that large subunit protein production is controlled posttranscriptionally in the mutants. The antisense leaves accumulate near-normal levels of chlorophyll and representative photosynthetic proteins throughout development, suggesting that photosynthetic gene expression is not feedback regulated by Rubisco abundance. Considered together, the data in this paper indicate that leaf developmental programs are generally insensitive to sharp reductions in Rubisco content and emphasize the metabolic plasticity of plant cells in achieving optimal photosynthetic rates.