Selection and Characterization of Tobacco Plants with Novel O2-Resistant Photosynthesis

Plants were obtained with novel O(2)-resistant photosynthetic characteristics. At low CO(2) (250-350 muL CO(2) L(-1)) and 30 degrees C when O(2) was increased from 1% to 21% to 42%, the ratio of net CO(2) uptake in O(2)-resistant whole plants or leaf discs compared to wild type increased progressively, and this was not related to stomatal opening. Dihaploid plantlets regenerated from anther culture were initially screened and selected for O(2)-resistant growth in 42% O(2)/160 muL CO(2) L(-1) and 0.18% of the plantlets showed O(2)-resistant photosynthesis. About 30% of the progeny (6 of 19 plants) of the first selfing of a fertile plant derived from a resistant dihaploid plant had O(2)-resistant photosynthesis, and after a second selfing this increased to 50% (6 of 12 plants). In 21% O(2) and low CO(2), net photosynthesis of the resistant plants was about 15% greater on a leaf area basis than wild type. Net photosynthesis was compared in leaf discs at 30 and 38 degrees C in 21% O(2), and at the higher temperature O(2)-resistant plants showed still greater photosynthesis than wild type. The results suggest that the O(2)-resistant photosynthesis described here is associated with a decreased stoichiometry of CO(2) release under conditions of rapid photorespiration. This view was supported by the finding that leaves of O(2)-resistant plants averaged 40% greater catalase activity than wild type.