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

Abstract

Plants were obtained with novel O2-resistant photosynthetic characteristics. At low CO2 (250-350 .mu.L CO2 L-1) and 30.degree. C when O2 was increased from 1% to 21% to 42%, the ratio of net CO2 uptake in O2-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 O2-resistant growth in 42% O2/160 .mu.L CO2 L-1 and 0.18% of the plantlets showed O2-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 O2-resistant photosynthesis, and after a second selfing this increased to 50% (6 of 12 plants). In 21% O2 and low CO2, 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.degree. C in 21% O2, and at the higher temperature O2-resistant plants showed still greater photosynthesis than wild type. The results suggest that the O2-resistant photosynthesis described here is associated with a decreased stoichiometry of CO2 release under conditions of rapid photorespiration. This view was supported by the finding that leaves of O2-resistant plants averaged 40% greater catalase activity than wild type.