NON-AUTOTROPHIC CO2 FIXATION AND DROUGHT TOLERANCE IN MOSSES

Cratoneuron filicinum, a drought-sensitve moss, and Tortula ruralis, a drought-tolerant moss, fix CO2 non-autotrophically at a rate of about 1.2 and 2.2 .mu.mol h-1 dry wt, respectively. During drying, T. ruralis fixes CO2 at an undiminished rate until the tissue losses about 60% of the initial fresh weight. Thereafter, CO2 fixation rapidly declines to zero. Dark CO2 fixation by C. filicinum declines steadily during the dehydration period. On rehydration, dark CO2 fixation is resumed immediately in T. ruralis but not in C. filicinum. When dried T. ruralis is equilibrated with an atmosphere of nearly 100% relative humidity, its weight increases to about 40% of the original fresh weight and dark CO2 fixation resumes at a rate about 60% of the fresh moss. In C. filicinum there is only a small increase in weight and little CO2 fixation in the dark. The non-autotrophically fixed C, in both mosses studied, is incorporated into amino acids (more than 60% of the total, mainly into aspartate, alanine and glutamate) and organic acids (less than 40% of the total, mainly into malate). On rehydration immediate availability of NADPH, known to be produced by transhydrogenation from NADH during dark CO2 fixation, may be an important factor in the repair of drought-induced cellular damage by reductive biosynthesis of membrane components and other cellular constituents.