Increased Cuticle Permeability Caused by a New Allele of - Enhances CO Uptake.

Carbon dioxide (CO) is an essential substrate for photosynthesis in plants. CO is absorbed mainly through the stomata in land plants because all other aerial surfaces are covered by a waxy layer called the cuticle. The cuticle is an important barrier that protects against extreme water loss; however, this anaerobic layer limits CO uptake. Simply, in the process of adapting to a terrestrial environment, plants have acquired drought tolerance in exchange for reduced CO uptake efficiency. To evaluate the extent to which increased cuticle permeability enhances CO uptake efficiency, we investigated the CO assimilation rate, carbon content, and dry weight of the Arabidopsis () mutant (), whose cuticle is remarkably permeable to water vapor. We isolated the mutant as a new allele of -, encoding a critical enzyme for fatty acid synthesis, thereby affecting cuticle wax synthesis. Under saturated water vapor conditions, the mutant demonstrated a higher CO assimilation rate, carbon content, and greater dry weight than did the wild-type plant. On the other hand, the stomatal mutant --, whose stomata are continuously open, also exhibited a higher CO assimilation rate than the wild-type plant; however, the increase was only half of the amount exhibited by These results indicate that the efficiency of CO uptake via a permeable cuticle is greater than the efficiency via stomata and confirm that land plants suffer a greater loss of CO uptake efficiency by developing a cuticle barrier.