The rapid A-Ci response: photosynthesis in the phenomic era.

Phenotyping for photosynthetic gas exchange parameters is limiting our ability to select plants for enhanced photosynthetic carbon gain and to assess plant function in current and future natural environments. This is due, in part, to the time required to generate estimates of the maximum rate of ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco) carboxylation (Vc,max ) and the maximal rate of electron transport (Jmax ) from the response of photosynthesis (A) to the CO2 concentration inside leaf air spaces (Ci ). To relieve this bottleneck, we developed a method for rapid photosynthetic carbon assimilation CO2 responses [rapid A-Ci response (RACiR)] utilizing non-steady-state measurements of gas exchange. Using high temporal resolution measurements under rapidly changing CO2 concentrations, we show that RACiR techniques can obtain measures of Vc,max and Jmax in ~5 min, and possibly even faster. This is a small fraction of the time required for even the most advanced gas exchange instrumentation. The RACiR technique, owing to its increased throughput, will allow for more rapid screening of crops, mutants and populations of plants in natural environments, bringing gas exchange into the phenomic era.