Shining Light into a "Black Box": Essential Rationale Underlying Multiphase Flash Methodology.

The world we live in is very fragile. Sustainable food production is increasingly under intense pressure due to changing environmental conditions on many levels. Understanding the complexities of how to optimize food production under increasingly deleterious environmental conditions is dependent upon accurate and detailed analyses of plant productivity from the molecular-to-the-remote scales. One method that can link many of these scales has been around for decades, namely, pulse amplitude modulation (PAM) chlorophyll a fluorescence. This technique is used to measure an assortment of important parameters based on chlorophyll a fluorescence. One of the parameters measured by this method is termed the steady state maximum fluorescence yield ( Φ Fm ' ). This parameter, while extremely informative when used to quantify an assortment of processes of intense scientific interest, is nonetheless subject to intrinsic underestimation. A clever approach has evolved over several decades to more accurately estimate Φ Fm ' . The underlying rationale of the methodology requires a thorough and nuanced explanation, which is lacking in the literature. Herein, we systematically develop the essential rationale for accurately measuring Φ Fm ' based on the latest evolution of this approach, called multiphase flash (MPF) methodology.

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.