A high-throughput method for measuring critical thermal limits of leaves by chlorophyll imaging fluorescence

Abstract

Plant thermal tolerance is a crucial research area as the climate warms and extreme weather events become more frequent. We developed and tested a high-throughput method for measuring photosynthetic critical thermal limits at low (CTMIN) and high (CTMAX) temperatures to achieve pragmatic and robust measures of thermal tolerance limits using a Maxi-Imaging fluorimeter and a thermoelectric Peltier plate temperature ramping system. Leaves exposed to temperature extremes accumulate damage to photosystem II (PSII). Temperature-dependent changes in basal chlorophyll fluorescence (T-F0) can be used to identify the critical temperature at which PSII is damaged. We examined how experimental conditions: wet vs dry surfaces for leaves and temperature ramp rate, affect CTMIN and CTMAX across four species. CTMAX estimates were not different whether measured on wet or dry surfaces, but leaves were apparently less cold tolerant when on wet surfaces. Temperature ramp rate had a strong effect on both CTMAX and CTMIN that was species-specific. We discuss potential mechanisms for these results and recommend settings for researchers to use when measuring T-F0. The system described and tested here allows high-throughput measurement of critical temperature thresholds of leaf photosynthetic performance for characterising plant function in response to thermal extremes.

Photosynthetic heat tolerance in wheat: Evidence for genotype-by-environment interactions

“…The high T crit H 2 observed in some of our environments suggest that sustainable genetic gains could be achieved by including T crit as a selection criterion in wheat breeding. Availability of high throughput phenotyping tools for T crit including the one used in this study or reported in Arnold et al (2021) would make inclusion ofT crit in breeding easier. Indirect selection for higher grain yield through secondary traits with higher heritability and strong associations with grain yield can be more effective than direct selection for grain yield under stress (Bänziger and Lafitte, 1997).…”

“…T crit is widely used in ecological studies (Hüve et al, 2006;Knight and Ackerly, 2002;O'Sullivan et al, 2017;Zhu et al, 2018) and thought to be a more sensitive measure of thermal damage to PSII function than F V /F M (Lin, 2012;Marias et al, 2017).T crit is also relatively easier to measure than F V /F M because it does not need a saturating pulse and re-dark adaptation. The recent development of high-throughput phenotyping tools for measuringT crit (Arnold et al, 2021) has made it possible to include measurements of T crit in large scale trials, typical of breeding programmes.…”