Wheat photosystem II heat tolerance responds dynamically to short- and long-term warming

Abstract

Wheat photosynthetic heat tolerance can be characterized using minimal chlorophyll fluorescence to quantify the critical temperature (Tcrit) above which incipient damage to the photosynthetic machinery occurs. We investigated intraspecies variation and plasticity of wheat Tcrit under elevated temperature in field and controlled-environment experiments, and assessed whether intraspecies variation mirrored interspecific patterns of global heat tolerance. In the field, wheat Tcrit varied diurnally—declining from noon through to sunrise—and increased with phenological development. Under controlled conditions, heat stress (36 °C) drove a rapid (within 2 h) rise in Tcrit that peaked after 3–4 d. The peak in Tcrit indicated an upper limit to PSII heat tolerance. A global dataset [comprising 183 Triticum and wild wheat (Aegilops) species] generated from the current study and a systematic literature review showed that wheat leaf Tcrit varied by up to 20 °C (roughly two-thirds of reported global plant interspecies variation). However, unlike global patterns of interspecies Tcrit variation that have been linked to latitude of genotype origin, intraspecific variation in wheat Tcrit was unrelated to that. Overall, the observed genotypic variation and plasticity of wheat Tcrit suggest that this trait could be useful in high-throughput phenotyping of wheat photosynthetic heat tolerance.

Consistently high heat tolerance acclimation in response to a simulated heatwave across species from the broadly distributed

“…The T-F 0 curve to derive heat tolerance limits is a long-established and widely used technique across ecological and agricultural studies (e.g. Schreiber and Berry 1977;Seemann et al 1984;Hüve et al 2011;Arnold et al 2022;Marchin et al 2022;Posch et al 2022). T crit refers to the point of inactivation and potential damage to PSII, and T max represents its complete disruption (Schreiber and Berry 1977;Smillie and Nott 1979;Terzaghi et al 1989;Knight and Ackerly 2002;Ilík et al 2003;Neuner and Pramsohler 2006;Frolec et al 2008;Hüve et al 2011).…”

“…The active state of Rubisco declines with increasing leaf temperatures and PSII is very sensitive to high leaf temperatures, with heat stress causing unfolding of protein complexes and loss of manganese from the oxygen-evolving complex (Crafts-Brandner and Salvucci 2000;Takahashi and Badger 2011;Jajoo and Allakhverdiev 2017). A common method to quantify PSII Heat Tolerance (PHT) is to measure the critical temperature at which minimal chlorophyll a fluorescence (F 0 ) increases sharply as leaves are heated (Schreiber and Berry 1977;Smillie and Nott 1979;Seemann et al 1984;Knight and Ackerly 2002;Knight and Ackerly 2003;Neuner and Pramsohler 2006;Hüve et al 2011;Arnold et al 2021;Coast et al 2022;Posch et al 2022). This critical temperature indicates a threshold beyond which physiological and photochemical systems have impaired function and where membrane integrity is reduced such that damage might occur if temperatures are sustained.…”

Limits of thermal and hydrological tolerance in a foundation tree species (Populus fremontii) in the desert southwestern United States

“…However, maximum air temperatures before leaf collections ranged by 9.50°C, from 37.22°C to 46.72°C, indicating that strong contrasts in heat exposure were present among sites. One previous study also found no relationship between leaf T crit in wheat and latitude of origin (Posch et al ., 2022).…”

Heat tolerance of a tropical–subtropical rainforest tree species Polyscias elegans: time‐dependent dynamic responses of physiological thermostability and biochemistry

“…Our finding that T crit increases quickly is also supported by past studies using similar methods. For example, Posch et al (2022) reported a 1°C increase in T crit in two genotypes of wheat (Triticum aestivum) after 2 h of 36°C heat shock. Furthermore, Havaux (1993) reported that T crit in detached potato (Solanum tuberosum) leaf discs increased by 4°C from 39 to 43°C in < 1 h and observed a slow return (> 24 h) of T crit after plants returned back to control temperature.…”