Photosynthesis in newly-developed leaves of heat-tolerant wheat acclimates to long-term nocturnal warming

We examined photosynthetic capacity of newly-developed and pre-existing
flag leaves of four wheat genotypes under three night temperatures (15, 20
and 25 °C) and common day temperature of 26 °C in two controlled
environment experiments. In newly-developed leaves which acclimated (i.e.
maintained or increased) the maximum rate of net CO2 assimilation (An) to
long-term (9–13 weeks) nocturnal warming, acclimation was underpinned by
greater capacity of Rubisco carboxylation (Vcmax) and photosynthetic
electron transport (J). This indicates a night-dependent temperature
sensitivity of the activation state of Rubisco. Metabolite profiling
linked acclimation of An to greater accumulation of monosaccharides and
saturated fatty acids in leaves, suggesting roles for osmotic adjustment
of leaf turgor pressure and maintenance of cell membrane integrity. By
contrast, warm night-induced inhibition of An was related to reductions in
stomatal conductance of CO2 and J, despite higher basal electron transport
thermal stability: Tcrit 51 of 45–46.5 °C in non-acclimated versus Tcrit
of 43.8–45 °C in acclimated leaves. Pre-existing leaves exposed to
short-term nocturnal warming (5–7 nights) showed no change in
instantaneous temperature responses of An and photosynthetic capacity,
except for an elite heat-tolerant genotype. These findings can
be used to support strategies for developing climate-resilient
wheat.