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

Abstract

<p>We examined photosynthetic traits of pre-existing and newly developed flag leaves of four wheat genotypes grown in controlled-environment experiments. In newly developed leaves, acclimation of the maximum rate of net CO₂ assimilation (A_n) to warm nights (i.e. increased A_n) was associated with increased capacity of Rubisco carboxylation and photosynthetic electron transport, with Rubisco activation state probably contributing to increased Rubisco activity. Metabolite profiling linked acclimation of An to greater accumulation of monosaccharides and saturated fatty acids in leaves" these changes suggest roles for osmotic adjustment of leaf turgor pressure and maintenance of cell membrane integrity. By contrast, where A_n decreased under warm nights, the decline was related to lower stomatal conductance and rates of photosynthetic electron transport. Decreases in An occurred despite higher basal PSII thermal stability in all genotypes exposed to warm nights: T_crit of 45–46.5 °C in non-acclimated versus 43.8–45 °C in acclimated leaves. Pre-existing leaves showed no change in A_n–temperature response curves, except for an elite heat-tolerant genotype. These findings illustrate the impact of night-time warming on the ability of wheat plants to photosynthesize during the day, thereby contributing to explain the impact of global warming on crop productivity.</p>