Characterization of photosynthetic acclimation in Phoenix dactylifera by a modified Arrhenius equation originally developed for leaf respiration

Abstract

Instantaneous temperature responses of leaf respiration and photosynthesis can be described by the same equation, to help understand acclimation of primary metabolism to altered growth temperature and water supply. We used a three-parameter, modified Arrhenius equation, originally developed for leaf respiration, to characterize A/T curves of Date Palm and acclimation to elevated growth temperature and water deprivation: $$A_{\text{T}} = A_{\text{ref}} \times e^{{\left[ {\frac{{E_{\text{o}} (\text{Ref}_{\text{A}} )}}{\Re } \times \left( {\frac{{T - T_{\text{ref}} }}{{T \times T_{\text{ref}} }}} \right) + \delta_{\text{A}} \times \left( {\frac{{T - T_{\text{ref}} }}{{T \times T_{\text{ref}} }}} \right)^{2} } \right]}}$$ where A ref is the net CO2-assimilation (A) at fixed reference temperature (T ref), E o(RefA) is the activation energy of A close to T ref, and δ A describes the change of E o with increasing incubation temperature (T). Similar to respiration parameters, E o(RefA) and δ A-values were strongly correlated. Symmetry of A/T curves, i.e., constancy of dE o/dT between 20–45 °C incubation temperatures, suggests close coordination of component processes underlying A. This symmetry remained at high growth temperature, despite large reductions in biochemical capacity for P i regeneration relative to carboxylation capacity (i.e., increased abundance of RubisCO activase). Acclimation to higher temperature caused pronounced reductions in physiological capacity of respiration (R Cap) (type II acclimation, determined via gas exchange measurements). Reductions in R Cap were not a result of limitations in substrate availability (i.e., pyruvate), but were related to lower abundances of mitochondrial enzymes in well-watered plants (i.e., pyruvate dehydrogenase and cytochrome oxidase). Water shortage led to sucrose accumulation, with modest reductions in mitochondrial enzyme pools. R Cap remained low when growth temperature was increased.