Simultaneous Measurement of Stomatal Conductance, Non-photochemical Quenching, and Photochemical Yield of Photosystem II in Intact Leaves by Thermal and Chlorophyll Fluorescence Imaging
Plant and Cell Physiology
A new imaging system capable of simultaneously measuring stomatal conductance and fluorescence parameters, non-photochemical quenching (NPQ) and photochemical yield of photosystem II (F PSII ), in intact leaves under aerobic conditions by both thermal imaging and chlorophyll fluorescence imaging was developed. Changes in distributions of stomatal conductance and fluorescence parameters across Phaseolus vulgaris L. leaves induced by abscisic acid treatment were analyzed. A decrease in stomatal
... rease in stomatal conductance expanded in all directions from the treatment site, then mainly spread along the lateral vein toward the leaf edge, depending on the ABA concentration gradient and the transpiration stream. The relationships between stomatal conductance and fluorescence parameters depended on the actinic light intensity, i.e. NPQ was greater and F PSII was lower at high light intensity. The fluorescence parameters did not change, regardless of stomatal closure levels at a photosynthetically active photon flux (PPF) of 270 mmol m -2 s -1 ; however, they drastically changed at PPF values of 350 and 700 mmol m -2 s -1 , when the total stomatal conductance decreased to less than 80 and 200 mmol m -2 s -1 , respectively. This study has, for the first time, quantitatively analyzed relationships between spatiotemporal variations in stomatal conductance and fluorescence parameters in intact leaves under aerobic conditions. Keywords: Chlorophyll fluorescence imaging -Nonphotochemical quenching -Phaseolus vulgaris L. -Photochemical yield of photosystem II -Stomatal conductance -Thermal imaging. Abbreviations: ABA, abscisic acid; a p , absorption coefficient of short-wavelength radiation by the leaf; D H , thermal diffusivity in air; D W , water vapor diffusivity in air; e, emissivity of long-wavelength radiation of the leaf; E s , short-wavelength radiation from the environment; E w , long-wavelength radiation from the environment; i F, fluorescence intensity image measured under actinic light; i F m , fluorescence intensity image measured during a saturation light pulse during darkness after exposure of the leaf to darkness for at least 1 h; i F m ¢, fluorescence intensity image measured during a saturation light pulse during steady-state photosynthesis; g aH , boundary layer conductance to heat transfer; g aW , boundary layer conductance to water vapor diffusion; g sl , stomatal conductance to water vapor diffusion of the lower leaf sur-face; g st , total stomatal conductance to water vapor diffusion; g su , stomatal conductance to water vapor diffusion of the upper leaf surface; h, relative humidity of air; L, latent heat of evaporation; NPQ, non-photochemical quenching; PAR, photosynthetically active radiation; F PSII , photochemical yield of photosystem II; PPF, photosynthetically active photon flux; PSI, photosystem I; PSII, photosystem II; rc p , volumetric heat capacity of air; s, Stefan-Boltzmann constant; T a , air temperature; T l , leaf temperature; W, transpiration rate.