Sensitivity of Photosynthesis in a C4 Plant, Maize, to Heat Stress

Our objective was to determine the sensitivity of components of the photosynthetic apparatus of maize (Zea mays), a C4 plant, to high temperature stress. Net photosynthesis (Pn) was inhibited at leaf temperatures above 38 degrees C, and the inhibition was much more severe when the temperature was increased rapidly rather than gradually. Transpiration rate increased progressively with leaf temperature, indicating that inhibition was not associated with stomatal closure. Nonphotochemical fluorescence quenching (qN) increased at leaf temperatures above 30 degrees C, indicating increased thylakoid energization even at temperatures that did not inhibit Pn. Compared with CO(2) assimilation, the maximum quantum yield…