Increased photoinhibition in dehydrated leaves of hot pepper (Capsicum annuum L.) is not accompanied by an incremental loss of functional PSII

We examined the photosynthetic responses to photoinhibition in dehydrated leaves of hot pepper (Capsicum annuum L.). Stress was induced by immersing the roots of whole plants in Hoaglands solution containing polyethylene glycol (PEG) under high light (900 μmol photons m^-2 · s^-1). This PEG-treatment lowered the leaf water potential and the maximal rate of photosynthetic O₂ evolution (Pmax) linearly, in a time-dependent manner, to about 50% inhibition after 6 h. Pmax also decreased linearly as the period of high-light treatment lengthened. That inhibitory response was not as extreme, showing about 30% inhibition after 6 h. However, when the treatments of dehydration and high light were simultaneously administered, Pmax decreased more rapidly, in a synergistic fashion, showing about 90% inhibition within 2 h. Dehydration, in contrast to the light treatment, did not lower the maximal photochemical efficiency (Fv/Fm). Furthermore, this decline in Fv/Fm for light-treated, dehydrated leaves was almost identical to the response of photoinhibited leaves that were not dehydrated. Similar changes were observed in the number of functional PSII complexes. The decrease in Pmax and the amount of functional PSII was linearly correlated in photoinhibited leaves, but not in dehydrated leaves, regardless of light treatment. Therefore, we have demonstrated that exacerbated photoinhibition in dehydrated leaves occurs without an incremental loss of functional PSII.