Photosynthetic properties of leaves of Eupatorium makinoi infected by a geminivirus

We examined photosynthetic properties of Eupatorium makinoi leaves infected by a geminivirus. Since a major symptom of the geminivirus infection is variegation or yellowing of leaves, Chl content was used as an index of disease severity. As leaf Chl content was lowered, leaf absorptance, maximal quantum yield of photosynthesis on an absorbed quantum basis (φ(O₂,max)) and light-saturated rate of photosynthesis (P(max)) decreased. The share of energy allocated to PS II, which can be estimated from fluorescence parameters and oxygen evolution rate, was about 30% lower in the infected yellow leaves than in uninfected leaves. Analyses of the composition of thylakoid polypeptides by gel electrophoresis showed preferential loss of LHC II. The lower φ(O₂,max) in the infected leaves was, thus, attributed to the decreased energy allocation to PS II. These features were largely consistent with those of b-less mutants, but lowered P(max) has been never reported for b-less mutants. Possible mechanisms causing these changes in photosynthetic properties to the infected leaves are discussed.