Annals of Botany 72: 117-122, 1993
© 1993 Annals of Botany Company
Photosynthesis in the Tapinanthus-Diplorhynchus Mistletoe-Host Relationship
Department of Biological Sciences, University of Zimbabwe, P.O. Box MP167, Mount Pleasant, Harare, Zimbabwe
Hill reaction activity and gas exchange were studied in the southern African mistletoe Tapinanthus vittatus, its host tree Diplorhynchus condylocarpon and uninfected trees of the same species. Photosynthetic potential was assessed by measuring Hill reaction activities in isolated thylakoids: reaction rates in the parasite were less than half those of the host or uninfected trees. In addition, parasite thylakoids were more sensitive to heat treatment than those of the trees. Mean maximum CO2 assimilation rates (±s.e.) were significantly lower (4·2±0·24 µmol m-1 s-1) in the parasite, compared to both uninfected trees (7·6±0·22), and those of the infected host (5·2±0·27). Chlorophyll contents (±s.e.) were 800±40 mg m-2 in the parasite, lower in uninfected trees (490±80) and lowest in infected trees (310±70). CO2 assimilation rates calculated on a per unit chlorophyll basis were similar in parasitized and non-parasitized trees, 58±4·3 and 56±2·2 µmol mg chlorophyll-1 h-1 respectively, whereas the parasite's maximum CO2 assimilation rate was considerably lower (20±1·2). Parasite transpiration rates were approximately double those of infected trees throughout the daylight period, and somewhat higher than uninfected trees from mid-morning onwards. Overall, parasite were generally less photosynthetically active than host plants; additionally, parasite infection was seen to reduce host carbon assimilation rates compared to those of uninfected trees.Copyright 1993, 1999 Academic Press
Tapinanthus vittatus, Diplorhynchus condylocarpon, mistletoe, photosynthesis, Hill reaction, Zimbabwe