Influence of the Parasite Pilostyles ingae (Rafflesiaceae) on some Physiological Parameters of the Host Plant,Mimosa naguirei (Mimosaceae)*

plants found at this site were densely covered by flowers of the parasite on their stems indicating heavy development of cellular The holoparasite/host interaction of Pilostyles ingae (Karst.) Hook. f. (Rafflesiaceae) and Mimosa naguirei Barneby (Mimosaceae) was studied in the open campo rupestre vegetation of Serra do Cipó (State of Minas Gerais, Brazil). Infected M. naguirei threads of the parasite in the bark of the hosts. Cellular threads of the parasite are likely to be richer in lipids and hence depleted in ¹³C. This may explain the significantly more negative carbon isotope ratios (δ¹³C values) of the bark of infected host plants observed as compared to other tissues of infected and non-infected host plants. Photosynthetic parameters such as potential quantum yield of photosystem II (F_v/F_m), apparent photosynthetic electron transport rates (ETR) and effective quantum yield of photosystem II (A F/F'_m) in light dependence curves, as well as δ¹³C values of leaves as a relative measure of average intercellular CO₂ partial pressure during photosynthesis over the lifetime of the leaves, which is also related to average stomatal conductance via water use efficiency, were remarkably similar. This suggests a well balanced relation between the Mimosa host and the Pilostyles parasite, in contrast to other hemiparasitic angiosperm parasite/host interactions where the parasite (e.g. Striga) is known to have strong detrimental effects on host photosynthesis.