✍ Scribed by Ora Canaani; Reuven Ronen; Jacob Garty; David Cahen; Shmuel Malkin; Margalith Galun
No coin nor oath required. For personal study only.
Photosynthetic parameters of the lichen Ramalina duriaei were investigated in vivo, by the photoacoustic method using intensity -modulated exciting light (frequency range 5-300 Hz). The photoacoustic signal in intact lichens was similar in its general characteristics to that obtained from intact leaves of higher plants (Poulet et al., Biochim. Biophys. Acta 724, 433-446, 1983). It included two components interpreted to be due to modulated heat and modulated oxygen evolution. The quantum yield of the oxygen evolution component was maximal in the red spectral region and exhibited the 'red drop' decrease at wavelengths larger than 680 nm, similar to observations in higher plants. In contrast to those however, there was a pronounced decrease in this yield in the region below about 600 rim, indicating that pigments absorbing at shorter wavelengths are inefficient energy transfer agents. Similar results were observed for the quantum yield spectrum of photochemical energy storage. Analysis of oxygen diffusion in the symbiont alia, from the modulation frequency dependence of the ratio of oxygen evolution to photothermal signal component is consistent with an average diffusion path of about 4 ~m, compared to a smaller, 1 ~m, average diffusion path obtained in green leaves.
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