Desiccation-induced changes of photosynthetic transport in Parmelina tiliacea (Hoffm.) Ach. analysed by simultaneous measurements of the kinetics of prompt fluorescence, delayed fluorescence and modulated 820 nm reflection

Simultaneous in vivo measurements of prompt fluorescence (PF), delayed fluorescence (DF) and modulated reflection (MR) at 820-nm were used to assess effect of short desiccation period (4.5 h) on Parmelina tiliacea lichen. The two performance indexes (PIABS and PItotal) as a measure of an overall photosynthetic thalli performance showed a negative effect of desiccation treatment on photosynthetic activity. The maximal intensity of PF and DF recorded during desiccation treatment decreased and at 4.5 h desiccation time Parmelina tiliacea thalli loss their variable fluorescence and DF amplitude. This loss of variable fluorescence was due to an increase in inactive reaction centers and a limitation of electron donation on the donor side of photosystem II (PSII) that caused a down-regulation of electron transport chain at the PSII level. However, the efficiency with which an electron can move from the reduced intersystem electron acceptors to the PSI end electron acceptors was less affect by desiccation treatment. In respect to MR change, re-reduction kinetics of the primary electron donors of photosystems I (P700) and plastocyanin (PC) in desiccated thalli seem to be faster, their amplitudes gradually decrease and a disconnection between the two photosystem (PSII and PSI) were observed. These responses allow to Parmelina tiliacea lichen a photoprotection mechanism from the excess light excitation.