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The paper focus sensitivity of an Antarctic lichen Usneaantarctica to photoinhibition studied under controlledlaboratory conditions. Main emphasis was given to the analysisof quenching mechanisms, i.e. deexcitation pathways of absorbedlight energy exploited in non-photochemical processes. Thalliof U. antarctica were collected at the James Ross Island,Antarctica (57°52´57´´ W, 63°48´02´´ S) and transferred in drystate to the Czech Republic. After rewetting in a laboratory,they were exposed to medium light intensities (300, 600 and1000 micromol m-2 s-1 of photosynthetically active radiation)for 6 h. Before and during photoinhibitory treatments,chlorophyll fluorescence parameters, photoinhibitory (qI),state 1-2 transition (qT), and energy-dependent quenching (qE)in particular were measured to evaluate dose- andtime-dependent changes in these parameters. The results showedthat among the components forming non-photochemical quenching(qN), qI contributes to the largest extent to qN, while qE andqT contribute less. This finding differs from our earlierstudies made in a short term-, and high light-treated U.antarctica that found qE together with qI is the most importantpart of non-photochemical quenching. Possible explanation isthat photoinhibition in PS II in U. ant-arctica, when inducedby low to medium light, activates qE to only limited extend andfor a relatively short time (tens of minutes). With prolongedhigh light treatment lasting several hours, qE tends to bereduced to the values close to zero and qI then forms a majorpart of qN.

czech polar reports

Photoinhibition of photosynthesis in Antarctic lichen Usnea antarctica. II. Analysis of non-photochemical quenching mechanisms activated by low to medium light doses