Vitality and growth rate of agar plate-cultivated Antarctic microautotrophs: Analysis of PSII functioning by chlorophyll fluorescence parameters

In our study, we focused on the growth of three different microautotrophs isolated from Antarctic lichens (Placopsis contortuplicata, Solorina spongiosa) and cryptoendolithic algal vegetation. The isolates were purified and inoculated on agar plates, Bold´s Basal Medium (BBM). The growth of the cultures and the markers of physiological (photosynthetic) activity were monitored by chlorophyll fluorescence in 1 week intervals for 3 months after inoculation. For the assessment of photosynthetic activity, the method of slow Kautsky kinetics supplemented with saturation pulses was applied. Four chlorophyll fluorescence parameters calculated: (1) maximum quantum yield of PSII (FV/FM), (2) effective quantum yield of photosynthetic processes in PSII (ΦPSII), (3) non-photochemical quenching of chlorophyll fluorescence, and (4) background chlorophyll fluorescence ratio (F0/F0´). Troughout the cultivation period, the maximum quantum yield of PSII (FV/FM) showed high values in all three autotrophs with only slight increase in the first part of the cultivation period, followed by slight decrease in the second part. The ΦPSII values showed a rapid decline within the first 4 weeks of cultivation followed by more or less constant values in the isolates from P. contortuplicata and cryptoendolithic alga. Contrastingly, time course of ΦPSII rather showed an increase followed by a decrease in S. spongiosa isolate. NPQ (related to the activation of protective mechanisms) increased in the second part of cultivation period, the rate of increase and maximum values were species-specific. The species-specific differences in chlorophyll fluorescence parameters are discussed as well as their potential for evaluation of photosynthetic performance of in vitro cultivated algal/cyanobacterial cultures on agar plates.