Research PaperTemporal dynamics in photosynthetic activity of Spirodela polyrhiza turions during dormancy release and germination

•Dormant turions of giant duckweed are photosynthetically comparable organs to active fronds.•Decrease of photosynthetic activity of turions was transient during after-ripening in cold and dark.•Photosynthetic activity of germinating turions acclimated rapidly to light.

Turions (vegetative propagules) of aquatic plants functionally resemble seeds but in fact they are overwintering buds having the ability to photosynthesize. They spend long periods in dormant state in the dim and cold bottom layer of natural waters during winter of temperate regions. In this study photosynthetic acclimation of Spirodela polyrhiza (L.) Schleiden (giant duckweed) turions to contrasting environments was assessed in laboratory experiments by means of chlorophyll fluorescence induction and O2-evolution methods and photosynthetic pigment content.Photosynthetic performance of turions had been monitored for 5 weeks in dark and cold (after-ripening) and then for 48 h under continuous irradiation at room temperature (germination induction).Photosynthetic activity of turions displayed biphasic acclimation during after-ripening. A gradual decrease in O2-evolution, variable fluorescence and relative fluorescence decrease was observed during the first 3 weeks with a parallel increase in chlorophyll fluorescence parameters indicative of excitation energy dissipation. Most interestingly later, while turions were still kept in dark and cold, their photosynthetic activity increased again to the level of newly-formed turions. This temporal pattern suggests that changes in photosynthetic performance might be regulated in close connection with dormancy release of turions.After transferring after-ripened turions to warm and illuminated conditions their photosynthetic acclimation took place rapidly. All parameters reflecting photosynthetic efficiency of germinating turions reached or even exceeded the respective levels of newly formed control turions within 24-48 h.