PHOTOSYNTHETIC INSENSITIVITY OF THE TERRESTRIAL CYANOBACTERIUM NOSTOC FLAGELLIFORME TO SOLAR UV RADIATION WHILE REHYDRATED OR DESICCATED¹

Abstract

Photosynthetic performance of the terrestrial cyanobacterium Nostoc flagelliforme (M. J. Berkeley et M. A. Curtis) Bornet et Flahault during rehydration and desiccation has been previously characterized, but little is known about the effects of solar UV radiation (280-400 nm) on this species. We investigated the photochemical activity during rehydration and subsequent desiccation while exposing the filamentous colonies to different solar radiation treatments. Photochemical activity could be reactivated by rehydration under full-spectrum solar radiation, the species being insensitive to both ultraviolet-A radiation (UVAR; 315-400 nm) and ultraviolet-B radiation (UVBR). When the rehydrated colonies were exposed for desiccation, the effective PSII photochemical yield was inhibited by visible radiation (PAR) at the initial stage of water loss, then increased with further decrease in water content, and reached its highest value at the water content of 10%-30%. However, no significant difference was observed among the radiation treatments except for the moment when they were desiccated to critical water content of about 2%-3%. At such a critical water content, significant reduction by UVBR of the effective quantum yield was observed in the colonies that were previously rehydrated under indoor light [without ultraviolet radiation (UVR)], but not in those reactivated under scattered or direct solar radiation (with UVR), indicating that preexposure to UVR during rehydration led to higher resistance to UVR during desiccation. The photosynthetic CO 2 uptake by the desiccated colonies was enhanced by elevation of CO 2 but was not affected by both UVAR and UVBR. It increased with enhanced desiccation to reach the maximal values at water content of 40%-50%. The UV-absorbing compounds and the colony sheath were suggested to play an important role in screening harmful UVR.

In situ response of Nostoc commune s.l. colonies to desiccation in Central Svalbard, Norwegian High Arctic.

“…Contrary to many previous studies on desiccation injuries in Nostoc (Scherer et al 1984;Scherer & Zhong 1991;HAwes et al 1992;GAo et al 1998b;GAo & Ye 2007;FuKudA et al 2008), our experiments lasted almost three weeks. Our results, similar to those of DAvey 1989; HAwes et al 1992;Novis et al 2007, suggest that even a partially hydrated Nostoc commune s.l.…”

Freezing and desiccation injury resistance in the filamentous green alga Klebsormidium from the Antarctic, Arctic and Slovakia

“…This decline was invoked by high levels of photosynthetically active radiation (PAR). High levels of PAR led to enhanced thermal dissipation of excessive excitation energy and damage to PS II (Franklin et al 2003;Gao & Ye 2007). In another study (Šabacká & Elster 2006), desiccation was more injurious than freezing, especially for green algae which showed high mortality.…”

Screening and partial purification of photoprotective pigment scytonemin from cyanobacterial crusts dwelling on the historical monuments in and around Varanasi, India

“…[45][46][47] In N. flagelliforme the combination of compounds having complementary absorption maxima at 370 nm, corresponding to in vivo absorption of scytonemin, 26 and 312/335 nm, corresponding to MAAs, 48 is very likely to induce the photosynthetic insensitivity to UVR. 44 In addition to the mutual shading of cells in the multiserate filaments of N. flagelliforme, the predominant localization of scytonemin in the outer layer was likely to increase the protection of this organism from harmful UV-radiation. 46,49 Our study reveals that most of the blackish brown crust appeared on exposed roof surfaces and composition of the microbial crust varies greatly according to different environmental condition and nature of the substratum.…”

“…16,17 Nostoc flagelliforme containing UV-absorbing compounds showed photosynthetic insensitivity to solar UVR. 44 Such studies reflect the involvement of UV-screening compounds as efficient protective mechanisms in cyanobacteria.…”