Reversible Photoinhibition in Antarctic Moss during Freezing and Thawing

Abstract

Tolerante of antarctic moss to freezing and thawing stress was investigated using chlorophyll a fluorescence. Freezing in darkness caused reductions in FJF, (ratio of variable to maximum fluorescence) and F, (initial fluorescence) that were reversible upon thawing. Reductions in FJF, and F, during freezing in darkness indicate a reduction in the potential efficiency of photosystem I1 that may be due to conformational changes in pigment-protein complexes due to desiccation associated with freezing. l h e absorption of light during freezing further reduced FJF, and F, but was also reversible. Using dithiothreitol (DTT), which inhibits the formation of the carotenoid zeaxanthin, we found reduced fluorescence quenching during freezing and reduced concentrations of zeaxanthin and antheraxanthin after freezing in DTT-treated moss. Reduced concentrations of zeaxanthin and antheraxanthin in DTT-treated m o s were partially associated with reductions in nonphotochemical fluorescence quenching. The reversible photoinhibition observed in antarctic m o s during freezing indicates the existence of processes that protect from photoinhibitory damage in environments where freezing temperatures occur in conjunction with high solar radiation levels. These processes may limit the need for repair cycles that require temperatures favorable for enzyme activity.Physiological mechanisms that allow plants to freeze or desiccate without incurring tissue damage have allowed plants to survive in extremely cold and dry environments. Both freezing and desiccation in the light have been observed to cause irreversible reductions in the efficiency of PSII electron transport in plants that are intolerant of desiccation or freezing (Somersalo and Krause, 1990;Oquist and Huner, 1991). In contrast, freezing and desiccation lead to reversible reductions in the efficiency of PSII electron transport in plants acclimated to low temperatures (Hallgren et al

Chlorophyll a fluorescence transient during freezing and recovery in winter wheat

“…This is connected also with decreasing plasma membrane ATPase activity (Arora and Palta 1991). Further dysfunction of cellular functions after freezing may be due both to desiccation (Levitt 1972), increase in reactive oxygen species formation (McKersie et al 1997), and photoinhibition in photosynthetically active cells (Lovelock et al 1995, Verhoeven et al 1996.…”

Tolerance to environmental desiccation in moss sperm

“…Similarly, our understanding of the relationship between sexual reproduction in mosses and environmental stress is limited (Convey & Smith, 1993;Stark et al, 2000), despite the fact that mosses are globally prevalent and well known for their ability to tolerate environmental stress (Seel et al, 1992;Lovelock et al, 1995;Meyer & Santarius, 1998;Minami et al, 2003;Oliver et al, 2005;Clarke & Robinson, 2008). The majority of research previously conducted on moss sperm focused on sperm architecture and the composition of the sperm mass (Paolillo, 1977(Paolillo, , 1979(Paolillo, , 1981Bernhard & Renzaglia, 1995;Renzaglia et al, 2001), the mechanism of initial sperm release (Paolillo, 1975), and the behavior of the released sperm mass upon encountering the air-water interface (Muggoch & Walton, 1942;Paolillo, 1981).…”

Photoinhibition of photosynthesis in Antarctic lichen Usnea antarctica. I. Light intensity- and light duration-dependent changes in functioning of photosystem II

“…Kappen et al 1998). Among them, the study made on Antarctic mosses (Lovelock et al 1995) pointed out reversible photoinhibition in an Antarctic moss measured at wet state. Field studies made on Antarctic lichens could hardly distiguish between limitation of photosynthetic processes related to thallus dehydration and progressive photoinhibition because the processes co-occur simultaneously.…”