Xanthophyll cycles in the juniper haircap moss (Polytrichum juniperinum) and Antarctic hair grass (Deschampsia antarctica) on Livingston Island (South Shetland Islands, Maritime Antarctica)

Abstract

The summer climate in Maritime Antarctica is characterised by high humidity and cloudiness with slightly above zero temperatures. Under such conditions, photosynthetic activity is temperature-limited and plant communities are formed by a few species. These conditions could prevent the operation of the photoprotective xanthophyll (VAZ) cycle as low irradiance reduces the excess of energy and low temperatures limit enzyme activity. The VAZ cycle regulates the dissipation of the excess of absorbed light as heat, which is the main mechanism of photoprotection in plants. To test whether this mechanism operates dynamically in Antarctic plant communities, we characterised pigment dynamics under natural field conditions in two representative species: the moss Polytrichum juniperinum and the grass Deschampsia antarctica. Pigment analyses revealed that the total VAZ pool was in the upper range of the values reported for most plant species, suggesting that they are exposed to a high degree of environmental stress. Despite cloudiness, there was a strong conversion of violaxanthin (V) to zeaxanthin (Z) during daytime. Conversely, the dark-induced enzymatic epoxidation back to V was not limited by nocturnal temperatures. In contrast with plants from other cold ecosystems, we did not find any evidence of overnight retention of Z or sustained reductions in photochemical efficiency. These results are of interest for modelling, remote sensing and upscaling of the responses of Antarctic vegetation to environmental challenges.

Stevia rebaudiana under a CO2 Enrichment Atmosphere: Can CO2 Enrichment Overcome Stomatic, Mesophilic and Biochemical Barriers That Limit Photosynthesis?

“…This range is 6-to 35-fold higher than those described for grapevine [98] or Quercus ilex [99]. However, our values were 99% lower than those described for two Antarctic species [100]. Moreover, it should be noted that the simple expression of VAZ in the chlorophyll base is not a sufficient argument to support the greater or lesser VAZ:Chl ratio.…”

The outstanding capacity of Prasiola antarctica to thrive in contrasting harsh environments relies on the constitutive protection of thylakoids and on morphological plasticity

“…VAZ) is variable in response to cumulative demanding requirements (Esteban et al., 2015). So, the high VAZ/Chl repeatedly found in different species at high latitudes may indicate a pre‐emptive protective stage of the photosynthetic membranes in these harsh environments where low temperature, intermittent water availability and irradiance converge (Fernández‐Marín, Gago, et al., 2019; Fernández‐Marín, López‐Pozo, et al., 2019; García‐Plazaola, López‐Pozo, & Fernández‐Marín, 2022). The elevated VAZ/Chl values obtained in P. antarctica are in agreement with previous reports at high latitudes, where most photosynthetic organisms are subjected to high thylakoid protection requirements.…”

“…In that sense, a large pool of the carotenoids involved in the so-called xanthophyll cycle, with relevant roles in excess energy dissipation, thylakoid membrane stabilisation and as antioxidants, seems to be determinant in environments with high photoprotective demand such as polar tundra (Fern andez-Mar ın, Atherton, et al, 2018;Fern andez-Mar ın, Gago, et al, 2019;Magney et al, 2017;Schroeter et al, 2012). Fast and dynamic de-epoxidation of the violaxanthin into the protective zeaxanthin within the xanthophyll cycle, in response to either increasing irradiance, sub-zero temperatures or severe desiccation, it is equally relevant for suitable photoprotection of the photosynthetic machinery in species tolerant to either desiccation, intra-tissular ice formation, or both (Fern andez-Mar ın, Arzac, et al, 2021;Fern andez-Mar ın, Neuner, et al, 2018) and for species in polar tundra too (Fern andez-Mar ın, Gago, et al, 2019;Garc ıa-Plazaola, L opez-Pozo, & Fern andez-Mar ın, 2022). The fine tuning and responsiveness of the xanthophyll cycle to the environmental conditions acquires even more relevance when considering that too slow re-epoxidation of zeaxanthin back to violaxanthin represents an important payback for net photosynthesis estimated in a 20% reduction for crop-plants (Kromdijk et al, 2016).…”

Basking in the sun: how mosses photosynthesise and survive in Antarctica

“…However, in the austral summer, mosses lose their protective cover and are exposed to high light stress, compounded by cold temperatures and desiccation events. At this point, the percentage of VAZ sustained as Z is usually high in Antarctic mosses (Lovelock et al 1995b ; Lovelock and Robinson 2002 ; Martínez-Abaigar and Núñez-Olivera 2022 ; García-Plazaola et al 2022 ), similar to that of sun plants (Demmig-Adams and Adams III 1992 ; Lovelock and Robinson 2002 ; García-Plazaola et al 2022 ). For instance, when S. antarctici samples were moved from the field into the laboratory, 50% of the VAZ pool remained as A+Z after 24 h in low light (Lovelock et al 1995a ).…”

“…Antarctic mosses acclimate their pigment concentrations to seasonal changes and between sites presumably in response to microclimate variation (see above) (Schroeter et al 2012 ; Snell et al 2007 ; Lovelock and Robinson 2002 ; Robinson et al 2005 ; García-Plazaola et al 2022 ). When mosses are covered by ice and snow during the long winter, their pigments adjust to cope with the shaded environment by reducing photosynthetic rates and carotenoid concentrations whilst increasing chlorophyll levels (Post 1990 ; Post and Vesk 1992 ; Robinson et al 2005 ).…”