Ana Gutierrez

The role of photochemical quenching and antioxidants in photoprotection of Deschampsia antarctica

Deschampsia antarctica Desv. (Poaceae) is the only grass that grows in the maritime Antarctic. Constant low temperatures and episodes of high light are typical conditions during the growing season at this latitude. These factors enhance the formation of active oxygen species and may cause photoinhibition. Therefore, an efficient mechanism of energy dissipation andu2009/u2009or scavenging of reactive oxygen species (ROS) would contribute to survival in this harsh environment. In this paper, non-acclimated and cold-acclimated D. antarctica were subjected to high light andu2009/u2009or low temperature for 24 h. The contribution of non-photochemical dissipation of excitation light energy and the activities of detoxifying enzymes in the development of resistance to chilling induced photoinhibition were studied by monitoring PSII fluorescence, total soluble antioxidants, and pigments contents and measuring variations in activity of superoxide dismutase (SOD; EC 1.15.1.1), ascorbate peroxidase (APX; EC 1.11.1.11), and glutathione reductase (GR; EC 1.6.4.2). The photochemical efficiency of PSII, measured as Fvu2009/u2009F m, and the yield of PSII electron transport (ΦPSII) both decreased under high light and low temperatures. In contrast, photochemical quenching (qP) in both non-acclimated and cold-acclimated plants remained relatively constant (approximately 0.8) in high-light-treated plants. Unexpectedly, qP was lower (0.55) in cold-acclimated plants exposed to 4°C and low light intensity. Activity of SOD in cold-acclimated plants treated with high light at low temperature showed a sharp peak 2-4 h after the beginning of the experiment. In cold-acclimated plants APX remained high with all treatments. Activity of GR decreased in cold-acclimated plants. Compared with other plants, D. antarctica exhibited high levels of SOD and APX activity. Pigment analyses show that the xanthophyll cycle is operative in this plant. We propose that photochemical quenching and particularly the high level of antioxidants help D. antarctica to resist photoinhibitory conditions. The relatively high antioxidant capacity of D. antarctica may be a determinant for its survival in the harsh Antarctic environment.

Identification and characterization of three novel cold acclimation-responsive genes from the extremophile hair grass Deschampsia antarctica Desv.

Deschampsia antarctica Desv. is the only monocot that thrives in the harsh conditions of the Antarctic Peninsula and represents an invaluable resource for the identification of genes associated with freezing tolerance. In order to identify genes regulated by low temperature, we have initiated a detailed analysis of its gene expression. Preliminary 2-D gels of in vivo-labeled leaf proteins showed qualitative and quantitative differences between cold-acclimated and non-acclimated plants, suggesting differential gene expression. Similarly, cold-acclimation-related transcripts were screened by a differential display method. Of the 38 cDNAs initially identified, three cDNA clones were characterized for their protein encoding, expression pattern, response to several stresses, and for their tissue-specific expression. Northern blot analysis of DaGrx, DaRub1, and DaPyk1 encoding a glutaredoxin, a related-to-ubiquitin protein, and a pyruvate kinase-like protein, respectively, showed a distinct regulation pattern during the cold-acclimation process, and in some cases, their cold response seemed to be tissue specific. All three transcripts seem to be responsive to water stress as their levels were up-regulated with polyethyleneglycol treatment. DaRUB1 and DaPyk1 expression was up-regulated in leaf and crown, but down-regulated in roots from cold-acclimated plants. The significance of these results during the cold-acclimation process will be discussed.

Light regulation of sucrose-phosphate synthase activity in the freezing-tolerant grass Deschampsia antarctica

Deschampsia antarctica, a freezing-tolerant grass that has colonized the Maritime Antarctic, has an unusually high content of sucrose (Suc) in leaves, reaching up to 36% of dry weight. Suc accumulation has often been linked with increased activity of sucrose phosphate synthase (SPS; EC: 2.4.1.1.14). SPS, a key enzyme in sucrose biosynthesis, is controlled by an intricate hierarchy of regulatory mechanisms including allosteric modulators, reversible covalent modification in response to illumination, and transcriptional regulation. We hypothesized that during long day conditions in the Antarctic summer D. antarctica can maintain high SPS activity longer by indirect light regulation, thereby leading to a high sucrose accumulation in the leaves. The objectives of this study were to investigate a possible indirect light regulation of SPS activity and the effect of cold and day length on transcriptional and protein level of SPS in D. antarctica. Although SPS activity did not display an endogenous rhythm of activity in continuous light, activation of SPS at the end of the dark period was observed in D. antarctica. This activation of SPS is possibly controlled by covalent modification, because it was inhibited by okadaic acid while the SPS protein level did not significantly change. The highest SPS activity increase was observed after 21 days of cold-acclimation under long day conditions. This increased activity was not related to an increase in SPS gene expression or protein content. High SPS activity in cold long days leading to hyper accumulation of Suc appears to be among the features that permit D. antarctica to survive in the harsh Antarctic conditions.

The transcriptional dynamics of two filmy ferns from Hymenophyllaceae with different niche preferences unravel key aspects of their desiccation tolerance and vertical distribution along host trees

Ferns from the Hymenophyllaceae family are one of the main components of the epiphytic species diversity in the Chilean temperate rain forest. Having membranous fronds of a single layer of cells, they show a poikilohydric strategy most typical from bryophytes. Although Hymenophyllaceae species shows the ability to tolerate desiccation, there are interspecific differences in their water loss kinetic. Counter-intuitively, those species that have rapid desiccation kinetic are able to reach higher host height and tolerate higher light exposure and vapor pressure deficit. Therefore, what are the mechanisms (constitutive and/or induced) responsible of the desiccation tolerance in this fern family? As this primitive fern family is closely related with mosses, it can be hypothesized that desiccation tolerance in this particular group would be associated with constitutive features rather than induced responses during dehydration. However, the inter-specific differences in water loss and vertical distribution would be associated to different degrees of induction either within the dehydration or rehydration phases. We applied an ecophysiological transcriptomic approach to study the dynamic of gene expression in two species of filmy ferns with contrasting desiccation kinetics and vertical distribution on the host tree. Our analysis identified commonalities and differences in gene regulation, and key genes correlated with the fronds hydration state, providing the patterns of gene expression responding to microenvironmental signals and behind the physiology of their resurrection strategy