Deschampsia antarctica Desv. (Poaceae) and Colobanthus quitensis (Kunth) Bartl. (Cariophyllaceae) are the only two vascular plants that have colonized the Maritime Antarctic. The primary purpose of the present work was to determine cold resistance mechanisms in these two Antarctic plants. This was achieved by comparing thermal properties of leaves and the lethal freezing temperature to 50% of the tissue (LT50). The grass D. antarctica was able to tolerate freezing to a lower temperature than C. quitensis. The main freezing resistance mechanism for C. quitensis is supercooling. Thus, the grass is mainly a freezing‐tolerant species, while C. quitensis avoids freezing. D. antarctica cold acclimated; thus, reducing its LT50. C. quitensis showed little cold‐acclimation capacity. Because day length is highly variable in the Antarctic, the effect of day length on freezing tolerance, growth, various soluble carbohydrates, starch, and proline contents in leaves of D. antarctica growing in the laboratory under cold‐acclimation conditions was studied. During the cold‐acclimation treatment, the LT50 was lowered more effectively under long day (21/3 h light/dark) and medium day (16/8) light periods than under a short day period (8/16). The longer the day length treatment, the faster the growth rate for both acclimated and non‐acclimated plants. Similarly, the longer the day treatment during cold acclimation, the higher the sucrose content (up to 7‐fold with respect to non‐acclimated control values). Oligo and polyfructans accumulated significantly during cold acclimation only with the medium day length treatment. Oligofructans accounted for more than 80% of total fructans. The degrees of polymerization were mostly between 3 and 10. C. quitensis under cold acclimation accumulated a similar amount of sucrose than D. antarctica, but no fructans were detected. The suggestion that survival of Antarctic plants in the Antarctic could be at least partially explained by accumulation of these substances is discussed.

We evaluated the genotype and maturity effects on antioxidant activity and phenolic compounds of whole, skin and pulp fruits from three highbush blueberry cultivars (cv. Brigitta, cv. Bluegold and cv. Legacy) grown in southern Chile. Total antioxidant activity (TAA) in ripe fruits varied among the cultivars in the order Legacy > Brigitta > Bluegold. We found that TAA in unripe green and fully ripe fruits was high and similar between them, whereas the lowest levels were found in intermediate ripe fruits. The same trend was observed for fruit total phenolic content. This could be attributed to the higher concentrations of phenolic acids (mainly chlorogenic acid) and flavonols (mainly rutin) at immature fruit stages; whereas the high TAA in mature fruits could be explained by the elevated amounts of anthocyanin. All antioxidant compounds were mostly located in the skin. High amounts of delphinidin aglycone were found. HPLC-DAD/MS revealed that the main contents of skin anthocyanins are petunidin-3-glucoside and petunidin-3-arabinnoside followed by malvidin-3-galactoside. It is noticeable that highbush blueberry fruits grown in southern Chile have exceptionally higher antioxidant activity and anthocyanins contents compared with those cultivated in the northern hemisphere.

Central chemoreception is essential for adjusting breathing to physiological demands, and for maintaining CO2 and pH homeostasis in the brain. CO2-induced ATP release from brainstem astrocytes stimulates breathing. NMDA receptor (NMDAR) antagonism reduces the CO2-induced hyperventilation by unknown mechanisms. Here we show that astrocytes in the mouse caudal medullary brainstem can synthesize, store, and release d-serine, an agonist for the glycine-binding site of the NMDAR, in response to elevated CO2 levels. We show that systemic and raphe nucleus d-serine administration to awake, unrestrained mice increases the respiratory frequency. Application of d-serine to brainstem slices also increases respiratory frequency, which was prevented by NMDAR blockade. Inhibition of d-serine synthesis, enzymatic degradation of d-serine, or the sodium fluoroacetate-induced impairment of astrocyte functions decrease the basal respiratory frequency and the CO2-induced respiratory response in vivo and in vitro. Our findings suggest that astrocytic release of d-serine may account for the glutamatergic contribution to central chemoreception.

This summer, a heatwave across Antarctica saw temperatures soar above average. Temperatures above zero are especially significant because they accelerate ice melt. Casey Station had its highest temperature ever, reaching a maximum of 9.2°C and minimum of 2.5°C. The highest temperature in Antarctica was 20.75°C on 9 February. Here we discuss the biological implications of such extreme events.

The role of ABA in freezing resistance in nonacclimated and cold‐acclimated barley (Hordeum vulgare L.) was studied. Eleven nonacclimated cultivars differed in their LT50, ranging from −10.8 to −4.8°C. Sugars, free proline, soluble proteins and ABA were analyzed in nonacclimated cultivars and during cold acclimation of one cultivar. There was an inverse correlation between LT50 and both ABA and sucrose contents. Exogenous ABA caused a decrease in the freezing point of leaf tissue in the cultivar with the lowest level of endogenous ABA, but not in the cultivar with the highest level, suggesting that ABA in the latter may be near the optimum endogenous level to induce freezing tolerance. Plants of cv. Aramir treated with ABA or allowed to acclimate to cold temperature increased their soluble sugar content to a similar level. The LT50 of leaves of cold‐acclimated cv. Aramir decreased from −5.8 to −11.4°C, with biphasic kinetics, accumulating proline and soluble sugars with similar kinetics. The biphasic profile observed during cold acclimation could be a direct consequence of cryoprotectant accumulation kinetics. ABA and soluble protein accumulation showed a single step profile, associated mainly with the second phase of the LT50 decrease. Thus, a significant increase in endogenous ABA is part of the response of barley to low temperature and may be required as a signal for the second phase of cold acclimation. Endogenous ABA contents in the nonacclimated state may determine constitutive freezing tolerance.