Exploring lipophilic antioxidants accumulation in field-grown low temperature-stressed Ephedra monosperma

The seasonal patterns of changes in the content of lipophilic antioxidants $\beta$-carotene ($\beta$-Car), zeaxanthin (Zx), $\alpha$-tocopherol ($\alpha$-Toc), plastoquinone (PQ)/plastoquinol ($PQH_{2}$) were studied in the assimilating shoots of evergreen shrub Ephedra monosperma J.G. Gmel ex C.A. Mey under natural conditions of Central Yakutia. The shortening of the photoperiod and the seasonal decrease in temperature induced a 1.4-fold increase in $\alpha$-Toc content. The fall in the average daily temperature from 0.1 to $-8.1^{\circ}C$ in October led to a decrease in the content of $\beta$-Car as a result of the accumulation of rhodoxanthin (Rhd). In this period a sharp increase in the content of Zx retained overnight was also detected. In winter, elevated content of Zx and $\alpha$-Toc persisted. During September, the content of PQH2 increased by 2.5 times and PQ by 1.4 times (compared to July). The beginning of exposure to freezing average daily temperatures from -3 to $-5^{\circ}C$ led to the depletion of the total PQ pool by 18%. However, the content of $PQ_{tot}$ in the winter months was 1.5 times higher than at the end of July. The results revealed different timing and temperature ranges of variation for individual antioxidants during the development of frost resistance in ephedra.