Energy and Pro-/Antioxidant Metabolism of Heracleum sosnowskyi Manden. Buds during the Winter Dormancy

Abstract

Data on changes in energy status, activity of pro-/antioxidant metabolism during overwintering of Heracleum sosnowskyi vegetative buds were obtained. The buds of H. sosnowskyi are not endodormant and their growth is limited by the decrease of the soil temperature to negative values at the end of November. The optimum temperature for energy storage in autumn was found to be in the range of low positive temperatures (2–5°C). The autumn buds were characterized a high capacity for the cytochrome respiratory pathway (CP, V_cyt), which accounted for 78% of the total respiration. During autumn morphogenesis and winter dormancy of buds, the levels of pro-oxidants, which are the content of thiobarbituric acid reactive substances (TBARS) and H₂O₂ content, remained stable. In December, when a stable snow cover and negative soil temperatures were established, the dormant buds showed 2.5 times lower rate of energy storage and activated alternative respiration capacity (AP, V_alt), as indicated by a 2 times lower V_cyt/V_alt ratio. In early spring, compared to winter dormancy, H₂O₂ levels increased 2-fold and antioxidant enzymes activity increased by 27–78% as insolation increased. Spring buds showed an increase in rate of heat production and a decrease in rate of energy storage, which may be due to spring stress caused by increased insolation. It was concluded that in the tissues of H. sosnowskyi buds subjected to exogenous dormancy, an energy balance between dormancy and growth processes is achieved at the level of respiratory capacity and pro-/antioxidant metabolism.