Photochemical response in 0-year-old and 1-year-old needles of Picea glehnii during cold acclimation and low temperature

P. glehnii, an evergreen conifer found in northern areas, Is known as a cold-resistant species. In this experiment, we measured the water content, PS II efficiency, chlorophyll fluorescence, pigments of the xanthophyll-cycle and activity of enzymes of the ascorbate-glutathlone cycle during cold acclimation and at subsequent low-temperature conditions to examine the Importance of acclimation to cold tolerance. P. glehnii showed a decrease in PS II efficiency (especially in Fv) during cold acclimation and at subsequent low temperatures. However, cold-acclimated needles showed higher PS II efficiency at low temperatures than nonacclimated needles. In addition, 0-YON (first-year needles) showed an Increase In β-carotene and lutein, while 1-YON (one-year-old needles) immediately developed an antioxidant mechanism in the ascorbate-gluthathione cycle as soon as they were exposed to low temperature and both 0-YON and 1-YON showed Increased zeaxanthin and de-epoxidation ratios at continuous low temperature. Based on our results, we suggest that P. glehnii maintain PS II efficiency at low temperature by effectively protecting the photosynthetic apparatus from photo-damage by rapid induction of an antioxidant mechanism in 1-YON and dissipation of excess energy by β-carotene and lutein In 0-YON.