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. Inthis experiment, we measured the water content, PSⅡ efficiency, chlorophyll fluorescence, pigments of thexanthophyll-cycle and activity of enzymes of the ascorbate-glutathione cycle during cold acclimation and atsubsequent low-temperature conditions to examine the importance of acclimation to cold tolerance. P. glehniishowed a decrease in PSⅡ efficiency (especially in Fv) during cold acclimation and at subsequent low temperatures.However, cold-acclimated needles showed higher PSⅡ efficiency at low temperatures than nonacclimatedneedles. In addition, 0-YON (first-year needles) showed an increase in β-carotene and lutein, while1-YON (one-year-old needles) immediately developed an antioxidant mechanism in the ascorbate-gluthathionecycle as soon as they were exposed to low temperature and both 0-YON and 1-YON showed increasedzeaxanthin and de-epoxidation ratios at continuous low temperature. Based on our results, we suggest that P.glehnii maintain PSⅡ efficiency at low temperature by effectively protecting the photosynthetic apparatus fromphoto-damage by rapid induction of an antioxidant mechanism in 1-YON and dissipation of excess energy byβ-carotene and lutein in 0-YON.