title: The xanthophyll cycle and acclimation of Pinus ponderosa and Malva neglecta to winter stress.
abstract: Seasonal differences in the efficiency of open PSII units (Fv/Fm), leaf pigment composition and xanthophyll cycle conversion (Z+A)/(V+A+Z), leaf adenylate status, and photosynthetic capacity were investigated in Pinus ponderosa (Ponderosa pine) and Malva neglecta. In P. ponderosa, acclimation to winter involved a lower photosynthetic capacity, higher carotenoid to chlorophyll ratio, persistent reductions in Fv/Fmcorresponding to persistent retention of Z+A, and no change in foliar ATP/ADP ratios. In contrast, M. neglecta characterized in winter exhibited higher rates of photosynthesis than in summer with no change in carotenoid to chlorophyll ratio, while small nocturnally persistent reductions in Fv/Fmwere observed exclusively on colder winter nights when nocturnal retention of Z+A, and high ATP/ADP ratios were also present. Upon removal of winter-stressed leaves or needles from the field to room temperature, a portion of Fv/Fmrelaxed within 15 min of warming and recovery was completed within 5 h in M. neglecta but required 100 h in P. ponderosa. In M. neglecta, the entire recovery of Fv/Fmcorrelated with decreases in the foliar ATP/ADP ratio, while in P. ponderosa this ratio remained unchanged. Possible ATP-dependent forms of sustained (Z+A)-dependent energy dissipation are discussed including a nocturnally retained pH gradient on cold winter nights. The slow recovery in pine involved not only retention of Z+A, but apparently also a persistent engagement of Z+A for energy dissipation via an unidentified mechanism.
authors.affiliation: Department of Environmental, Population, and Organismic Biology, University of Colorado, Boulder, CO 80309-0334, USA e-mail: william.adams@colorado.edu, Fax: +1-303-4928699, , , , , , US.
authors.forename: A S
authors.initials: AS
authors.lastname: Verhoeven
authors.affiliation: Department of Environmental, Population, and Organismic Biology, University of Colorado, Boulder, CO 80309-0334, USA e-mail: william.adams@colorado.edu, Fax: +1-303-4928699, , , , , , US.
authors.forename: W W
authors.initials: WW
authors.lastname: Adams Iii
authors.affiliation: Department of Environmental, Population, and Organismic Biology, University of Colorado, Boulder, CO 80309-0334, USA e-mail: william.adams@colorado.edu, Fax: +1-303-4928699, , , , , , US.
authors.forename: B
authors.initials: B
authors.lastname: Demmig-Adams
keywords: Key words Energy dissipation; Low-temperature stress; Malva neglecta; Pinus ponderosa; Xanthophyll cycle; Zeaxanthin