title: The effects of moderately high temperature on zeaxanthin accumulation and decay.
abstract: Moderately high temperature reduces photosynthetic capacities of leaves with large effects on thylakoid reactions of photosynthesis, including xanthophyll conversion in the lipid phase of the thylakoid membrane. In previous studies, we have found that leaf temperature of 40°C increased zeaxanthin accumulation in dark-adapted, intact tobacco leaves following a brief illumination, but did not change the amount of zeaxanthin in light-adatped leaves. To investigate heat effects on zeaxanthin accumulation and decay, zeaxanthin level was monitored optically in dark-adapted, intact tobacco and Arabidopsis thaliana leaves at either 23 or 40°C under 45-min illumination. Heated leaves had more zeaxanthin following 3-min light but had less or comparable amounts of zeaxanthin by the end of 45 min of illumination. Zeaxanthin accumulated faster at light initiation and decayed faster upon darkening in leaves at 40°C than leaves at 23°C, indicating that heat increased the activities of both violaxanthin de-epoxidase (VDE) and zeaxanthin epoxidase (ZE). In addition, our optical measurement demonstrated in vivo that weak light enhances zeaxanthin decay relative to darkness in intact leaves of tobacco and Arabidopsis, confirming previous observations in isolated spinach chloroplasts. However, the maximum rate of decay is similar for weak light and darkness, and we used the maximum rate of decay following darkness as a measure of the rate of ZE during steady-state light. A simulation indicated that high temperature should cause a large shift in the pH dependence of the amount of zeaxanthin in leaves because of differential effects on VDE and ZE. This allows for the reduction in ΔpH caused by heat to be offset by increased VDE activity relative to ZE.
authors.affiliation: Department of Plant Biology, Carnegie Institution for Science, 260 Panama Street, Stanford, CA 94305, USA. ruzhang@stanford.edu
authors.forename: Ru
authors.initials: R
authors.lastname: Zhang
authors.forename: David M
authors.initials: DM
authors.lastname: Kramer
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Cruz
authors.forename: Kimberly R
authors.initials: KR
authors.lastname: Struck
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Sharkey
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000378:metabolism* / Q000528:radiation effects; D002245:Carbon Dioxide / Q000378:metabolism; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration / Q000528:radiation effects; D008027:Light; D010088:Oxidoreductases / Q000378:metabolism; D010788:Photosynthesis / Q000528:radiation effects; D054046:Plant Stomata / Q000378:metabolism / Q000528:radiation effects; D014026:Nicotiana / Q000201:enzymology / Q000378:metabolism* / Q000528:radiation effects; D024341:Xanthophylls / Q000378:metabolism*; D065146:Zeaxanthins
chemical_list: D024341:Xanthophylls; D065146:Zeaxanthins; D002245:Carbon Dioxide; D010088:Oxidoreductases; C023290:violaxanthin de-epoxidase; C097153:zeaxanthin epoxidase