Murakami P F, Schaberg P G, Shane J B
Forest Service, U.S. Department of Agriculture, Northern Research Station, 705 Spear Street, South Burlington, VT 05403, USA.
Tree Physiol. 2008 Oct;28(10):1467-73. doi: 10.1093/treephys/28.10.1467.
To better understand the effects of sugar accumulation on red color development of foliage during autumn, we compared carbohydrate concentration, anthocyanin expression and xylem pressure potential of foliage on girdled versus non-girled (control) branches of 12 mature, open-grown sugar maple (Acer saccharum Marsh.) trees. Half of the study trees were known to exhibit mostly yellow foliar coloration and half historically displayed red coloration. Leaves from both girdled and control branches were harvested at peak color expression (i.e., little or no chlorophyll present). Disruption of phloem export by girdling increased foliar sucrose, glucose and fructose concentrations regardless of historical tree color patterns. Branch girdling also increased foliar anthocyanin expression from 50.4 to 66.7% in historically red trees and from 11.7 to 54.2% in historically yellow trees, the latter representing about a fivefold increase compared with control branches. Correlation analyses indicated a strong and consistent relationship between foliar red coloration and sugar concentrations, particularly glucose and fructose, in both girdled and control branches. Measures of xylem pressure potentials confirmed that girdling was a phloem-specific treatment and had no effect on water transport to distal leaves. Results indicate that stem girdling increased foliar sugar concentrations and enhanced anthocyanin expression during autumn in sugar maple foliage. Native environmental stresses (e.g., low autumn temperatures) that reduce phloem transport may promote similar physiological outcomes.
为了更好地理解糖分积累对秋季树叶红色发育的影响，我们比较了12棵成熟、自然生长的糖枫（Acer saccharum Marsh.）树木环剥枝与未环剥枝（对照）上树叶的碳水化合物浓度、花青素表达和木质部压力势。已知一半的研究树木大多呈现黄色叶色，另一半历来呈现红色叶色。在颜色表达高峰期（即几乎没有叶绿素或不存在叶绿素）采集环剥枝和对照枝上的树叶。无论树木的历史颜色模式如何，环剥造成的韧皮部输出中断都会增加树叶中蔗糖、葡萄糖和果糖的浓度。在历来呈红色的树木中，枝条环剥还使树叶花青素表达从50.4%增加到66.7%，在历来呈黄色的树木中从11.7%增加到54.2%，后者与对照枝相比增加了约五倍。相关性分析表明，在环剥枝和对照枝上，树叶红色与糖分浓度，特别是葡萄糖和果糖浓度之间存在强烈且一致的关系。木质部压力势的测量结果证实，环剥是一种韧皮部特异性处理，对水分向远端树叶的运输没有影响。结果表明，茎环剥增加了糖枫树叶秋季的树叶糖分浓度并增强了花青素表达。降低韧皮部运输的自然环境胁迫（如秋季低温）可能会促进类似的生理结果。
