BACKGROUND & AIMS:
:The association between plant water stress and synthesis of red, anthocyanin pigments in leaves has led some plant biologists to propose an osmotic function of leaf reddening. According to this hypothesis, anthocyanins function as a solute in osmotic adjustment (OA), contributing to depression of osmotic potential (Ψ(π)) and maintenance of turgor pressure during drought-stressed conditions. Here we calculate the percent contribution of anthocyanin to leaf Ψ(π) during OA in two angiosperm evergreen species, Galax urceolata and Gaultheria procumbens. Both species exhibit dramatic leaf reddening under high light during winter, concomitant with declines in leaf water potential and accumulation of solutes. Data previously published by the authors on osmotic potential at full turgor (Ψ(π,100)) of G. urceolata and G. procumbens leaves before and after leaf reddening were used to estimate OA. In vivo molar concentrations of anthocyanin, glucose, fructose, and sucrose measured from the same individuals were converted to pressure equivalents using the Ideal Gas Law, and percent contribution to OA was estimated. Estimated mean OA during winter was -0.7MPa for G. urceolata and -0.8MPa for G. procumbens. In vivo concentrations of anthocyanin (3-10mM) were estimated to account for ∼2% of OA during winter, and comprised <0.7% of Ψ(π,100) in both species. Glucose, fructose, and sucrose combined accounted for roughly 50 and 80% of OA for G. urceolata and G. procumbens, respectively, and comprised ∼20% of Ψ(π,100). We observed that a co-occurring, acyanic species (Vinca minor) achieved similar OA without synthesizing anthocyanin. We conclude that anthocyanins represent a measurable, albeit meager, component of OA in red-leafed evergreen species during winter. However, due to their low concentrations, metabolic costliness relative to other osmolytes, and striking red color (unnecessary for an osmotic function), it is unlikely that they are synthesized solely for an osmoprotectant role.
背景与目标:
: 植物水分胁迫与叶片中红色,花色苷色素的合成之间的联系已导致一些植物生物学家提出了叶片变红的渗透功能。根据该假设,花青素在渗透调节 (OA) 中起溶质作用,有助于在干旱胁迫条件下降低渗透势 (Ψ(π)) 和维持膨大压力。在这里,我们计算了两种被子植物常绿物种Galax urceolata和procumberns在OA期间花青素对叶 Ψ(π) 的贡献百分比。两种物种在冬季在高光下均表现出明显的叶片变红,同时叶片水势下降和溶质积累。作者先前发表的关于叶片变红之前和之后的大叶和平卧叶片全膨大 (Ψ(π,100)) 渗透势的数据用于估计OA。使用理想气体法将从同一个体测得的体内花青素,葡萄糖,果糖和蔗糖的摩尔浓度转换为压力当量,并估算了对OA的贡献百分比。冬季,G. urceolata的估计平均OA为-0.7MPa,G.Procumens的估计平均OA为-0.8MPa。据估计,花青素的体内浓度 (3-10mm) 占冬季OA的约2%,并且在两种物种中均 <Ψ(π,100) 的0.7%。葡萄糖、果糖和蔗糖的组合分别占牛膝和牛膝G的OA的大约50和80%,并且包括20% 的 Ψ(π,100)。我们观察到,共生的acyanic物种 (Vinca minor) 在没有合成花青素的情况下获得了相似的OA。我们得出的结论是,花青素代表冬季红叶常绿物种中OA的可测量成分,尽管微不足道。但是,由于它们的低浓度,相对于其他渗透物的代谢成本以及醒目的红色 (对于渗透功能而言是不必要的),因此不太可能仅出于渗透保护剂的作用而合成它们。