Molekulare Pflanzenphysiologie, Institut für Pflanzenbiologie, Universität Zürich, Zollikerstrasse 107, 8008 Zürich, Switzerland.
Plant Cell Physiol. 2009 Dec;50(12):2174-82. doi: 10.1093/pcp/pcp151.
In chloroplasts, several water-soluble carbohydrates have been suggested to act as stress protectants. The trisaccharide raffinose (alpha-1,6-galactosyl sucrose) is such a carbohydrate but has received little attention. We here demonstrate by compartmentation analysis of leaf mesophyll protoplasts that raffinose is clearly (to about 20%) present in chloroplasts of cold-treated common bugle (Ajuga reptans L.), spinach (Spinacia oleracea L.) and Arabidopsis [Arabidopsis thaliana (L.) Heynh.] plants. The two dedicated enzymes needed for raffinose synthesis, galactinol synthase and raffinose synthase, were found to be extra-chloroplastic (probably cytosolic) in location, suggesting that the chloroplast envelope contains a raffinose transporter. Uptake experiments with isolated Ajuga and Arabidopsis chloroplasts clearly demonstrated that raffinose is indeed transported across the chloroplast envelope by a raffinose transporter, probably actively. Raffinose uptake into Ajuga chloroplasts was a saturable process with apparent K(m) and v(max) values of 27.8 mM and 3.3 micromol mg(-1) Chl min(-1), respectively.
在叶绿体中，有几种水溶性碳水化合物被认为具有应激保护作用。三糖棉子糖（α-1,6-半乳糖基蔗糖）就是这样一种碳水化合物，但它的关注度较低。我们通过对叶片叶肉原生质体的区室分析表明，棉子糖明显（约 20%）存在于冷处理的普通喇叭（Ajuga reptans L.）、菠菜（Spinacia oleracea L.）和拟南芥（Arabidopsis thaliana (L.) Heynh.）植物的叶绿体中。合成棉子糖所需的两种专用酶，半乳糖苷合酶和棉子糖合酶，被发现位于叶绿体之外（可能在细胞质中），这表明叶绿体被膜含有棉子糖转运蛋白。用分离的 Ajuga 和拟南芥叶绿体进行的摄取实验清楚地表明，棉子糖确实通过棉子糖转运蛋白被主动转运穿过叶绿体被膜。Ajuga 叶绿体对棉子糖的摄取是一个饱和过程，表观 K(m)和 v(max)值分别为 27.8 mM 和 3.3 micromol mg(-1) Chl min(-1)。
