Trevanion Stephen J, Castleden C Kate, Foyer Christine H, Furbank Robert T, Quick W Paul, Lunn John E
Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK.
CSIRO Plant Industry, PO Box 1600, Canberra, ACT 2601, Australia.
Funct Plant Biol. 2004 Aug;31(7):685-695. doi: 10.1071/FP04038.
The regulation of sucrose-phosphate synthase (SPS, E.C. 2.4.1.14), a key enzyme of sucrose synthesis, was investigated in wheat (Triticum aestivum L.) leaves. Wheat SPS was activated in the light, with an increased affinity for its substrates and the activator glucose-6-phosphate, reduced sensitivity to inhibition by P, but no change in maximum catalytic activity. Based on these properties, assays to measure the total activity and activation state of the enzyme were established and validated using several different wheat cultivars, grown under different environmental conditions. As found in previous studies on other species, e.g. spinach, activation appeared to be linked to the prevailing rate of photosynthesis rather than light per se. Long-term exposure to higher light levels increased total SPS activity in the leaves, and some experiments indicated that this response could occur within 1 h of exposure of low-light-grown plants to high light. However, activation of pre-existing enzyme was a more common short-term response to high light. Wheat, like many important cereal species, stores a large amount of sucrose in its leaves. In contrast with spinach, which stores more starch in its leaves, accumulation of sucrose in wheat leaves did not lead to inactivation of SPS or inhibition of sucrose synthesis. In conclusion, the mechanisms linking the rates of sucrose synthesis and photosynthetic CO fixation in wheat leaves appear to be similar to those in other species, but the mechanisms involved in short-term feedback inhibition of sucrose synthesis by sucrose, found in starch-storing species, are lacking in wheat.
对小麦（Triticum aestivum L.）叶片中蔗糖合成关键酶蔗糖磷酸合酶（SPS，E.C. 2.4.1.14）的调控进行了研究。小麦SPS在光照下被激活，对其底物和激活剂葡萄糖-6-磷酸的亲和力增加，对P抑制的敏感性降低，但最大催化活性没有变化。基于这些特性，建立了测量该酶总活性和激活状态的分析方法，并使用在不同环境条件下生长的几个不同小麦品种进行了验证。正如之前对其他物种（如菠菜）的研究所发现的，激活似乎与光合作用的主导速率而非光照本身有关。长期暴露于较高光照水平会增加叶片中SPS的总活性，一些实验表明，这种反应可能在低光照生长的植物暴露于高光下1小时内发生。然而，预先存在的酶的激活是对高光更常见的短期反应。与许多重要的谷物物种一样，小麦在其叶片中储存大量蔗糖。与在叶片中储存更多淀粉的菠菜不同，小麦叶片中蔗糖的积累并未导致SPS失活或蔗糖合成受到抑制。总之，小麦叶片中蔗糖合成速率与光合CO固定之间的联系机制似乎与其他物种相似，但在储存淀粉的物种中发现的蔗糖对蔗糖合成的短期反馈抑制机制在小麦中并不存在。
