Villadsen Dorthe, Rung Jesper Henrik, Nielsen Tom Hamborg
Plant Biochemistry Laboratory, Department of Plant Biology, Royal Veterinary and Agricultural University, 40 Thorvaldsensvej, DK-1871 Frederiksberg C, Denmark.
Funct Plant Biol. 2005 Nov;32(11):1033-1043. doi: 10.1071/FP05102.
Carbohydrate metabolism was investigated in barley leaves subjected to drought or osmotic stress induced by sorbitol incubation. Both drought and osmotic stress resulted in accumulation of hexoses, depletion of sucrose and starch, and 5-10-fold increase in the level of the regulatory metabolite fructose-2,6-bisphosphate (Fru-2,6-P). These changes were paralleled by an increased activity ratio of fructose-6-phosphate,2-kinase / fructose-2,6-bisphosphatase (F2KP). The drought-induced changes in carbohydrate content and Fru-2,6-P metabolism were reversed upon re-watering. This reveals a reversible mechanism for modification of the F2KP enzyme activity. This suggests that F2KP might be involved in altering carbohydrate metabolism during osmotic stress. However, labelling with [C]-CO showed that sucrose synthesis was not inhibited, despite the increased Fru-2,6-P levels, and demonstrated that increased flux into the hexose pools probably derived from sucrose hydrolysis. Similar effects of osmotic stress were observed in leaf sections incubated in the dark, showing that the changes did not result from altered rates of photosynthesis. Metabolism of [C]-sucrose in the dark also revealed increased flux into hexoses and reduced flux into starch in response to osmotic stress. The activities of a range of enzymes catalysing reactions of carbohydrate metabolism in general showed only a marginal decrease during osmotic stress. Therefore, the observed changes in metabolic flux do not rely on a change in the activity of the analysed enzymes. Fructose-2,6-bisphosphate metabolism responds strongly to drought stress and this response involves modification of the F2KP activity. However, the data also suggests that the sugar accumulation observed during osmotic stress is mainly regulated by another, as yet unidentified mechanism.
在经山梨醇处理诱导干旱或渗透胁迫的大麦叶片中研究了碳水化合物代谢。干旱和渗透胁迫均导致己糖积累、蔗糖和淀粉消耗，以及调节性代谢物果糖-2,6-二磷酸（Fru-2,6-P）水平增加5至10倍。这些变化伴随着6-磷酸果糖-2-激酶/果糖-2,6-二磷酸酶（F2KP）活性比的增加。重新浇水后，干旱诱导的碳水化合物含量和Fru-2,6-P代谢变化得以逆转。这揭示了一种F2KP酶活性修饰的可逆机制。这表明F2KP可能参与渗透胁迫期间碳水化合物代谢的改变。然而，用[C]-CO标记表明，尽管Fru-2,6-P水平升高，但蔗糖合成并未受到抑制，并且表明进入己糖库的通量增加可能源于蔗糖水解。在黑暗中培养的叶片切片中观察到了类似的渗透胁迫效应，表明这些变化并非由光合作用速率改变所致。黑暗中[C]-蔗糖的代谢也显示，响应渗透胁迫，进入己糖的通量增加，进入淀粉的通量减少。一般来说，一系列催化碳水化合物代谢反应的酶活性在渗透胁迫期间仅略有下降。因此，观察到的代谢通量变化并不依赖于所分析酶活性的改变。果糖-2,6-二磷酸代谢对干旱胁迫反应强烈，这种反应涉及F2KP活性的修饰。然而，数据还表明，渗透胁迫期间观察到的糖积累主要受另一种尚未确定的机制调节。
