Núcleo de Pesquisa em Fisiologia e Bioquímica de Plantas, Instituto de Botânica, C Postal 3005, 01031-970 São Paulo, Brazil.
Plant Physiol Biochem. 2011 Jun;49(6):664-70. doi: 10.1016/j.plaphy.2011.03.014. Epub 2011 Mar 31.
Vernonia herbacea (Vell.) Rusby, a native species from the Brazilian Cerrado, accumulates about 80% of fructans in the rhizophores, the underground reserve organs. Besides their role as reserve, fructans have been recognized as protective compounds against drought. This physiological function attributed to fructans seems consistent with the wide occurrence of these carbohydrates in the cerrado, a biome that undergoes seasonal drought. The aim of this work was to analyze fructan composition and the activities of the enzymes involved in fructan synthesis, sucrose:sucrose 1-frutosyltransferase (1-SST) and fructan:fructan 1-frutosyltransferase (1-FFT), and depolymerization, fructan 1-exohydrolase (1-FEH) in plants submitted to water suppression. The plants were divided into 3 groups receiving 3 treatments: daily watering (control), water suppression for 23 days (WS) and re-watering after 15 days (RW). Samples were taken at the beginning of the experiment (Time 0) and after 3, 7, 11, 15, 17 and 23 days of water suppression. 1-SST and 1-FFT activities increased at the beginning of the water restriction period, coinciding with a decrease in 1-FEH activity, the onset of the reduction in soil water potential and in leaf water potential. Increases in 1-FEH and invertase activities led to a high yield of reducing sugars at the 23rd day after water suppression, and together with 1-FFT, 1-FEH also seemed to act in the redistribution of fructan molecules after re-watering. The increase in reducing sugars and in the fructo-oligo:fructo-polysaccharide ratio were associated to the maintenance of rhizophore turgor. Considering that WS plants showed changes in fructan metabolism that favored water retention and absorption after re-watering, the occurrence of osmotic adjustment mechanisms is suggested, reinforcing the hypothesis of fructans as protective agents against abiotic stresses, such as drought.
牛膝菊（Vell.）Rusby，一种来自巴西塞拉多的本地物种，在地下储备器官根状茎中积累约 80%的果聚糖。除了作为储备物质的作用外，果聚糖还被认为是抗旱的保护化合物。这种归因于果聚糖的生理功能似乎与这些碳水化合物在塞拉多的广泛存在是一致的，塞拉多是一个经历季节性干旱的生物群落。本工作的目的是分析在水分抑制下植物中果聚糖的组成以及参与果聚糖合成、蔗糖：蔗糖 1-果糖基转移酶（1-SST）和果聚糖：果聚糖 1-果糖基转移酶（1-FFT）以及分解、果聚糖 1-外切水解酶（1-FEH）的活性，这些植物被分为 3 组，分别接受 3 种处理：每天浇水（对照）、抑制水分 23 天（WS）和 15 天后重新浇水（RW）。在实验开始时（时间 0）和水分抑制后 3、7、11、15、17 和 23 天取样。1-SST 和 1-FFT 活性在水分限制期开始时增加，与 1-FEH 活性下降、土壤水势和叶片水势降低同时发生。1-FEH 和转化酶活性的增加导致在水分抑制后的第 23 天产生大量还原糖，与 1-FFT 一起，1-FEH 似乎也在重新浇水后参与了果聚糖分子的再分配。还原糖和果聚糖：果寡糖-果聚糖比例的增加与根状茎膨压的维持有关。考虑到 WS 植物在重新浇水后表现出有利于水分保持和吸收的果聚糖代谢变化，建议发生渗透调节机制，这加强了果聚糖作为抗旱等非生物胁迫保护剂的假说。
