Marschall Mariann, Proctor Michael C F, Smirnoff Nicholas
Department of Biological Sciences, University of Exeter, Hatherly Laboratories, Prince of Wales Road, Exeter EX4 4PS, UK.
Present address: Botanical Department, Eszterházy Károly Teacher Training College, 3301 Eger, Eszterházy tér 1. pf. 43 Hungary.
New Phytol. 1998 Feb;138(2):343-353. doi: 10.1046/j.1469-8137.1998.00102.x.
The major soluble carbohydrates in the desiccation-tolerant leafy liverwort Porella platyphylla (L.) Lindb. are sucrose and a homologous series of fructans including the trisaccharide 1-kestose. Exogenous glucose and fructose (10 mol m ) did not affect the composition of the soluble carbohydrate pool. Sucrose caused an increase in the fructan pool. Sucrose also inhibited photosynthetic oxygen evolution and respiration. The fructan pool was maintained in preference to sucrose during dark starvation. Low temperature and low water potential increased the fructan pool whereas desiccation increased the proportion of high molecular weight fructan. Acid invertase activity was detected in a taxonomically diverse range of liverworts but was very low or undetectable in a range of mosses. The invertase activity from P. platyphylla was partially purified by ammonium sulphate precipitation. The reaction products of the partially purified enzyme were equimolar glucose and fructose. Kestose and higher DP fructans were not detected suggesting that, at least under the assay conditions used, the enzyme does not have sucrose∶sucrose fructosyl transferase activity. The pH optimum was 4·5-5 and the K for sucrose was 1·7 mol m . Pyridoxal hydrochloride (5 mol m ) caused 50% inhibition. The coexistence of sucrose and invertase suggests that either the invertase is inactive in vivo or is in a different subcellular compartment from sucrose. The pH response shows that it would have very low activity at cytosolic pH. A large acidic vacuole was detected in P. platyphylla leaf cells by neutral-red staining in which either invertase or sucrose could be sequestered. Rehydrating desiccated P. platyphylla for 10 min resulted in a 60% loss of extractable invertase activity. By contrast, extractable malate dehydrogenase activity increased during rehydration. Rehydrating desiccated leaves caused an increase in glucose and fructose suggesting that the sucrose pool was susceptible to invertase at this time. It is suggested that the partial inactivation of invertase during rehydration minimizes sucrose hydrolysis while membrane structure and subcellular compartmentation are re-established.
耐旱叶状苔类植物阔叶小石藓（Porella platyphylla (L.) Lindb.）中的主要可溶性碳水化合物是蔗糖和一系列包括三糖1-蔗果三糖的果聚糖同系物。外源葡萄糖和果糖（10 mol m）不影响可溶性碳水化合物库的组成。蔗糖导致果聚糖库增加。蔗糖还抑制光合放氧和呼吸作用。在黑暗饥饿期间，优先维持果聚糖库而非蔗糖库。低温和低水势增加了果聚糖库，而干燥则增加了高分子量果聚糖的比例。在分类学上不同的苔类植物中检测到酸性转化酶活性，但在一系列藓类植物中活性很低或未检测到。阔叶小石藓的转化酶活性通过硫酸铵沉淀进行部分纯化。部分纯化酶的反应产物是等摩尔的葡萄糖和果糖。未检测到蔗果三糖和更高聚合度的果聚糖，这表明至少在所使用的测定条件下，该酶不具有蔗糖∶蔗糖果糖基转移酶活性。最适pH为4.5 - 5，蔗糖的K值为1.7 mol m。盐酸吡哆醛（5 mol m）导致50%的抑制。蔗糖和转化酶的共存表明，要么转化酶在体内无活性，要么与蔗糖处于不同的亚细胞区室。pH响应表明它在细胞质pH下活性会非常低。通过中性红染色在阔叶小石藓叶细胞中检测到一个大的酸性液泡，其中可能隔离了转化酶或蔗糖。将干燥的阔叶小石藓复水10分钟导致可提取的转化酶活性损失60%。相比之下，复水过程中可提取的苹果酸脱氢酶活性增加。干燥叶片复水导致葡萄糖和果糖增加，这表明此时蔗糖库易受转化酶作用。有人认为，复水过程中转化酶的部分失活在重新建立膜结构和亚细胞区室化的同时，使蔗糖水解最小化。
