BIOCHEMICAL-MECHANISM FOR REGULATION OF SUCROSE ACCUMULATION IN LEAVES DURING PHOTOSYNTHESIS
BIOCHEMICAL-MECHANISM FOR REGULATION OF SUCROSE ACCUMULATION IN LEAVES DURING PHOTOSYNTHESIS
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DOI：
10.1104/pp.91.2.656
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发表时间：
1989-10-01
期刊：
影响因子：
7.4
通讯作者：
HUBER, SC
中科院分区：
文献类型：
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作者：
HUBER, SC
众所周知，为什么有些物种在光合作用期间在叶子中积累高浓度的蔗糖，而另一些物种则不然。为了确定可能的依据，我们研究了 10 种已知在蔗糖积累方面与蔗糖水解酶活性不同的物种。一般来说，酸性蔗糖酶活性随着叶子的扩展而降低；然而，成熟、完全展开的叶子中剩余的活性范围从低（<10微摩尔每克鲜重每小时）到非常高（>100微摩尔每克鲜重每小时）。相比之下，不同物种之间的蔗糖合酶活性较低且相对相似（每小时每克鲜重 4-10 微摩尔）。重要的是，下午测量的叶片蔗糖浓度与酸性转化酶活性呈负相关。我们提出，酸性转化酶介导的水解可以防止蔗糖在大豆和烟草等物种的液泡中积累。初步尝试表征成熟大豆叶中酸性转化酶的相对高活性。通过 Mono Q 色谱法解析了该酶的两种表观形式。这两种形式对底物具有相似的亲和力（表观 Km [蔗糖] = 3 毫摩尔），并且在重色谱时不会相互转化。看来，在扩张过程中全叶蔗糖酶活性的丧失主要是由于其中一种酶形式发生变化的结果。总体而言，这些结果提供了一种机制来解释为什么某些物种不在其叶子中积累蔗糖。据推测，这些物种中会发生蔗糖和己糖之间的一些无效循环，因此，蔗糖生产的能源成本可能比通常认为的要高。
It is known why some species accumulate high concentrations of sucrose in leaves during photosynthesis while others do not. To determine the possible basis, we have studied 10 species, known to differ in the accumulation of sucrose, in terms of activities of sucrose hydrolyzing enzymes. In general, acid invertase activity decreased as leaves expanded; however, activites remaining in mature, fully expanded leaves ranged from low (< 10 micromoles per gram fresh weight per hour) to very high (>100 micromoles per gram fresh weight per hour). In contrast, sucrose synthase activities were low and relatively similar among the species (4-10 micromoles per gram fresh weight per hour). Importantly, leaf sucrose concentration, measured at midafternoon, was negatively correlated with acid invertase activity. We propose that sucrose accumulation in vacuoles of species such as soybean and tobacco is prevented by acid invertase-mediated hydrolysis. Initial attempts were made to characterize the realtively high activity of acid invertase from mature soybean leaves. Two apparent forms of the enzyme were resolved by Mono Q chromatography. The two forms had similar affinity for substrate (apparent Km [sucrose] = 3 millimolar) and did not interconvert upon rechromatography. It appeared that the loss of whole leaf invertase activity during expansion was largely the result of changes in one of the enzyme forms. Overall, the results provide a mechanism to explain why some species do not accumulate sucrose in their leaves. Some futile cycling between sucrose and hexose sugars is postulated to occur in these species, and thus, the energy cost of sucrose production may be higher than is generally thought.