A cell wall invertase controls nectar volume and sugar composition
A cell wall invertase controls nectar volume and sugar composition
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DOI：
10.1111/tpj.15357
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发表时间：
2021-07-29
期刊：
影响因子：
7.2
通讯作者：
Carter，Clay J.
中科院分区：
文献类型：
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作者：
Minami，Anzu;Kang，Xiaojun;Carter，Clay J.
蜜量和糖组成是植物-传粉者相互作用强度的关键决定因素。主要的花蜜糖是蔗糖、葡萄糖和果糖，它们在不同物种间的比例和浓度差别很大。生产以己糖为主的花蜜（单糖葡萄糖和果糖含量高），双糖蔗糖含量极低。细胞壁转化酶（CWINVs）在外质体中催化蔗糖不可逆水解为葡萄糖和果糖。我们发现brcwinv4is在油菜的蜜腺中高表达。此外，abcwinv4anull突变体：(i)大大降低了CWINV在蜜腺中的活性；（ii）产生富含蔗糖的花蜜；但（iii）体积明显减少。这些结果明确地表明，CWINV的活性不仅是生产富含己糖的花蜜所必需的，而且还支持了一种假设的花蜜分泌模型，在这种模型中，CWINV的水解酶活性是维持高细胞内与细胞外蔗糖比例的必要条件，从而促进蔗糖持续输出到蜜质外体。BrCWINV4A在细胞外将每个蔗糖水解成两个己糖也可能产生形成花蜜液滴所需的渗透电位。这些结果累积表明，CWINV活性的调节至少可以部分解释自然发生的花蜜体积和糖组成的差异。最后，蜜蜂更喜欢含有一些蔗糖的花蜜，但是野生型b。rapflower的访虫量远高于brcwinv4a的访虫量，这表明brcwinv4的花蜜虽然富含蔗糖，但无法弥补其较少的访虫量。
Nectar volume and sugar composition are key determinants of the strength of plant–pollinator mutualisms. The main nectar sugars are sucrose, glucose and fructose, which can vary widely in ratio and concentration across species.Brassicaspp. produce a hexose‐dominant nectar (high in the monosaccharides glucose and fructose) with very low levels of the disaccharide sucrose. Cell wall invertases (CWINVs) catalyze the irreversible hydrolysis of sucrose into glucose and fructose in the apoplast. We found thatBrCWINV4Ais highly expressed in the nectaries ofBrassica rapa. Moreover, abrcwinv4anull mutant: (i) has greatly reduced CWINV activity in the nectaries; (ii) produces a sucrose‐rich nectar; but (iii) with significantly less volume. These results definitively demonstrate that CWINV activity is not only essential for the production of a hexose‐rich nectar, but also support a hypothetical model of nectar secretion in which its hydrolase activity is required for maintaining a high intracellular‐to‐extracellular sucrose ratio that facilitates the continuous export of sucrose into the nectary apoplast. The extracellular hydrolysis of each sucrose into two hexoses by BrCWINV4A also likely creates the osmotic potential required for nectar droplet formation. These results cumulatively indicate that modulation of CWINV activity can at least partially account for naturally occurring differences in nectar volume and sugar composition. Finally, honeybees prefer nectars with some sucrose, but wild‐typeB. rapaflowers were much more heavily visited than flowers ofbrcwinv4a, suggesting that the potentially attractive sucrose‐rich nectar ofbrcwinv4acould not compensate for its low volume.