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荔枝(Litchi chinensis)是无患子科荔枝属热带、亚热带常绿果树,起源于中国云南[1],是“南国四大果品”之一。我国荔枝年产量占世界总产量的70%以上[2],‘妃子笑’荔枝属于中早熟品种,是海南省的主栽品种之一,具有较高的商业价值,然而‘妃子笑’荔枝果实在成熟期内外品质发育不一致,果皮完全转红时果实糖含量下降,即“退糖”[3],这严重影响了果实品质,降低了‘妃子笑’荔枝的商品价值。
糖是影响果实内在品质的关键因素之一,‘妃子笑’荔枝主要积累果糖、葡萄糖和蔗糖,其中以己糖(果糖、葡萄糖)居多[4]。高等植物叶片光合作用产生的光合产物主要以蔗糖的形式[5]运输到果实中。蔗糖代谢酶在果实糖代谢中起关键作用[6],蔗糖代谢酶包括酸性转化酶(AI)和中性转化酶(NI)、蔗糖合成酶(SS)、蔗糖磷酸合成酶(SPS)。蔗糖合成酶催化果糖、UDPG与蔗糖之间的可逆反应[7],蔗糖磷酸合成酶催化蔗糖的合成,转化酶催化蔗糖水解生成果糖和葡萄糖[8]。另外,磷酸果糖激酶(PFK1)是糖酵解途径中的第二个关键酶,催化6磷酸果糖转化为1,6二磷酸果糖,之前的研究表明,叶面钙处理可能通过下调磷酸果糖激酶基因的表达从而降低其酶活性,导致糖代谢受到抑制,最终使得荔枝果实糖含量得以积累[9]。
果实衰老时细胞壁开始降解,果实硬度随之降低,呼吸增强。钙镁在果实的生长发育过程中十分重要,有研究表明钙能延缓成熟和抑制果实衰老[10],主要是通过减少果实呼吸[11]。甜樱桃果实中钙含量的提高伴随着果实呼吸速率的下降和果皮硬度的提升[12]。钙还能够维持细胞壁结构[13],减少果实的变质[14-15]。 镁是植物的必需元素,它在光合同化物从韧皮部到库组织的装载和运输中起重要作用[16],并参与叶片光合作用、碳水化合物、脂肪、蛋白质和核酸的合成[17-19]。
前期笔者所在课题组已发现,钙镁混合叶面肥可以解决荔枝“退糖”问题[20],但其机理还不清楚。本研究通过以叶面喷施0.3%CaCl2+0.3%MgCl2混合水溶液为处理,以喷清水为对照,测定果实糖含量、蔗糖代谢酶活性,旨在初步探讨钙镁叶面肥解决“退糖”问题的生理机制。
Effect of calcium and magnesium foliar fertilizer on sugar contents and sugar metabolizing enzyme activities in 'Feizixiao' litchi pulp
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摘要: 为探究叶面喷施钙镁肥解决‘妃子笑’荔枝果实成熟期“退糖”问题的原因,本研究以16年生‘妃子笑’荔枝树为试验材料,以叶面喷施0.3%CaCl2 +0.3%MgCl2混合水溶液为处理,喷清水为对照,测定果实糖含量和糖代谢酶活性。结果表明:‘妃子笑’荔枝在果实生长发育前中期果糖、葡萄糖和蔗糖迅速积累,成熟期对照果实果糖、葡萄糖含量保持稳定,蔗糖、可溶性糖含量下降,在花后69 d处理果实果糖、总糖含量显著高于对照;喷施叶面肥处理使糖代谢酶活性发生显著变化,在花后69 d处理使中性转化酶活性和蔗糖代谢酶净活性显著升高,酸性转化酶、蔗糖磷酸合成酶、蔗糖合成酶合成方向和磷酸果糖激酶活性显著降低。总之,钙镁叶面肥处理通过提高中性转化酶活性、降低蔗糖磷酸合成酶和蔗糖合成酶合成活性来提高蔗糖代谢酶净活性,促进蔗糖的分解,同时降低磷酸果糖激酶活性抑制糖酵解途径,从而引起果糖和可溶性糖积累,进而解决了‘妃子笑’荔枝成熟期“退糖”的问题。Abstract: In order to explore the reason why the "sugar receding" problem of 'Feizixiao' litchi fruit can be solved by the foliar nutrient of calcium and magnesium, the 16-year-old 'Feizixiao' litchi trees were taken as the experimental material, sprayed 0.3% CaCl2+0.3% MgCl2 mixed water solution on the leaf surface as the treatment, and sprayed water as the control, and the sugar contents and sugar metabolism enzyme activities of the fruit were determined. The results showed that fructose, glucose and sucrose accumulated rapidly in the early and middle stages of fruit growth and development, and the contents of fructose and glucose in the control fruit remained stable in the mature stage, while the contents of sucrose and soluble sugar decreased. The contents of fructose and total sugar in the fruit of the treatment were significantly higher than that of the control at 69 days after anthesis. The treatment significantly changed the activities of sugar metabolizing enzymes. At 69 days after anthesis, the treatment significantly increased the activities of neutral invertase and net activities of sucrose metabolizing enzymes, while the activities of acid invertase, sucrose phosphate synthase, sucrose synthase synthesis direction and phosphofructokinase significantly decreased. In summary, calcium and magnesium foliar fertilizer treatment enhances the net activities of sucrose metabolizing enzymes by increasing the activity of neutral invertase, reducing the activities of sucrose phosphate synthase and sucrose synthase synthesis, promoting sucrose decomposition, and reducing the activity of phosphofructokinase to inhibit glycolysis pathways, thereby causing the accumulation of fructose and soluble sugars, solving the problem of "sugar receding" during the mature stage of 'Feizixiao' litchi.
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Key words:
- calcium and magnesium fertilizer /
- litchi /
- sugar /
- sucrose metabolizing enzyme
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