香榧种实膨大过程中蔗糖代谢及其基因表达

Sucrose metabolism and gene expression during seed expansion of Torreya grandis‘Merrillii’

【目的】研究香榧Torreya grandis‘Merrillii’种实膨大过程中蔗糖及其产生的己糖在假种皮和种仁中积累与分配规律,初步阐明蔗糖变化对香榧种实库活力的影响,深入探讨蔗糖代谢关键酶活性及其基因表达模式对香榧种实膨大的影响。【方法】以香榧种实膨大不同阶段的种仁和假种皮为研究材料,测定蔗糖、葡萄糖、果糖及淀粉质量分数,蔗糖代谢相关酶活性,激素质量分数以及蔗糖代谢相关酶编码基因的表达量变化。【结果】随着香榧种实膨大,假种皮中的蔗糖、葡萄糖、果糖先上升后下降,淀粉质量分数不断下降,至种实突破种鳞后90 d时下降至254.05 mg·g^(-1)。种仁中蔗糖质量分数则持续下降,至种实突破种鳞后90 d时下降了61.24%;淀粉逐渐积累,由种实突破种鳞后30 d时的105.29 mg·g^(-1)增加至90 d时的149.72 mg·g^(-1);蔗糖磷酸合成酶在假种皮中活性上升,而在种仁中活性下降,至种实突破种鳞后90 d时约降低了28.82%;蔗糖转化酶活性在香榧假种皮中也显著上升(P<0.05),种实突破种鳞后90 d时细胞质蔗糖转化酶和液泡蔗糖转化酶分别上升至21.52和23.49μmol·mg^(-1)·min^(-1)。基因表达分析发现:参与蔗糖及还原糖运输的基因在种实膨大过程中显著上调表达(P<0.05),参与蔗糖水解的基因部分转录本也随着种实膨大显著上调(P<0.05)。种仁中参与淀粉合成的基因在种实膨大后期均显著上调表达(P<0.05)。相关性分析发现:假种皮和种仁中多种激素均与葡萄糖、果糖、蔗糖以及淀粉质量分数和酶活性间呈现一定的相关关系。【结论】膨大前期香榧假种皮中的蔗糖以积累为主,种实膨大后期蔗糖和淀粉以分解为主。种仁中蔗糖则一直以分解为主。假种皮和种仁之间,以及种仁内部存在活跃的碳水化合物运输和代谢过程。负责蔗糖水解的酶主要是蔗糖转化酶,细胞质蔗糖转化酶和液泡蔗糖转化酶起到重要作用。图6表1参42。

[Objective]This study is designed to investigate the accumulation and distribution of sucrose and hexose in aril and kernel tissue during seed expansion of Torreya grandis‘Merrillii’,clarify the effect of sucrose metabolism on the sink vitality of seeds,and explore the effects of key enzyme activity of sucrose metabolism and gene expression patterns on seed expansion.[Method]The kernel and aril at different stages of T.grandis‘Merrillii’seed expansion were used as research materials.The contents of sucrose,glucose,fructose and starch,the activity of enzymes related to sucrose metabolism,the contents of hormones and changes in the expression of genes encoding enzymes related to sucrose metabolism were measured.[Result]With the expansion of T.grandis‘Merrillii’seeds,the contents of sucrose,glucose and fructose in the aril first increased and then decreased,while the starch content decreased continuously to 254.05 mg·g^(-1)at 90 d after seed protrusion.Sucrose content in seed kernel decreased by 61.24% at 90 d after seed protrusion,and starch content gradually increased from 105.29 mg·g^(-1)at 30 d after seed protrusion to 149.72 mg·g^(-1)at 90 d after seed protrusion.The activity of sucrose phosphate synthase increased in seed aril,but decreased in seed kernel by 28.82% at 90 d after seed protrusion.The activity of sucrose invertase also increased significantly(P<0.05)in seed aril.At 90 d after seed protrusion,cytoplasmic invertase and vacuolar invertase increased to 21.52 and 23.49μmol·mg^(-1)·min^(-1).Gene expression analysis showed that genes involved in sucrose and hexose transport were significantly up-regulated(P<0.05)during seed expansion,and several transcripts of genes involved in sucrose hydrolysis were also significantly up-regulated(P<0.05).The genes involved in starch synthesis in seed kernel were significantly up-regulated(P<0.05)at the later stage of seed expansion.Correlation analysis showed there was a certain correlation between various hormones in aril and kernel and the contents of glucose,fructose,sucrose,starch and enzyme activity.[Conclusion]The accumulation of sucrose in the aril tissue mainly occurs during the early stage of seed expansion,while the hydrolysis of sucrose and starch occurs in the later stage of seed expansion.Sucrose in seed kernel is mainly decomposed.There are active carbohydrate transport and metabolism between seed aril and kernel,as well as within kernel.Sucrose invertase is the key enzyme responsible for sucrose hydrolysis,and cytoplasmic invertase and vacuolar invertase play an important role.[Ch,6 fig.1 tab.42 ref.]