定植早期多效唑处理对甘薯块根发育及其蔗糖代谢的影响

Effects of Paclobutrazol Treatment in Early Stage of Planting on the Development and Sucrose Metabolism of Storage Root in SweetPotato

施用多效唑(PBZ)可显著提高甘薯块根产量并改善其品质,同时蔗糖分解酶在甘薯块根发育中发挥着重要的调控作用。但目前尚不清楚PBZ调控甘薯块根发育的生理生化机制,更不清楚蔗糖代谢在其中发挥的具体作用。本研究以海南鲜食甘薯主栽品种高系14为材料,研究栽培早期(定植后20~30 d)喷施PBZ对其块根产量、单薯鲜重和单株结薯数,以及不同发育阶段(定植后30、60、90、120 d)块根中的淀粉和可溶性糖(葡萄糖、果糖和蔗糖)含量、蔗糖分解酶活性及其基因家族成员表达水平的影响,以明确PBZ调控甘薯块根发育的蔗糖代谢相关生理生化机制。结果表明:(1)PBZ可通过提高块根单薯鲜重而不是单株结薯数来增加甘薯产量,同时还可以增加块根中的可溶性糖含量和淀粉含量,改善块根品质;但PBZ的增产和改善品质的效果仅发生在处理后的定植早期(定植后30~60 d),在定植后期(定植后90~120 d),PBZ处理对产量和品质无显著影响。(2)PBZ处理显著增加块根的蔗糖合成酶(Sus)、细胞壁转化酶(CWIN)和细胞质转化酶(CIN)活性,但对液泡转化酶(VIN)活性无显著影响。与CWIN和CIN相比,Sus活性上升的时间更早、幅度更大,即PBZ处理下Sus的活性在定植后30 d即显著上升,而CWIN和CIN的活性在定植后60 d才显著上升;在其他时期(特别是定植后期),PBZ处理对Sus、CWIN和CIN活性均无显著影响。(3)对Sus、CWIN和CIN基因表达量的测定表明,在块根中表达的5个Sus基因(IbSus2、IbSus5~7和IbSus9)的表达量在块根发育早期(定植后30 d)均受到PBZ的显著诱导。此外,在块根中表达的7个CIN基因中有3个CIN基因(IbCIN3、IbCIN7和IbCIN8)、在块根中表达的3个CWIN基因中有2个(IbCWIN2和IbCWIN4)基因的表达水平在定植后60 d受到显著诱导。但在其他时期(特别是定植后期),PBZ处理对相关基因家族成员表达水平均无显著影响。结合前人的研究结果,推测PBZ处理下Sus表达和活性增加的时间更早、幅度更大,可以促进淀粉的快速积累和块根的快速膨大,而随后CWIN和CIN表达和活性的上升则可增加块根中的可溶性糖含量,改善甘薯品质,同时为淀粉的合成和块根的膨大提供一定的能量供应。本研究还鉴定出上述3种蔗糖分解酶基因家族中受PBZ诱导表达的特定成员。PBZ对甘薯块根产量、品质、蔗糖分解酶活性及其基因表达水平的影响主要发生在PBZ处理后的短时期内,随着时间的延长,PBZ对上述指标的影响逐渐消失。因此,生产上为了提高甘薯产量,有必要在全生育期进行PBZ处理。上述研究结果可为下一步通过品种选育和栽培措施等手段实现优质、高产甘薯生产提供理论依据。

The yield and quality of sweetpotato root tubers can be significantly improved by applying paclobutrazol(PBZ),and sucrose-degrading enzymes play important roles in the development of storage roots of sweetpotato.However,the physiological and biochemical mechanisms underlying PBZ-regulated storage root development is still unclear,and especially it remains to be investigated whether sucrose metabolism is involved in the PBZ-regulated development of storage roots.In this paper,sweetpotato cultivar Kokei 14 was used,a predominant cultivar planting in Hainan.After applying PBZ treatment in the early stage of cultivation(20-30 d after planting,dap),the following phenotypic parameters were investigated at 120 dap including the fresh weight of storage root per plant,fresh weight per storage root and storage root number per plant.To elucidate the physiological and biochemical mechanisms relevant to sucrose metabolism underlying PBZ-regulated storage root development,the following physiological and molecular parameters were also examined in storage roots at different development stages(30,60,90 and 120 dap)including the content of starch and soluble sugars(glucose,fructose and sucrose),the activities of sucrose-degrading enzymes and expression levels of the gene families.PBZ increased the yield of sweetpotato by increasing the fresh weight per storage root,but without affecting storage root number per plant.PBZ increased the content of soluble sugar and starch in storage root.However,the effect of PBZ on the yield and quality of storage roots only occurred in the early stage(30-60 d after planting)after treatment,and in the late stage(90-120 d),PBZ treatment had no significant effect on yield and quality.PBZ treatment significantly increased the activities of sucrose synthase(Sus),cell wall invertase(CWIN)and cytoplasmic invertase(CIN).However,PBZ had no significant effects on vacuolar invertase(VIN).As compared to CWIN and CIN,Sus activity was induced by PBZ treatment much earlier and more dramatic.Sus activity was significantly induced at 30 dap,whereas the activity of CWIN and CIN were significantly induced at late stage i.e.60 dap.In other periods(especially 90-120 d),PBZ treatment had no significant effect on the activities of Sus,CWIN and CIN.The determination of the expression level of Sus,CWIN and CIN genes showed that IbSus2,IbSus5-7 and IbSus9 highly expressed in storage tuber were all significantly induced by PBZ at 30 dap.IbCIN3,IbCIN7 and IbCIN8 expressed in storage roots,and IbCWIN2 and IbCWIN4 expressed in storage roots were significantly induced by PBZ at 60 dap.However,in other periods(especially 90-120 d),PBZ treatment had no significant effect on the expression level of the relevant genes.It is speculated that the increase of Sus expression and activity under PBZ treatment is earlier and more dramatic,which can promote the rapid and biosynthesis and accumulation of starch and the rapid expansion of storage roots,while the subsequent increase of CWIN and CIN expression and activity can increase the content of soluble sugar in root tubers thus improving the quality of storage roots,and can also provide energy supply for starch biosynthesis and storage root expansion.The specific members of Sus,CWIN and CIN genes induced by PBZ had also been identified.Notably,the effects of PBZ on the yield and quality of storage roots,and activities and gene expression levels of sucros-degarding enzymes in storage roots mainly occurred in the short period after PBZ treatment.With the extension of time,the effects of PBZ on the above indicators gradually disappeared.Therefore,in order to improve the yield of sweetpotato in production,it is necessary to conduct PBZ treatment throughout the entire growth period of sweetpotato.The above results can provide a theoretical basis for achieving high-quality and high-yield sweetpotato production by variety breeding or cultivation measures.