日灼对石榴果皮蜡质结构和组分的影响

Effects of sunburn on the structure and component changes in pomegranate cuticular wax

【目的】探明日灼对石榴果皮蜡质结构及其组分的影响,明晰石榴果皮蜡质响应日灼胁迫的生理机制。【方法】以日灼易感品种红玉石籽为材料,采用扫描电镜观察受不同程度日灼影响的果实表面蜡质结构;采用气相色谱-质谱联用技术(GC-MS)测定果实表面蜡质组分及含量。【结果】日灼引起石榴果皮蜡质结构的改变,根据日灼程度不同表现出蜡质层不平整、起砂或片状脱落等现象;石榴果皮中共检测出67种蜡质成分,主要包括超长链脂肪族化合物(26.36μg·cm^(-2),占总量的74.95%)和萜类化合物(8.81μg·cm^(-2),占总量的25.05%),超长链脂肪族化合物主要由烷烃、脂肪酸、烯烃、醇类和酯类物质组成。日灼显著提高了石榴果皮蜡质总量,尤其提高了酯类和醇类含量,但显著降低了萜类物质的含量,并且影响各个蜡质组分的含量。【结论】日灼改变石榴果皮蜡质的结构和组分,石榴果皮通过提高蜡质含量尤其是酯类和醇类含量来响应日灼胁迫。

【Objective】Cuticular wax acts as a protective barrier that covers the surface cells of leaves,stems,flowers,and fruits,playing a crucial role in resisting heat and UV radiation damage.Pomegranate fruits sensitive to sunburn can easily suffer from sunburn when exposed to intense sunlight and high temperatures from July to September.This study investigated the effects of sunburn on the structure and components of cuticular wax in the Hongyushizi pomegranate variety,known for its susceptibility to sunburn.The aim of this research is to elucidate the physiological mechanisms underlying the response of cuticular wax to sunburn and to establish a theoretical framework for breeding sunburn-resistant pomegranate varieties.【Methods】The sunburn-susceptible variety Hongyushizi was used as the material to study the wax structure of fruits at different sunburn degrees using scanning electron microscopy.The wax content was determined using gas chromatography-mass spectrometry(GC-MS).【Results】(1)Scanning electron microscopy revealed sunburn caused changes in the wax structure in pomegranate fruit,leading to irregular wax layer,sanding,or flaking depending on the degree of sunburn.(2)A total of 67 wax compounds were detected,mainly including very-long-chain aliphatics(26.36μg·cm^(-2),accounting for 74.95%of the total)and terpenoid(8.81μg·cm^(-2),accounting for 25.05%of the total).The very-long-chain aliphatics were mainly composed of alkanes(19.70μg·cm^(-2)),fatty acids(2.49μg·cm^(-2)),olefin(0.19μg·cm^(-2)),alcohols(3.78μg·cm^(-2)),and esters(0.20μg·cm^(-2)).Sunburn significantly increased the total wax content(by 6.96%),especially increasing the contents of esters(by 82.78%)and alcohols(by 64.71%).However,it decreased the content of terpenoid by 27.48%compared to the control.(3)A total of 7 terpenoid compounds were detected in the pomegranate pericarp,namely ursolic acid,α-tocopherol,β-sitosterol,β-amyrin,ginkgolide,β-tocopherol and betulin.The total amount of terpenoid in the healthy Hongyushizi pomegranate pericarp was 8.81μg·cm^(-2),with ursolic acid being the most abundant at 8.66μg·cm^(-2)(98.30%of the total).Sunburn significantly reduced the total amount of terpenoids,which was 6.39μg·cm^(-2)in the sunburned Hongyushizi pericarp(SB2)being a decrease of 26.21%compared to the healthy fruit.The content of ursolic acid was significantly reduced(by 29.00%)in the sunburned pericarp.However,sunburn increased the content ofα-tocopherol,β-sitosterol,β-amyrin,ginkgolide,β-tocopherol,and betulin,but the differences were not significant.(4)A total of 20 alkanes compounds were detected in the Hongyushizi fruit pericarp.The healthy pericarp had a total amount of 19.70μg·cm^(-2),including C29(7.32μg·cm^(-2)),C31(6.70μg·cm^(-2))and C40(4.24μg·cm2),which accounted for 92.69%of the total alkanes.Sunburn increased the alkanes content to 22.53μg·cm^(-2).Additionally,12 alcohol compounds were detected in Hongyushizi fruit pericarp,primarily C30,which accounted for 81.04%of the total alcohol compounds.Sunburn significantly increased the alcohol compound content from 3.78μg·cm^(-2)to 6.34μg·cm^(-2),with the C30 content increasing by 49.15%.The fruit pericarp also contained 11 fatty acids,mainly C16 and C18,which accounted for 50.22%and 42.79%of the total fatty acid content,respectively.The content of fatty acids in healthy fruit was 2.49μg·cm^(-2),and decreased to 2.13μg·cm^(-2)under sunburn stress.Furthermore,14 lipid compounds were detected,mainly C19,C34,C22,C10,and C12,which accounted for 30.36%,11.33%,10.11%,9.64%,and 8.89%of the total lipid content,respectively.Sunburn increased the lipid content from 0.20μg·cm^(-2)to 0.37μg·cm^(-2).Lastly,3 olefin compounds with C17 having the highest content of lipid(0.18μg·cm^(-2)),constituting 95.03%of the total olefins.Sunburn decreased the lipid content,particularly C17(by 19.20%),while significantly increased the content of C30.【Conclusion】The cuticular wax of pomegranate pericarp contains alkanes,terpenoids,fatty acids,olefins,alcohols,and lipids,with alkanes and terpenoids being the main compounds.Sunburn results in changes in the structure and total amount of wax in the pomegranate pericarp,with a significant increase in the content of lipids and alcohols,but a significant decrease in the content of terpenoids.Pomegranate pericarps can respond to sunburn stress by altering the wax structure and the contents of its components.The research provides a theoretical basis for further understanding the mechanism of the response of the cuticular wax to sunburn stress.