不同果实发育时段遮光对红阳猕猴桃果实香气的影响

Effects of shading on the aroma component of fruits at different develop-mental periods in Hongyang kiwifruit

[目的]探究遮光对猕猴桃发育期间果实香气的影响,为猕猴桃精细栽培管理提供参考。[方法]以猕猴桃红阳为试验材料,从花后20~140 d,以20 d为一个时段将其分为6个时段(时段Ⅰ~时段Ⅵ),每个时段为一组使用套袋进行遮光处理(T1~T6组),T7为全时段遮光,对照(CK)为全时段未遮光。采用顶空固相萃取(HS-SPME)和气相色谱-质谱联用(GC-MS)测定香气,并对T7和对照果实进行转录组测序分析。[结果]在不同遮光处理下,共检测出38种香气物质,包括15种酯类、11种醛类、8种萜烯类和3种醇类。各组香气种类介于19~37种之间,其中T6种类最多,T2和T5最少。总香气含量T4最高,其次为T2和T5。除T4处理外,其他试验组果实酯类含量均显著降低;T4、T5和T6处理组醛类含量与对照无显著差异,其他处理组显著低于对照;T1和T2处理组萜烯类含量与对照无显著差异,T4处理组无累积,其他处理组显著高于对照。醇类物质含量在T6处理果实中显著高于对照,T2和T5处理组无累积,其他处理组低于对照。聚类分析显示,T4处理与对照成分组成最相似。主成分分析显示,T6处理组综合得分最高,其次为T4、T5和T2。转录组分析共发现1248个差异表达基因,T7较对照下调基因788个,上调基因460个。筛选出了15个与香气合成相关的差异表达基因,其中遮光处理降低了T7果实中乙醇脱氢酶(ADH)、丙酮酸转氨酶(AGXT)、天冬氨酸转氨酶(COT1)和糖醇-4-磷酸胞苷酰转移酶(IspD)基因的表达量,升高了焦磷酸脱羧酶(MDV)、醛脱氢酶(ALDH)和苯丙氨酸解氨酶(PAL)基因的表达量。[结论]红阳猕猴桃的各类香气成分具有不同的合成时期,其中时段Ⅵ为酯类合成重要时期;时段Ⅰ-时段Ⅲ对醛类物质合成积累有重要意义;时段Ⅳ为萜烯类物质合成关键时期。遮光抑制了ADH、AGXT和COT1基因的表达,同时上调了MVD和ALDH基因的表达量,是导致遮光果实中萜烯类香气物质含量升高和酯类、醛类、醇类含量下降的可能因素。综合分析表明,T2、T4和T5处理的猕猴桃果实香气含量较高,受遮光影响较小,即时段Ⅱ(40~60DAA)、时段Ⅳ(80~100DAA)和时段Ⅴ(100~120DAA)为适宜遮光时段。结合前人研究,建议从时段Ⅱ到时段Ⅴ(40~120DAA)进行果实遮光,时段Ⅵ去除套袋使果实正常接收光照。研究结果可以为猕猴桃精细管理提供参考。

【Objective】Aroma is an important trait of fruit quality,constituted by a variety of com-pounds including esters,aldehydes,ketones,alcohols,terpenes and volatile phenols,as well as a range of other aromatics.The compound and content of aroma undergo consistent changes throughout fruit de-velopment,and can be affected by various environmental factors.It has been demonstrated that sun-light,as a crucial factor influencing fruit development,has a significant effect on the content and com-position of aroma.Bagging is widely practiced in fruit cultivation.The fruit with bagging tends to exhib-it a superior external appearance and neater shapes compared to non-bagged,which makes them more popular by consumers.However,the practice of bagging limits the fruit’s exposure to sunlight,which in turn affects the formation of fruit aroma.In this study,the effects of shading on fruit aroma types and content at different developmental periods were determined to explore the significance of each period in aroma compounds synthesis,and identify the optimal timing for bagging.Furthermore,a transcriptome analysis was employed to explore the molecular mechanisms underlying the impact of shading on aro-ma synthesis.The findings of this study will serve as a valuable reference for the refined cultivation of kiwifruit.【Methods】The experimental design spanned from 20 days after anthesis(20 DAA)to 140 DAA,dividing the maturation process into six periods(periodsⅠtoⅥ)with 20-day intervals.Each pe-riod underwent light exclusion using double-layer black bags(Groups T1 to T6),with T7 representing total shading and CK representing no shading.The fruits were harvested when the soluble solids con-tent reached 7%and allowed to ripen at room temperature until the soluble solids content reached 20%.Aroma compounds were then analyzed by headspace solid-phase microextraction(HS-SPME)and gas chromatography-mass spectrometry(GC-MS).Data were processed and analyzed using Excel 2016 and SPSS 20.0,and graphs were created using Origin 2021.Samples from T7 and CK fruits were sent for transcriptome sequencing and KEGG and GO enrichment analysis of DEGs were conducted using the company's platform.【Results】A total of 38 aroma compounds were detected in Hongyang kiwifruits with different treatments,including 15 esters,11 aldehydes,8 terpenes,3 alcohols and a single other compound.The number of aroma compounds in each group ranged from 19 to 37,with T6 exhibiting the highest diversity at 37 types.In contrast,T2 and T5 exhibited the lowest diversity,with both groups containing 19 compounds.The highest total aroma content was observed in T4,followed by T2 and T5 among the groups with shading.The proportions of the major aroma constituents in the Hongyang kiwi-fruit remained largely unchanged by the exclusion of sunlight.Ester compounds consistently accounted for over 90%of the total content in each treatment group,with aldehydes comprising 1%to 7%and ter-penes and alcohols each accounting for less than 2%.The ester content was found to be significantly re-duced under shading in all groups with the exception of T4,which exhibited the highest ester content,followed by T2 and T5.The aldehyde content of T4,T5 and T6 exhibited no significant difference com-pared to CK,whereas the other groups displayed a significantly lower content than CK.The terpene lev-els in T1 and T2 were not significantly different from CK,which exhibited no accumulation in the fruit of T4.In contrast,the other treatment groups displayed significantly higher terpene levels than CK.Fur-thermore,all groups except T4,which was bagged,showed an increase in terpene compound diversity,with the highest variety found in T7,followed by T6.The only treatment group in that the alcohol con-tent was significantly higher than CK was T6.No accumulation of alcohol was observed in T2 and T5,while all other treatment groups exhibited lower alcohol levels compared to CK.The results of the clus-ter analysis indicated that the aroma composition of T4 was most similar to that of CK.T2 and T5 were grouped together,while T1 and T3 were placed in a separate cluster.T6 and T7 were classified into their own distinct categories.The principal component analysis demonstrated that T6 exhibited the high-est overall score,followed by T4,T2 and T5.Transcriptome analysis identified 1,248 differentially ex-pressed genes,with 788 downregulated and 460 upregulated ones in T7 compared to CK.15 genes relat-ed to aroma synthesis were selected,with shading resulting in reduced expression of ethanol dehydroge-nases(ADH),alanine aminotransferase(AGXT),and aspartate aminotransferase(GOT)genes in T7 fruit,while increasing the expression of pyrophosphate decarboxylase(MDV),and aldehyde dehydroge-nases(ALDH).【Conclusion】The impact of shading in different developmental periods resulted in vary-ing degrees of aroma content and compound constitution,indicating that the synthesis of various aroma components in Hongyang kiwifruit occurred at disparate optimal periods.The results demonstrated that periodⅥwas a critical period for ester synthesis;periodsⅠtoⅢwere significant for the accumula-tion of aldehydes;and periodⅣwas crucial for terpene synthesis.Comprehensive analysis showed that kiwifruits from T4,T5 and T2 had higher aroma content and demonstrated reduced sensitivity to shad-ing,showing superior aroma quality.Shading suppressed the expression of ADH,AGXT and COT1 genes while increased the expression levels of MVD and ALDH genes,which may account for the in-creased content of terpene aroma compounds and the decreased levels of ester,aldehyde and alcohol compounds in shading fruit.Thus,periodⅡ(40-60 DAA)and periodsⅣtoⅤ(80-120 DAA)were identified as suitable periods for bagging.Combined with previous research,it was recommended to be-gin bagging kiwifruits in the late portion of periodⅠand continue from periodⅡto periodⅤ(40-120 DAA).The bagging process should be discontinued upon the completion of periodⅤto permit the fruits to receive sunlight in a natural manner.These results can serve as a valuable reference for the pre-cise management of kiwifruit cultivation.