温州蜜柑与椪柑果实日灼发生差异及机制

doi:10.16420/j.issn.0513-353x.2023-0513

摘要/Abstract

摘要：

日灼是柑橘生产中常见的生理障碍，但其形成机制不清晰。2021年在湖北省当阳市半月镇凤凰山，以温州蜜柑和椪柑果实为试材，通过日灼果皮受伤程度对比、细胞形态学观察以及抗氧化物质含量和基因表达量差异等多角度综合比较二者的日灼差异并分析可能机制。结果表明，温州蜜柑（日灼发生率43.12%）比椪柑（22.52%）更易遭受日灼伤害；日灼对于温州蜜柑果皮细胞紧密度造成严重影响的同时还造成木质素的积累，并积累更多的活性氧。聚甲氧基黄酮途径中的代谢物川皮苷在椪柑日灼伤害过程中显著富集。类黄酮代谢中关键酶基因CrCHS2、CrCHI和CrFNS以及聚甲氧基黄酮合成关键基因CrOMT2在椪柑日灼果皮中均显著上调，并且表达水平显著高于相同日灼等级的温州蜜柑。上述结果表明，温州蜜柑和椪柑果实产生日灼差异的主要原因是椪柑含有更多抗氧化物质，能够更有效地减少活性氧积累，从而减弱日灼造成的伤害。

关键词: 柑橘, 日灼, 黄酮, 黄酮醇, 代谢途径, 聚甲氧基黄酮

Abstract:

Sunburn is a common physiological disorder in citrus production，but the underlying mechanism remains largely unknown. The study was carried out at Fenghuang Mountain，Banyue Town，Dangyang City，Hubei Province in 2021. Satsuma mandarin（Citrus unshiu Marc.）and Ponkan（C. reticulata）were used as experimental materials to investigate the difference in sunburn and potential mechanisms by examining peel injury degree，performing cytological observation，measuring antioxidant content and gene expression levels. The results showed that Satsuma mandarin was more susceptible to sunburn than Ponkan. Significant difference in the incidence rates of sunburn was observed between the two varieties，43.12% for Satsuma mandarin and 22.52% for Ponkan. Sunburn seriously influenced the compactness of pericarp cells and resulted in the accumulation of lignin. Satsuma mandarin fruits were found to accumulate greater level of reactive oxygen species（ROS）. In addition，nobiletin，a critical metabolite in the polymethoxyflavone metabolic pathway，was significantly enriched in Ponkan fruit peel. Consistently，transcript levels of CrCHS2，CrCHI and CrFNS，encoding crucial enzymes involved in biosynthesis of flavonoid，and CrOMT2 in the polymethoxyflavone pathway were significantly induced in the sunburnned Ponkan fruit peel. Taken together，these findings indicate that the main reason for the difference in sunburn between Satsuma mandarin and Ponkan is that the latter contains more antioxidant that can effectively decrease the ROS accumulation，thus leading to mitigation of sunburn-derived damage.

Key words: citrus, sunburn, flavone, flavonol, metabolic pathway, polymethoxyflavone

吴卓群, 陈鹏旭, 陈思怡, 张福琼, 方红, 祝建, 谢宗周, 李春龙, 刘继红. 温州蜜柑与椪柑果实日灼发生差异及机制[J]. 园艺学报, 2024, 51(12): 2743-2757.

WU Zhuoqun, CHEN Pengxu, CHEN Siyi, ZHANG Fuqiong, FANG Hong, ZHU Jian, XIE Zongzhou, LI Chunlong, LIU Jihong. Differences in Occurrence of Fruit Sunburn Between Satsuma Mandarin and Ponkan Tangerine and Possible Mechanisms[J]. Acta Horticulturae Sinica, 2024, 51(12): 2743-2757.

图/表 11

表1 柑橘果实日灼等级划分标准

Table 1 Standard for grading sunburn of citrus

日灼等级 Sunburn grade	日灼特征 Sunburn characteristic
SB-0	正常青色果皮 Normal cyan pericarp
SB-1	微微变淡黄的日灼面积小于1/5，无褐色斑 The peel turned slightly yellowish，the area of sunburn was less than 1/5，and there was no brown part
SB-2	黄色或深黄色日灼面积1/5 ~ 1/3，有褐色斑点 The skin turns yellow/dark yellow with some brown spots in the area where sunburn occurs
SB-3	黄色日灼面积大于1/3，褐色斑点变成褐面 The yellow area of the peel is more than 1/3，and the brown spots become brown

表2 实时定量PCR分析基因表达所用的引物

Table 2 Primers used for gene expression analysis by real time quantitative PCR

引物 Primer	上游引物（5′-3′） Forward primer	下游引物（5′-3′） Reverse primer
Actin	CCGACCGTATGAGCAAGGAAA	TTCCTGTGGACAATGGATGGA
CrCHS2	GTTCCAAATTGTGTCGGGGG	CGGACTAAACGCCTCATCCA
CrCHI	CCGAAAGATGGTGTTGCGGT	CAGAGCTAAGGCGACGATGT
CrFNS	TGTGTTGTTTGTGAACCTTTGGT	TCCAATGGGTTCTTCCAAATTT
CrLAR	GAAAAGCGCAGAGTAAGGCG	CCAATGTCAGTGCCTGCAAC
CrOMT2	ATGGCTGCGAATCGGGAAG	TGAAGTCATCATGGGGCTCAA
CrOMT3	TGCGAATCGGGAAGGTCAG	ATGGATGCTTGTCCGTCAACT

图1 不同时期温州蜜柑与椪柑果实表面温度不同小写字母表示材料间差异显著（P < 0.05）。下同。

Fig. 1 Fruit surface temperature of Satsuma and Ponkan at different periods Different lowercase letters indicate significant differences between varieties of different grades at P < 0.05. The same below.

图2 不同日灼等级（SB-0 ~ SB-3）的温州蜜柑与椪柑果实特征与色泽（a*/b*）

Fig. 2 Fruit characteristics and color（a*/b*）of Satsuma and Ponkan with different sunburn grades（SB-0-SB-3）

图3 不同日灼等级（SB-0 ~ SB-3）的温州蜜柑和椪柑果皮厚度和硬度

Fig. 3 Pericarp thickness and hardness of peel of Satsuma and Ponkan at different grades（SB-0-SB-3）

图4 不同日灼等级（SB-0 ~ SB-3）的温州蜜柑和椪柑果皮显微结构观察

Fig. 4 Microscopic observation of fruit peel from Satsuma and Ponkan with different sunburn grades（SB-0-SB-3）

图5 不同日灼等级（SB-0 ~ SB-3）的温州蜜柑和椪柑果皮扫描电镜观察箭头表示裂缝与塌陷。

Fig. 5 Observation of Satsuma and Ponkan fruit peel with different sunburn grades（SB-0-SB-3）by scanning electronic microscope Arrows indicate cracks and collapses.

图6 不同日灼等级（SB-0 ~ SB-3）的温州蜜柑和椪柑果皮活性氧（绿色荧光）的分布

Fig. 6 Distribution of reactive oxygen species in Satsuma and Ponkan fruit peel with different sunburn grades（SB-0-SB-3）

图7 不同日灼等级（SB-0 ~ SB-3）的温州蜜柑和椪柑果皮抗氧化能力

Fig. 7 Antioxidant ability of Satsuma mandarin and Ponkan fruit peel with different sunburn grades（SB-0-SB-3）

图8 不同日灼等级（SB-0 ~ SB-3）的温州蜜柑和椪柑果皮类黄酮含量

Fig. 8 Flavonoid content in Satsuma mandarin and Ponkan fruit peel with different sunburn grades（SB-0-SB-3）

图9 不同日灼等级（SB-0 ~ SB-3）的温州蜜柑和椪柑果皮聚甲氧基黄酮合成关键基因的表达量

Fig. 9 Expression of key genes for synthesis of polymethoxyflavone in Satsuma mandarin and Ponkan fruit peel of different sunburn grades（SB-0-B-3）

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