钙参与柑橘果皮细胞壁修饰及影响果皮陷痕的研究

Citrus pericarp physiological disease, such as internal crack in mesocarp and invagination in epicarp, are very common in agricultural production. It may affect the appearance and storage property of fruit, even cause heavy cracking and lead to serious economic loss. Especially in high-value citrus cultivars such as 'Navel Orange' and 'Shatangju' , the incidence of creasing fruit could rearch 15% ~ 40%. Our previous studies have shown that mineral elements could influence pericarp cell wall ultrastructure, composition and metabolic enzyme activity. By analyzing the correlation of mineral elements and pitting fruit incidence, it indicated that Ca could affect pericarp cell wall modification, and be closely related to the occurrence of pitting fruit. Therefore, this project would research the Ca2+ messenger systems that are involved in pericarp cell wall substances metabolism, study cell wall ultrastructure observations on pericarp and the changes of Ca2+ level, explore the pericarp hardness properties and cell wall modification process under the effect of Ca2+, reveal the role of PME and pectins in creasing, reveal he Ca2+ role and action site , and develop an agricultural management that decreases incidence of pitting fruit to lower than 30%.

柑橘果皮生理病害（中果皮内裂、外表皮内陷）是生产中常见的问题，轻者影响果实外观品质和贮藏性能，重者造成裂果及严重的经济损失；特别是商品价值比较高的柑橘品种如脐橙、砂糖橘等陷痕果率都在15％～40％。我们研究发现矿质元素影响果皮细胞壁超微结构、组分及其代谢酶活性，并分析了矿质元素含量的差异与陷痕果发生的相关性，初步明确了Ca影响果皮细胞壁的修饰，并与陷痕果发生密切相关。因而，本项目将研究Ca2+信使系统参与果皮细胞壁物质的相关代谢，观察果皮细胞壁超微结构（包括金属-果胶结构）及其Ca2+的变化水平，探索Ca2+对果皮力学性能的影响，揭示果胶甲酯酶PME及其调控的不同甲酯化程度果胶在柑橘果皮内陷过程中的作用机理，明确Ca2+信使系统参与果皮细胞壁修饰的过程，揭示Ca2+在柑橘陷痕果发生过程的中的作用位点及功能，制定减少柑橘陷痕果发生率的农业栽培技术措施，使陷痕果发生率降低30％以上。

生产上柑橘常发生陷痕果及裂果，特别是品质优良的品种脐橙和红江橙等陷痕果及裂果率高达13-40%，造成重大经济损失。我们在以前研究的基础上，在果实膨大期，对高陷痕果率的品种进行钙调素Ca2+促控剂（细胞外Ca2+螯合剂EGTA、Ca2+竞争性抑制剂La3+）处理，然后观察了果皮超显微结构的改变，测定了相关酶活性及基因表达量的变化。RNA-Seq数据分析表明，注释到与细胞壁合成相关基因的差异表达基因共12个，UDP-葡萄糖醛酸异构酶3个，纤维素合成酶13个；与细胞壁降解相关的果胶酯酶差异表达基因共28个，多聚半乳糖醛酸酶12个，果胶裂解酶7个，纤维素酶9个，半乳糖苷酶14个，木葡聚糖内转糖苷酶/水解酶11个，扩展蛋白11个。喷施0.5% Ca(NO3)2处理增加了果皮Ca含量，降低了果皮细胞壁代谢酶（PG、PE和Cx）的活性，减少代谢酶基因（PG、Cx和PE）的表达量，而喷施钙的抑制剂（EGTA和LaCl3）则增加了PG、PE和Cx的活性，结果表明Ca2+参与到了果皮细胞壁的代谢过程，喷施0.5% Ca(NO3)2可以显著降低陷痕果的发生率。因此，为了提高‘红江橙’果实品质和贮藏性能，我们制定了相应的柑橘防控裂果技术措施，目前该技术在广东省廉江市推广了3000亩，已经取得明显的经济效益。.本项目培养培养了博士1人，硕士5人；在国内外学术刊物发表论文8篇，其中SCI收录论文4篇。在广东省惠州、阳江、云浮、韶关等市举办柑橘丰产优质栽培技术培训6场，印发柑橘栽培技术资料500份。