钾水平对富士苹果果实膨大期13C同化物向果实转运的影响

以6年生‘烟富3’/M26/平邑甜茶为试材,采用¹³C同位素标记技术,在果实膨大期用不同浓度钾素水溶液(K₂O浓度分别为0、0.5%、1.0%、1.5%、2.0%,分别用CK、K₁、K₂、K₃、K₄表示)涂抹果实周围20 cm范围内叶片,研究其对叶片叶绿素荧光参数、光合性能、糖转运蛋白基因表达、¹³C同化能力及¹³C同化物向果实转运的影响。结果表明: 与其他处理相比,K₃处理显著提高了叶片Rubisco酶活性、净光合速率、PSII原初光能转化效率、PSII实际光化学效率、光化学淬灭系数、山梨醇和蔗糖含量、6-磷酸山梨醇脱氢酶(S6PDH)和蔗糖磷酸合酶(SPS)活性及¹³C同化能力;提高了果柄组织山梨醇转运蛋白基因MdSOT1、MdSOT2和蔗糖转运蛋白基因MdSUT4的表达,促进了糖在果实中的卸载。¹³C自留量(自身叶片+自身新梢)以CK最高,为82.6%,K₃处理最低,为60.5%。果实¹³C吸收量随钾素浓度增加呈先升后降趋势,以K₃处理最高(1.31 mg·g^-1),CK最低(0.57 mg·g^-1)。表明叶施钾素水溶液不同程度提高了叶片PSII光化学效率和碳同化关键酶活性,进一步提高了叶片同化物的合成能力和向外输送能力,促进了糖向果实的定向转运。同化物向果实转运数量以1.5% K₂O涂抹叶片处理(K₃)最多。

Effects of potassium levels on translocation of 13C-photoassimilates to fruit in ‘Fuji’ apple during fruit expanding period

A field experiment was carried out in a six-year old ‘Fuji’3/M26/Malus hupehensis Rehd. apple with the ¹³C tracer method to examine the changes of chlorophyll fluorescence parameters, photosynthetic characteristics of leaf, sugar transporter gene expression, ¹³C assimilation capability and the characteristics of translocation and distribution of ¹³C-photoassimilates to fruit under different levels of potassium addition (K₂O 0, 0.5%, 1.0%, 1.5%, 2.0%, expressed by CK, K₁, K₂, K₃, K₄, respectively). Potassium aqueous solution smear the leaves within 20 cm around the fruit at fruit enlargement stage. Compared with other treatments, K₃ treatment significantly increased Rubisco enzyme activity, net photosynthetic rate, maximal photochemical efficiency of PSII, actual photochemical efficiency of PSII, coefficient of photochemical quenching, sorbitol and sucrose content, sorbitol 6-phosphate dehydrogenase (S6PDH) and sucrose phosphate synthase (SPS) enzyme activities and ¹³C assimilation capability of leaves. Furthermore, K₃ treatment increased gene expression of sorbitol transporter MdSOT1 and MdSOT2 and sucrose transporter MdSUT4, and promoted the unloading of sugar in fruit. The ¹³C of self retention (self leaves and self branches) was the highest in CK (82.6%) and the lowest in K₃ treatment (60.5%). With increasing potassium concentration, the ¹³C absorption of fruit first increased and then decreased, which was the highest in K₃ treatment (1.31 mg·g^-1) and the lowest in CK (0.57 mg·g^-1). Our results indicated that foliage application of potassium solution improved PSII photochemical efficiency, activities of key enzymes related with carbon assimilation, synthesis ability, and outward transport ability of photosynthates in leaves, and consequently promoted the directional transportation of sugar to fruit. The amount of photoassimilates transported to fruit was the most under 1.5% K₂O treatment (K₃).