Aims To determine whether xylem sap and leaf cytokinin levels were associated with live root length density (LRLD) and leaf senescence, these variables were measured in intact (control) plants and those from which florets were removed, in hybrids of contrasting post-anthesis senescence patterns. Methods Field experiments were carried out during two consecutive seasons using sunflower hybrids (Paraiso75, stay-green [SG]; and Paraiso65, fast dry down [FDD]) of contrasting canopy senescence patterns. Crop carbon partitioning was altered by removing all florets (-F treatment) before anthesis. At crop level, the dynamics of LRLD, xylem sap flow rate, cytokinins in the xylem sap, and green leaf area index (GLAI) were measured, while at leaf level, dynamics of total chlorophyll content, trans-Zeatin content, and net photosynthesis were recorded for leaf positions 17, 20, 22, 24 and 27. Results In both hybrids, the –F treatment had higher LRLD, cytokinins in the xylem sap, and leaf trans-Zeatin concentration at anthesis and during the grain filling period than control plants. All measured variables decreased earlier in the control treatment than the -F treatment (in both hybrids), and in the FDD hybrid than the SG hybrid. Conclusions The dynamics of xylem sap cytokinins were related to the dynamics of LRLD and that of leaf trans-Zeatin levels, contributing to contrasting canopy senescence patterns and underlying the responses to defruiting in both hybrids.

中文翻译：

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开花和灌浆期间对比开花后冠层衰老模式的结果和去果向日葵杂种的木质部汁液和叶子中的细胞分裂素动态

目的 为了确定木质部汁液和叶细胞分裂素水平是否与活根长度密度 (LRLD) 和叶衰老相关，在完整（对照）植物和那些去除了小花的植物中，在对比开花后衰老的杂种中测量了这些变量模式。方法 使用对比树冠衰老模式的向日葵杂交种（Paraiso75，保持绿色 [SG]；和 Paraiso65，快干 [FDD]）在连续两个季节进行田间试验。通过在开花前去除所有小花（-F 处理）来改变作物碳分配。在作物水平上，测量了 LRLD、木质部汁液流速、木质部汁液中的细胞分裂素和绿叶面积指数 (GLAI) 的动态，而在叶子水平上，测量了总叶绿素含量、反式玉米素含量、叶位置 17、20、22、24 和 27 的净光合作用和净光合作用被记录。 结果 在两个杂种中，–F 处理具有更高的 LRLD、木质部汁液中的细胞分裂素以及开花期和灌浆期间的叶片反式玉米素浓度时期比对照植物。所有测量变量在对照处理中比 -F 处理（在两种杂种中）更早下降，在 FDD 杂种中比 SG 杂种更早。结论 木质部汁液细胞分裂素的动态与 LRLD 的动态和叶反式玉米素水平的动态相关，有助于形成对比的冠层衰老模式和两种杂种对脱果的反应。开花期和灌浆期叶片反式玉米素浓度高于对照植株。所有测量变量在对照处理中比 -F 处理（在两种杂种中）更早下降，在 FDD 杂种中比 SG 杂种更早。结论 木质部汁液细胞分裂素的动态与 LRLD 的动态和叶反式玉米素水平的动态相关，有助于形成对比的冠层衰老模式和两种杂种对脱果的反应。开花期和灌浆期叶片反式玉米素浓度高于对照植株。所有测量变量在对照处理中比 -F 处理（在两种杂种中）更早下降，在 FDD 杂种中比 SG 杂种更早。结论 木质部汁液细胞分裂素的动态与 LRLD 的动态和叶反式玉米素水平的动态相关，有助于形成对比的冠层衰老模式和两种杂种对脱果的反应。