Department of Environmental Biology, 'Sapienza' University of Rome, Rome, Italy.
Ann Bot. 2013 Oct;112(6):1045-55. doi: 10.1093/aob/mct173. Epub 2013 Aug 21.
Dioecism characterizes many crop species of economic value, including kiwifruit (Actinidia deliciosa). Kiwifruit male sterility occurs at the microspore stage. The cell walls of the microspores and the pollen of the male-sterile and male-fertile flowers, respectively, differ in glucose and galactose levels. In numerous plants, pollen formation involves normal functioning and degeneration timing of the tapetum, with calcium and carbohydrates provided by the tapetum essential for male fertility. The aim of this study was to determine whether the anther wall controls male fertility in kiwifruit, providing calcium and carbohydrates to the microspores.
The events occurring in the anther wall and microspores of male-fertile and male-sterile anthers were investigated by analyses of light microscopy, epifluorescence, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL assay) and transmission electron microscopy coupled with electron spectroscopy. The possibility that male sterility was related to anther tissue malfunctioning with regard to calcium/glucose/galactose provision to the microspores was also investigated by in vitro anther culture.
Both tapetum and the middle layer showed secretory activity and both degenerated by programmed cell death (PCD), but PCD was later in male-sterile than in male-fertile anthers. Calcium accumulated in cell walls of the middle layer and tapetum and in the exine of microspores and pollen, reaching higher levels in anther wall tissues and dead microspores of male-sterile anthers. A specific supply of glucose and calcium induced normal pollen formation in in vitro-cultured anthers of the male-sterile genotype.
The results show that male sterility in kiwifruit is induced by anther wall tissues through prolonged secretory activity caused by a delay in PCD, in the middle layer in particular. In vitro culture results support the sporophytic control of male fertility in kiwifruit and open the way to applications to overcome dioecism and optimize kiwifruit production.
雌雄异株是许多具有经济价值的作物物种的特征，包括猕猴桃（Actinidia deliciosa）。猕猴桃雄性不育发生在小孢子阶段。小孢子和花粉的细胞壁在葡萄糖和半乳糖水平上存在差异，分别来自雄性可育和雄性不育花朵的小孢子和花粉。在许多植物中，花粉的形成涉及绒毡层的正常功能和退化时间，绒毡层提供的钙和碳水化合物对雄性育性至关重要。本研究旨在确定花粉壁是否控制猕猴桃雄性育性，为小孢子提供钙和碳水化合物。
通过对光镜、荧光、末端脱氧核苷酸转移酶介导的 dUTP 缺口末端标记（TUNEL 测定）和透射电子显微镜结合电子能谱的分析，研究了雄性可育和雄性不育花药中花药壁和小孢子的发生事件。还通过离体花药培养研究了雄性不育是否与花药组织功能障碍有关，即向小孢子提供钙/葡萄糖/半乳糖的能力。
绒毡层和中层均表现出分泌活性，均通过程序性细胞死亡（PCD）退化，但在雄性不育花药中比在雄性可育花药中更晚。钙积累在中层和绒毡层的细胞壁以及小孢子和花粉的外壁中，在雄性不育花药的花药壁组织和死亡小孢子中达到更高水平。离体培养的雄性不育基因型的花药中，葡萄糖和钙的特定供应诱导了正常花粉的形成。
研究结果表明，猕猴桃雄性不育是由花药壁组织通过延长 PCD 引起的分泌活性引起的，尤其是中层。离体培养结果支持猕猴桃花粉育性的孢子体控制，并为克服雌雄异株和优化猕猴桃生产开辟了应用途径。
