Mesejo Carlos, Yuste Roberto, Reig Carmina, Martínez-Fuentes Amparo, Iglesias Domingo J, Muñoz-Fambuena Natalia, Bermejo Almudena, Germanà M Antonietta, Primo-Millo Eduardo, Agustí Manuel
Instituto Agroforestal Mediterráneo, Universitat Politècnica de València, Spain.
Dipartimento Scienze Agrarie e Forestali, Università degli Studi di Palermo, Italy.
Plant Sci. 2016 Jun;247:13-24. doi: 10.1016/j.plantsci.2016.02.018. Epub 2016 Feb 27.
Citrus is a wide genus in which most of the cultivated species and cultivars are natural parthenocarpic mutants or hybrids (i.e. orange, mandarin, tangerine, grapefruit). The autonomous increase in GA1 ovary concentration during anthesis was suggested as being the stimulus responsible for parthenocarpy in Citrus regardless of the species. To determine the exact GA-role in parthenocarpic fruit set, the following hypothesis was tested: GA triggers and maintains cell division in ovary walls causing fruit set. Obligate and facultative parthenocarpic Citrus species were used as a model system because obligate parthenocarpic Citrus sp (i.e. Citrus unshiu) have higher GA levels and better natural parthenocarpic fruit set compared to other facultative parthenocarpic Citrus (i.e. Citrus clementina). The autonomous activation of GA synthesis in C. unshiu ovary preceded cell division and CYCA1.1 up-regulation (a G2-stage cell cycle regulator) at anthesis setting a high proportion of fruits, whereas C. clementina lacked this GA-biosynthesis and CYCA1.1 up-regulation failing in fruit set. In situ hybridization experiments revealed a tissue-specific expression of GA20ox2 only in the dividing tissues of the pericarp. Furthermore, CYCA1.1 expression correlated endogenous GA1 content with GA3 treatment, which stimulated cell division and ovary growth, mostly in C. clementina. Instead, paclobutrazol (GA biosynthesis inhibitor) negated cell division and reduced fruit set. Results suggest that in parthenocarpic citrus the specific GA synthesis in the ovary walls at anthesis triggers cell division and, thus, the necessary ovary growth rate to set fruit.
柑橘属是一个广泛的属，其中大多数栽培种和品种都是天然单性结实突变体或杂种（如橙子、橘子、蜜柑、葡萄柚）。花期子房内赤霉素1（GA1）浓度的自主增加被认为是柑橘属单性结实的刺激因素，无论其种类如何。为了确定GA在单性结实坐果中的具体作用，对以下假设进行了测试：GA触发并维持子房壁中的细胞分裂，从而导致坐果。专性和兼性单性结实的柑橘种类被用作模型系统，因为与其他兼性单性结实的柑橘（如克莱门氏小柑橘）相比，专性单性结实的柑橘种（如温州蜜柑）具有更高的GA水平和更好的天然单性结实坐果率。温州蜜柑子房内GA合成的自主激活先于细胞分裂和CYCA1.1上调（一种G2期细胞周期调节因子），在花期形成了高比例的果实，而克莱门氏小柑橘缺乏这种GA生物合成和CYCA1.1上调，导致坐果失败。原位杂交实验表明，GA20ox2仅在果皮的分裂组织中具有组织特异性表达。此外，CYCA1.1表达将内源GA1含量与GA3处理相关联，GA3处理主要在克莱门氏小柑橘中刺激细胞分裂和子房生长。相反，多效唑（GA生物合成抑制剂）抑制细胞分裂并降低坐果率。结果表明，在单性结实的柑橘中，花期子房壁中特定的GA合成触发细胞分裂，从而产生坐果所需的子房生长速率。
