Gibberellin reactivates and maintains ovary-wall cell division causing fruit set in parthenocarpic Citrus species.
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.
Instituto Agroforestal Mediterráneo, Universitat Politècnica de València, Spain.
Carlos
C
Mesejo
Dipartimento Scienze Agrarie e Forestali, Università degli Studi di Palermo, Italy.
Roberto
R
Yuste
Instituto Agroforestal Mediterráneo, Universitat Politècnica de València, Spain.
Carmina
C
Reig
Instituto Agroforestal Mediterráneo, Universitat Politècnica de València, Spain.
Amparo
A
Martínez-Fuentes
Centro de Citricultura y Producción Vegetal, Instituto Valenciano de Investigaciones Agrarias, Spain.
Domingo J
DJ
Iglesias
Dipartimento Scienze Agrarie e Forestali, Università degli Studi di Palermo, Italy.
Natalia
N
Muñoz-Fambuena
Centro de Citricultura y Producción Vegetal, Instituto Valenciano de Investigaciones Agrarias, Spain.
Almudena
A
Bermejo
Dipartimento Scienze Agrarie e Forestali, Università degli Studi di Palermo, Italy.
M Antonietta
MA
Germanà
Centro de Citricultura y Producción Vegetal, Instituto Valenciano de Investigaciones Agrarias, Spain.
Eduardo
E
Primo-Millo
Instituto Agroforestal Mediterráneo, Universitat Politècnica de València, Spain. Electronic address: magusti@prv.upv.es.
Manuel
M
Agustí
D002455:Cell Division; D002473:Cell Wall / Q000378:metabolism; D002957:Citrus / Q000235:genetics / Q000254:growth & development / Q000502:physiology* / Q000648:ultrastructure; D035264:Flowers / Q000235:genetics / Q000254:growth & development / Q000502:physiology / Q000648:ultrastructure; D005638:Fruit / Q000235:genetics / Q000254:growth & development / Q000502:physiology* / Q000648:ultrastructure; D018506:Gene Expression Regulation, Plant; D005875:Gibberellins / Q000378:metabolism*; D008855:Microscopy, Electron, Scanning; D010802:Phylogeny; D010937:Plant Growth Regulators / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D015854:Up-Regulation
D005875:Gibberellins; D010937:Plant Growth Regulators
Citrus; Flower; Fruit set; Fruit tree; Gibberellins; Parthenocarpy