Species of the genus Citrus grow in different parts of Fars province. The present study aimed at investigating the ontogeny of Citrus grandis pollen grains and petal secretory sacs. Flowers and blossoms were collected from the gardens located in Jahrome during the flowering period, fixed in FAA and stored in 70% ethanol. Samples were prepared and embedded in paraffin and sectioned using a rotary microtome. To examine petal secretory sacs, petals were placed in a glycerine-alcohol mixture, and sections were prepared for light microscopy using a sterilized razor blade. Results showed anthers with four pollen sacs. Cytokinesis appeared simultaneous, and the microspore tetrads were of a tetrahedral type. Pollen grains at a time of dispersal have two cells, containing four vegetative openings with reticulo-faveolate decorations. In the initial petals, three tissues were detected with tightly packed dividing cells. Throughout petal developmental stages, the rate of epidermal cell division was reduced, while parenchymal tissue differentiation was limited to an increase in cell dimensions, cell wall thickening and the intercellular space. In addition, the number and size of the vascular bundles increased during growth. The formation of petal secretory sacs is limited to the first stage of its development, while later in the development, this structure only increased in dimensions.  In conclusion, based on our histological examinations, Citrus grandispetal secretory sacs change in a five stage process

Keywords: microsporogenesis, secretory sac development, Rutaceae

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