Pollen Tube Pathway and Stimulation of Embryo Sac Development inPistacia vera(Anacardiaceae)

Abstract

Abstract Pistil anatomy of thePistacia veracultivars Kerman and Sirora was studied in relation to the pathway of pollen tube growth using fluorescence, bright field and scanning electron microscopy. The pistil comprised a three-lobed stigma, a short style and a unilocular ovary containing a single ovule with a large funicle. The ovule was crassinucellate and anatropous, with the mid-point of the funicle directly below the base of the style. The transmitting tissue comprised the stigma, the style, the funicle and the ovary wall. The upper style had three transmitting tracts, which in the lower style joined into a single core of tissue, half of which ended at a protuberance of the ovary wall. The ovary wall protuberance lay opposite a protuberance of the funicle which comprised loose papillate cells connecting with the single core of transmitting tissue in the distal funicle. The other half of the stylar transmitting tract entered the ovary wall, lining up with the suture join of the two smaller stigma lobes. At the base of the ovary the transmitting tissue divided into three tracts which entered the funicle. The three tracts of transmitting tissue in the lower part formed one large tract in the upper funicle. Most pollen tubes grew towards the embryo sac via the stigma and the style, and penetrated the funicle via the ovarian and funicular protuberances and the ovarian cavity at the base of the style. They grew through the distal funicular transmitting tissue and penetrated the nucellus via the chalaza. A minority of pollen tubes grew via the ovary wall transmitting tissue before penetrating the proximal funicular transmitting tissue. Some tubes grew in the space between the inner integument and nucellus, and some stopped growing in the nucellus or integument. Successful tubes entered the embryo sac via the egg apparatus. At anthesis unpollinated embryo sacs were immature and comprised a megaspore mother cell, a tetrad or a one cell embryo sac. Following anthesis unpollinated embryo sacs developed slowly and a maximum of 50% reached maturity by 4 d after anthesis. In contrast all embryo sacs of pollinated pistils were mature by 1 or 2 d after pollination. In the cultivar Kerman approx. 25% of embryo sacs were penetrated and fertilized at the second day after pollination compared to 43% fertilization of Sirora at 3 d. Up to 60% of pistils had no pollen tube, and up to 50% of unpollinated and 29% of pollinated pistils had no embryo sac.