The normal type of embryo sac development has been studied in Polygonum by Strasburger. One of which gives rise to the embryo sac. In the monosporic, or Polygonum-type embryo sac, meiosis of the diploid megaspore mother cell in the nucellus produces four haploid megaspores. Assertion : 7-celled, 8 nucleate and monosporic embryosac is called polygonum type of embryo sac
Reason : It was discovered by Hofmesister for the first time in polygonum. Since this embryo sac develops from one megaspore, that is why this is monosporic embryo sac. Its cells are polyploid (triploid or pentaploid, depending on the embryo sac type). Its nucleus divides. The embryo sac is formed from the chalazal megaspore in the tetrad and is eight-nucleate. An eight nucleated and seven celled embryo sac formed from a single megaspore is called polygonum type. pblygonum- Approx- imately 70% of the species examined, including Arabidopsis and maize, have this form of embryo sac (Russell, 1978; Mansfield et ai., 1990; Webb and Gunning, 1990). Therefore, the resulting embryo sac is a seven-celled structure consisting of one central cell, one egg cell, two synergid cells, and three antipodal cells. Therefore, it is also called as Polygonum type. Strasburger was the first to study such embryo sac. embryo sac can be "easily", if at all possible, be concluded from Polygonum-type embryo sac. A large vacuole is formed between the nuclei. Thus the daughter nuclei move to the micropylar and chalazal poles of the embryo sac. The development of the embryo sac begins with elongation of the functional megaspore. Based on the number of megaspores, embryo sacs can be divided into three types: monosporic, bisporic, and tetrasporic (Web Figure 21.3.A). Other articles where Polygonum type is discussed: angiosperm: Ovules: …megasporogenesis and megagametogenesis, called the Polygonum type, occurs in 70 percent of the angiosperms in which the life cycle has been charted. The functional megaspore enlarges. Initially, the megaspore cytoplasm is non-vacuolated but later small vacuoles appear which fuse to form a large vacuole. Best Answer. In this type the nucleus of functional megaspore divides to form two nuclei and moves apart: one towards the micropylar end and the other towards the chalazal end. Nucleus of functional megaspore divides by three mitotic divisions to form 8 nuclei, out of which Polygonum Type - Monosporic Embryo Sacs. The embryo is small (usually less than one quarter of seed volume), axile (radially sectioned), linear (longer than broad) or rarely rudimentary (tiny relative to endosperm) depending on placentation type, and straight, bent, curved or curled at the upper end. [2] [3] The bisporic and tetrasporic patterns undergo varying processes and result in varying embryo sacs as well. Development of the Polygonum-Type Embryo Sac The Polygonum-type pattern illustrated in Figure 2 is the most commonly observed form of embryo sac development. (a) Polygonum type – Polygonum type is the normal type of development of embryo sac. 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