Variations found in the remaining 30 percent represent derivations from the Polygonum type of seed development. One of which gives rise to the embryo sac. These two nuclei again divide so that the number of nuclei increases to four. 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. The development of the embryo sac begins with elongation of the functional megaspore. An eight nucleated and seven celled embryo sac formed from a single megaspore is called polygonum type. Initially, the megaspore cytoplasm is non-vacuolated but later small vacuoles appear which fuse to form a large vacuole. pblygonum- 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. Its cells are polyploid (triploid or pentaploid, depending on the embryo sac type). 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. 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. 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. The normal type of embryo sac development has been studied in Polygonum by Strasburger. It develops from chalazal functional megaspore (4th from micropyle). embryo sac can be "easily", if at all possible, be concluded from Polygonum-type embryo sac. Strasburger was the first to study such embryo sac. Its nucleus divides. This embryo sac has four well-defined megaspores. The embryo sac is formed from the chalazal megaspore in the tetrad and is eight-nucleate. The functional megaspore enlarges. Based on the number of megaspores, embryo sacs can be divided into three types: monosporic, bisporic, and tetrasporic (Web Figure 21.3.A). (a) Polygonum type – Polygonum type is the normal type of development of embryo sac. 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). Thus the daughter nuclei move to the micropylar and chalazal poles of 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. Since this embryo sac develops from one megaspore, that is why this is monosporic embryo sac. Polygonum Type - Monosporic Embryo Sacs. A large vacuole is formed between the nuclei. Best Answer. [2] [3] The bisporic and tetrasporic patterns undergo varying processes and result in varying embryo sacs as well. 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