. What is Microsporogenesis.Determine also its type
The process of the formation and differentiation of microspores (pollen grains) from microspore mother cells (MMC) by reductional division is called microsporogenesis.
The young anther consists of homogenous mass of paranchymatous cells surrounded by epidermis. It soon becomes four lobed. In each of the four lobes, some of the hypodermal cells begin to act as archesporial initials. Each archesporial initial divides into an outer primary parietal cell and an inner primary sporogenous cell. The primary parietal cell divides to form 3-5 wall layers, i.e., endothecium, middle layers and tapetum. The primary sporogenous cells divide to produce a mass of sporogenous cells or microsporocyte.
Each microspore mother cell divides meiotically to form four haploid microspores or pollen grains and remains arranged in tetrads. The arrangement of pollen grains in a tetrad is affected by cytokinesis during meiosis. Each cell of the sporogenous tissue is capable of giving rise to a microspore tetrad. It is of two types :
i. Simultaneous type: The cytokinesis occurs simultaneously at the end of meiosis II to form tetrahedral tetrad. Here wall formation is centripetal. It is common in dicotyledons.
ii. Successive type: The cytokinesis occurs twice i.e. each of the two nuclear division is followed by wall formation to form an isobilateral tetrad. Here the wall formation is centrifugal. It is found in monocotyledons.
Besides tetrahedral and isobilateral tetrads, other types of tetrads are linear (e.g. Halophila), T-shaped (e.g. Aristolochia, Butomopsis) and decussate (e.g. Magnolia). Now the microspores are separated from tetrad.