Prepared for B.Sc. Part II Botany Hons. by Prof. (Dr.) Manorma Kumari

Microsporogenesis Microsporogenesis consists of the formation of microsporangium and microspores inside the anther. The microspores then give rise to the male gametophyte. In angiosperm, the male reproductive organ of the plant is stamen which consists of three parts i.e., anther, connective and filament anther is the part where microsporangia are formed. Anther – The anther is the apical part of the stamen. A typical anther consists of two anther lobes. These two lobes are held together by a narrow strip of tissue called connective. Each anther lobe has two locules or microsporangia. Thus, there are four microsporangia in each anther. These microsporangia are separate from each other in the beginning but become united at maturity by the dissolution of the separation wall between them. In young anther, chambers or locules are not formed. A young anther consists of a mass of homogenous cells surrounded by the epidermis. Soon four lobes are differentiated in the young anther, and four rows of cells are differentiated from hypodermal layer by having large size, more conspicuous nuclei, these cells constitute archesporium. Archesporium – The archesporial cell may be present either singly in each lobe (in the T.S. of anther) e.g. Sanseviera (Guerin, 1927) and Boerheavia (Maheshwari, 1929) or may be present in number more than one forming plates at four lobes e.g. Urginea (Cooper, 1937) and Ophiopogon (Maheshwari, 1934). The archesporial cells then divide to form two layers of cells, the one towards the outside is known as Primary Parietal layer and the other towards the inner side is known as the primary sporogenous layer. The Primary parietal layer divides by periclinal and anticlinal divisions to form a several layered wall of the anther. The primary sporogenous cells either directly function as the microspore mother cell or divides and redivides to form a large number of microspore mother cells. Anther wall – Anther wall consists of following layers – (i) Epidermis – It is outermost layer and consists of cells which divide only by the anticlinal divisions to keep pace with the enlargement of the anther. (ii) Endothecium – Endothecium is the second layer next to epidermis. The cells of this layer are radially elongated. Fibrous bands of callose 2

run upward from the inner tangential wall and end near the outer wall of each cell. There are few exceptions where fibrous bands are absent eg. Musa (Juliano and Alcala, 1933), Sesamum (Nohara, 1934) Anona (Juliano, 1935) etc. Endothecium attains its maximum development when anthers become ready to dehisce. It is hygroscopic in nature; it helps in dehiscence. (iii) Middle layer – Next to the endothecium lies middle layer. This layer may consist of one to three or more layers of cells. Cells of middle layer become crushed at the time when microspore mother cells start reduction division with a few exceptions like Ranunculus and Lilium where one or two layers do not undergo disorganisation. (iv) Tapetum – This is the innermost layer of the anther wall. Food is supplied through this layer to the developing microspore mother cells and the microspores. It is now established that the tapetal cells are parietal in origin (Maheshwari, 1971). It is composed of a single layer of cells characterised by the presence of dense cytoplasm and conspicuous nuclei.

Development of Anther Wall

To be continued…