Question

what is the difference between tapetum and nucellus? please reply fast. it's very urgent.

Answer 1

The tapetum of the anther or microsporangium in flowering plants has evolved functions related to the needs of the seed habit in addition to that of nourishing the microspore. A tapetum is available to megaspores where they are subsequently shed from the plant, as in Selaginella and Isoetes. Where the megaspore is retained, as in the seed plants, the typically transient tapetum is replaced by a more sustained nutrient supply, of which the so-called “integumentary tapetum” is a component. In flowering plants, in order from the exterior to the interior of the anther, are the epidermis, endothecium, middle layers, tapetum, and sporogenous tissue. The sporogenous tissue provides the contents of the pollen chamber and to which the tapetum forms a lining. At meiosis the four microspores are encased in the callose wall of the pollen mother cell for a period. If pollen development, including wall deposition, is well advanced before the callose wall is broken down, the direct tapetal contribution is smaller than where the breakdown happens earlier. Glandular and amoeboid tapeta remove the callose wall relatively earlier and later, respectively. Pollen therefore, surrounded by a glandular tapetum, derives more of its wall-forming precursors directly from the tapetum.

Answer 2

The tapetum of the anther or microsporangium in flowering plants has evolved functions related to the needs of the seed habit in addition to that of nourishing the microspore. A tapetum is available to megaspores where they are subsequently shed from the plant, as in Selaginella and Isoetes. Where the megaspore is retained, as in the seed plants, the typically transient tapetum is replaced by a more sustained nutrient supply, of which the so-called “integumentary tapetum” is a component. In flowering plants, in order from the exterior to the interior of the anther, are the epidermis, endothecium, middle layers, tapetum, and sporogenous tissue. The sporogenous tissue provides the contents of the pollen chamber and to which the tapetum forms a lining. At meiosis, the four microspores are encased in the callose wall of the pollen mother cell for a period. If pollen development, including wall deposition, is well advanced before the callose wall is broken down, the direct tapetal contribution is smaller than where the breakdown happens earlier. Glandular and amoeboid tapeta remove the callose wall relatively earlier and later, respectively. Pollen, therefore, surrounded by a glandular tapetum, derives more of its wall-forming precursors directly from the tapetum.