The main difference between micropyle and chalaza is that a micropyle is a small opening in the outer integument of an ovule, whereas a chalaza is the base of the ovule where the nucellus and the integuments join.
Ovule is an outgrowth of the ovary of a seed plant, that is, the megasporangium, which encloses an embryo sac within a nucellus. Micropyle and chalaza are two structures in the ovule.
Key Areas Covered
What is a Micropyle
A micropyle is a small opening in the outer integument of an ovule. The micropyle is typically situated at the distal end of the ovule, which is opposite the chalaza. The integument, a layer that covers the developing embryo sac, protects the ovule. There are two layers in the integument, the inner and outer integument, which are fused at the micropyle. In certain plant species, the micropyle converts into an operculum, which opens during fertilization, allowing the pollen tube to enter.
In certain species of plants, the micropyle can be a simple opening, whereas, in other species, it can be a complex structure containing more specialized tissues and cells. Hence, the shape and size of the micropyle can vary. The shape of the micropyle helps in the determination of the mode of pollination.
Micropyle is also involved in the regulation of pollen tube growth. This happens due to the secretion of signalling molecules that attract or repel the pollen tubes. It also prevents polyspermy, which is the fertilization of an egg cell by more than one sperm cell. This is facilitated by the micropyle having a small opening, which allows only one sperm to enter at a time. Micropyle also contains specialized cells that release chemicals. These chemicals inhibit the growth of additional pollen tubes. The main function of the micropyle is to act as the entrance point for the pollen tube to deliver sperm cells to the egg cell for fertilization.
What is Chalaza
Chalaza is the basal part of the ovule in plants where the nucellus and the integuments join. It is located opposite the micropyle of the ovule. Through the chalaza, the nutrients are transported from plants to the nucellus. Moreover, the chalaza is composed of a dense mass of cells rich in nutrients nourishing the developing embryo. In fact, the ovule anchors to the ovary at the chalaza. This helps to maintain its position during the growth and development of the plant.
Chalaza contains many structures within it. One such structure is the nucellus, which is a central mass of tissue within the ovule. Another such structure is the funiculus, which is a narrow stalk-like structure that connects the ovule to the placenta. In addition, the chalaza provides the necessary nutrients and structural support for the proper development and maturation of the ovule.
Difference Between Micropyle and Chalaza
A micropyle is a small opening in the outer integument of an ovule, whereas a chalaza is the base of the ovule where the nucellus and the integuments join.
While a micropyle is a small opening in the integuments, and it is a few cells wide, a chalaza is a more complex structure with a thickened tissue region at the ovule’s base.
Micropyle serves as the entry point for the pollen tube during fertilization, while chalaza serves as a nutrient source, supports the developing embryo, and helps to anchor the ovule within the ovary.
In brief, the micropyle and chalaza are two structures in the ovule. The main difference between micropyle and chalaza is that a micropyle is a small opening in the outer integument of an ovule, whereas a chalaza is the base of the ovule where the nucellus and the integuments join.