Anatomy

structure ,origin, development and function of parenchyma

1. ANATOMY OF VASCULAR PLANTS Presentation Origin, Structure, Development and Function specialization of Parenchyma

2. Parenchyma is a cell and tissue type in which the cells have only thin primary walls; the cells are unspecialized, lack the characteristic wall of collenchyma and the secondary walls of sclerenchyma; the cells have live nucleate protoplast concerned with various physiological activities in plants; the cells are meristematic, or permanent, simple homogeneous (i.e. composed of one type of cells only), fundamental or ground tissue upon which other simple and conducting tissues appear to be embedded. Parenchyma

3. Parenchyma cells present in the primary plant body, i.e. pith and cortex, originates from the ground meristem. Procambium and cambium give rise to xylem and phloem parenchyma of the primary and secondary conducting tissues respectively. Phelloderm originates from phellogen . In leaves, protoderm and ground meristem give rise to parenchymatous epidermis and mesophyll respectively. Origin of parenchyma cells

4. Mature parenchyma tissues may be compactly set without any intercellular spaces. Ex endosperm tissue of seeds. They may also be arranged loosely so that well spaces are present between them. Ex stems and leaves of hydrophytes developed intercellular .

5. Parenchyma cells usually have primary walls (e.g., storage and chlorophyllous parenchyma). The storage parenchyma cells of endosperm of Phoenix, Asparagus have very thick walls. The thickness of wall is due to the deposition of hemicellulos. Usually parenchyma cells contain living protoplast with single or numerous vacuoles. They may also contain leucoplasts, chloroplasts etc. (chloroplast containing parenchyma cells are termed as chlorenchyma ). Various carbohydrates, nitrogenous and fatty substances are found in the cell sap of parenchyma. The parenchyma cells of the roots of sugar beet and the bulb scales of onion contain amides, proteins, sugars etc. in their cell sap . Structure of parenchyma cells

6. From the evolutionary point of view, the parenchymatic cell is regarded as the ancestor or precursor of the other cell types of the plant because it is not much differentiated and shows similar behavior as meristematic cells. For example, it can dedifferentiate by decreasing the thickness of the cell wall, and becomes a totipotent cell that can proliferate. Thus, parenchyma is an excellent source to produce callus ( in vitro  mass of undifferentiated cells that proliferate and differentiate to give an adult plant). Development and function of Parenchyma

7. This type of parenchyma, also known as  chlorenchyma , is specialized in photosynthesis thanks to the many chloroplasts present in the cells. Photosynthetic parenchyma is commonly found under the epidermis, where light is more intense, and it is abundant in leaves, but also in the cortex of green shoots. The photosynthetic parenchyma of the leaves is known as mesophyll, which is usually divided in two types: palisade and spongy mesophyll. Palisade mesophyll is close to the upper epidermis of the leaves, where it gets more light. Photosynthetic P arenchyma .

8. The cells in this tissue synthesize and stores a number of substances. Although these substances can be solid, like starch grains and crystallized proteins, they are mostly found in solution, such as lipids, proteins, and others. Usually they are stored in vacuoles, which are the compartment specialized in storing molecules. In the cytoplasm, some moleculars are also stored like carbohydrates and nitrogenated substances. Some parenchymatic cells store only one type of substance, but a mix of different substances can also be found in the same cell. Storage parenchyma

9. Although all parenchymatic cells store some amount of water, those of the aquiferous parenchyma are specialized in this function. They are large cells, with a thin cell wall and a very large vacuole where water is stored. In the cytoplasm or in the vacuole, there is a mucilaginous substance that increase the capacity of absorption and retention of water. Aquiferous parenchyma

10. Aquiferous parenchyma of a cactus

11. There are large interconnected empty intercellular spaces, where gases can diffuse and aerate the root. Aeriferous parenchyma or  aerenchyma  contains large intercelular empty spaces, larger than in other plant tissues. This tissue is well-developed in plants living in wet or aquatic environments (these plants are known as hydrophytes), although it can be also found in non aquatic plants under stress. Both, stem and root can developed aerenchyma Aeriferous parenchyma ( aerenchyma )