What is Physiology: Root Pressure explain briiefly?
Transport of water, minerals and nutrients within vascular plants is dramatically different from animals such as humans. Whereas humans have a closed circulatory system powered by a pump - the heart- plants with open vessel systems must rely on a passive system to move materials around. This is a considerable task, given that some giant redwood trees like Sequoia sempirvirens must lift water to leaves in excess of 110 meters (360 feet) above the ground. While the transport of water and minerals can be explained, not all of the transport processes of photosynthetic food products are well understood.
Water and minerals are thought to be transported up to the leaves by two processes: root pressure and transpirational pull.
Root Pressure
Root pressure results from the net movement of water from the soil into the stele of the root because of an osmotic gradient. You may recall that the stele is that part of the internal root consisting of the endodermis tissues, the cells of which are surrounded by the Casparian Strip, and the tissues within the endodermis, including the pericycle (parenchyma cells) and the xylem and phloem.
We can trace the path of water and minerals from the soil, where they are absorbed by the root hairs near the root tip. Older root hairs farther removed from the growing root tip do not absorb as much water as do the younger root hairs near the tip of the root. Root hairs are projections formed from epidermal cells, and they pass the absorbed water to the parenchyma cells of the cortex tissue, located just inside the epidermis. The water and minerals move through the cortex by either going around the outside of the cells, or by being absorbed and moving from cell to cell through intercellular cytoplasmic connections. The region outside the cells is referred to as the "apoplast," and the connected cytoplasm is referred to as the "symplast." The soil solution is usually low in terms of mineral concentration, and through active transport the cells of the cortex can build up the cells' concentration 100's of times greater than that of surrounding soil. This produces a higher solute, or osmotic concentration within the cells relative to that in the soil, and osmosis then drives the net movement of water into the cell.
The endodermis has a Casparian Strip that prevents water from passing between the endodermal cells into the vascular tissues. As a result, all water and minerals are forced to enter the stele through the front and back cell membranes of the endodermal cells. The endodermis is thus able to control all movement of ions into the vascular system. Active transport of minerals results in a build up of ion concentration within the stele, and osmosis can occur, drawing water into the root system. This osmosis produces positive water pressure for the root system, which results in something called"guttation" in short, low plants. Guttation is the name for the phenomenon usually seen early in the morning when little tiny droplets of water get squeezed out on the leaf edges of grasses and herbaceous plants.
Root pressure can actually be demonstrated in the lab using a grapevine or Coleus plant. Usually the stem is removed and a micropipette is attached to the remaining stem and root system.