MECHANISM FOR UPTAKE OF NUTRIENT IN PLANTSM.Nadeem AshrafSoil & Environmental sciencesFaculty of agriculture, Rawalakot
RecallTransport Mechanism Passive vs. ActivePlant Transport Tissues Xylem Vessel elements Tracheids Phloem Sieve tube member Companion cells
The apoplastic and symplastic pathwaysApoplast Within a plant, the apoplast is the free diffusional space outside the plasma membrane. It is interrupted by the Casparian strip in roots, air spaces between plant cells and the cuticula of the plant. Structurally, the apoplast is formed by the continuum of cell walls of adjacent cells as well as the extracellular spaces, forming a tissue level compartment comparable to the symplast. The apoplastic route facilitates the transport of water and solutes across a tissue or organ. This process is known as apoplastic transport.
PATHWAYS FOR WATER UPTAKEPlasmodesmat a Plasmodesmata Plasmodesma allow molecules to travel between plant cells through the symplastic pathway
symplast The symplast of a plant is the inner side of the plasma membrane in which water (and low-molecular- weight solutes) can freely diffuse. The plasmodesmata allow the direct flow of small molecules such as sugars, amino acids, and ions between cells. Larger molecules, including transcription factors and plant viruses, can also be transported through with the help of actin structures
A variety of physical processes Are involved in the different types of transport 5 Sugars are produced by 4 Through stomata, leaves photosynthesis in the leaves. take in CO2 and expel O2. CO2 O2 The CO2 provides carbon for Light photosynthesis. Some O2 produced by photosynthesis H 2O Sugar is used in cellular respiration.3Transpiration, the loss of water from leaves (mostly through stomata), creates a force within leaves that pulls xylem sap upward. 6 Sugars are transported as phloem sap to roots and other parts of the plant. 2 Water and minerals are transported upward from roots to shoots as xylem sap. 7 Roots exchange gases 1 Roots absorb water with the air spaces of soil, and dissolved minerals O2 taking in O2 and discharging from the soil. H 2O CO2. In cellular respiration, CO2 O2 supports the breakdown Minerals of sugars. Figure 36.2
Transport of Xylem SapWater Movement in Xylem through TACT Mechanism;Four important forces combine to transport water solutions from the roots, through the xylem elements, and into the leaves. These TACT forces are:transpirationadhesioncohesiontension
Transport of Xylem Sap Transpiration involves the pulling of water up through the xylem of a plant utilizing the energy of evaporation and the tensile strength of water. The previous section describes transpiration more fully. Adhesion is the attractive force between water molecules and other substances. Because both water and cellulose are polar molecules there is a strong attraction for water within the hollow capillaries of the xylem.
Transport of Xylem Sap Cohesion is the attractive force between molecules of the same substance.. Tension can be thought of as a stress placed on an object by a pulling force. This pulling force is created by the surface tension which develops in the leafs air spaces. A combination of adhesion, cohesion, and surface tension allow water to climb the walls of small diameter tubes like xylem. This is called capillary action
Root Pressure: A Mechanism to "Push" Xylem Sap Up the Plant At night, transpiration is almost nil. However, the root cells continue to actively transport minerals into the xylem and the phloem). This active transport lowers the water potential within the stele Water passively flows into the roots, pushing the water up against gravity Water that reaches the leaves is often forced out, causing a beading of water upon the leaf tips known as guttation In most plants, however, root pressure is not the primary mechanism for transporting the xylem Tall trees generate
The Translocation of Phloem Phloem loading results in a high solute concentration at the source end. This creates hypnotic conditions in the phloem, causing water to flow into the phloem Hydrostatic pressure builds in the sieve tube, but it is greatest in the source At the sink, osmosis occurs with the unloading of sugar - water flows out of the phloem The buildup of pressure at the source and the reduction of that pressure at the sink causes water to flow from source to sink, carrying the sugar along with it. Water is recycled via transport in the xylem