Translocation plant physiology and phloem water

Jump to navigation Jump to search Translocation in plants means the movement organic molecules and some mineral ions. Movement of water from the soil to the leaves occurs in xylem vessels in a process called Transpiration.

Translocation plant physiology and phloem water

Anette Linnea Rasmus Translocation is the movement of materials from leaves to other tissues throughout the plant. Plants produce carbohydrates sugars in their leaves by photosynthesis, but nonphotosynthetic parts of the plant also require carbohydrates and other organic and nonorganic materials.

For this reason, nutrients are translocated from sources regions of excess carbohydrates, primarily mature leaves to sinks regions where the carbohydrate is needed.

Some important sinks are roots, flowers, fruits, stems, and developing leaves. Leaves are particularly interesting in this regard because they are sinks when they are young and become sources later, when they are about half grown.

Source and Sink in Phloem Translocation | Plant Physiology

Phloem Structure and Function The tissue in which nutrients move is the phloem. The phloem is arranged in long, continuous strands called vascular bundles that extend through the roots and stem and reach into the leaves as veins.

Vascular bundles also contain the xylemthe tissue that carries water and dissolved minerals from the roots to the shoots. When plants increase in diameter secondary growth they do so by divisions of a layer of cells just under the bark; this cell layer makes new xylem to the inside forming the wood of the tree trunk and a thin, continuous cylinder of new phloem to the outside.

The contents of the phloem can be analyzed by cutting off the stylets mouth parts of phloem-feeding insects such as aphids and collecting the drops of sap that exude. Phloem sap is composed largely of sugar dissolved in water. All plants translocate sucrose table sugar and some also transport other sugars such as stachyose, or sugar alcohols such as sorbitol.

Translocation in plants means the movement organic molecules and some mineral ions. Movement of water from the soil to the leaves occurs in xylem vessels in a process called Transpiration. Transpiration, the evaporation of water from leaves, causes a pull on the water column due to the forces of cohesion between water molecules formed due to. In vascular plants, phloem to parts of the plant where needed. This transport process is called translocation. In trees, the phloem is the innermost layer of the bark, hence the name, The sap is a water-based solution, but rich in sugars made by photosynthesis. In this review, we summarize the current understanding of As transport in plants, with an emphasis on As uptake, mechanisms of As resistance and the long-distance translocation of As, especially the accumulation of As in grains through phloem-mediated transport.

Many other organic compounds are found, including amino acidsproteinsand hormones. Glucosethe sugar found in the circulatory system of animals, is not translocated. In order to accommodate the flow of sap, the internal structure of the conducting cells of the phloem, the sieve elements, is drastically altered.

As the sieve elements mature, they lose many of the organelles commonly found in living cells and they modify others. The nucleus disappears, as do the vacuoles, microfilaments, microtubules, ribosomesand Golgi bodies.

Therefore, the inside lumen of the cell is left essentially open. The sieve elements are greatly elongated in the direction of transport and are connected to one another to form long sieve tubes.

Large pores perforate the end walls of the sieve elements to facilitate flow through the tube. The connecting walls thus look like a sieve, giving the cell type its name.

Some sieve elements can live for a long time, as many as one hundred years in palm trees, even though they have no nucleus or any of the machinery needed for protein synthesis. Cells closely associated with them, called companion cells, apparently keep them alive.

Translocation plant physiology and phloem water

The association of sieve elements and companion cells is one of the most intimate and complex in nature, and one of the least understood. It now appears that both small and large molecules can move from companion cells to sieve elements through the plasmodesmata that connect them.

Plasmodesmata are minute pores that traverse the common walls between plant cells. They have an intricate internal structure. Interest in plasmodesmata is high because viruses move through them to cause infections. If a virus enters the phloem this way it will travel with the sap, spread widely around the plant, and infect sink organs.

Since viruses are much larger than plasmodesmata, they must be disassembled in one cell and reassembled when they get to their destination. Sugars synthesized in the chloroplasts are actively pumped into the sieve tubes. Water follows by osmosis, creating high pressure. Sugar is then removed by active transport, and water again by osmosis, lowering the pressure in the sieve tube.

The Pressure-Flow Mechanism The rate of translocation in angiosperms flowering plants is approximately 1 meter per hour.The advantages in maintaining an uninterrupted supply of nutrients and phloem water to meristematic zones, and the pressure needed for effective regulation, are obvious.

A relay mechanism for phloem translocation. Plant Physiology Oct , (2) ; DOI: /pp Share This Article: Copy.

Translocation plant physiology and phloem water

Plant Physiology (Biology ) Solute transport in plants, translocation, primarily occurs in the phloem, but it can occur in the xylem. II. Solute Transport in the Xylem. Some solutes are transported in the xylem; Water and dissolved ions are the main substances in vessels/tracheids; These materials are transported via transpiration stream;.

Organic materials, mainly produced in the leaves, are moved around the plant in the living cells of the phloem by a process called translocation. Unlike xylem (which is composed of dead cells), the phloem is composed of still-living cells that transport sap.

Translocation is the movement of materials from leaves to other tissues throughout the plant. Plants produce carbohydrates (sugars) in their leaves by photosynthesis, but nonphotosynthetic parts of the plant also require carbohydrates and other organic and nonorganic materials.

Abstract. Satisfactory measurements of phloem water potential of trees can be obtained with the Richards and Ogata psychrometer and the vapor equilibration techniques, although corrections for loss of dry weight and for heating by respiration are required for the vapor equilibrium values.

Translocation Translocation is the movement of materials from leaves to other tissues throughout the plant. Plants produce carbohydrates (sugars) in their leaves by photosynthesis, but nonphotosynthetic parts of the plant also require carbohydrates and other organic and nonorganic materials.

Phloem Water Relations and Translocation | Plant Physiology