Plant Solute Transport PDF

ABSORPTION AND TRANSPORT OF SOLUTES IN PLANTS Dr. R. Ravindhran Dept. of Plant Biology and Biotechnology Loyola College (Autonomous) Chennai -34  Absorption and Transport of solutes Absorption of minerals from the soil and translocation of minerals...

ABSORPTION AND TRANSPORT OF SOLUTES IN PLANTS Dr. R. Ravindhran Dept. of Plant Biology and Biotechnology Loyola College (Autonomous) Chennai -34  Absorption and Transport of solutes Absorption of minerals from the soil and translocation of minerals to aerial parts of the plant. Passive Absorption Active Absorption Passive Absorption- Theories – Mass Flow – Ion Exchange Contact exchange Caronic acid exchange – Donnan Equilibirium Ion Exchange Theory Ion Exchange Theory Donnan Equilibrium  Active Absorption Carrier concept Protein-Lecithin as carrier Goldacre's theory Cytochrome pump theory Carrier Concept Theory Carrier(Ion) Concept theory Protein – Lecithin carrier concept theory Cytochrome Pump theory  Solute Transport Direction of phloem transport ○Plantstransport substances in the phloem downward toward the roots. ○Substances in the phloem are transported downward towards the roots or upwards toward the shoot meristem. ○The typical direction of transport is downward from the primary source (leaves) to the major sink (roots). Direction of phloem transport  TRANSLOCATION OF FOOD ○ Food and other organic substances (e.g., Some plant hormones and even messenger RNAs manufactured in the cells of the plant are transported in the phloem. I. Sugars (usually sucrose), II. Amino acids, and III. Other organic molecules. ○ Enter the sieve tubes through plasmodesmata. ○ Once within the sieve tubes,these molecules can be transported either up or down to any region of the plant. 44  TRANSLOCATION OF FOOD Sugar Loading into Sieve-tube Members  THE PRESSURE-FLOW HYPOTHESIS ○ The best-supported theory to explain the movement of food through the phloem is called the pressure-flow hypothesis.  PRESSURE-FLOW THEORY ○ The pressure-flow theory explains how sap moves in a plant from source to sink: Sugars begin at a source and are pumped into phloem tube cells. Osmosis moves water into the cells and raises pressure. Pressure moves the sap.  PRESSURE FLOW 1 ○ The leaf is a source of sugar, since it makes sugar by photosynthesis. ○ Glucose and fructose made by photosynthesis are linked to make sucrose.  PRESSURE-FLOW 2 ○ Active transport is used to load sucrose into phloem tubes against a diffusion gradient.  PRESSURE-FLOW 3 ○ The high concentration of sucrose in the sieve tube cells of the phloem causes water to move in by osmosis, which raises pressure and causes the sap to move.  PRESSURE-FLOW 4 ○ A developing fruit is one example of a sink. ○ Sucrose may be actively transported out of phloem into the fruit cells. ○ In a root, sucrose is converted into starch, which keeps sugar moving in by diffusion.  PRESSURE-FLOW 5 ○ As the sugar concentration drops in the sieve tube cells, osmosis moves water out of the tube.  PRESSURE-FLOW 6 ○ As water moves out by osmosis, the pressure in the sieve tube cells drops. ○ The pressure difference along the column of sieve tube cells keeps the sap flowing.  PRESSURE-FLOW: REVIEW ○ Thus it is the pressure gradient between "source" (leaves) and "sink" (shoot and roots) that drives the contents of the phloem up and down through the sieve tubes. THE PRESSURE-FLOW