PPT – PHLOEM TRANSLOCATION PowerPoint presentation | free to download - id: 2bOWEyY
plants can be generally divided into source and sink organs (Turgeon, ). . For example, starch synthesis was stimulated without an increase in 3-PGA. TOPIC: CONCEPTS OF SOURCE AND SINK –TRANSLOCATION OF PHOTOSYNTHATES Presentation Courses · PowerPoint Courses; by LinkedIn Learning .. This relationship can be used for single plant or for a crop depending upon the objective of study. . Example: crop yield weather models. • 2. SINK. SOURCE. Young leaf. Mature Leaf – A free PowerPoint PPT presentation PowerPoint Templates - Are you a PowerPoint presenter looking to impress your Transport in the Phloem of Plants PowerPoint PPT Presentation.
Received Apr 13; Accepted Jul 2. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc. This article has been cited by other articles in PMC. Abstract Source-to-sink transport of sugar is one of the major determinants of plant growth and relies on the efficient and controlled distribution of sucrose and some other sugars such as raffinose and polyols across plant organs through the phloem.
In this paper, we summarize current knowledge about the phloem transport mechanisms and review the effects of several abiotic water and salt stress, mineral deficiency, CO2, light, temperature, air, and soil pollutants and biotic mutualistic and pathogenic microbes, viruses, aphids, and parasitic plants factors.
Concerning abiotic constraints, alteration of the distribution of sugar among sinks is often reported, with some sinks as roots favored in case of mineral deficiency. Many of these constraints impair the transport function of the phloem but the exact mechanisms are far from being completely known.
Phloem integrity can be disrupted e. Photosynthesis inhibition could result from the increase in sugar concentration due to phloem transport decrease. Biotic interactions aphids, fungi, viruses… also affect crop plant productivity. Recent breakthroughs have identified some of the sugar transporters involved in these interactions on the host and pathogen sides.
The different data are discussed in relation to the phloem transport pathways.
SOURCE AND SINK RELATIONSHIP |authorSTREAM
The evidences are as follows: There are only two paths for long distance translocation, tracheary elements and sieve tubes. The former are dead while the latter are living.
Translocation of organic solutes seems to be through sieve tubes because it is inhibited by steam girdling which kills living cells. In girdling or ringing experimentsa ring of bark is cut from the stem. It also removes phloem. Nutrients collect above the ring where the bark also swells up and may give rise to adventitious roots Fig.
Growth is also vigorous above the ring. The tissues below the ring not only show stoppage of growth but also begin to shrivel Roots can be starved and killed if the ring is not healed after some time. Killing of roots shall kill the whole plant clearly showing that bark or phloem is involved in the movement of organic solutes which occurs in one direction, i. Girdling experiments are performed in fruit trees to make more food available to fruits.
However, the rings are kept narrow and cambium is not touched so that the incision heals up after some time. Girdling experiments cannot be carried out in monocots and dicots with bi-collateral bundles because of the absence of a single strip of phloem.
Mason and Maskell inserted a wax paper between phloem and xylem. Parts of the bark were also removed except for a narrow strip.
They found evidence that the organic solutes passed through the narrow strip of bark containing the phloem. By means of aphid stylets, Weatherley found that sieve tubes contained a concentrated solution of organic substances under a pressure.
Radio-autographs show that assimilates with incorporated radioactive elements pass out of the leaves and travel towards the sink ends through phloem.
Sucrose is most suitable form of carbohydrate translocation as it is non-reducing and chemically stable. It does not react with other substances during translocation. Tonoplast is absent in sieve tube cells so that cytoplasm is in direct contact with vacuolar contents.
Sieve tube cytoplasm can tolerate high concentration of solutes without being plasmolysed. Cytoplasm of one sieve tube cell is continuous with that of the adjacent sieve tube cells through sieve plates so as to form continuous filaments. The centre of sieve tube cells is empty with cytoplasmic strands being peripheral.
Source and Sink in Phloem Translocation | Plant Physiology
Sieve tube cells possess granules and filaments of P-protein with ATPase activity. Relatively large amounts of organic solutes are trans-located. The rate of translocation of organic nutrients is such that a sieve tube must be refilled times per second. Crafts and Lorenz found that a pumpkin fruit receives gm of the organic solution in 33 days with a rate of 0. Lateral movement from phloem to living cells or from source to phloem occurs through transfer cells and symplasm.
Mechanism of Phloem Translocation: Several theories have been put forward to explain the mechanism of translocation of organic nutrients through the phloem e.