Auxins. Cytokinins. 1. Auxin is first introduced by F.W. Went. 1. Cytokinin is first isolated by Miller and Skoog. 2. It is produced in the shoot apex and leaf. The hormones auxin and cytokinin are key regulators of plant growth and for mutual feed back and feed forward control of auxin and cytokinin levels. . illustrates the complexity and depth of the interrelationship between the two hormones. Difference between Auxin and Gibberellin Difference # Auxin: 1. Auxin has a Auxin does not mobilise food reserve during seed germination. Auxin has.
Cytokinin alone has no effect on parenchyma cells. When cultured with auxin but no cytokinin, they grow large but do not divide. When cytokinin is added, the cells expand and differentiate. When cytokinin and auxin are present in equal levels, the parenchyma cells form an undifferentiated callus. More cytokinin induces growth of shoot buds, while more auxin induces root formation. They are known to regulate axillary bud growth and apical dominance. The "direct inhibition hypothesis" posits that these effects result from the cytokinin to auxin ratio.
This theory states that auxin from apical buds travels down shoots to inhibit axiliary bud growth. This promotes shoot growth, and restricts lateral branching. Cytokinin moves from the roots into the shoots, eventually signaling lateral bud growth. Simple experiments support this theory. The roots of the plant act as miners moving through the soil and bringing needed minerals into the plant roots. Structure of soil, indicating presence of bacteria, inorganic, and organic matter, water, and air.
Image from Purves et al. Plants use these minerals in: Structural components in carbohydrates and proteins Organic molecules used in metabolism, such as the Magnesium in chlorophyll and the Phosphorous found in ATP Enzyme activators like potassium, which activates possibly fifty enzymes Maintaining osmotic balance Mycorrhizae, bacteria, and minerals Plants need nitrogen for many important biological molecules including nucleotides and proteins.
However, the nitrogen in the atmosphere is not in a form that plants can utilize. Many plants have a symbiotic relationship with bacteria growing in their roots: These plants tend to have root nodules in which the nitrogen-fixing bacteria live. Development of a root nodule, a place in the roots of certain plants, most notably legumes the pea familywhere bacteria live symbiotically with the plant.
Images from Purves et al. All the nitrogen in living systems was at one time processed by these bacteria, who took atmospheric nitrogen N2 and modified it to a form that living things could utilize such as NO3 or NO4; or even as ammonia, NH3 in the example shown below.
Pathway for converting fixing atmospheric nitrogen, N2, into organic nitrogen, NH3. Not all bacteria utilize the above route of nitrogen fixation. Many that live free in the soil, utilize other chemical pathways. Nitrogen uptake and conversion by various soil bacteria. Roots have extensions of the root epidemal cells known as root hairs.
While root hairs greatly enhance the surface area hence absorbtion surfacethe addition of symbiotic mycorrhizae fungi vastly increases the area of the root for absorbing water and minerals from the soil. Role of the root hairs in increasing the surface area of roots to promote increased uptake of water and minerals from the soil. Water and Mineral Uptake Back to Top Animals have a circulatory system that transports fluids, chemicals, and nutrients around within the animal body.
Some plants have an analogous system: Root hairs are thin-walled extensions of the epidermal cells in roots. They provide increased surface area and thus more efficient absorption of water and minerals.
Water and dissolved mineral nutrients enter the plant via two routes.
Difference between Auxin and Gibberellin
Water and selected solutes pass through only the cell membrane of the epidermis of the root hair and then through plasmodesmata on every cell until they reach the xylem: Water and solutes enter the cell wall of the root hair and pass between the wall and plasma membrane until the encounter the endodermisa layer of cells that they must pass through to enter the xylem: The paths of water into the xylem of a root.
The endodermis has a strip of water-proof material containing suberin known as the Casparian strip that forces water through the endodermal cell and in such a way regulates the amount of water getting to the xylem.
Only when water concentrations inside the endodermal cell fall below that of the cortex parenchyma cells does water flow into the endodermis and on into the xylem. Details of the Casparian strip.
Xylem and Transport Back to Top Xylem is the water transporting tissue in plants that is dead when it reaches functional maturity. Tracheids are long, tapered cells of xylem that have end plates on the cells that contain a great many crossbars. Tracheid walls are festooned with pits. Vesselsan improved form of tracheid, have no or very few obstructions crossbars on the top or bottom of the cell.
- Difference Between Auxin and Cytokinin
The functional diameter of vessels is greater than that of tracheids. Water is pulled up the xylem by the force of transpirationwater loss from leaves. Mature corn plants can each transpire four gallons of water per week.
Transpiration rates in arid-region plants can be even higher. Water molecules are hydrogen bonded to each other. Water lost from the leaves causes diffusion of additional water molecules out of the leaf vein xylem, creating a tug on water molecules along the water columns within the xylem. This "tug" causes water molecules to rise up from the roots to eventually the leaves. The loss of water from the root xylem allows additional water to pass throught the endodermis into the root xylem.
Cohesion is the ability of molecules of the same kind to stick together. Water molecules are polar, having slight positive and negative sides, which causes their cohesion. Inside the xylem, water molecules are in a long chain extending from the roots to the leaves. Adhesion is the tendency of molecules of different kinds to stick together.
Water sticks to the cellulose molecules in the walls of the xylem, counteracting the force of gravity and aiding the rise of water within the xylem. Cohesion-Adhesion Theory Transpiration exerts a pull on the water column within the xylem. The lost water molecules are replaced by water from the xylem of the leaf veins, causing a tug on water in the xylem. Adhesion of water to the cell walls of the xylem facilitates movement of water upward within the xylem.
This combination of cohesive and adhesive forces is referred to as the Cohesion-Adhesion Theory. Guard cells are crescent-shaped cells of the epidermis that flank the stoma and regulate the size of the opening. Together, the guard cells and stoma comprise the stomatal apparatus. The inner wall of the guard cell is thicker than the rest of the wall.
Difference between auxin and cytokinin? - Lifeeasy Biology: Questions and Answers
When a guard cell takes up potassium ions, water moves into the cell, causing the cell to become turgid and swell, opening the stoma. When the potassium leaves the guard cell, the water also leaves, causing plasmolysis of the cells, and a closing of the stoma.
Ions and stomatal function. Transportation and Storage of Nutrients Back to Top Plants make sugar by photosynthesis, usually in their leaves. Some of this sugar is directly used for the metabolism of the plant, some for the synthesis of proteins and lipids, some stored as starch.Plant Control
Other parts of the plant also need energy but are not photosynthetic, such as the roots. Food must therefore be transported in from a source, an action accomplished by the phloem tissue. Phloem, Sugar, and Translocation Phloem consists of several types of cells: Sieve cells are tubular cells with endwalls known as sieve plates. Most lose their nuclei but remain alive, leaving an empty cell with a functioning plasma membrane.