MYCORRHIZAL SYMBIOSIS DEFINITION

MYCORRHIZAL SYMBIOSIS DEFINITION

The terms symbiotic and mutualistic have been used interchangeably to describe mycorrhizal associations. Symbiosis was originally used to define both lichens and parasites, but many scientists now use this term to describe beneficial associations only. Fungal symbioses have been defined as ‘all associations where fungi come into contact with living host from which they obtain, in a variety of ways, either metabolites or nutrients’. However, this definition excludes associations of myco-heterotrophic plants that are entirelysupported by a fungus. Only the broadest definition of symbiosis (e.g. ‘living together of two or moreorganisms’) applies universally to mycorrhizal associations.

THE TERM OF MYCORRHIZA

The term mycorrhiza (meaning fungus-root) was originated by Frank (1885), who was fairly certain that these symbiotic plant-fungus associations were required for the nutrition of both partners. More recently, mycorrhizas have been defined as associations between fungal hyphae and organs of higher plants concerned with absorption of sub stances from the soil. Broader definitions have also been published, but are of little value as they do not exclude pathogenic associations. Mycorrhizas are now considered to differ primarily from other plant-fungus associations because they are intimate associations with a specialised interface whereexchange of materials occurs between living cells.

 

MOST MYCORRHIZAS OCCUR IN ROOTS

Most mycorrhizas occur in roots, which evolved to house fungi, but they also occur in the subterranean stems of certain plants and the thallus of bryophytes. Pathogenic associations also involve intimate plant-fungus contact, but differ from mycorrhizas because they lack fungus to plant nutrient transfer, and are highly detrimental to their host plants – resulting in disease symptoms. Pathogenic fungi are typically not specialised for efficient mineral nutrient acquisition from soil. A new, broader definition of mycorrhizas that embraces the full diversity of mycorrhizas while excluding all other plant-fungus associations is presented here.

DEFINITON OF MYCORRHIZA

Definition of Mycorrhiza is a symbiotic association essential for one or both partners, between a fungus (specialised for life in soils and plants) and a root (or other substrate-contacting organ) of a living plant, that is primarily responsible for nutrient transfer. Mycorrhizas occur in a specialised plant organ where intimate contact results from synchronised plant-fungus development.

THE IMPORTANCE OF FUNGI | Fungi play a major role in a number of foods and Some molds produce antibiotics.

The Importance of Fungi. 

Fungi break down complex animal and plant matter into simple compounds. This process of decomposition enriches the soil and makes essential substances available to plants in a form they can use. Through decomposition, fungi also return carbon dioxide to the atmosphere, where green plants reuse it to make food.

Fungi play a major role in a number of foods. 

For example, mushrooms and truffles are considered delicacies by many people. Cheese manufacturers add molds to Camembert and Roquefort cheeses to ripen them and provide their distinctive flavors. Yeasts cause the fermentation that produces alcoholic beverages. In the fermentation process, yeasts break down sugar into carbon dioxide and alcohol. Baker's yeast causes bread to rise by producing carbon dioxide from the carbohydrates in the dough. The carbon dioxide gas bubbles up through the dough and causes it to rise. Someday, yeasts may become an important new source of food. Some people already eat yeasts as a rich source of protein and B vitamins.

Fungsi Pictures

Some molds produce important drugs called antibiotics. 

Antibiotics weaken or destroy bacteria and other organisms that cause disease. Penicillin, the first and most important antibiotic, was discovered in 1928 by Sir Alexander Fleming, a British bacteriologist. Penicillium notatum is one of several green molds that produce penicillin, which physicians use in treating many diseases caused by bacteria.

Penicillin is a powerful drug used to treat infections caused by bacteria. It was the first antibiotic (drug produced by microbes) used successfully to treat serious diseases in human beings. Sir Alexander Fleming, a British scientist, discovered penicillin in 1928. Various forms of the drug, called penicillins, have become widely available for medical use since the mid-1940's. Penicillins have played a major role in treating pneumonia, rheumatic fever, scarlet fever, and other diseases. The development of penicillins had a tremendous impact on medicine and encouraged research that led to the discovery of many other antibiotics.

Tree Damage by Fungi

Some fungi cause great damage. 

Parasitic fungi destroy many crops and other plants. Important parasitic fungi that attack plants include mildews, rusts, and smuts. Others produce diseases in animals and people. Some mushrooms are poisonous and can cause serious illness or death if eaten. Molds spoil many kinds of food. In damp climates, mildews and other fungi can ruin clothing, bookbindings, and other materials. Fungi may also cause wood to decay or rot.

FUNGI DEFINITION | Fungi are organisms that lack chlorophyll.

FUNGI DEFINITION

Definition of Fungi are organisms that lack chlorophyll, the green coloring matter that many plants use to make food. Fungi cannot make their own food. Instead, they absorb food from their surroundings. There are over 70,000 species of fungi. Yeasts and other one-celled fungi are too small to be seen without a microscope. But most types can be seen with the unaided eye. Some of the most common fungi include mildews, molds, mushrooms, and plant rusts.

 Fungi Pictures

Fungi structure : Parts of a fungus. 

Fungi structure Except for yeasts and other one-celled fungi, the main part of a fungus consists of thousands of threadlike cells called hyphae. These tiny, branching cells form a tangled mass called a mycelium. In many kinds of fungi, the mycelium grows beneath the surface of the material on which the organism is feeding. For example, the mycelium of a mushroom often grows just beneath the surface of the soil. The umbrella-shaped growth known as a mushroom is actually the fruiting body of the fungus. The fruiting body produces cells called spores, which develop into new hyphae. Spores are smaller and simpler than the seeds of plants, but both enable an organism to reproduce.

Some bread molds and microscopic species of fungi bear spores in tiny structures called sporangia. In black bread mold, the sporangia form at the tips of upright hyphae called sporangiophores. Other hyphae called stolons spread over the surface of the bread. They are anchored by rhizoids (rootlike structures). Groups of sporangia usually form above the rhizoids.

Fungi Pictures

Fungi characteristics How a fungus lives. 

Fungi characteristics  Fungi live almost everywhere on land and in water. Some fungi are parasites that feed on living plants and animals. Other fungi, called saprophytes, live on decaying matter. Still other fungi live together with other organisms in ways that are mutually beneficial. Such a relationship is called symbiotic. For example, a fungus and an organism called an alga may live together symbiotically to form a lichen. Some fungi also live with the roots of plants in a symbiotic relationship known as a mycorrhiza. The fungus takes carbohydrates from the plant. In return, the fungus helps supply the plant with water and such important minerals as phosphorus, potassium, iron, copper, and zinc. Most species of trees, shrubs, and herbs have mycorrhizal relationships with fungi.



Mycorrhiza is the symbiotic association of the mycelium of certain fungi with the roots of certain higher plants,living in close relationship with the surface cells. Ex. It is possible with many, if not all, species of plant which normally form mycorrhizas in natural conditions to grow them in artificial surroundings without their appropriate fungi.

Fungi cannot produce their own food because they do not contain chlorophyll. They take carbohydrates, proteins, and other nutrients from the animals, plants, or decaying matter on which they live. Fungi discharge chemicals called enzymes into the material on which they feed. The enzymes break down complex carbohydrates and proteins into simple compounds that the hyphae can absorb.

Fungi Pictures

Types of Fungi.

Most kinds of fungi reproduce by forming spores. Some spores are produced by the union of gametes (sex cells). Others, called asexual or imperfect spores, are produced without the union of gametes. Many fungi produce spores both sexually and asexually. Many spores are scattered by the wind, and others are transported by water or by animals. Mushrooms and some other fungi forcefully discharge their spores. A spore that lands in a favorable location germinates (starts to grow) and eventually produces a new mycelium.

Types of Fungi. Yeasts can reproduce by forming spores, but many kinds of yeasts reproduce by budding. When a yeast buds, a bulge forms on the cell. A cell wall grows and separates the bud from the original yeast cell. The bud then develops into a new cell. Budding produces a large number of yeast cells rapidly.