Showing posts with label nutrients and nutrition. Show all posts
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4:08 PM
Biofertilizers
Biofertilizers
The use of biofertilizers, biological systems that supply plant nutrients such as nitrogen to agricultural crops, could reduce agriculture’s dependency on chemical fertilizers, which are often detrimental to the environment.

Plants require an adequate supply of the thirteen mineral nutrients necessary for normal growth and reproduction. These nutrients, which must be supplied by the soil, include both macronutrients (nutrients required in large quantities) and micronutrients (nutrients required in smaller quantities). As plants grow and develop, they remove these essential mineral nutrients from the soil.

Because normal crop production usually requires the removal of plants or plant parts, the nutrients are continuously removed from the soil. Therefore, the long-term agricultural utilization of any soil requires periodic fertilization to replace lost nutrients.

Nitrogen is the plant nutrient that is most often depleted in agricultural soils, and most crops respond to the addition of nitrogen fertilizer by increasing their growth and yield. Therefore, more nitrogen is applied to cropland than any other fertilizer component.


In the past, nitrogen fertilizers have been limited to either manures, which have low levels of nitrogen, or chemical fertilizers, which usually have high levels of nitrogen. However, the excess nitrogen in chemical fertilizers often runs off into nearby waterways, causing a variety of environmental problems.

Less Harmful Alternatives

Biofertilizers offer a potential alternative: They supply sufficient amounts of nitrogen for maximum yields yet have a positive impact on the environment. Biofertilizers generally consist of either naturally occurring or genetically modified microorganisms that improve the physical condition of soil, aid plant growth, or increase crop yield.

Biofertilizers provide an environmentally friendly way to increase plant health and yields with reduced input costs, new products and additional revenues for the agricultural biotechnology industry, and cheaper products for consumers.

Nitrogen Fixing

Nitrogen Fixing
Nitrogen Fixing
While biofertilizers could potentially be used to supply a number of different nutrients, most of the interest is focused on nitrogen. The relatively small amounts of nitrogen found in soil come from a variety of sources.

Some nitrogen is present in all organic matter in soil; as this organic matter is degraded by microorganisms, it can be used by plants. A second source of nitrogen is nitrogen fixation, the chemical or biological process of taking nitrogen from the atmosphere and converting it to a form that can be used by plants.

Bacteria such as members of Rhizobium can live symbiotically in the roots of certain plants, such as legumes. Rhizobia and plant root tissue form root nodules, which house the nitrogen-fixing bacteria; once inside the nodules, the bacteria use energy supplied by the plant to convert atmospheric nitrogen to ammonia, which nourishes the plant.

Natural nitrogen can also be supplied by free-living microorganisms, which can fix nitrogen without forming a symbiotic relationship with plants. The primary objective of biofertilizers is to enhance any one or all of these processes.

One of the major goals for the genetic engineering of biofertilizers is to transfer the ability to form nodules and establish effective symbiosis to non-legume plants. The formation of nodules in which the Rhizobia live requires plant cells to synthesize many new proteins, and many of the genes required for the expression of these proteins are not found in the root cells of plants outside the legume family (Fabaceae). If transfer of the appropriate genes could be accomplished, Rhizobia could be used as a biofertilizer for a variety of plants.

There is also much interest in using the free-living, soil-borne organisms that fix atmospheric nitrogen as biofertilizers. These organisms, including types bacteria and algae, live in the rhizosphere (the region of soil in immediate contact with plant roots) or thrive on the surface of the soil.

Because the exudates from these microorganisms contain nitrogen that can be used by plants, increasing their abundance in the soil could reduce the dependency on chemical fertilizers. Numerous research efforts have been designed to identify and enhance the abundance of nitrogen-fixing bacteria in the rhizosphere.

Soil microorganisms primarily depend on soluble root exudates and decomposed organic matter to supply the energy necessary for fixing nitrogen. Hence, there is also an interest in enhancing the biodegradation of organic matter in the soil.

This research has primarily centered on inoculating the soil with cellulose-degrading fungi and nitrogen fixing bacteria or applying organic matter, such as straw that has been treated with a combination of the fungi and bacteria to the soil.
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4:23 AM

Common organic chemicals found in all living organisms, important in energy metabolism and structural polymers, carbohydrate molecules are made up of carbon, hydrogen, and oxygen.

Carbohydrates are made of carbon, hydrogen, and oxygen molecules in a 1:2:1 ratio, respectively. This is often simplified using the formula nCH2O, where n represents the number of CH2O subunits in a carbohydrate. This formula should make it clear how the name carbohydrate was derived, as nCH2O is essentially carbon and water.

The simplest carbohydrates are the monosaccharides, or simple sugars. Individual monosaccharides can be joined together to make disaccharides (composed of two monosaccharides), oligosaccharides (short polymers composed of two to several monosaccharides), and polysaccharides (longer polymers composed of numerous monosaccharides).


Monosaccharides

The common monosaccharides found in plants have from three to six carbon atoms in a straight chain with one oxygen atom. Most of the oxygen atoms also have a hydrogen atom attached, making them hydroxyl groups (–OH). One of the oxygen atoms is connected to a carbon by a double covalent bond, while the hydroxyl groups are attached to carbon atoms by single covalent bonds.

If the double-bonded oxygen is on a terminal carbon (as an aldehyde group), the monosaccharide is called an aldose. If the double-bonded oxygen is on an internal carbon, the monosaccharide is called a ketose.

The simplest monosaccharides are the three carbon sugars, or trioses. Pentoses, with five carbons, are also important in plants.

Ribose and deoxyribose are found in RNA(ribonucleic acid) and DNA(deoxyribonucleic acid), respectively. Ribulose bisphosphate is an important intermediate in the incorporation of carbon dioxide into carbohydrates during photosynthesis. Xylose and arabinose are found as components of some plant polysaccharides.

Hexoses, six-carbon monosaccharides such as glucose, fructose, and galactose, are the most common monosaccharides in plants. These sugars all have the same formula, C6H12O6 (note the 1:2:1 ratio of C:H:O), but their atoms are arranged differently. Glucose is the primary carbon-containing product of photosynthesis and reverse glycolysis and later can be metabolized through glycolysis and the Krebs cycle to release energy or can be converted to other carbohydrates needed by the plant.

Oligosaccharides

Oligosaccharides are made by joining two or more monosaccharides. The smallest are the disaccharides, formed from two monosaccharides that are joined together by a condensation reaction. Condensation reactions get their name from the fact that when the two monosaccharides are joined together, a molecule of water is released.

Sucrose (glucose-fructose) is the most common plant disaccharide and is the principal molecule of short-term energy storage and of translocation (transport) in the phloem. Many plants, including sugarcane (Saccharum officinarum) and sugar beets (Beta saccharifera), have high concentrations of sucrose, which can be extracted and refined for use as table sugar.

Other disaccharides found in plants are maltose, which is a glucose disaccharide formed from the hydrolysis (the reverse of a condensation reaction, wherein water is used to “split” the bond between the monosaccharides) of starch, and trehalose, also a glucose disaccharide, which is the primary molecule of translocation in species of Selaginella and is seen in cyanobacteria (blue-green algae or blue-green bacteria), red algae, and fungi. Cellobiose, another glucose disaccharide, is formed by the hydrolysis of cellulose.

The trisaccharide raffinose (galactose-glucose-fructose) is a storage molecule in sugar beets and in cotton and legume seeds. Stachyose (galactose-galactose-glucose-fructose) and verbascose (galactose-galactose-galactose-glucose-fructose) are also storage oligosaccharides, seen mainly in Fabaceae (the legume or pea family).

Polysaccharides

The two main functions of polysaccharides in plants are long-term energy storage and structure. Glucose is the most common subunit in plant polysaccharides. The glucose molecules in these polymers are joined together in different ways. The carbon atoms in glucose molecules are numbered from one to six.

In some, the 1-carbon of a glucose is attached to the 4-carbon of the next, and this linkage is repeated throughout the molecule. At other times, an additional bond is formed between the 1-carbon and the 6-carbon of adjacent glucoses, which results in a branched polysaccharide.

Starch is the most common storage polysaccharide of plants. Two forms of this glucose polymer exist. Amylose is a linear polymer made up of between one hundred and several thousand glucose units. Amylopectin is very similar, but it is a branched polymer.

In most plants, starch is 15-25 percent amylose and 75-85 percent amylopectin. However, starch in some waxy varieties of corn is nearly 100 percent amylopectin and in some wrinkled varieties of peas is as high as 80 percent amylose. Phytoglycogen found on corn (Zea mays) is an even more branched glucose polymer.

Fructosans are another type of storage polysaccharide in plants. They are branched or unbranched fructose polymers with a terminal glucose subunit. Inulin is found in the tubers or rhizomes of plants in Campanulaceae (the bellflower family) and Asteraceae (the sunflower or aster family) and usually has thirty to fifty fructose subunits.

Levans, used for temporary storage by several monocots, especially in Poaceae (the grass family), range from seven to eight fructose subunits in the unbranched levans to seventy-two fructose subunits in some highly branched ones.

Structural Polysaccharides

Structural polysaccharides form the fibrous material in plant cell walls. Cellulose, an unbranched glucose polymer that averages about eight thousand glucose subunits per molecule, is the main cell wall component of plants, a few fungi, and some algae. Cellulose molecules form microfibrils, many individual cellulose molecules held together by hydrogen bonds. Other microfibrillar cell wall polysaccharides are sometimes called the hemicelluloses.

Examples are mannans and glucomannans, found in the primary cell walls of several green algae and simple vascular plants and in the secondary cell walls of some conifers; xylans are found in other algae and in the secondary cell walls of many hardwoods. Chitin, a polymer of N-acetylglucosamine, is the main substance forming the cell walls of fungi. (Chitin is the same substance that forms the exoskeletons of most insects.)

Pectins are matrix polysaccharides found in plant cell walls. The most common pectin in higher plants is unbranched polygalacturonic acid (galacturan). Branched and unbranched rhamnogalacturans and arabinans are also present in smaller quantities.

Pectin is commercially important as a gelling agent in the production of jams and jellies. A similar pectin like polysaccharide found in brown algae is alginic acid, a mixture of mannuronic and guluronic acids. It is used as a thickener and a stabilizer in many prepared foods.

Other Plant Carbohydrates

Carbohydrates are often found attached to other cell components. In both cell membranes and cell walls, there are many glycoproteins, proteins with short oligosaccharides attached.

Glycosides are interesting carbohydrate-containing secondary metabolites found in many plants. Glycosides are formed when carbohydrates are attached to various plant chemicals. Anthocyanins, which give red to blue color to flowers, fruits, and autumn leaves, are glycosides.

Other glycosides include the cardiac glycosides of the foxglove (Digitalis purpurea) and milkweed (Asclepias) species, which have strong physiological effects on heart muscle, and the cyanogenic glycosides of the almond (Prunus amygdalus), which liberate cyanide.
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