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Home >>Botany Dictionary>>Red/Far Red Effects - Rf Value
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Red/Far Red Effects - The physiological responses of many plants when they are exposed to illumination by red or far red light. Generally effects of two lights get reversed on exposure of opposite type of light i.e., effect of red light gets reversed by exposure to far red light and vice versa.
Red and Yellow Forest Soil - A type of zonal soil which is acidic (a pedalfer and is formed in wet subtropical regions due to which leaching accumulates salts in B-horizon. Red colour is attributed to iron oxides in A-horizon but if soil is sandy, it is yellow. Such soils have. little humus and soon get exhausted on cultivation Soils get eroded easily.
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Red Desert Soil - A type of coarse, zonal soil which is rich in lime and salts (a pedocal) but poor in humus. It is formed in hot deserts and cultivable when irrigation is available.
Redox Potential - The tendency of a reducing agent to lose electrons or an oxidizing agent to gain electrons measured against a known standard, generally the hydrogen. Thus, it expresses the reducing or oxidizing capability of a substance. The reaction is conveniently written as follows:
Oxidant + ne = reductant
where n represents the number of electrons transferred.
Red Snow - Used for snow which is stained by a surface growth of unicellular algae, rich in haematochrome.
Red Tropical Soil - A type of zonal soil which has been formed in rain forests and savanna having alternating dry and wet seasons. It is heavily leached but balance of nutrients is maintained by decomposition of organic litter. The red colour has been attributed to the presence of iron, magnesium and aluminium oxides. Some tropical oils may form a hard crust of chemical on the surface.
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Reducing Sugar - Any sugar reducing an oxidizing agent. Such a sugar is having a potentially active aldehyde or ketone group and all monosaccharides are sugars. In reducing disaccharides, one of the reducing groups of either of component monosaccharides is left intact. Various solutions such as Fehling's solution or Benedict's solution detect reducing sugars.
Reductases - Used for flavoproteins which are enzymes that carry out reduction e.g., of nitrate (NO3) ions to ammonium
(NH4+)ions. They also play role in the oxidation of NAD and NADP.
Reduction Division - The nuclear division during meiosis in which chromosome number becomes halved.
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Reduction Separation - Using for the separation of homologous parts of non-sister chromatids at anaphase of one or other meiotic division.
Reductive Amination - Used for the reduction for a substance by the addition of an NH2- radical, e.g., α-ketoglutaric acid is converted into the glutamic acid.
COOH COOH
CH2 CH2
CH2 + DPNH + NH3 CH2 + DPN+ H2O
C=O HC-NH2
COOH COOH
α- Ketoglutaric acid Glutamic acid
Reflexed - Used for structure that is bent sharply backwards such
as the petals Cyclamen.
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Regeneration - (1) The growing again of a part or organ which has been lost by injury.
(2) In bryophytes, the growing of a diploid gametophyte directly from a sporophyte after injury.
Regma - A fruit, which breaks up into rounded one-seeded portions
when it is ripened.
Regulatory Gene - A gene whose product is able to prevent or promote the transcription of other genes.
Relative Humidity - Defined as the ratio of actual amount of water vapour present in a body of air at a temperature and the amount of water vapour required to completely saturate that body of air at that temperature. The figure is expressed in percentage.
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Relative Sexuality - The occurrence in a species of strains giving gametes which are able to fuse with those produced by either of the normal strains.
Renaturation - The process in which denaturated protein has regained its characteristic coiled structure (native form) and its activity.
Rendzina (calcisol). A shallow interzonal soil which is rich in lime (calcimorphic) formed from the underlying limestome or chalk rocks having brown or black A-horizon, B-horizon, if distinguishable, is grey or yellowish with limestone fragments.
Renner Effect - The competition between 4 genetically different spores which are formed at one meiosis is regard to which shall form the embryo-sac.
R-Enzyme - One of the enzymes which breaks down the 1 : 6 linkages in the starch.
Repeated Sequence - Any long base-pair sequence which is found at many different places throughout the chromosomes excluding the DNA coding for structural genes. These sequences could be divided into 3 categories, repetitive DNA, highly or repetitive satellite DNA and palindromes.
Repetitive DNA - Generally having widely scattered sequences of about 300 base pairs length, which are usually adjacent to structural genes. They are possibly equivalent to operator genes of bacteria functionally.
Replication - The equal incorporation of all combinations two or more times in an experimental design, which is then called replicated.
Repressor - Used for a protein product of a regulator gene that is able to prevent transcription of other genes by binding to the DNA, blocking attachment of m RNA polymerase.
Reproduction - The process of forming new individuals while the species is perpetuated.
Reproductive Isolation - The prevention of gene flow which is taking place between all the members of a population due to development of isolating mechanisms thereby forming distinct non-breeding groups that in the course of time, may undergo development to form new species.
Repulsion - (1) The presence of two given genes in different homologous chromosomes.
(2) The tendency shown by dominant characters to separate.
Resin - An acidic substance which is either a phenolic derivative or an oxidation product of terpenes. The resins are insoluble in water, but soluble in alcohol, either, and carbon disulphide, and burn with a sooty flame. They are products of secretion or disintegration which generally occur in special cavities or passages.
Resin Canal - An intercellular space, which is often bordered by secreting cells, and has resin or turpentine.
Resistance - (1) The capability of an organism to withstand more than the normally lethal dose of a toxic substance.
(2) The ability of a plant for remaining productive if it is attached by a parasite which would normally kill it, or reduce its productivity below an economic level.
Respiration - (1) The chemical reactions breaking down complex molecules to simple ones, releasing energy, sometimes called cell-, internal-, or issue-respiration .
(2) The taking in of oxygen and the releasing of carbon dioxide. This is better known as gaseous exchange.
Respiratory Chain - A series of membrane-bound oxidation-reduction reactions in mitochondra which involve the transfer of electors from reduced cofactors formed in TCA cycle and other dehydrogenase reactions to oxygen which then reacts with hydrogen ions to form water. Presently, there are seven different electron transferring enzymes or cofactors between starting point NAD and oxygen.
Respiratory Chromogen - A colourless substance which forms coloured one on oxidation or reduction. It may playa part in respiration.
Respiratory Enzyme - An enzyme catalysing oxidation-reduction reactions.
Respiratory Index - Defined as the number of milligrams of carbon dioxide liberated from t g of plant material (dry-weight) at 10°C, when the amount of respirable material is unlimited, and when the oxygen is present in the same proportion as it is present in the ordinary atmosphere.
Respiratory Quotient - Defined as the ratio of the volume of carbon dioxide expired to .the volume of oxygen consumed during the same time. It provides a rough idea of the food material that is being oxidized.
Response - The change in an organism, or part of it, usually adaptive, which is produced by a stimulus.
Response Curve - A graph obtained between the amount of a stimulus or substance applied, and the response. The term is useful especially in relation to experiments such as fertilizer trials etc.
Resting Nucleus-Metabolic Nucleus - A nucleus which is not undergoing division.
Resting Period, Resting Stage - Any time in the life of a plant or plant organ when there appears no growth or activity.
Resting Spore - (1) A spore germinating after a resting period.
(2) A thick-walled spore which can survive adverse conditions, remaining dormant for sometime before it gets germinated.
Resting Stage - Used for a nucleus, when the chromosomes are not clearly visible as individuals.
Restitution - The formation of the original chromosome after breakage, especially by X-ray.
Restitution Nucleus - The single nucleus formed instead of two due to the failure of the first or second division of meiosis.
Restriction Enzyme (restriction endonuclease). An enzyme recognising and binding to specific, short sequences of doublestranded DNA and cutting it at or near this point. Such enzymes are formed in certain bacteria in response to invasion by bacteriophage for cutting and destroying the phage DNA. These form a most useful tool in gene engineering.
Reticulate Chloroplast - A complex plastid which is forming cylindrical network in the peripheral region of the cells of some green algae e.g., Oedogonium.
Reticulate Thickening - A type of thickening pattern in secondary wall of tracheary elements in which secondary wall is forming a network. Such thickening does not permit much further elongation and is therefore, found in metaxylem which has already completed elongation.
Reticulodromous - Used for describing net-like, reticulate leaf venation e.g., in Rhododendron.
Reverse Transcriptase - An enzyme which is present in certain microorganisms. It reverses the normal transcription sequence and synthesizes DNA strand from mRNA. It finds use in producing intron-free DNA for gene engineering.
Revolute - Rolled back, specially onto the underside as the edges of some leaves.
Rf Value (relative front). A value in chromatography which is found out by dividing the distance moved by the solute spot on the chromatogram by the distance moved by the solvent front. As the value remains constant for a particular molecule, it is used in chromatographic identification of molecules.
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