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Home >>Botany Dictionary>>Rhamnose - Rusts
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Rhamnose - A methylated pentose sugar which does not occur in free state but generally as constituent of many glycosides e.g., flavonol glycoside quercitrin. It also occurs in certain gums e.g., gum arabic, mucilages and in bacterial polysaccharides and is also identified in free state in Rhus toxicodendron.
Rhipidium - A monochasial cyme in which the branches are lying in one plane, so that the whole appears fan-shaped, e.g., incertain species of Iris.
Rhzanthous - Used for forming flowers from the root.
Rhizoid - Any of the thin root-like outgrowths in Musci, Filicales,
and certain Fungi and Algae, by which the fruit-producing plant gets fixed to the earth.
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Rhizodermis - (epiblem). Used for outermost layer of cells in roots. Term epidermis is also employed for this layer.
Rhizome - A thick root-like stem under the earth. It is frequently parallel to the top of it. It is sending roots down from its lower side and stems up from its top side and living from, year to year.
Rhizomorph - A tough cord-like mass of fused hyphae which are used for moving a fungus from one favourable location to another across unsuitable substrates e.g., in three parasite Armillaria mellea.
Rhizophore - In many species of Selaginella, a thin forked branch without flowers, going down into the earth and producing roots from the ends.
Rhizopodium - A thin cytoplasmic out-rowth in certain algae that do not have rigid cell walls. Rhizopodial cells are found in Chrysophyta, Xanthophyta and Dinophyta.
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Rhytidome - Bank having both phellem and dead cortex, occurring in some species in which a new phellogen evenly becomes active each year.
Riboflavin - Vitamin B2. It occurs in all plant cells, and forms a coenzyme which takes part in cellular oxidations.
Ribonuclease - The enzyme used for breaking down RNA.
Ribonucleic Acid - It is present on the nucleolus, ribosomes, endoplasmic reticulum and free in the cytoplasm. On the ribosome and endoplasmic reticulum there is 'messenger' RNA the template for protein synthesis, and that in the cytoplasm is 'transfer' RNA which helps to transfer amino-acids to the correct site on the 'messenger' RNA.
Ribose - A pentose sugar existing naturally in the furanose form.
HOH2C OH
C H H C
H C C H
OH OH
D-Ribofurnose
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Ribose-9-Adenonine=Adenosine - A nucleoside having ribose linked to the prurine adenine.
Ribose-3-Uracil - A nucleoside having ribose linked to the pyrimidine uracil.
Ribosomal RNA (RNA) - A form of RNA which is confined entirely to ribosomes. It is synthesized on nucleolus organizers, base composition remaining same in all the species. After synthesis, RNA reads with protein from nucleous forming nucleoprotein and partly constructed ribosome leaves nucleus via. nuclear pores and enters the cytoplasm where synthesis gets completed. Compare messenger RNA, transfer RNA.
Ribulose Diphosphate - A carbon dioxide receptor during, photosynthesis. Each molecule is converted into two molecules of phosphoglyceric acid.
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Ring Porous - A wood having more vessels, or larger vessels in the spring wood than elsewhere, so that it gets marked in cross section by rings or portions of rings of small holes.
Root - Used for the lower portion of axis of a higher plant which is branching and does not have leaves or buds. It anchors the plant in the soil.
Root Cap - A cap of loosely arranged cells covering the apex of the growing point of a root. It protects it as it grows through the soil and is formed from the promeristem.
Root Hair - A tubular outgrowth from the cells of the piliferous layer of a root. It is having thin walls, and is in close contact with the soil particles, so that it can absorb water and dissolved materials.
Root Nodules - Small swelling on the roots of various plants (especially legumes) which are formed by the invasion of nitrogen-fixing bacteria.
Root Pressure - The force per unit a
rea by which aqueous solutions from the living cells in the root are transported to the xylem.
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Root Rot A plant disease which is characterized by disintegration of root tissues. Armillaria mellea. Phytophthora, Fusarium and corticium are root-infecting fungi. Disease ultimately causes death of the affect plant.
Rootstock - (1) A short, erect underground stem which is equivalent to a vertical rhizome and is seen in many angiosperms e.g., Plantago and certain pteridophytes e.g., lsoetes, Osmunda.
(2) Any underground part of plant. See Stock.
Root Tuber - A swollen root having reserved food material.
Rosette - (1) A group of leaves which are arising form a short stem, and therefore lying close together on or near the ground.
(2) The 4 cells in the embryo of a pine, that are lying just above the suspensor.
Rostellum - Used for a break-like outgrowth from the column in the flower of an orchid.
Rot - A plant disease which is characterized by disintegration of tissues. Rots are especially important as post harvest diseases.
Rouge - Used for any plant which varies from rest of the crop and is unwanted e.g., wild oat growing in fields of cultivated oats. This term is also used for removal and destruction of such plants.
Rough Endoplasmic Reticulum - Used for describing cisternae of endoplasmic reticulum on which ribosomes get attached imparting it a rough appearance.
Ruminate - (1) Used for an endosperm into which the inner layer of the testa protrudes.
(2) Used for an endosperm which gets mottled in two or more different colours.
Runcinate - Used for a leaf having a lamina which is composed of lobes with their points pointing backwards.
Runner - A stem running over the earth, putting out roots and forming a new plant at the end of every division.
Russetting - Used for the development of brown, corky patches
on certain fruits, especially the varieties of apple, in response
various chemicals.
Rusts - The plant diseases which are caused by fungi of order Uredinales. These diseases are recognized by characteristic streaks of dark pustules on leaves or stems. Some rusts are able to complete their life-cycle on two different hosts (heteroecious rusts) where as some on one host only (autoecious rusts). Some important rusts are Black stem rusts of cereals (by Puccinia), rust of current (by Cronartium ribicola).
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