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Home >>Botany Dictionary >>Heteroblastic Development - Histogen Theory
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Heteroblastic Development - Said of progressive change which takes place in the form and size of successive organs as in many grasses. The leaf blades become progressively longer and flowering in the plant starts only after a maximum length gets achieved or as in hemp. Successive leaves are having a greater number of lobes and margins are becoming more serrated. This trend to greater complexity gets often reversed after flowering.
Heterochromatin - Part of a chromosome having no known genes, but differing in nucleic acid content from euchromatin, and staining darker than it. It probably controls the nucleic acid metabolism of the nucleus.
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Heterocyst - A special type of cell which is produced in most filamentous Myxophyceae. They differ from the other cells in the structure of the walls and their transparent contents. They function as spores.
Heteroecius - Used for parasitic fungi which produce different forms of spores on different and unrelated hosts.
Heteroecius - A rust fungus in which various spore forms get developed on two different and usually unrelated hosts as Puccinia graminis.
Heterofertilization. Said of the fertilization of the endosperm nucleus and egg-nucleus by gametes of different genetic constitution.
Heterogeneous RNA (hn RNAP). Used specifically to newly formed introncontaining In RNA.
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Heterogenic - Of a population, or, gamete having more than one allelomorph of a particular gene or genes.
Heteroicous - Said of the Bryophyta which are having more than one kind of arrangement of the antheridia and archegonia on the same plant.
Heterokaryosis - Of a cell having more than one genetically different nucleus.
Heterokaryotise - Used for describing the fusion of haploid structures of opposite sex, which does not give a conjugate ar rangement of the nuclei.
Heterokont - Said of the condition where all the flagella in a cell are of unequal length and usually are of different morphological types also.
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Heterolactic Fermentation (mixed lactic fermentation). A type of anaerobic respiration in certain microorganisms having end products as one molecule each of lactic acid, ethanol and CO2.
Heteromerous - Used for a lichen thallus in which the layer of algal cells is lying between two layers of fungus hyphae.
Heteromorphie (anthithetic). Used for the type of alternation of generations where morphologically different gametophytic and sporophytic generations altemate with each other so as to complete sexual cycle of organism.
Heteromorphous - (1) Existing in more than one form (2) Having more than one kind of flower on the same plant.
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Heterosis - Hybrid vigour. The increase in vigour, size, and fertility of a hybrid as compared with its parents, resulting from the union of genetically different gametes, and considered to be due to special recombinations of dominant and recessive, genes.
Heterophy By - Refers to the possession of two or more leaf types. They often differ widely in morphology and function. Hetero phylly in aquatic species is shown in Fig.
Heterosporangy - The formation of more than one kind of sporan gium, having more than one kind of spore.
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Heterosporous - Producing large megaspores that give rise to the female gametophyte, and small microspores that give rise to male gametophytes.
Heterostyly - The division of a species into two or three kinds of individual by the relative positions of the stigma(ta) and anthers.
Heterosynapsis - The pairing of two dissimilar chromosomes.
Heterothalism - Referred to Algae and Fungi that are having separate, physiologically different, male and female thalli; or in the fungi, both types of sex-organs may be present on the same thallus, but self-fertiliation is impossible. Sexual reproduction only takes place when two appropriate strains come together.
Heterotrichous - A branched filamentous plant body made up of two different types of branches; some are prostrate branches which grow parallel to the substratum while others are erect branches which come out of prostrate branches and grow perpendicular to the substratum. They are common in order Chaetophorales of green algae and brown algae of order Ectocarpaler.
Heterotroph - An organism that cannot synthesize its organic food material but depends for its nourishment on organic food synthesized by other organisms. All animals and fungi, parasitic plants and many becteria are heterotrophic.
Heterozygote - A zygote which is derived from the union of gametes disssimilar in respect for the quality, quantity or arrangement of their genes, so that it is heterozygous for one or more allelomorphs.
Hexokinase - The enzyme catalysing the combination of the phosphate in A TP with glusoce to give glucose 6-phosphate.
Hexosans - Hemicelluloses formed from hexose sugars.
Hexose - A monosaccharide sugar, having six carbon atoms. The general formula is C6H12O6.
Hexose Monophosphate Shunt (phosphogluconale pathway, pentosephosphate pathway). Said of a complex, multifunctional pathway which is involving oxidation of glucose to finally form 3-,4-,5-,6-,7- carbon sugars. Glucose 6-phosphate is first oxidized and then decarboxylated to yield a 5-carbon sugar alongwith NADPH formation. This sugar, by various combinations and transformations similar to those of Calvin cycle, results in the formation of glucose 6-phosphate again.
Hexose Phosphates - Hexose sugars in which one or more of the -OH groups has been replaced by a H2PO4 group, e.g. C6H11O5 (PO4H2).
Hexophosphate Dehydrogenases - A enzyme catalysing thereaction: Glucose-6-phosphate+ NAD 6-phosphogluconate +NADH+H+.
Hierarchial Classification - Used for the system in which individuals have been grouped into ascending series of successively larger and broader catagories so that lower groups are laways subordinate to and included in those higher in the hierarchy. Within the hierarchy, classification has been done on the basis of the affinities of component units. According to International Code of Botanical Nomenclature there are 12 principal ranks and additional subcategories, one of each rank, thus 24 ranks in total in classification of plants. In asecending order, principal ranks are form, variety, species, series, section, genus, tribe, family, order, class, division and kingdom. Though use of all the catagories is not necessary, yet the order of categories should always be maintained.
High Energy Phorphate Bond - Used for describing a bond by which a phosphate group is linked and that is having negative standard energy of hydrolysis i.e., it gets hydrolysed spontaneously to release energy. For example, last two linkages of ATP.
Hill Reaction - Isolated chloroplasts, in suspension, when illuminated reduce ferricions, and produce oxygen a t the same time They cannot utilize carbon dioxide, so that it was assumed that the illuminated chloroplasts, on their own, reduced water, the hydrogen being removed by an oxidizing agent
light
4Fe3++ 2H2O.4Fe2++ 4(H)+ + O2.
Chloroplasts
Hilum - (1) The scar on the tests of a seed where it got attached to hairs as the leaves of Crepis setosa.
Histochemistry - Dealing with the study of distribution of certainchemical substances in cells and tissues by performing their colour reaction with specific chemicals e.g., cellulose by its blue colour which is developed on addition of Schultz's solution.
Histogen Theory - Used for the concept of organization and development of apical meristem in which the meristematic region is differentiated into three main zones, dermatogen, periblem and plerome. Dennatogen forms epidennis, periblem the cortex and plerome all the primary tissues inner to cortex. The theory is now replaced by tunica-corpus theory.
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