Plant Bible

                                                            EMBRYOGENY BY DICOTYLEDON   Based on the plane of division of the apical cell in the 2-celled proembryo, and the contribution of the basal cell ( cb ) and the apical cell ( ca ) in the formation of embryo proper, five chief types of embryogeny have been recognized by Maheshwari (1950) A. The apical cell of the 2-celled proembryo divides longitudinally (1) The basal cell plays only a minor role or none in the subsequent development of the embryo proper Crucifer Type or Onagrad Type (eg., Annonaceae, Brassicaceae, Onagraceae, Pedaliaceae, Ranunculaceae. Scrophulariaceae) (2) The basal cell and apical cell both contribute to the development of embryo - Asterad Type (eg. Asteraceae, Balsaminaceae. Violaceae, Vitaceae) B. The apical ...

                                                                 Embryogeny in Monocotyledons   The main difference between the mature embryos of monocotyledon and dicotyledon is in the number of cotyledons. The single cotyledon in monocotyledons has been regarded by many authors as a terminal structure. Wardlaw (1955) remarked: “In the dicotyledonous embryo the plumule is typically distal and is situated symmetrically between two equivale cotyledons in the monocotyledonous embryo the shoot apex occupies a lateral position in the somewhat cylindrical embryo and cotyledon terminal”. However, extensive ontogenetic work on monocot Swamy and his co-workers is Lakshmanan, 1972) has established that the epicotyl in monocotyledonous embryos is truly a terminal structure both epicotyl and cotyl...

                                                                                       APOMIXIS   The normal sexual cycle (amphimixis) involves two important processes (a) Meiosis, this transforms a diploid sporophytic cell (megaspore mother cell, MMC) into four haploid gametophytic cells, and (b) Fertilization, In which two haploid gametes of opposite sex fuse re-establishing the diploid sporophytic generation. Thus, in a sexual cycle a diploid generation (sporophytic) alternates with a haploid generation (gametophytic) In angiosperms the gametophytic generations are very short and are represented by embryo sac on the female side and microspores or pollen grains on the male side. In some plants meiosis and syngamy are int...

  EMBRYO The fertilized egg is called zygote Following a predetermined mode f development (embryogeny) it gives rise to an embryo, which has the potentiality form a complete plant. A typical dicotyledonous embryo seen in median longitudinal section. It comprises an embryonal axis with two cotyledons attached to laterally. The portion of embryonal axis above the level of cotyledons is called epicotyl, and the portion below the level of cotyledons is known as hypocotyl. The epicotyl terminates into plumule (embryonic shoot), and the hypocotyl at its lower end bears radicle (embryonic root). The embryo of a monocotyledon differs from that of a dicotyledon mainly in having only one cotyledon. The embryos of grasses show a highly specialized structure. In this chapter the chief structural changes associated with principal types of embryogeny in angiosperms are described. At the end some aspects of the physiology, genetics and nutrition of embryo are discussed. ZYGOTE: From the tim...

                                                                                     Heterosis Discovery: Heterosis (hetero- different; sis - condition) G.H. Shull was the first scientist to use the term heterosis in 1912.  Definition: The superiority of the F1 hybrid in performance over its parents is called heterosis or hybrid vigour. Vigour refers to increase in growth, yield, greater adaptability of resistance to diseases, pest and drought. Vegetative propagation is the best suited measure for maintaining hybrid vigour, since the desired characters are not lost and can persist over a period of time. Many breeders believe that the magnitude of heterosis is directly related to the degree of genetic diversity between the two par...

                                                                                SEED DORMANCY Definition: The seeds of most plants germinate under favourable environmental condition but some seeds do not germinate when suitable conditions like water, oxygen and favourable temperature are not available. Germination of such seeds may be delayed for days, months or years. The condition of a seed when it fails to germinate even in suitable environmental condition is called seed dormancy. There are two main reasons for the development of dormancy: Imposed dormancy  innate dormancy. Imposed dormancy is due to low moisture and low temperature. Innate dormancy is related to the properties of seed itself. Factors causing dormancy of seeds: ...

                                                                                  Plant Movements Definition: Plants have the capacity for changing their positions in response to external or internal stimuli, which are known as plant movements. Movements are basically of two types: I. Vital movements and II.   Physical movements (hygroscopic). I. Vital movements Vital movements are those which are exhibited by the living cells or plants or organs and they are always related to the irritability of the protoplasm. These movements are of two types: A. Movements of locomotion B. Movements of curvature A. Movements of locomotion: These movements include the movement of protoplasm inside the cell or movement of whole unicellular or...

                                                                                Photoperiodism The physiological mechanisms in relation to flowering are controlled by  (i) light period (Photoperiodism)  (ii) temperature (Vernalization). Definition: The physiological change on flowering due to relative length of light and darkness (photoperiod) is called Photoperiodism. The term photoperiodism was coined by Garner and Allard (1920) when they observed this in ‘Biloxi’ variety of soybean (Glycine max) and ‘Maryland mammoth’ variety of tobacco (Nicotiana tabacum). The photoperiod required to induce flowering is called critical day length. Maryland mammoth (tobacco variety) requires 12 hours of light and cocklebur (Xanthium pensylvanicum) r...

                                                                           Vernalization Definition: Vernalization (Vernal – Spring Like) Besides photoperiod certain plants require a low temperature exposure in their earlier stages for flowering. Many species of biennials and perennials are induced to flower by low temperature exposure (0 ⁰ C to 5 ⁰ C). This process is called Vernalization. The term Vernalization was first used by T. D. Lysenko (1938). Mechanism of Vernalization: Two main theories to explain the mechanism of vernalization are: i. Hypothesis of phasic development ii. Hypothesis of hormonal involvement i. Hypothesis of phasic development: According to Lysenko, development of an annual seed plant consists of two phases. First phase is t...

                                                              RESPIRATORY SUBSTRATES The usual respiratory substrate is glucose. Some cells can only respire glucose, such as brain neurones Other cells can oxidize lipids or amino acids. Definition: Respiratory substrates are the organic nutrients oxidized at the time of respiration. At the time of cellular respiration, oxidation of organic nutrients occurs to obtain energy (ATP). The order of preference of organic nutrients as respiratory substrates are – Carbohydrates, Lipid, Proteins. Lipids: These are broken down to fatty acids and glycerol Fatty acids are then broken into pairs of Carbon atoms As Acetyl CoA which enters the Krebs cycle Fatty acids:   These are then broken into pairs of Carbon atoms As Acetyl CoA which enters the Kreb...

         Respiratory Quotient (RQ) Definition: The ratio of volume of carbon dioxide given out and volume of oxygen taken in during respiration is called Respiratory Quotient or Respiratory ratio. RQ value depends upon respiratory substrates and their oxidation. RQ = Volume of CO2 liberated / Volume of O2 consumed 1. The respiratory substrate is a carbohydrate, it will be completely oxidised in aerobic respiration and the value of the RQ will be equal to unity. C ₆ H ₁₂ O ₆ + 6O ₂ → 6CO ₂ ↑+ 6H ₂ O +Energy RQ of glucose = 6 molecules of CO2 / 6 molecules of O2 = 1 (unity) 2. If the respiratory substrate is a carbohydrate it will be incompletely oxidised when it goes through anaerobic respiration and the RQ value will be infinity. C ₆ H ₁₂ O ₆ →   2CO ₂ ↑+ 2C ₂ H ₅ OH + Energy RQ of glucose = 2 molecules of CO ₂ / Anaerobically zero molecule of O ₂ = ∞ (infinity) 3. In some succulent plants like Opuntia, Bryophyllum carbohydrate...

  LIPIDS Definition: Lipids are diverse group of chemicals that are fats and oily substances. Lipids are hydrophobic. These are insoluble in water. Lipids are in soluble in organic solvents, such as Ether, Ethanol, Acetone, Chloroform, Benzene, etc. Lipids contain Carbon, Hydrogen and Oxygen, as in Carbohydrates. But in lipids the proportion of Oxygen is much less. Having only two Oxygen atoms at one end of long molecule. Classification of Lipids: Simple Lipids: Simple Lipids are esters of fatty acids with alcohols. Simple Lipids can be sub-divided into: 1. Fats 2. Waxes. Fats: Esters of fatty acids with glycerol. Solid at room temperature. Some are liquid at room temperature, and are known as oils. Physical state depends upon the nature of fatty acids. Fats are rich in saturated fatty acids. Oils are rich in unsaturated fatty acids. Waxes: They are esters of higher fatty acids with higher mono hydroxy aliphatic alcohols(e.g. Cetyl alcohol). Have very long straight ...