Plant Bible

                                                                                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...

                                                                                            Cytokinin Discovery: The presence of cell division inducing substances in plants was first demonstrated by Haberlandt in 1913 in Coconut milk (liquid endosperm of coconut) which contains cell division inducing substances. In 1954, Skoog and Miller discovered that autoclaved DNA from herring sperm stimulated cell division in tobacco pith cells. They called this cell division inducing principle as kinetin (chemical structure: 6-Furfuryl Amino Acid). This does not occur in plants. In 1963, Lethan introduced the term cytokinin. In 1964, Lethan and Miller isolated and identified a new cytokinin called Zeatin from unripe grains ...

  Gibberellins Discovery: The effect of gibberellins had been known in Japan since early 1800 where certain rice plants were found to suffer from ‘Bakanae’ or foolish seedling disease. This disease was found by Kurosawa(1926) to be caused by a fungus Gibberella fujikuroi. The active substance was separated from fungus and named as gibberellin by Yabuta (1935). These are more than 100 gibberellins reported from both fungi and higher plants. They are noted as GA1, GA2, GA3 and so on. GA3 is the first discovered gibberellin. In 1938, Yabuta and Sumiki isolated gibberellin in crystalline form. In1955, Brain et al., gave the name gibberellic acid. In 1961, Cross et al., established its structure. Occurrence: The major site of gibberellin production in plants is parts like embryo, roots and young leaves near the tip. Immature seeds are rich in gibberellins. Precursors: The gibberellins are chemically related to terpenoids (natural rubber, carotenoids and steroids) formed by 5...

                                                                      PHYTOHORMONES   Definition: The term phytohormones is implied to those chemical substances which are synthesized by plants and thus, naturally occurring. On the other hand, there are several manufactured chemicals which often resemble the hormones in physiological action and even in molecular structure. Recently, another two groups, the brassinosteroids and polyamines were also known to behave like hormones. Characteristics of phytohormones: Usually produced in tips of roots, stems and leaves. Transfer of hormones from one place to another takes part through conductive systems. They are required in trace quantities. All hormones are organic in nature. There are no specialized cells or organs for their secretion. They are capable of i...

  MECHANISM OF STOMATAL MOVEMENTS   1) STARCH- SUGAR HYPOTHESIS: It is proposed by sayer in 1923 IN LIGHT: IN DARK: Photosynthesis occurs Respiration occurs pH increases ↑ pH decreases ↓ Carbon dioxide Co ₂↓ Carbon dioxide Co ₂ ↑ Enzyme: phosphorylase is used Enzyme: phosphorylase is used Sugar increases ↑ so endosmosis take place Starch increases ↑ so exosmosis take place Turgor pressure increases ↑ Turgor pressure decreases ↓ Diffusion pressure deficit (DPD) increases ↑ Diffusion pressure deficit (DPD) decreases ↓ Stomata = opens Stomata = closes Starch is converted in to glucose -1- phosphate glucose -1- phosphate is converted in to Starch       2) STEWARD HYPOTHESIS: It is proposed by steward in ...