Stenospermocarpy Biological Mechanism That Produces Seedlessness in Some Fruits (Many Table Grapes, Watermelon)

Phytohormones The growth and development of a plant are influenced by: •ꢀGeneꢀc factors •ꢀExternal environmental factors •ꢀChemical hormones inside the plant Secondary messengers 1.ꢀ Involve in the transfer informaꢀon from sources to targets 2.ꢀ Amplify the signal produced by the phytohormone Phytohormones Plant hormones are organic compounds that are effecꢀve at very low concentraꢀon (1g 20,000 tons-1) They interact with specific target ꢀssues to cause physiological responses •ꢀGrowth •ꢀFruit ripening Phytohormones •ꢀHormones sꢀmulate or inhibit plant growth Major groups of hormones: 1.ꢀ Auxins 2.ꢀ Gibberellins 3.ꢀ Ethylene 4.ꢀ Cytokinins 5.ꢀ Abscisic acid 6.ꢀ Brassinostereoids 7.ꢀ Salicylic acid 8.ꢀ Polyaminas 9.ꢀ Jasmonates 10.ꢀSystemin 11.ꢀNitric oxide Arabidopsis thaliana Phytohormones EARLY EXPERIMENTS ON PHOTROPISM SHOWED THAT A STIMULUS (LIGHT) RELEASED CHEMICALS THAT INFLUENCED GROWTH Auxins Auxin causes several responses in plants: * Phototropism * Geotropism * Promoꢀon of apical dominance * Flower formaꢀon * Fruit set and growth * Formaꢀon of advenꢀꢀous roots * Differenꢀaꢀon of vascular ꢀssues (de novo or repairing existent vascular ꢀssue) Auxins Addiꢀon of auxins produce parthenocarpic fruit. Stenospermocarpy Biological mechanism that produces seedlessness in some fruits (many table grapes, watermelon) diploid + tetraploid parent = triploid seeds vegetaꢀve parthenocarpy Plants that do not require pollinaꢀon or other sꢀmulaꢀon to produce parthenocarpic fruit (cucumber) Auxins Syntheꢀc auxins Widely used in agriculture and horꢀculture •ꢀ prevent leaf abscission •ꢀ prevent fruit drop •ꢀ promote flowering and fruiꢀng •ꢀ control weeds Agent Orange - 1:1 raꢀo of 2,4-D and 2,4,5-T Dioxin usually contaminates 2,4,5-T, which is linked to miscarriages, birth defects, leukemia, and other types of cancer. Cytokinins In 1964, zeaꢀn was the first naturally occurring cytokinin isolated from corn. Zeaꢀn and zeaꢀn riboside are found in coconut milk. Natural Syntheꢀc Cytokinins Lateral bud development •ꢀshoot iniꢀaꢀon •ꢀroots •ꢀseeds Callus development <[auxin] = roots <[kineꢀn] = buds Move non-polarly in xylem, phloem, and parenchyma cells. •ꢀfruits •ꢀyoung leaves •ꢀchloroplast development Ethylene •ꢀIs found only in the gaseous form •ꢀInduces ripening (e.g., green bananas). •ꢀEpinasty (causes leaves to droop in the fall ) •ꢀCauses abscission of fruits and flowers Ethylene Most produced organic compound 107 million metric tons in 2005 Once fruit iniꢀated red coloraꢀon, ethylene release becomes elevated in a linear fashion (without diurnal fluctuaꢀons). Abscisic acid (ABA) Abscisin is made from carotenoids and moves non-polarly through plant ꢀssue. Abscisic acid (ABA) is a general plant-growth inhibitor. Induces dormancy Prevents seeds from germinaꢀng Viviparous mutants Reduced sensiꢀvity for ABA Gibberellins In 1930's, Ewiꢀ Kurosawa and colleagues were studying plants suffering from bakanae, or "foolish seedling" disease in rice. •ꢀSynthesized in apical porꢀons of stems and roots Thompson seedless grapes (Viꢀs vinifera) Can be readily obtained in large quanꢀꢀes from fermentaꢀons of the fungus Gibberella fujikuroi •ꢀcell division and elongaꢀon •ꢀbreak seed dormancy •ꢀspeed germinaꢀon Gibberellins bolꢀng External factors and plant growth. Tropic responses Tropic responses Direcꢀonal movements by growth in response to a direcꢀonal sꢀmulus Phototropism is a response to blue light Phytphormone: Auxin Second messenger: Calcium Geotropism or gravitropism Phytphormones: cytokinin and auxin External factors and plant growth. Thigmotropism Thigmotropism is direcꢀonal growth response to contact with an object. Greek thigma = touch Rapid response Diferenꢀaꢀon in the elongaꢀon of the cells tendrils External factors and plant growth. Nasꢀc movements and heliotropism Nasꢀc movements are independent of the sꢀmulus' posiꢀon Touch, mechanical, electrical, thermal or chemical Venus Flytrap, Dionaea muscipula. Acid growth (cells that to elongate or expand quickly at low pH) and turgor External factors and plant growth. Heliotropism Heliotropism is the diurnal moꢀon of plant parts (flowers or leaves) in response to the direcꢀon of the sun. During the night, the flowers may assume a random orientaꢀon Heliotropism is a response to blue light. External factors and plant growth. Circadian rhythms Roughly 24-hour cycle in the biochemical, physiological, or behavioral organisms’ processes Hours of light <ul style="display: flex;"><li style="flex:1">Day </li><li style="flex:1">Night </li></ul>Endogenous and synchronized by the environment Biological clock Photosynthesis Movement External factors and plant growth. Photoperiodism According to their photoperiods, plants can be classified into three groups: a)ꢀ Short day plants. Examples: Nico8ana tabacum, soybean, strawberry, and chrysanthemum. b) Long day plants. Examples: Onion, carrot and spinach. c)ꢀ Day neutral plants. Examples: Tomatoes, cucumbers, sunflower, dandelions and coꢁon.

Stenospermocarpy Biological Mechanism That Produces Seedlessness in Some Fruits (Many Table Grapes, Watermelon)

Details

Download

Copyright

We respect the copyrights and intellectual property rights of all users. All uploaded documents are either original works of the uploader or authorized works of the rightful owners.

Support