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Lecture 20100928 - Biol 111-2010-Lecture 8(Rajinder Dhindsa...

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1 Growth, Development and Responses to Environmental Stresses Biol 111-2010-Lecture 8 (Rajinder Dhindsa) But first, some clicker questions on the material in the last lecture !
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2 What do we mean by Growth and Development? Growth: Irreversible quantitative increase. Irreversible increase in height, volume, weight, volume, or number in case of populations. Development: Qualitative changes in body structure or function. Examples: Development of organs, (organogenesis), achieving final shape and size (morphogenesis), Juvenile phase, adult phase (sexual maturity, flowering, senescence or physiological aging.
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3 Plant hormones or phytohormones
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4 Seed Germination Seeds are generally dormant just after being shed. They won’t germinate even if temperature, soil and moisture conditions are optimal. This is seed dormancy. Seed dormancy is most frequently due to the presence of the hormone abscisic acid (ABA). ABA has to degrade or leach out before the seed will germinate Sometimes seed dormancy is due seed coat is mechanically too strong. Seed coat has to be cracked by freeze-thaw cycles in nature or weakened by micro-organisms. Small wild seeds frequently need light signal ( What kind of light ?) to make them germinate. Because small seed have only a small amount of stored food, they have to germinate close to the soil surface. If they “see” the light they are close to the soil surface. If they germinate deep down below the soil surface, their food material runs out before they can come above the soil and start photosynthesis .
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5 Light requirement for seed germination What kind of light is required? White or Red light for germination, far red light to keep them from germinating.
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6 A single pigment that has two conformational forms to absorb two different wavelengths of light: Phytochrome P r is phytochrome that absorbs red light and gets converted to P fr .
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