BIOB 110CS 1st Edition Lecture 18 Seed dispersal and dormancy Seeds represent spatial and temporal distribution of plant reproductive effort Plants either make many little seeds or a few big seeds Seed dispersal vectors Wind dandelions and tumbleweed use this to spread seeds over a great distance Forrible seed dispersal the seed is ejected from the plant wisteria and mistletoe use this Water streams and other water can carry seeds that float for long distances Animals cockleburs stickers stick to animals and spread fruit is eaten by the animal and not fully digest the seed excrete the seed and fertilize it in the process Humans seeds stick to our cars are on boats or are planted Seed protection Self burial seeds such as wild oat seeds will bury themselves into the ground using a geniculate awn Dormancy seeds or buds will not germinate or grow even under proper environmental conditions This can be considered temporal life insurance If these types of seeds are used as crops they need to scarified Hormones in dormancy and germination ABA abscisic acid peaks during embryogenesis induces dormancy helps maintain dormancy GA gibberellic acid synthesized during germination breaks dormancy in some species controls dormancy release Ethylene C2H4 relieves dormancy in some species These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Mechanisms for seed dormancy Hard seed coat water and oxygen uptake are prevented cell expalnsion and raicle protrusion may also be prevented o Mechanical or chemical scarification required to germinate and let water in Presence of chemical inhibitors usually in seed coat mosly phenolic compounds protects against pathogens relieved by water leaching Physiological requirements o dry after ripening warm 23 degrees Celsius dry 20 30 RH storage required for many grass seeds o stratification cool 4 10 degrees Celsius moist storage required for many flower bulbs potatoes fruit trees completion of post maturation processes true embryo dormancy dormancy is controlled by unknown factors in the embryo polygenic quantitative trait many genotype x environment G x E interactions
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