Plant hormones are involved in many aspects of plant function and development

Plant hormones are involved in many aspects of plant

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Plant hormones are involved in many aspects of plant function and development Hormones guide growth 8 major types Auxin One of first plant hormones to be discovered Stem elongation o In the stem’s phototrophic response, auxin migrates to the dark side of the stem, causing more elongation in these cells Cell expansion Makes cell walls soft and plastic and allows cells to enlarge Produced in shoot tip o produced in shoot apical meristem Most well studied auxin – indoleacetic acid (IAA) Synthetic auxin o Used as herbisides by disrupting plant growth as a result of high concentrations that are applied Cytokinins Cell division and differentiation Interacts with auxin o Sometimes works in opposition to auxin o Cytokinin promotes growth of lateral buds in the shoot and auxin suppresses the growth of lateral buds o Suppression of lateral buds by auxin is called apical dominance o Cytokinin inhibits lateral roots and auxin promotes lateral roots o Interaction of these two hormones can influence the production of lateral shoot branches and root branches and the overall form of the plant Produced in root tip and travel throughout plant Strigolactones Newly discovered hormone Help shape plant form in conjunction with auxin and cytokinin Derived from carotenoid pigments Inhibits axillary bud growth Moves upward from roots through shoot Gibberellins or gibberellic acid (GA) Produced in root and shoot tip Stem elongation
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Can work in conjunction with auxin Sometimes used commercially to increase internode length between grape flowers so fruits have more room to grow Promotes seed germination in some plants Ethylene Gas Stimulated by release of auxin from developing fruits Fruit ripening o Break down of complex carbs to simple sugars o Chlorophyll degradation o Softening of cell walls o Release of volatile or airborne compounds associated with odors and taste of ripe fruits o Ethylene speeds up ripening o CO 2 slows down ripening Abscisic acid – growth suppressant and dormancy ABA, does not play role in abscission Important in maintaining dormancy in winter buds and seeds Seems to counteract the effects of other hormones that promote growth and germination such as auxin and gibberellin To break dormancy – levels of ABA must decrease in buds and seeds Bud dormancy Seed dormancy Stomatal opening and closing o Triggers movement of potassium ions out of the guard cells Two additional hormones Brassinosteroids o Structurally similar to animal steroid hormones o Stem elongation o Cell division o Bending of stems o Delayed senescence Oligosaccharins o Formed from oligosaccharides o Defense signaling o Play role in growth and organ development Reproductive Development Flower production is just one phase in development
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Flowers o Reproductive maturity – must gain confidence to response to internal signals and environment cues that regulate flowering
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