Chapter 36 Overview of plant behavioral responses Behavior is a response of an organism to an internal or external stimulus types of plant behavior movement bending,twisting, or rotating nutation rapid movement as in sensitive plants response to touch growth seed germination seasonal production of reproductive structures defensive responses to attacks thorns, spines, chemicals Responses to internal and external stimuli Internal Internal biological clock circadium rhythms chemical signals transcriptions factors and other proteins or hormones often interact with each other and external signals External light atmospheric gases (CO2 and water vapor) temperature, touch, wind, gravity, water, rocks, and soil minerals Herbivors, pathogens, organic chemicals from neighboring plants, and beneficial or harmful organisms Plant Behavior Involves internal and external stimuli tropism growth response that is dependent on a stimuli that occurs in a particular direction Reception molecules located in plant cells sense stimuli and cause response Phototropism Growth response to light light causes movement of hormone auxin away from said light result in unequal distribution of auxin causing unequal cell elongation positive tropism Gravitropism growth response to gravity positive tropism roots negative tropism shoots columella cells in root cap/tip region sense gravity  Thigmotropism  Growth response to touch roots columella cells cause roots to grow around obstacles Regulation of plant growth Hormones chemical messengers that regulate plant growth most transported in phloem tissue all require an expenditure of energy on part of the plant (ATP) for transport interact with external environmental stimuli Hormones control growth seed germination flowering fruiting shedding of leaves color change of leaves Hormones of two broad categories growth inhibiting mostly fall/winter certain times of the year growth is not good growth promoting mostly spring/summer Auxins first group of plants hormones to be described growth promoting produced in shoot tips, seeds, fruits, leaves, stem NOT in the roots Effects of auxin Promotes cell elongation shoot elongation production of wood fruit development Inhibits lateral bud development absission (falling off) of leaves, flowers, fruits Cytokinins Originally detected in coconut "milk" growth promoting prodiced in seed, fruits, roots Effects of Cytokinins Promotes cellular division named derived from Cytokenesis Inhibits senesence change of color due to breakdown of pigments Gibberellins (giberellic acids) many types >200 more than any other group growth promoting found throughout the plant but concentrated in seeds Effects of Gibberellins Promotes stem elongation by cell division and cell elongation intake of water causes swelling and embryo hydration embryo secretes gibberellins gibberellins transported to cells of aleurone layer to secrete enzyme (alpha-amaylase) for breakdown of endosperm (starchy stored food) to glucose embryo will respire glucose to produce ATP embryo is directing the timing of plant germination Advantage seed plants Brassinosteriods growth promoting Effects of Brassinosteriods Promotes cell expansion shoot elongation xylem tissue development stress response Inhibits leaf abscission Abscisic Acids (ABA) Growth inhibiting found in large quantities in seeds. mature leaves, and dormant buds Effects of ABA Promotes senesence production of storage molecules in seeds Inhibits cell elongation alpha-amaylase production Ethylene growth inhibiting actually a gas produced by incomplete metabolism interacts with the 4 growth promoting hormones to determine cell size and shape Effects of Ethylene Promotes fruit ripening abscission of leaves, fruits, flowers Seed germination requires breaking of dormancy combination of internal and external factors Internal hormones stored food H2O absorption embryo swelling External sunlight temperature longer day light soil moisture Generalized Seed Seed coat(s) as seed coat cracks Radical comes out first then then shoot Seedling result of cellular reproduction and increase size internal development cells>tissues>organs>organism