Tropisms, Nastic Movements, & Photoperiods Plant Growth & Development Tropisms Defined as: ____________________________ ______________________________________ ______________________________________ 3 Types: - Phototropism - ____________ - Thigmotropism Tropisms Defined as: Plant growth responses to environmental stimuli that occur in the direction of the stimuli 3 Types: - Phototropism - Gravitropism - Thigmotropism Phototropism Defined as: the tendency of a plant to grow toward a light source Cool corn - Can be within hours - Caused by ________________ ____________________________ ____________________________ Phototropism Defined as: the tendency of a plant to grow toward a light source Cool corn - Can be within hours - Caused by changes in auxin concentrations; auxins migrate to shaded tissue, causing elongation of cells Gravitropism Defined as: tendency of shoots to grow upwards (_________ gravitropism) and roots to grow downwards (____________ gravitropism) - Also related to auxin migration - Photoreceptors in shoots determine the light source Arabidopsis Gravitropism Defined as: tendency of shoots to grow upwards (negative gravitropism) and roots to grow downwards (positive gravitropism) - Also related to auxin migration - Photoreceptors in shoots determine the light source Arabidopsis Gravitropism - __________ (cells with starch grains instead of chloroplasts) in roots determine the gravitational pull Gravitropism - Stratoliths (cells with starch grains instead of chloroplasts) in roots determine the gravitational pull Thigmotropism Defined as: _________________ ___________________________ - Usually found in plants that need structures to wrap around as they grow (vines, climbing plants) - Stems or ________ may wrap tightly around objects they encounter to reach light Thigmotropism Defined as: a plant’s response to touch - Usually found in plants that need structures to wrap around as they grow (vines, climbing plants) - Stems or tendrils may wrap tightly around objects they encounter to reach light Nastic Movements Defined as: a plant’s response to an environmental stimulus ___________________ ______________________________________ ____________________________ Example: Venus flytrap, sensitive plant Nastic Movements Defined as: a plant’s response to an environmental stimulus that does not necessarily take place in the direction of the stimulus Example: Venus flytrap, sensitive plant Response to Seasons ______________determines growth and flowering of plants at various times of the year - Phytochrome responsible for _____ ________________________________ ________________________________ ________________________________ Response to Seasons Photoperiod determines growth and flowering of plants at various times of the year - Phytochrome responsible for plants’ photoperiod responses by detecting red light and activating signaling pathways in plant cells 4 Effects of Photoperiod on Flowering: _____________: flowers only when exposed to an extended period of darkness (Ex. Poinsettia) Long-Day Plant: flowers when exposed to a___________________________(Ex. Iris) 4 Effects of Photoperiod on Flowering: Short-Day Plant: flowers only when exposed to an extended period of darkness (Ex. Poinsettia) Long-Day Plant: flowerswhen exposed to a short period of darkness (Ex. Iris) 4 Effects of Photoperiod on Flowering: ________________________: flowers when exposed to days & nights of approximately the same length (Ex. cone flower) Day-Neutral Plant: _____________ ____________________________ ____________________________ (Ex. corn) 4 Effects of Photoperiod on Flowering: Intermediate-Day Plant: flowers when exposed to days & nights of approximately the same length (Ex. cone flower) Day-Neutral Plant: flowers regardless of day or night length (Ex. corn).