Plant tropisms and hormonal control Chapter 14

Aims: > describe the hormonal system of plants & list the 5 main groups > environmental stimuli & plant response > phototropism, geotropism & thigmotropism = movements > how light effects seedlings > rel’ship btw photoperiod & flowering in plants > turgor (water pressure) leads to movement in plants > describe bud dormancy, seed dormancy & vernalisation

Plants > fixed position (therefore have to make do with the environment) > have to become TOLERANT of changes > communication between cells is controlled by HORMONES

What is a Hormone? A c_____ produced by cells in the plant that can be transported to other cells in the plant. Hormones help with the TIMING of responses (eg. when to flower or produce new buds) Hormones TARGET particular cells for them to RESPOND. Less specific in plants than in animals.

Tropisms A DIRECTIONAL growth response of a plant to a stimulus. Growth is either towards or away from a stimulus

The 5 things that PLANT hormones are responsible 4: 1) Phototropism – growth in response to light. Photo = light. 2) Geotropism (Growth in response to Gravity) 3) Apical dominance – stopping lateral branches from growing – gardeners would rely on this hormone if they wanted their plant to grow TALL without side branches 4) Ripening of fruit 5) Abscission – shedding of leaves and flowers (particularly with deciduous trees – in autumn)

Shedding of leaves – Deciduous trees!

5 types of HORMONES to affect the changes of the plant > 1) Auxins: produced in the meristem (tip of plant), concentrates on the opposite side of the plant to the light source & when in excess it INHIBITS buds on the sides > 2) Gibberellins – whole plant growth > 3) Cytokinins – cell division > 4) Inhibitors – one type = abscisic acid (ABA) – helps plants to adapt to their enviro. STOPS growth. Concentration increases in stressed conditions. Therefore conserve resources. > 5) Ethylene – for ripening fruits and flowers. It’s a gas.

Hormone Where produced Effective site Action Visible effect Auxins Shoot tip (meristem) Growing region of shoot Cells elongated under turgor pressure Tip bends towards light; apical dominance; used as herbicides; stimulate cuttings to root Gibberellin Fruits, seeds growing buds, elongated stems Roots, shoots, seeds; also found in fungi Growth of cells Shoot elongation, germination of seeds, flowering fruit enlargement Cytokinins Roots and developing fruits Branch and leaf buds; moves through xylem and phloem Stimulates cell division, cell enlargement and tissue differentiation Growth of lateral branches; used to promote life of vegetables in storage Abscisic acid chloroplasts Gene expression in nuclei Growth inhibition Seed dormancy; vernalisation; drought-tolerance Ethylene Ripening fruits; flowers, seeds, leaves and roots Cellular metabolism Fruit ripening; leaf drop Fruit ripening; leaf and fruit drop; used commercially to ripen bananas and pineapples

Environmental Stimuli What is a stimuli? 2 types: chemical & physical PHOTOTROPISM – seed growth towards light – mostly BLUE light. What wavelength? GEOTROPISM – shoots grow away from gravity (negatively geotropic) THIGMOTROPISM – touch & contact with a surface (eg. vines twirl around objects). Create a table that summarises the similarities and differences between these different types if tropisms. https://www.youtube.com/watch?v=ktIGVtKdgwo&sns=em&hd=0

Photoperiod Length of the NIGHT affects growth = PHOTOPERIOD. Short day & long day plants. Therefore can only flower in certain environments with the RIGHT night length. Note: Day length does NOT affect growth

Turgor Turgor = water pressure. Stomata -> respond to the pressure by opening or closing. Respond to the levels of CO2, light, humidity (water in the air)

Dormancy Seeds remain dormant until conditions are RIGHT (dormant during winter). Vernalisation = exposure to cold conditions to break seed dormancy

Questions: How do we use plant responses to our advantage in agriculture? What is the advantage of being anchored to the ground if you are alive? Answers: Via location, soil moisture, sunlight Constant nutrient access