Plant responses This weeks homework Any workbook pages between 40 - PDF document

25/07/2016 • Workbook from last week – 86-94 – questions? Plant responses • This weeks homework – Any workbook pages between 40 and 94 that you haven’t done (we have done most of these). • Holidays – Plant responses pg’s 99-110 – Facebook me if you get stuck – highlight any you want to ask about next term. Tropisms Phototropisms • Direction of plant growth plants grow in response to light in response to a stimuli Positive phototropism: growth towards light (stems) • Compared with Taxis and Kinesis (movement of animals) Negative phototropism: growth away from light (roots) thigmotropism hydrotropism gravitropism chemotropism 1

25/07/2016 Do plants grow towards or away from light? https://www.pathwayz.org/Tree/Pl Why? ain/PHOTOTROPISM+- How? MECHANISM • A hormone called auxin (eg indole acetic acid or IAA) is made by the growing tips, or meristem, of shoots and roots. • How can we prove that auxin is made in the meristem? • This means there is more auxin on the shaded side just below the tip. • Auxins change the flexibility of cell walls and this allows for more rapid growth of the cells. • The net result is that the shoot tip grows towards the light (remember photosynthesis requires light). 2

25/07/2016 What do these experiment suggest? What does this experiment suggest? What does this experiment suggest? • The auxin is water soluble and diffuses from the tip • Therefore removing the tip and placing it on Agar - will not stop it diffusing In a bioassay, concentration is expressed in terms of biological effect rather than quantitatively. Went (1926) • The auxin is water soluble and diffuses from the tip • Therefore removing the tip and placing it on A sheet of mica or foil - will stop the diffusion 3

25/07/2016 • Stem growth is faster with HIGHER auxin concentrations. • But root tip growth is faster with LOWER auxin concentrations • In shoots, auxin stimulates growth. • In roots, auxin inhibits growth. Conclusions? • When a shoot tip is exposed to light the auxins move to the shaded side of the tip. • How can we prove this? 4

25/07/2016 https://www.youtube.com/watch?v=H9 MV5CgPgIQ • This weeks homework – Any workbook pages between 40 and • Always – link to survival 94 that you haven’t done (we have done most of these). • Holidays – Plant responses pg’s 99-110 – Facebook me if you get stuck – highlight any you want to ask about next term. Plant Hormones Plant 1. State the effect of auxin on roots, shoots and lateral buds. Hormones 2. Describe and explain apical dominance. 3. Describe the origin and effects of - gibberellins. - cytokinins. - ethene (ethylene) gas. - abscisic acid. 4. What are some applications of each of these plant hormones in industry? Apical dominance and auxins Apical dominance • auxins from the apical meristem inhibit the • Apical dominance is where the lateral buds central stem of the plant is dominant over (i.e., grows more strongly than) other • If the apical meristem is lost, side stems. then the lateral buds start growth due to the lower auxin levels. • Apical dominance is caused by auxin produced in the growing tips 5

25/07/2016 1. Low [auxin] stimulates root and lateral bud growth. High [auxin] inhibits. High [auxin] stimulates shoot growth. 2. Apical buds inhibit lateral bud growth. Remove the apical bud and lateral buds grow as [auxin] drops. The effect of Gibberellic acid • Gibberellins play an important role in germination, initiating the mobilisation of nutrients stored within the seed. • Absorption of water by the seed causes production of GA (gibberellic acid) . • They also promote the elongation of stems, flowering and cell division (growth). Overcomes seed dormancy Increases height of plants The he ef effec ect of of Ab Abscisic acid Abscisic acid (ABA) • Causes leaf fall • In general, abscisic acid inhibits growth / germination. • Controls stomatal opening • Abscisic acid induces bud and seed dormancy, preventing germination during winter. • Abscisic acid also preventing seeds from germinating within the fruit • It slows growth in more "mature" parts of the plant and closes stomata (tiny pores on the undersides of the leaves) in response to a lack of water. 6

25/07/2016 The effect of ethylene Ethylene • A gas that promotes fruit ripening and abscission (drop) of leaves and fruit. • Ethylene production increases when the seeds are mature, ensuring the fruit is released when only when the seeds are capable of germination. ripens • Fruit often releases ethylene gas as it ripens (this is why storing unripened fruit with a ripening apple will accelerate the ripening process). Recap • Many plants have their time of flowering delayed unless they • Plants respond to their environment by growing – a response have undergone a preceding called a __ 1 ___. period of wintertime cold. • They can do this because of hormones called ___ 2 ____ which are made in the ____3____ . Growth can be towards a • The change brought about by this stimulus eg ___ 4 _____ or away from it. prolonged exposure to the cold is called vernalisation . • Early experiments were done with sheaths covering grass shoots called ___ 5 ____ Expts showed that the sensitive part is the ___ 6 ___ and it causes its affects by _ _ 7 _ Recap Summary of Functions of Major Plant Hormones Hormone Function Location stem elongation produced in shoot Auxins (IAA)* apical dominance apical meristem • Lots of hormone in stem cells cause _ 8 _ _ whereas in root formation root cells it causes _ _ 9 _ _ . cell division Cytokinins produced in roots differentiation • Non directional responses to a stimulus eg a flower stem & intemode closing at night are called __ 10 ___ responses. Gibberellins produced in apical portion of root & elongation (GA)* shoot seed germination • Being positively thigmotropic is of adaptive value abscission produced in leaves, stems & young because _ _ _ 11 _ _ _ Ethene/ethylene* fruit ripening fruits supression of bud growth 12. Draw the resulting Abscisic Acid stomatal opening mature leaves, fruits & root caps leaf senescence root tip showing WHY Root tip *most horticultural/ agricultural applications this is what happened light 7

25/07/2016 3.Giberellins produced in young leaves, buds and 4. Giberellins used to increase height of plants, roots. Stimulate internode growth, flowering induce flowering, induce germination of grain and germination. Breaks dormancy. in brewing process. Cytokinins produced in roots. They promote Cytokinins extend shelf-life of plants by cell division and slow the aging process. preventing abscission. Ethene gas produced by all parts of plant. It Ethene gas used to ripen fruit and cause causes fruit to ripen and leaves to age. fruit abscission on demand. Abscisic acid produced in stalks. Inhibits bud development, seed germination and causes leaf and fruit abscission. Summary of Functions of Major Plant Hormones Hormone Function Location IS stem elongation • Complete worksheet and practice questions produced in shoot Auxins (IAA)* apical dominance apical meristem root formation • To discuss on Thursday cell division Cytokinins produced in roots differentiation • This weeks homework – Any workbook pages between 40 and stem & intemode Gibberellins produced in apical portion of root & elongation 94 that you haven’t done (we have done most of these). (GA)* shoot seed germination Ethene/ethylen abscission produced in leaves, stems & young e* fruit ripening fruits supression of bud growth stomatal opening Abscisic Acid mature leaves, fruits & root caps leaf senescence *most horticultural/ agricultural applications Today Remember Kinesis ??? • Describe Nastic responses • A kinesis is non-directed orientation – moves, but not towards or away from a stimulus. • Explain the adaptive advantage of nastic responses • The amount of movement is related to the extent of the stimulus 8

25/07/2016 Nastic Responses in Plants Nastic responses: • Plant reacts to strength of stimulus • https://www.youtube.com/watch?v=bczox-dDKP0 • https://www.youtube.com/watch?v=L9cxT0Uv9n4 • eg light, touch, temperature but not to • https://www.youtube.com/watch?v=n859bkmNXsU the direction of the stimulus • What would happen with thigmonasty? • What would happen with photonasty? • Leaves move to touch • flower opens/closes in response to light • What is the adaptive advantage? • What is the adaptive advantage? Do Workbook pages Etiolation • Stimulus is… • 107-109 – Nastic responses. lack of light What is the adaptive advantage? 9