Contents: Environment Plant Movements Phototropism Tropism Mechanism Other Tropisms Nastic Responses Hormones Ti

1. PLANT RESPONSES Contents: Environment Plant Movements Phototropism Tropism Mechanism Other Tropisms Nastic Responses Hormones Timing Plant Rhythms Flowering Phytochrome More Phytochrome Plant Relationships US 8934 Relate aspects of plant responses to environmental factors AND AS 90716 Describe animal Behaviour and Plant Responses to Environmental factors

2. ENVIRONMENT The environment of an organism is made up of all of the factors that affect it. A habitat is a zone with a certain range of factors, such as a savannah. An organism has adaptations that help it survive in its habitat. The better adapted it is, the more chance it has of successful reproduction – survival of the fittest. Biotic Factors: Intraspecific Competition Cooperation Aggression Reproduction Interspecific Competition Exploitation Mutualism Commensalism Abiotic Factors: Light Water Wind Humidity Nutrients Gravity Temperature

3. PLANT RESPONSES Plants can move to respond to the environment. There are two types of movement… TROPISMS are growth responses, and act in a direction relative to the stimulus (positive or negative). NASTIC RESPONSES are fast, reversible movements and are non-directional. The stimuli for growth may be: Light Water Gravity Chemicals Touch Temperature This is called a: Photo Hydro Gravi/Geo Chemo Thigmo Thermo For instance: the opening and closing of flowers during the day is a type of… Photonasty Nasty or Tropism Manual pg 178/9

4. PHOTOTROPISM A well-studied example of a tropism is Phototropism. Many experiments have been done using coleoptiles (growing shoots). What is the adaptive advantage of this response? Increased light… more photosynthesis. Check out some time-lapse footage of TROPISMS.

5. POSSIBLE TROPISM MECHANISM An explanation for what is happening inside the plant is that a hormone called auxin (or IAA – indoleacetic acid) controls the elongation of cells. Cells on the shady side elongate more – plant bends. Light breaks down auxin on the sunny side. Auxin sent out from the tip – encourages cell elongation. Manual pg 180

6. AUXIN Auxin has a number of functions, and can affect different cells in different ways. Auxin naturally moves down the plant due to gravity and so collects on the lowest surfaces of stems and roots. In the stem it promotes cell elongation, leading to negative geotropism. In the roots it inhibits elongation → positive geotropism. As it comes from the tip, the concentration decreases down the plant. In high conc. It inhibits lateral buds, in lower conc. It promotes the buds. This leads to apical dominance. Removing the tip of a plant makes it grow bushy.

7. OTHER TROPISMS What is the advantage of this? Stem: Gets light, PS, reproduce more Roots: Gain water, nutrients, stability. Roots are positively hydrotropic Collect more water Some stems are positively thigmotropic and grow around other objects Increased light without energy output on structure Roots, either positive or negative Gain or avoid chemicals Manual pg 181

8. NASTIC RESPONSES They provide much faster response to a stimulus than tropisms. They are often controlled by water (turgor) pressure. Some examples are: The opening and closing of stomata Sleep movements (leaf droop at night time) The opening and closing of flowers during the day Check out some time-lapse footage of NASTIC RESPONSES (esp. 1st three and last one - sunflower nutation) Manual pg 182

9. HORMONES Plant hormones (unlike animals’) can produce a number of responses, many of which overlap, and interact with other hormones to promote or inhibit them, depending on the conditions. Some of the main aspects of each type… Manual pg 183/4

10. TIMING Both plants and animals need to be able to detect time in order to coordinate activities in appropriate conditions. • There are a number of environmental cues. • These include astronomically caused cycles, such as... • The earth orbiting the sun (seasons) “circannual” • The Moon orbiting the Earth (phases of the moon) “circalunar” • The Earth spinning on its axis (day/night) “circadian” Manual pg 187

11. PLANT RHYTHMS A plant’s “Biological Clock” is controlled by either: endogenous factors (inside the plant – genetic) exogenous factors (outside the plant) – environmental Some circadian rhythms are: flower opening and closing, leaf tilt, stomata opening and closing, and sun tracking. Some seasonal rhythms are: acclimationdormancy vernalisation stratification Most seasonal rhythms are in response to temperature, moisture or photoperiod. Find definitions for these on page 196 of the manual. Manual pg 195

12. Pr Pfr FLOWERING Flowering (as well as a number of other responses) is controlled by the phytochrome system. Leaf Detects light Flower bud Begins development Message sent with hormone called Florigen (theoretically). Phytochrome has 2 forms: Fast with red light (from the sun) Slow overnight Pr is “phytochrome red” Pfr is “phytochrome far-red”

13. Pr Pfr PHYTOCHROME SYSTEM Fast with red light (from the sun) After a short night (summer) there will still be lots of Pfr left. After a long night (winter) there will be lots of Pr. Fast with far red light Slow overnight Pfr→ Pr can also be achieved quickly (for experimental purposes) by using far-red light (hence it’s name). Pfrpromotes flower growth in long-day (summer) plants. Pfrinhibits flower growth in short-day (winter) plants. Day neutral plants tend to flower all of the time. Confused? DON’T PANIC!

14. MORE ON PHYTOCHROME Some experiments on the phytochrome system: Long day plant Short day plant Manual pg 197-8

15. PLANT RELATIONSHIPS Plants compete with other plants for resources, such as light, water, and minerals. Plants can reduce competition by producing chemicals that harm other species. This is called allelopathy. Some plants also protect themselves from herbivory by using spines, waxy cuticles, hard seed coats, and divaricating habit. They may also produce chemicals that are toxic or unpalatable to animals. In response, some animals have produced a resistance to these chemicals (coevolution). Plants may also undergo commensalism, mutualism or parasitism.

16. GERMINATION Why don't tomato (and other) seeds germinate when they are still in the fruit? Perhaps there is some sort of chemical inhibition going on that stops the seed growing until it has been eaten or the fruit has rotted down. The plant practical on tomato seed germination.

17. GERMINATION PRAC. RESULTS