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

ENVIRONMENT Biotic Factors: Intraspecific Competition Cooperation Aggression Reproduction Interspecific Competition Exploitation Mutualism Commensalism Abiotic Factors: Light Water Wind Humidity Nutrients Gravity Temperature 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.

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 Nasty or Tropism For instance: the opening and closing of flowers during the day is a type of… Photonasty Manual pg 178/9

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.TROPISMS

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. Auxin sent out from the tip – encourages cell elongation. Light breaks down auxin on the sunny side. Cells on the shady side elongate more – plant bends. Manual pg 180

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.

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

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 Manual pg 182 Check out some time-lapse footage of NASTIC RESPONSES (esp. 1 st three and last one - sunflower nutation)NASTIC RESPONSES

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… Auxins (IAA)CytokininsGibberellinsAbscissic acid (ABA) Ethylene (Ethene) Role Promote cell elongation in stems, inhibit in roots. (And others) Cell division, lateral bud growth. Inhibits leaf drop. Stem elongation. Promotes leaf fall abscission). Inhibits some other hormones, and germination, closes stomata in drought. Promotes fruit ripening, abscission of fruit leaves and flowers. Place Growing points (tips) Root tips, unripe fruit Growing points (tips) All over.All over (aging / damaged areas) Transport From shoot and root tips to other places by active transport. Through Xylem and Phloem Diffusion Normal growthFast growthProtectionRipening Manual pg 183/4

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

PLANT RHYTHMS Manual pg 195 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: acclimation dormancy vernalisation stratification Most seasonal rhythms are in response to temperature, moisture or photoperiod. Find definitions for these on page 196 of the manual.

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: P r is “phytochrome red” P fr is “phytochrome far-red” PrPr P fr Fast with red light (from the sun) Slow overnight

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

MORE ON PHYTOCHROME Some experiments on the phytochrome system: Manual pg Short day plant Long day plant

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.

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.plant practical

GERMINATION PRAC. RESULTS Conc. of juice % Germ. Ave. seedling length (mm)