Phytochrome red far red light involved in o

This preview shows 13 out of 17 pages.

Phytochrome (red/ far red light) involved in o Photoperiodism Photoperiod: the relative lengths of night and day, is the environmental stimulus plants use most often to detect the time of year Photoperiodism: a physiological response to photoperiod Plants near the equator are more likely to be day neutral; those away from the equator more likely to use daylength as a seasonal cue Long-day plants flower whenteh daylength is logner than some critical photoperiod
Image of page 13

Subscribe to view the full document.

Short-day plants flower when the daylength is shorter than some critical photoperiod Some plants are day-neutral Flash of light in dark period must contain red wavelengths for the plant to respond o Shade detection and avoidance o Germination response to increased light o o A phytochrome exists in two photoreversible states, with conversion of Pr to Pfr triggering many developmental responses Often there is a slow conversion back to Pr at night Daylength is detected by leaves and communicated to the meristem(s) via florigen o Florigen (FT) Produced in leaf phloem companion cells Transported in sieve cells Appropriate light environment stabilizes product of another gene (CO) in the
Image of page 14
compantion cells; CO product stimulates production of FT o Phytochromes and seed germination Many seeds remain dormant until light conditions increase In the 1930s scientists at the USDA determined the action spectrum for light- induced germination of lettuce seeds Red light increased germination of lettuce seeds, while far-red light inhibited germination The photoreceptor responsible for the opposing effects of red and far-red light is a phytochrome o Phytochromes and shade-avoidance Phytochromes detect shading from neighbors Light passing through another plant has a reduced ratio of red/far red wavelengths Shading results in proportionately less Pfr form of phytochrome o Vernalization is a flowering response after a cold treatment (doesn’t involve phytochrome) but some plants require vernalization AND the correct photoperiod Plant response to mechanical stimuli Thigmotaxis o Ability of tendrils to wrap around objects is an example of thigmotropism Plant Diversity o Response to herbivores and pathogens Eating of leaves, even herbivores (like worms) eating in the roots Galls on oaks- insect causes the plant to make galls Types of plant defenses to herbivores Structural: spines, barbs, thorns Chemical Regrowth potential: intercalary meristem Examples of chemical defenses Alkaloids- strychnine, cocaine, nicotine, morphine, caffeine Terpenoids- cinnamon, cloves, cannabinoids Tannins- components of tea and wine Glycosides- mustard oils (cabbage family) or cyanogenic gylcosides that release HCN when plant is injured Resins- as in pines
Image of page 15

Subscribe to view the full document.

Latex- as in rubber trees Chemical defenses against herbivores can be broadly classified into constitutive (always there) and inducible (only when needed) o
Image of page 16
Image of page 17
You've reached the end of this preview.
  • Fall '08
  • FevziDaldal
  • Vacuole, Xylem, vascular tissue

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern