39 - Plant Responses to Internal and External Factors

39.1 - Signal transduction pathways link signal reception to response

• plants have some of the largest genomes on record

• plants respond to external stimula by altering development

• etiolation - physical adaption for growing in the dark

  • High shoot growth

  • no leaves

  • short root

  • de-etiolation - when a plant reverses etiolation

Reception

• signals detected by proteins that change shape in response to a stimulus

• in deetiolation, the protein is called a pyhtochrome

  • this is uniquelly locating in cytoplasm, not the membrane

Transduction

• transduction of weak stimuli require second messengers

  • second messengers - molecules and ions that amplify a response and transfer it

• In de-etiolation, both calcium ions and cyclic GMP are used

  • phytochrome activiation leads to a 100 fold increase in calcium ions in the cell

  • the shape change also means that guanalyl cyclase is activated, creating GMP

  • both must be activated to work

Response

• the activities involved with second receptors lead to a response

• transcriptional response alters mRNA encoding of an enzyme

• post-translational response - activates preexisting enzymes

39.2 - Plants use chemicals to communicate

• plant growth regulator - hormones tha tcontrol 1 or more physiological aspects of a plant

Survey of Plant Hormones

• Auxin

  • tropism - turn

  • phototropism - plant turn to light

  • auxin - any gormone that causes coleptile curvature

  • moves only tip to base

  • polarly distributed

  • also elongates cells in shoots

    • onlt in 10^-8 to 10^-4 M

    • auxin stimulates proton pumps

      • reduces ph

      • actives expansins that loosen wall fabric