BIOL 2500Botany

1
BIOL 2500--Botany

• Lecture 29
• Chapter 28 The Plant Hormones

2
Learning Objectives

• Define
• Totipotency
• Extensibility
• Contrast
• Coding vs. regulatory sequences
• Turgid vs. flaccid

3
Totipotency

• A single plant cell contains all genetic
  information to make an entire adult plant
• All plant cells have all the plants genes
• Differences in cell function in structure are due
  to differences in gene expression

4
Coding vs. Regulatory Sequences

• Useful DNA can serve 2 functions
• Serving as a recipe for proteins (these are
  coding sequences)
• Acting as a switch to turn coding sequences on
  off

5
Alpha Amylase Regulation

• Experiments in germinating barely show
• Gibberellic acid increases a-amylase production
• Abscissic acid decreases it

6
Extensibility

• If cells enlarge, the cell wall must stretch
• Extensibility is the ability of the cell wall to
  stretch permanently
• Turgor pressure important
• Not very well understood
• Two alternative hypotheses

7
Cellulose Review

• Note hydrogen bonds (dots)

8
Extensibility Hypotheses

• 1) Acid growth hypothesis Proton pump in plasma
  membrane activated by hormones
• Non-cellulose cross-bridges broken
• 2) Auxin may also stimulate delievery of new wall
  materials

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Microtubules

• Microtubles are the biggest cytoskeletal elements
• Quick for cell to produce

10
Microtubule Orientation

• Error in figure!!!
• Random orientation
• Growth in all directions
• Auxins cause transverse orientation
• Causes longitudinal expansion
• Primary growth increasing plant height
• Ethylene causes longitudinal orientation
• Lateral expansion occurs

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Elongation
12
7th Inning Stretch
13
Tonicity

• Always remember to ask How is the concentration
  OUTSIDE of the cell

14
Opening Stomata

• Guard cells must uptake solutes
• Outside of cell is now LOWER in solutes
• Becomes. (starts with an H)

15
Abscisic Acid Stomata

• High turgor pressure keeps guard cells turgid,
  stomate open
• When water stress occurs, ABA produced
• Signals cell to let ions through cell membrane
• Osmotic gradient destroyed
• Guard cells become flaccid