Mebranes and Cell Signalling Plants

Question 1

What is development of a) plant cells and b) animal cells determined by?

Answer 1

a) genetically determined but also plastic as the plant responds to the environment by adaption at the biochemical, physiological and developmental level
b) predominantly genetically determined

Question 2

What do animals do to their environment?

Answer 2

They interact with it through behaviour.

Question 3

Describe plant meristems?

Answer 3

Occur at various locations: shoot apical meristem and root apical meristem are most important. Auxiliary meristems and lateral root meristems are also found.

Question 4

What does the removal of shoot apical meristems allow for?

Answer 4

Auxiliary meristems to grow

Question 5

What affects the lateral root meristems?

Answer 5

Nutrient status

Question 6

What does immobile but not inactive mean?

Answer 6

A plant cannot move or run from danger but it can produce toxins or unpleasant features. They do not have a central processor (eg. Brain) instead perceive the environmental signals and reposed by generating a diverse array of signal molecules that integrate their response.

Question 7

What are plant hormones?

Answer 7

Signals that coordinate the spatial differentiation of tissues and cell types within organs. Each has many different actions on differing aspects of plant growth- they have pleiotropic effects.

Question 8

What does pleiotropic mean?

Answer 8

The production of a single gene of two or more apparently unrelated effects.

Question 9

What’s the difference between plant and animals hormones in where they are produced?

Answer 9

Plant hormones are produced throughout the plant and animal hormones are produced in specialised glands.

Question 10

What’s the difference between plant and animals hormones in their types?

Answer 10

Plants have small organic molecules and peptides, animals have peptides, proteins and/or small organic molecules.

Question 11

What’s the difference between plant and animals hormones in their targets?

Answer 11

Plants have local and distinct targets and animal hormones action at distance.

Question 12

What’s the difference between plant and animals hormones in their effects?

Answer 12

Plants have varying effects dependent on interactions between other hormones and plants have specific effects.

Question 13

What’s the difference between plant and animals hormones regulation?

Answer 13

Plant hormones are locally regulated and animal hormones are centrally regulated.

Question 14

Name the types of plant hormones to be discussed?

Answer 14

Auxins and jasmonates.

Question 15

What are jasmonates analogous to in animal cells?

Answer 15

Prostaglandins

Question 16

What are jasmonates important for in normal plants?

Answer 16

Carbon partitioning, mechani transduction, senescence, reproductive development, stress responses, biotic-insects (microbes), abiotic-UV (ozone) etc.

Question 17

When are jasmonates produced?

Answer 17

In response to wounds

Question 18

What do jasmonates do to gene expression?

Answer 18

Local and systemic responses: production of volatiles, attract parasitoids, prime defences of nearby plants and up regulation of proteinase inhibitors which blocks insect digestion.

Question 19

How are jasmonates synthesised?

Answer 19

Begins in the chloroplast with cleavage of alpha-linolenic acid from chloroplast phospholipids and continues in the peroxisome where the beta oxidation pathway produces jasmonic acid.

Question 20

How does OPDA (12-oxo-phytodienoic acid) get into cells?

Answer 20

It’s a slow pathway by ion trapping but mostly by active transport through the ABC transporter.

Question 21

What regulates jasmonates activity?

Answer 21

Conjugation to amino acids, collectively know as oxilipins. Most important are jasmonate-Isoleucine and methyl-jasmonate.

Question 22

What have experiments with mutated jasmonates revealed?

Answer 22

That the plants are make sterile and they are more susceptible to disease. Both of which are rescued by application of jasmonates.

Question 23

How does jasmonate turn genes on?

Answer 23

Jasmonate Z proteins act as transcriptional repressors. Jasmonate response gene expression is low.
Jasmonate-Isoleucine promotes interaction between jasmonate Z repressors and SCF coi1 which is part of the ubiquitin mediated protein degradation pathway. Jasmonate Z proteins are degraded allowing the expression of response genes.

Question 24

What processes are auxins involved in?

Answer 24

Tropic growth, apical dominance, organogenesis and pattern formation/polarity.

Question 25

Why is auxin suggested to be essential?

Answer 25

No mutants exist that completely lack auxin.

Question 26

What’s the difference between natural and synthetic auxins?

Answer 26

IAA (indole-3-acetic acid) is a major natural and widespread auxin.

Synthetic auxins are more stable which makes them more suitable for experimental use.

Question 27

How are auxins synthesised?

Answer 27

From tryptophan via multiple routes regulated by different developmental and environmental signals. They have an indole side chain.

Question 28

How can auxin activity be modulated?

Answer 28

By conjugation, often as sugar esters, as an inactive storage form.

Question 29

How are auxins transported?

Answer 29

Moved around the plant quickly within the vascular tissue and slowly via polar transport from cell to cell.

Question 30

What does polar auxin transport allow for?

Answer 30

Concentration gradients that can shape cell responses.

Question 31

What protein is responsible for localisation of auxin?

Answer 31

PIN, multiple PIN proteins in different areas of the plants. Positioned at the top or bottom of cells to determine the direction of transport from cell to cell

Question 32

Which PIN is known to relocate due to gravitational changes?

Answer 32

PIN3 due to starch granule sedimentation.

Question 33

How does the localisation of PIN proteins and auxin concentrations change?

Answer 33

Cycling between internal membrane compartments and the site of vesicle fusion with the plasma membrane is regulated to change the distribution of PIN proteins. The levels of PIN proteins on the membrane are dynamically regulated by control the rates of export and internalisation, recycling and degradation. PIN phosphorylation states regulates the delivery to the apical or basal membranes.

Question 34

How do auxins turn on genes?

Answer 34

Like jasmonate the degradation of repressor proteins by the ubiquitin/proteasome pathway is central. No auxin causes AUX/IAA proteins to repress the gene, when auxin is expressed F-box protein SCFTIR1 degrades AUX/IAA allowing expression of the gene

Question 35

What’s the differences between plant and animal development?

Answer 35

Both develop from a zygote, both divide and differentiate.
Plant cells: expand and divide and meristems retain stem cell characteristics.
Animals cells: extensive migration and most cells become terminally differentiated, germ line is segregated very early on.