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The life of a Higher Plant
Seed Biology
-Break of Dormancy
-Hormones
1)abscisic acid [ABA]
2)cytokinin
3)giberellin
• The kind of dormancy break thats not really visible- Example is of a Red
Maple leaf
...
The time it will take for the flowers to bud
out really depends on the temperature
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If you place these flowers in a
warm environment, they will not flower out or break dormancy because
they haven’t accumulated sufficient cold in order to flower out
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• [Refer to notebook] - diversity of structures that are involved in hormones
involved with higher plants
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• Ethylene is a gas that often plays a crucial role in ripening and can cause
germination as well
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In the fall this hormone causes
leaves to fall
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• The cytokinin in terms of cell division is actually a chemical that tends to
induce cellular division and has an effect on the plant and animal system
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Can see that the
nitrogen base component is DNA related
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• Giberellins are absolutely brutal in terms of their structure
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One of the
reasons its bad is because its related to biological warfare
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this is a hormone that is generally
synthesized inside a plant- it falls over the fungi eats it resulting in a
happy fungi
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• Indole-3’-acetic acid, an auxin is interesting and is a natural synthesized
hormone inside a plant- plays a crucial role in the development of a plant

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and if you spray this hormone on the outside of a plant
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These
compounds or hormones are then used as herbicides
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This ideology goes a long way back
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Not bad is true
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Humans have auxin as a by product or the urinary tract and has
minimal crossover to humans
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Bad history is that this chemical is used in
warfare- in the Vietnam war
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It is toxic to
humans in high levels so the possibility of humans being affected is quite
possible
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We are more closely related to
insects and so the possibility of a crossover is more likely with an
insecticide of which there are many many kinds
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In terms
of the media its both weed killers and insects as well
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Some of
the more natural ones are quite poisonous to humans as well
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This particular picture is shown as a function of a particular hormone inside a
seed
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Increase of hormone with growth is correlated with germination and have been
said to be stratified
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Just because germination has
occurred after 8 days of warmth, doesn’t mean that giberellin caused the seed
to germinate
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We shall use GA which is the
inducer of germination and ABA which is the inhibitor
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Add giberrellin and we got 81% germination
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So virtually no germination occurs when we do the exogenous treatment with
ABA
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ABA inhibits germination and gibberellin [GA] overcomes
the ABA inhibition of germination and doesn’t actually cause germination to
occur
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The above picture looks at the endogenous process and this is actually during
stratification within a period of 60 days
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Get
a cytokine peak and a GA “flush” when sufficient stratification has actually

occurred
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Exploring in the next couple of lectures is a process known as inhibition and
uptake of water by the seed and then germination occurs
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The food reserves allow the seed to engage in inhibition and thus
germinate
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Water is very important in the initial vulnerability
of the seed
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Another thing it does is that it effectively anchors it to the soil
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Needs to effectively anchor itself in order to effectively push up
through the barrier of soil and then the way it actually pushes it up from the soil
varies
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