Plant Hormones
Read pp. 748-758, & pp. 760-61 in
your text books.
Also review your CD-ROMs. Look under
Plants, then pick the Topic: Plant Response
Plant hormones are proteins produced by the plant and moved throughout the
phloem by translocation. Hormones help control the differentiation of cells,
growth, and maturation of a plant. Hormones are chemical messengers produced
in one part of an organism & transported to another where their effects
are felt.
A. Auxins: Plant hormones stimulating cell enlargement.
Found at apical meristem (stem tips) 7 causes growth toward light (phototropism).
Causes dominance of terminal bud over lateral buds.
Industry use:
1) Pruning- cut off terminal bud reduces auxins so lateral buds develop.
2) Root hormone- stimulates root formation from nodes on stem.
3) Used in weed killers (causes weeds to grow to fast).
B. Ethylene: Gassy hormone that stimulates fruit
ripening (starch changed to sugar in fruit). Example: ripe banana or apple emits
ethylene to ripen other fruit near by.
Industry use:
1) Ripen green fruit at correct time for sale.
C. Gibberellins: Stimulates cell enlargement
(growth of leaves and stems at expense of roots) & enzyme production in
germinating seeds.
Industry use:
1) Faster germination of seeds.
2) Application to plant causes larger or faster growth.
D. Abscisic Acid: Stimulates formation of winter
buds (winter survival). Controls opening & closing of stomata.
E) Cytokinins: Stimulates (in conjunction with
auxins) stimulate cell growth. If auxins are absent, they promote lateral bud
growth (make plants more bushy).
Long & Slichter