Believe it or not, there are other plant growth regulators besides auxin! Gibberellin is a plant growth regulator that
stimulates both cell elongation and cell division. There are over fifty known
gibberellins, identified as GA1, GA2, GA3, etc. Even very tiny amounts of these substances
can cause dramatic changes in growth in plants. Gibberellins affect the length of the stem
between nodes (the internodes), and therefore the overall height of the plant.
Gibberellins also influence flowering cycles and can cause seeds to break out of dormancy
and begin to grow.Generally speaking, gibberellin
has a lesser effect in bright light, resulting in a plant with a compact form and
relatively short internodes. In low light levels, gibberellin acts to increase internode
length, allowing the plant to stretch and reach for light. At the extreme, the stem grows
so tall it becomes too weak to support the plant, a condition called etiolation. This phenomenon is familiar to seed
starters—especially those who forget to turn on the lights once their seeds have
sprouted!
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