Can plants take hormones to improve their performance?

GIBBERELLINS Plant hormones that cause stem elongation and cell division.

ANSWER: In a manner of speaking, yes. Gibberellins are plant hormones that promote growth. Scientists have identified more than 100 different types of gibberellin. One effect of gibberellins is to provide the chemical cue for seeds to germinate and grow. When conditions are right for a seed to germinate—when rising temperatures begin to melt frost, for example—these growth-promoting hormones give the green light for a seedling to grow.

ABSCISIC ACID (ABA) A plant hormone that helps seeds remain dormant.

Applying gibberellins to a young plant can increase the length of its stem, which also indirectly increases the size of its fruits—a fact that makes them very useful in agriculture. Gibberellins are commonly used to increase the size of seedless grapes, for example. On an untreated seedless grape plant, the stem remains relatively short, so the bunches of grapes growing on the stem are clustered densely together, resulting in small grapes. When sprayed with gibberellins, the stems grow longer, giving the grapes more room to grow. Because seeds are the normal source of gibberellins, seedless grapes have no source of gibberellins to help them grow naturally, which is why farmers need to spray them in the first place.

In many species of plant, seed germination is controlled by the balance between the growth-promoting properties of gibberellins and the growth-inhibiting effects of another hormone, abscisic acid (ABA). ABA is the plant hormone that keeps seeds dormant—for example, over the cold winter months, when conditions for growth are not ideal. With appropriate environmental cues—the right combination of temperature, moisture, and light—ABA is degraded and gibberellins are synthesized, leading to the end to dormancy and the start of germination. You can think of ABA as the brakes and gibberellins as the gas pedal: as the brakes on growth are lifted, the gas pedal is pressed, ushering in a new season’s blooms (INFOGRAPHIC 32.10).

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INFOGRAPHIC 32.10 HORMONES TRIGGER PLANT GROWTH AND DEVELOPMENT
Certain plant hormones regulate growth and development of plants. When humans apply these hormones to crops, plant growth can be dramatically enhanced.