The discoveries of gibberellins and auxin led to the isolation of additional classes of plant hormones (see Table 36.2). These hormones have multiple effects, and they interact with one another in many cases.
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Cytokinins are plant hormones that affect many plant growth functions related to cell division, growth, and senescence.
The gaseous hormone ethylene has several functions related to senescence, including fruit ripening; it also affects auxin gradients during shoot development.
Brassinosteroids, or plant steroid hormones, have a variety of functions that vary among plants.