Table 10.2: (continued)Hormone Function
Cytokinins Promote cell division; prevent senescence
Abscisic Acid Close the stomata ; maintain dormancy
Auxins Involved in tropisms and apical dominance(Source:Jessica Harwood,License:CC-BY-SA)
Ethyleneis the plant hormone involved in ripening fruit and withabscission,the dropping
of leaves, fruits and flowers. When a flower is done blooming or a fruit is ripe and ready
to be eaten, ethylene stimulates the production of enzymes that allow the petals or fruit to
separate from the plant (Figures10.27and10.28). Ethylene is an unusual plant hormone
because it is a gas. That means it can move through the air, and a ripening apple can cause
another to ripen, or even over-ripen. That’s why one rotten apple spoils the whole barrel!
Figure 10.27: The hormone ethylene is signaling these tomatoes to ripen. ( 25 )Gibberellinsare growth-promoting hormones. When gibberellins are applied artificially
to plants, the stems grow longer. Therefore, gibberellins can be used in horticulture to
increase the growth of ornamental plants, whereas dwarf plants have low concentrations of
gibberellins (Figure10.29). Another function of gibberellins is to break the dormancy of