Gibberellins comprise over 136 different molecules known to scientists in all vascular plants and fungi. These plant hormones play many roles in plants, including stem and shoot elongation, sex expression of male flowers, seed or spore germination and development of flowering. Not all gibberellins in a plant are active; some are intermediate molecules that are stored and/or used to construct larger molecules that do play roles in plant growth, according to "Plant Growth and Development" author Lalit Srivastava.
Each plant species relies on various types of gibberellin for its own growth. These plant hormones cause many different physiological effects in plants. Thus, one plant species may employ gibberellins that another may not, or use different combinations of the hormones to complete growth and conduct certain functions, according to the Plant-Hormones website.
Gibberellins are created in three steps in three different areas within the plant cells. Initial atoms and molecules of gibberellins are fused together with the assistance of enzymes. All three stages occur in various locations and solutions within the cytoplasm inside a living plant cell. These hormones are created anywhere in a plant and gibberellins are both stored in cells or relocated via the vascular system to other areas of a plant, according to the Plant-Hormone website. Some are produced locally in only specific areas of a plant, such as in a sex organ in a flower.
When present, the various gibberellins stimulate shoot elongation, whether of stems, leaves or flower buds. They also help release seeds, embryos and branch tip buds from dormancy, according to an online plant propagation course reference outline from the University of Florida. However, an abundance of gibberellins in plants can inhibit formation of adventitious roots---those that develop from stems that come in contact with soil, for example.
Gibberellins do not exist in a vacuum within the plant. They co-exist with other plant hormones with complementary or opposing roles. The interaction between these hormones, concentrations in cell cytoplasm or in various plant parts, regulates plant growth overall. For example, auxin is a hormone known to encourage root growth and cytokinin tends to inhibit shoot elongation. Depending on the concentration of these hormones alongside gibberellin, the plant responds. Too much cytokinin limits the shoot-elongation initiated by gibberellin. Too much gibberellin limits formation of roots even if auxin is present. All effects of variable hormone concentrations are dependent on the plant species, according to the University of Florida.
While there is great scientific understanding of the role of gibberellins---their number, structure or effects---there is much less overall understanding across all plants on formation, consequences and interactions of these plant hormones. General rules seem to exist, but exceptions or mysteries remain. While research can prove a specific role or means of gibberellin synthesis in one plant, the rules often do not directly apply to another plant. In other words, there is little understanding on how and why gibberellins act or seemingly are turned "on" or "off" in plants.