Gibberellic acid (GA) is a kind of hormone that is important for plant growth. The “green revolution” of farming occurred largely due to the application of gibberellic acid to crops. Scientists are discovering the many ways in which gibberellins aid plant development, while discerning the methods by which they are transported and synthesized in plants.
Gibberellic acid (GA) is a hormone found in plants that aids in plant growth and development. It is commonly used in agriculture to increase crop yields.
Gibberellic Acid Description
Gibberellic acid, or GA, is a hormone found in plants. Gibberellic acid can be found in growing plant tissues like shoots, young leaves and flowers. It is weakly acidic. Another name for gibberellic acid is gibberellin. Gibberellic acid can enter cell membranes via simple diffusion. The acids can also be aided by influx transporters, which are proteins that can move GAs across the cell membrane. One kind of influx transporter is a nitrate transporter 1/peptide transporter (NPF). Other such transporters include SWEET13 and SWEET14, which apparently transport sucrose to the phloem of the plant. The inside of the cell possesses lower acidity (a higher pH), and so GA becomes negative in charge. After that point, the gibberellin cannot escape the cell without being joined to another component. Scientists presume that there must be transporters that can move gibberellin out of the cytoplasm again, but so far these “efflux transporters” have not been found.
Over 130 types of gibberellic acids have been discovered so far. Several of these are not biologically active (bioactive), so they serve as precursors for bioactive GAs such as GA1, GA3, GA4 and GA7. The biosynthesis of these active GAs is not well understood, but scientists are making gains in this area. While nonbioactive GAs appear to move long distances in plants, bioactive ones do not tend to do this. It is clear that GA can move into phloem sap of plants, and that it aids growth and development of the plants, as well as their flowering. Apparently GAs can move across short distances as well. In the case of GA9, this gibberellin is made in plant ovaries and is relocated to petals and sepals. From there, it undergoes changes to become GA4. This bioactive hormone in turn affects plant organ growth. Scientists continue to seek answers for how mobile gibberellic acids are in plants.
GA3 Growth Hormone
GA3 growth hormone is a kind of gibberellin that is bioactive. A Japanese scientist discovered AC3 in the 1950s. At that time, a fungus affected rice crops so that it caused the plants to grow tall while halting the production of seeds. These lanky, infertile plants could not even support their weight. When scientists studied this fungus, they found that it contained compounds that could promote plant growth. The fungus was called Gibberella fujikuroi, which originated the name gibberellin. One of these compounds, now called GA3, is the most produced gibberellic acid for industrial use. GA3 growth hormone is important for agriculture, science and horticulture. GA3 stimulates the occurrence of male organs in certain species.
Gibberellic Acid and Crop Production
The discovery of gibberellic acids led to major developments in agriculture. Farmers found they could increase their grain yields by using GAs. This led to what was called a “green revolution” in agriculture. Farmers could add more nitrogen fertilizer to crops without worrying about too much stem elongation. The resulting increases in wheat and rice completely changed agriculture around the world, proving the great importance of gibberellic acid in modern farming.
To this day, gibberellic acids are used to treat plants that have dwarf phenotypes. The gibberellins stimulate plant growth in in these dwarf plants. Gibberellic acid can also be used to reduce flowering in young fruit tree orchards. This way, the fruit trees have more time to grow. It also aids as a preventive measure against plant viruses in young trees that are transmitted by pollen. Farmers decide how much gibberellic acid to use on their crops by determining what their production goal is. If they need to cut back on fruiting, they can use high amounts of gibberellic acid. On the other hand, if they use less GA, then the fruits or vegetables can produce more. Orchards that bear a lot of fruit will not need as much GA application. Generally, GAs should only be applied in warm weather, or they will not work to stimulate growth as well.
Gibberellic acid can also aid fruits like citrus. Application of gibberellic acid to citrus can prevent albedo breakdown, which is a creasing and cracking of orange rinds. Applying gibberellic acid can also reduce watermark spots on citrus fruit. Gibberellic acid therefore improves citrus rind quality. The application of GA yields a higher-quality fruit that is more resistant to adverse weather and other potential avenues of decay and injury. Close attention to applications to healthy plants in the right conditions can greatly improve a citrus crop. Typically the best results of GA application occur when it is not used alone, but rather in a mix with other compounds. It is clear that the improvements to crop yields and fruit quality make gibberellic acid an important tool in agriculture. The role in GAs of improving and increasing the food supply is impressive, and seems likely to remain for some time.
What Is the Function of Gibberellins?
Gibberellins function as controllers of growth in plants. They work to kickstart the germination of seeds, aid shoot growth and maturation of leaves, and affect flowering.
With seed germination, seeds remain dormant until they are triggered to germinate. When gibberellins are released, they start a process of weakening seed coats by beginning gene expression. This leads to the expansion of cells.
GAs are factors that contribute to flower development. In biennials, they will stimulate flower development. Interestingly, in perennials, gibberellins inhibit flowering. In addition, gibberellic acids are pivotal for internode elongation. Again, the result is an expansion of cells and cell division. This occurs as a response to light and dark cycles.
In mutant plants that are dwarf or late flowering, there is less gibberellic acid present. In these plants, more application of GA is needed to return the plants to a more normal growth pattern. Therefore gibberellin functions as a kind of reset for plants.
Another gibberellin function is to aid pollen germination. During pollen tube growth, the amount of gibberellin has been shown to increase. Gibberellins also affect male and female fertility in plants. Gibberellic acid plays a role in suppressing female flower formation.
The stamen is a chief site for making gibberellic acids.
Recent discoveries in botany have led to greater understanding of signaling pathways for gibberellic acids. Generally, these pathways require a GA receptor, growth repressors called DELLAs and proteins of various kinds. The DELLA proteins inhibit plant growth, while the GA signal aids growth. To get beyond this inhibition, gibberellic acids form a complex that leads to the breakdown of the DELLA growth repressors.
Scientists are still seeking to understand the process for how GAs make all of these things happen. Theoretically, gibberellins must be transporting long distances inside plants. The mechanism for this is not yet clear.
Since plants cannot move, the importance of signaling molecules and hormones is of great importance. Leaning more about the fundamental transport mechanisms of gibberellic acid, in addition to the hormones’ signaling pathways, will lead to greater understanding of plants. This, in turn, will aid agriculture as humans face the need for highly efficient crop yields.
- Plant Signaling & Behavior: Gibberellic Acid in Plant
- MSU Extension: Gibberellic Acid Applications in Cherries
- Development: Gibberellin Signaling in Plants
- Trends in Plant Science: Gibberellin Localization and Transport in Plants
- Government of Western Australia Department of Primary Industries and Regional Development's Agriculture and Food: Citrus Quality Using Gibberellic Acid
About the Author
J. Dianne Dotson is a science writer with a degree in zoology/ecology and evolutionary biology. She spent nine years working in laboratory and clinical research. A lifelong writer, Dianne is also a content manager and science fiction and fantasy novelist. Dianne features science as well as writing topics on her website, jdiannedotson.com.