We are part of an ecosystem where each one of us is intricately connected. It is of no surprise that certain processes and substances can be conserved in all. As an instance consider DNA, whose role is to carry the genetic information. Its function is conserved starting from a bacterium all the way to complex organisms like us. But, isn’t it surprising that a plant hormone can play an important role in humans as well? Before understanding the function of such a hormone in humans, we shall first take a look at its role in plants.
Abscisic acid (ABA), contrary to what the name suggests is not just about abscission. However, it plays an important role in plant growth and development, stress responses (like, drought, temperature, biotic stress etc.), seed and bud dormancy, reproduction etc. Then you must be curious as to why its name is Abscisic acid. A group working on the abscission of cotton plants, discovered a compound in the abscised leaves, and named it abscicin, concluding that its role was in abscission. Parallelly, there was another group which found a compound that helped in seed dormancy and named it dormin. Later, it was found that both the compounds were same and it was named ABA. Further insight into its role revealed its importance in the above-mentioned processes.
It is interesting to note that ABA is not restricted to plants. Its presence has been detected in fungi as well as the entire animal kingdom (starting from sponges to mammals). The presence of ABA in animals was first detected in brain tissues of pigs and rats. But there was a possibility that the source of ABA could have been their diets. Hence, to confirm it, rats on ABA-poor diet were compared with rats on normal diet. It was observed that the brain tissues produced more ABA in rats given ABA-poor diet than the controls. This confirmed that ABA is endogenously produced in animals. Since then, its functions have been characterized in various organisms like sponges, human parasites, humans (including different kinds of tissues) etc. Not only ABA, but its derivatives are also found in these organisms.
ABA presence in fungi helps to lower the immunity of plants, assisting in easy pathogenicity, whereas in animals it plays important role, in immunity, acts as a stress hormone, etc. In sponges (sessile organisms) it mediates response towards changing water temperature and light. In hydroids (which follow sponges in the evolutionary tree; however, these are sessile), light stimulates endogenous synthesis of ABA and helps in regeneration of tissues. This tells that the role of ABA is ubiquitous and its responses to changing environmental conditions are conserved among species. The signaling pathway of ABA is quite similar in plants and animals.
In humans, ABA has been detected in various immune cells (like granulocytes, monocytes), in pancreatic b-cells (also responsible for secretion of insulin), bone marrow, microglial cells (specialized macrophages present in CNS) etc. During inflammatory conditions, it is known to significantly increase immune cells, pancreatic cells and vascular cells. Whereas, it is known for its significant inhibition of cancer cells by allowing their apoptosis (programmed cell death) without causing toxicity to the normal cells, and for promoting normal cell growth and development.
ABA is also involved in maintaining glucose homeostasis in humans. ABA levels increase when there is high glucose uptake (ABA-free diet) in healthy individual. Hence, it tells that in addition to insulin and glucagon, ABA also has role in response to glucose uptake. Person suffering from type 1 diabetes has lower level of ABA than a normal person of same body mass index and age. In addition to pancreatic b-cells, adipose tissues (fat) also release ABA in response to high glucose levels. ABA also helps in modulating the process of platelet formation. Neuroinflammation caused due to a high fat diet can be controlled through ABA administration.
Therefore, ABA could serve as a good therapeutic drug for several human diseases. The application and function of plant hormones and growth regulators in animals and humans is not restricted to ABA. There are other phytohormones like jasmonates, cytokines, which are involved in various processes that protect humans from various diseased conditions. However, research in these fields are in early stages and various important aspects need to be studied before considering them as drugs for disease treatment.
By Eeshita Ghosh, Department of Biological Sciences, IISER Bhopal.
- Occurrence, function and potential medicinal applications of the phytohormone abscisic acid in animals and humans, Hai-Hang Li, Rui-Lin Hao, Shan-Shan Wu, Peng-Cheng Guo, Chang-Jian Chen, Li-Ping Pan, He Ni, Biochemical pharmacology, 2011
About the author:
Eeshita is a fourth-year BS-MS student at IISER Bhopal majoring in Biology. She is especially interested in molecular and plant biology. She loves painting and dancing other than reading interesting science articles and blogs. She also shows enough interest in sleeping, cooking new dishes and trying good food. She is a regular blogger of our blog page, ‘The Qrius Rhino’.