Abscisic acid and plant adaptation to abiotic stress
Population growth has put great pressure on agriculture to ensure food security. Meanwhile, at the rate of climate change like this day, crop loss is happening continuously around the world. One of the reasons is the lack of timely adaptation of plants to climate change.
>>> What is abiotic factor? Characteristics and importance
In recent decades, abiotic stress has become a major concern in agricultural production. Plant growth and development under stressful conditions can affect the crop. Under stressful conditions, plants still have mechanisms to adapt to varying degrees of stress, but these mechanisms are still not enough to help plants withstand. Currently, Abscisic Acid (ABA) is used to help plants better adapt to changes in the environment and current climate. So how did ABA help plants adapt?
* Abiotic stress is extreme conditions such as temperature, water, salt concentration, etc.
ROLE OF ABA FOR PLANT
Plant hormones are key in regulating growth and development as well as in response to different environmental conditions, including Abscisic Acid (ABA). When environmental conditions become extreme, plants increase ABA synthesis. ABA interacts with receptors to activate signaling pathways that help cells respond to stress, which is why ABA is also known as the stress hormone (1).
Seed is an important organ in the development of higher plants, the transition from dormancy to germination is an important stage in the life cycle and is considered an ecological feature. and traces of adaptation in plants. Two hormones that play a central role in controlling dormancy and germination are ABA and gibberellins (GAs). Both of these hormones control the balance between dormancy and germination. ABA plays a role in the induction and maintenance of seed dormancy. During the dry period, ABA metabolism needs to be regulated.
For root systems, abiotic stresses occur when water scarcity occurs, or the water environment is uneven (sometimes not). In these cases, ABA levels changed in response to water stress. As a result, changes in the root environment will affect the ABA response in the root zone of the whole plant (2).
Stomata are small stomata on the leaf surface formed by guard cells that control gas exchange. Light has the ability to stimulate stomatal opening. Meanwhile, ABA and CO2 content stimulated stomatal closure. During stomatal closure, a decrease in gas exchange can lead to a decrease in the photosynthetic yield, and the loss of water vapor from the leaves can be reduced. Under drought conditions, ABA alteration ensures ion exchange in guard cells, stimulates stomatal closure and prevents stomatal opening and reduces water loss (3).
>>> The difference between abiotic and biotic factors
SYNTHESIS, ACTIVITIES AND TRANSPORTATION OF ABA
Synthesis of ABA
ABA is synthesized in small organelles and stored in the cytoplasm. ABA is synthesized in higher plant cells through a mevalonic acid-dependent pathway, also known as the indirect pathway. In this pathway, ABA is synthesized by C40 ablation of the pro-carotenoid, by two-step conversion of intermediate xanthoxin to ABA via ABA aldehyde, and oxidized to ABA (Figure 1).
The first step of the ABA synthesis pathway is the conversion of all trans-violaxanthin to zeaxanthin and is catalyzed by zaxanthin epoxidase (ZEP) in the plastid. In this reaction, antheraxanthin as the intermediate is formed. Then, all trans-violaxanthin converts to 9-cis-violaxanthin or 9-cis-neoxanthin. Next, the enzyme 9-cis-epoxy carotenoid dioxygenase (NCED) catalyzes the oxidative degradation of 9-cis-violaxanthin and 9-cis-neoxanthin to produce a C15 intermediate called xanthoxin and a C25 metabolite. Finally, xanthoxin is exported to the cytosol, where xanthoxin is converted to ABA.
ABA Catalyst
When stress signaling decreases, ABA is converted to inactive products (1). This process is carried out by two pathways: hydroxylation and conjugation (4). In hydroxylation, ABA is hydroxylated by oxidation of the three methyl groups (C-7′, C-8′, and C-9′) in the ring structure.
ABA and the hydroxyl catalytic activity of ABA can be conjugated with glucose. ABA glucosyl ester (ABA-GE) is synthesized by glycosyltransferase and stored in vacuoles. Under abiotic stress conditions, ABA glucosyl ester can be converted to ABA by enzyme-catalyzed hydrolysis. The enzyme glycosidase catalyzes the hydrolysis of ABA-GE to release.
Shipping ABA
ABA transport between cells, tissues and organs also plays an important role in the physiological response of whole plants to stress conditions. ABA, being a weak acid, can passively diffuse across biological membranes when ABA is protonated (5). ABA can also be transported across the membrane by transporters.
>>> What are biotic and abiotic factors?
To be continued
References:
1. Ng, L. M., Melcher, K., Teh, B. T., and Xu, H. E., “Abscisic acid perception and signaling: structural mechanisms and applications.,” cta Pharmacol., vol. 35, p. 567–584, 2014.
2. Dodd, I. C., Egea, G., and Davies, W. J., “Abscisic acid signaling when soil moisture is heterogeneous: decreased photoperiod sap flow from drying roots limits abscisic acid export to the shoots,” Plant Cell Environ, pp. 31, 1263–1274, 2008.
3. Aswath, C. R., Kim, S. H., Mo, S. Y., and Kim, D. H., “Transgenic plants of creeping bent grass harboring the stress-inducible gene, 9-cis-epoxycarotenoid dioxygenase, are highly tolerant to drought and NaCl Stress,” Plant Growth Regul, pp. 47, 129–139, 2005.
4. Nambara, E., and Marion-Poll, “Abscisic acid biosynthesis and catabolism,” Annu. Rev. Plant Biol, pp. 56, 165–185, 2005.
5. Wilkinson, S., and Davies, W. J., “Drought, ozone, ABA and ethylene: new insights from cell to plant to community,” Plant Cell Environ., pp. 33, 510–525, 2010.
