This article was prepared and written by Jorge Luis Alonso G.
Researchers at the Universidade Estadual Paulista in Brazil and the Universidad Nacional de Colombia conducted a study to determine if applying salicylic acid to leaves could reduce the effects of oxidative stress caused by water deprivation.
This article is a summary of the the study and its outcomes. A scientific paper on the research was published in the journal Plant Stress here.
Introduction
Changes in environmental conditions, known as abiotic stress, significantly affect plant development. Some of the most common abiotic stresses include temperature extremes, drought, flooding, light and radiation fluctuations, salinity, heavy metal exposure, and changes in nutrient levels.
One of the major concerns is water deficiency (WD), which directly affects plant growth and productivity. This deficiency alters both the physical appearance and molecular structure of the plant. If left unchecked, WD causes premature leaf senescence, leading to wilting and eventual death.
The primary culprit is the accumulation of reactive oxygen species (ROS). These ROS are harmful; they damage cellular components, including DNA structure, proteins, and lipids. As a result, the proper functioning of cell membranes is compromised.
A major defense mechanism against ROS is the production of phenolic compounds. These are secondary metabolites in plants known for their antioxidant properties that increase during periods of stress.
Another critical component that helps plants during stress is salicylic acid (SA). This compound helps plants cope with various physiological challenges such as drought and temperature fluctuations. SA plays a key role in modulating plant growth and enhancing their ability to cope with stress by increasing antioxidants and other essential elements.
Potatoes are particularly vulnerable to water shortages. In regions where water is scarce, the growth and productivity of this crop are severely affected. The effect of drought on potato production isn’t constant; it depends on the growth stage and the duration and intensity of the drought.
Two stages — sprouting and tuber formation — are particularly critical. Here, lack of water can stunt growth, reduce the number and size of tubers, and impair photosynthesis. It can also lead to an increase in plant temperature, which negatively affects potato formation.
A specific study was conducted to determine if the application of SA could counteract the oxidative stress induced by WD, focusing on the physiological and anatomical response of potatoes to test the hypothesis.
Salicylic Acid: A shield against water deficiency in potato plants
Water deficiency adversely affects photosynthetic pigments. This is largely due to an increase in the activity of the enzyme chlorophyllase. As a result, chlorophyll is degraded, chloroplasts are destroyed, and the stability of protein complexes is compromised due to increased levels of ROS. Interestingly, the degradation of chlorophyll a and b seems to stabilize over time. This observation supports the hypothesis that SA may provide relief from the effects of WD.
Research consistently shows that foliar application of SA has promising benefits for stressed plants. Not only does it combat pigment degradation, but it also increases chlorophyll levels. In addition, SA has the ability to inhibit chlorophyllase activity, reduce ROS concentrations, and increase carotenoid levels. The importance of carotenoids cannot be overstated; they are critical in regulating ROS, ensuring the stability of photosynthetic complexes, and offsetting the negative effects of water deficit.
The benefits of salicylic acid go beyond these biochemical processes. When plants are exposed to WD, their foliage inevitably suffers damage. However, SA treatments have been shown to mitigate this damage by refining several physiological functions. Water deficiency naturally leads to reduced leaf water loss, which is achieved by reducing transpiration rates. This is accomplished by closing stomata. While this may sound beneficial, intense water stress can be detrimental. This is because an increased transpiration rate often equates to a reduced water use efficiency (WUE).
However, there’s a silver lining: studies suggest that applying SA under stress conditions helps keep stomata open, thereby regulating water flow. Specifically, in potato plants, results have shown a robust correlation between SA application and various photosynthetic measures. It appears that SA acts as a protective barrier that enhances the plant’s ability to resist the effects of WD.
It’s worth noting that limited water conditions can lead to early stomatal closure, which in turn reduces internal CO2 levels. When these plants are exposed to sunlight for prolonged periods, it promotes electron transfer, producing harmful superoxide ions. In certain plants that survive WD, it has been observed that the application of SA is largely dependent on this stomatal closure. This action limits both internal CO2 and water loss through transpiration.
Potato nutrition and water
Shifting the focus to the nutritional aspect of potato plants, it is evident that water deficiency triggers disturbances in the uptake of essential macronutrients.
The main reason for this could be the reduced availability of water, which has a direct impact on nutrient uptake. However, all is not doom and gloom. The use of SA seems to reverse these negative effects. For example, it particularly promotes the uptake of nitrogen, thereby improving plant metabolism.
Similarly, phosphorus, a critical element for energy transfer in cellular metabolism, finds its uptake inhibited by lack of water. However, in potato plants, the introduction of SA has been shown to enhance phosphorus uptake under WD conditions.
Also, potassium, which is essential for a variety of physiological functions such as water regulation, is also affected by water conditions. Its uptake is particularly affected by stomatal activity. Another mineral, magnesium, plays a crucial role in energy conservation and protein synthesis, and it’s essential for many enzymatic functions. Interestingly, in the research conducted, the application of SA was associated with a higher accumulation of magnesium in potato leaves.
Finally, it’s important to note that water deficiency can increase malondialdehyde (MDA) levels, leading to significant cellular damage due to an increase in ROS production.
Conclusion
The study showed that when the right soil water tension is combined with a foliar application of salicylic acid, it helps reduce the detrimental effects of water scarcity on potato plants. This is supported by the notable decrease in MDA accumulation in plant tissues and an increase in both bioactive compounds and antioxidant activity.
Notably, the application of salicylic acid proves effective in addressing abiotic stresses, especially water deficiency. Employing this method provides an additional layer of protection for plants in situations of limited water supply.
Additionally, these findings offer valuable insights into the intricate physiological and biochemical mechanisms that enable potato plants to endure water shortages and how metabolic regulation pathways play a role.
Source: Acevedo, A. F. G., Lacerda, V. R., Da Silva Gomes, J. W., Avilez, A. A., Sarria, S. D., Broetto, F., Vieites, R. L., & De Souza Guimarães, M. L. C. (2023). Foliar salicylic acid application to mitigate the effect of water deficiency on potato (Solanum tuberosum L.). Plant Stress, 7, 100135. https://doi.org/10.1016/j.stress.2023.100135
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