1. The Dry Future of Corn: Exogenous Applications of Salicylic Acid
Discussion
Abstract
Overall, the pretreatment groups were found to improve plant growth and development.
The difference between the percentages of relative water content of PT 0.1 and control was 4.5 and between PT 0.5 and control was 1.06.
On the other hand, Fol 10 and control group were the same and Fol 5 actually did worse with a difference of 0.5 in RWC %.
In both chlorophyll a and b, the pretreatment groups did way better than the foliar spray groups (differences = 3 with PT –0.5; 5 with 0.1)
The morphological parameters,shoot length and shoot weight, showed a better alleviation of drought stress in the pretreatment and foliar groups than the control group.
There was a decline in shoot length and shoot weight for Fol 5 mM compared to the others.
It had the lowest values between all groups: inches shoot length and grams for shoot weight
Difference of means between PT .1 and Fol. 5 was grams as a significant increase in shoot weight observed
Conflicting data with past results:
Manzoor found that lower concentration of SA, namely 5 mM, was more effective.
This study found that 10 mM fol is better than 5 mM.
Drought has been considered one of the most acute abiotic stresses presently affecting agriculture (Khan, et al.). Salicylic acid is a naturally occurring phenolic compound that plays an important role in the response to abiotic stress, specifically drought (Miura). However, the impact of SA depends on the concentration, mode of application, and state of the plants. This study examines the optimal mode of exogenous applications of salicylic acid on corn plants to alleviate the negative effects of drought. Modes of application include the foliar spray and seed pre-treatment. In this study, concentrations of 5 and 10 mM SA were used for the foliar spray and concentrations of 0.5 and 0.1 mM SA were used for the pretreatment solutions. It is predicted that the foliar spray with 5 mM of salicylic acid will best alleviate the negative effects of drought on Z. Mays.
Cindy Wang and Michelle Xing
Methods
All Z. Mays seeds are first sterilized with 1% sodium hypochlorite.
Foliar Spray
(5 and 10 mM SA(salicylic acid))
Pre-treatment (.1 and .5 mM SA)
Control
25 seeds planted in 5 pots per treatment group
25 seeds planted in 5 pots.
25 seeds soaked in SA solution for 24 hours and planted in 5 pots, per treatment group.
Background
Thinned to 3 seedlings per pot
Keep soil HYDRATED for 31 days
Inducing Drought Stress
20 days without water
Plants sprayed with SA solution at 10 day intervals
Figure 2: Model that shows loop between SA and ROS (reactive oxygen species) in response to stress.
Inducing Drought Stress
20 days without water
Regulation of stomatal guard cells is an adaptive mechanism that helps plants withstand pathogenic infection and weather conditions like drought. When pathogens enter through stomata, endogenous SA are increased to induce systemic acquired resistance. Salicylic acid induces ROS production which helps regulate homeostatic processes.
SA response genes turn on plant defenses against drought stress and pathogens.
Chlorophyll Extraction
Leaves placed in separate vials with 10 mL of 95% ethanol
Leaves cut into small pieces
Mixture is boiled and then strained into separate falcon tubes.
Absorbancy of leaf extract measured at 648 and 664 nm with spectrophotometer.
Relative Water Content
Relative Water Content calculated using equation:
RWC = fresh weight-dry weight/turgid weight-dry weight * 100
Leaves are soaked in water for 24 hrs, then the turgid weight of the leaves is measured.
Leaves are oven dried for 72 hrs at 70 degrees C.
Fresh weight is measured.
Figure 7: Living conditions for plants. 16 hours daylight and 8 hours of darkness cycle. –
Conclusion
Results
Goals
Find the method of exogenous application of Salicylic Acid that would be most beneficial for maize plants undergoing drought stress, a prevalent problem today.
Pretreatment with 0.1 mM SA was the most effective treatment
Reasoning: smallest concentration of SA.
The spraying of SA directly onto the leaves in the foliar spray treatment may have inhibited some chemical processes resulting in decreased levels of chlorophyll.
Future research: SA operates in a variable manner, promoting factors like growth, but inhibiting other plant functions. As seen in this project, the relative water content and chlorophyll content did not improve significantly compared to the control group.
Use SA in conjunction with another compound to more effectively ameliorate the effect of drought stress.
Shoot Length in inches
Relative Water Content percent
Figure 2: Representation NO, salicylic acid (SA), and jasmonic acid (JA) interactions during plant responses to biotic challenges.
Foliar Spray
Application of three concentrations of salicylic acid (5mM, 10mM and 15mM) were tested to ameliorate the effects of salinity and drought stress, two related abiotic stresses (Manzoor, et al.).
Significant role of SA in drought and salinity tolerance. Lower concentrations were seen to be more effective.
Figure 3: The effect of Salicylic Acid (SA) on shoot length. Error bars represent +/- one standard deviation of the mean. PT 0.1 = Pretreatment 0.1 mM SA; PT 0.5 = Pretreatment 0.5 mM SA; Foliar 5 = Foliar Spray 5 mM SA; Foliar 10 = Foliar Spray 10 mM SA. (n = per group)
Figure 4: The effect of Salicylic Acid (SA) on relative water content (RWC). Error bars represent +/- one standard deviation of the mean. Group PT 0.1 had the smallest P values when compared to each of the other groups. (n = 4 per group)
Seed Pretreatment
Two forms of the pretreatment method were used: the seed priming method and the presoaking method to test the effects of different reagents (water, NaCl, PEG, and GA) on Z. mays plants.
Results: the presoaking method is recommended to harvest better benefits in the plants compared to the priming method (Yu Tian, et al.). **
Bibliography **
Chlorophyll Concentration percent
Shoot Weight in Grams **
Idrees, M., Naeem, M., Khan, M. N., Aftab, T., Khan, M., & Moinuddin, K. (2011). Alleviation of Salt Stress in Lemongrass by Salicylic Acid. Springer-Verlag, 249,
Khan, M., Fatma, M., Per, T. S., Anjum, N. A., Khan, N. A. (2015). Salicylic Acid-Induced Abiotic Stress Tolerance and Underlying Mechanisms in Plants. Frontiers in Plant Science, 6, 462.
Manzoor, K., Ilyas, N., Batool, N., Ahmad B., & Arshad M. (2015). Effect of Salicylic Acid on the Growth and Physiological Characteristics of Maize under Stress Conditions. The Chemical Society of Pakistan, 37,
Premachandra G. S., Saneoka, H., Fujita K., & Ogata, S. (1993). Water Stress and Potassium Fertilization in Field Grown Maize {Zea mays L.): Effects on Leaf Water Relations and Leaf Rolling. J. Agronomy & Crop Science, 170,
Tian, Y., Guan, B., Zhou, D., Yu, J., Li, G., & Lou, Y. (2014). Responses of Seed Germination, Seedling Growth, and Seed Yield Traits to Seed Pretreatment in Maize (Zea mays L.). The Scientific World Journal.
Hypothesis
Figure 5: The effect of Salicylic Acid (SA) on shoot weight. Error bars represent +/- one standard deviation of the mean. There is significance (P<0.05) between groups PT 0.1 and Fol 5; PT 0.1 and Control. (n = per group)
Figure 6: The effect of Salicylic Acid (SA) on chlorophyll a and b content. Error bars represent +/- one standard deviation of the mean. Chlorophyll a had the most significance (P= .077). (n = 4 per group)
The maize plants treated with the 5 mM of SA by foliar spray will display the best results because lower concentrations have shown to work better than higher concentration (Manzoor).