Salicylic acid can be traced to the 18th century to an extract from the bark of the willow tree. An active component of aspirin salicylic acid occurs naturally in many plants at low levels where it functions as a plant hormone. It has been known for some time that increasing levels of salicylic acid can improve plants’ resistance to certain biotic stresses.
We hypothesized the same chemical compound could also make plants more resilient to abiotic stresses such as cool temperatures. Using spinach as a test we showed that small doses of salicylic acid can improve freezing tolerance. The same treatment also increased the plants’ antioxidant levels.
Freeze-thaw stress is one of the major constraints on crop performance and yield. Plants can be made more freeze tolerant through breeding, but that’s a long process. We found that very small doses of salicylic acid could be practical and inexpensive. We made plants significantly more cold-tolerant, at least for few days.
Two approaches were used to treat the spinach – both sub-irrigation and foliar application of salicylic acid. The plants were grown in environmentally controlled plant-growth chambers. Seedlings of the cultivar “Reflect” – an F1 hybrid – provided a population of uniform plants.
Temperatures were reduced slowly to simulate as much as possible natural frost conditions. Plants were tested at four sub-freezing temperatures and seedlings were studied to see how long the effect lasted. We also tested four concentrations of the salicylic-acid treatment.
The results varied a bit, but the salicylic acid-fed plants were always more freeze-tolerant than the controls, as measured visually and by cell leakage. Salicylic acid was taken up by the plant; it offered protection for at least four days and gradually tapered. None of the salicylic-acid concentrations had significant detrimental effects. The greatest concentrations slightly reduced leaf growth, but that small impact subsided as plants continued to grow.
Salicylic-acid treated plants had a greater amount of antioxidants such as vitamins C and E as well as certain carbohydrates. That may be linked to the compounds boosting the plants’ own protective mechanisms during stressful conditions. The changes could enhance a crop’s nutritional value for humans or livestock, an effect deserving further study.
We’re also studying the potential of ascorbic acid, better known as vitamin C, to enhance plants’ tolerance to freezing temperatures. The research recently was published in “Plant Direct.”
Spring and fall frosts are often a short-term phenomenon. Application of natural acids would be safe to use on food crops and could reduce crop loss from transient low temperatures, effectively extending the growing season.
The research on salicylic acid was published in “Environmental and Experimental Botany.” Visit sciencedirect.com and search for “salicylic acid-induced freezing tolerance” for more information.
The ascorbic-acid study recently was published in “Plant Direct.” Visit researchgate.net and search for “ascorbic acid-induced in situ freezing tolerance” for more information.