Investigating the Role of Salicylic Acid in Determining the Lifespan of Short-Lived and Long-Lived Flax Species and Lines

Abstract

Introduction: Reactive oxygen species (ROS) accumulation has been related to aging in both plant and human physiology. Leaked electrons from the electron transport system (ETS) react with molecular oxygen producing ROS, such as hydrogen peroxide (H2O2) and superoxide anions. There are numerous antioxidative mechanisms present in plants that aid in redox balance, one of which is the mild uncoupling of mitochondria. Uncoupling agents, such as salicylic acid (SA), can abolish the connection between oxidation and phosphorylation allowing electron transport to take place without the need for parallel ATP synthesis. “Uncoupling to Survive” Hypothesis states that uncoupling activity should be greater in long-lived species since uncoupled mitochondria result in reduced ROS production thereby increasing lifespan. Since ROS accumulation has been linked to lifespan in the Oxidative Stress Theory of Aging, the idea that long-lived species should exhibit greater antioxidative capacity than short-lived species is the foundation upon which this hypothesis is established. We tested this hypothesis in various flax species and lines differing in lifespan. Methods: Spectrophotometry was used to determine SA levels in plant tissue while respiration rates were measured using a dissolving oxygen electrode. Results: The “Uncoupling to Survive” Hypothesis does not seem to hold for flax since long-lived and short-lived species did not exhibit significant differences in oxygen consumption rates that would indicate differences in the uncoupling activity of their mitochondria. Discussion: However, early flowering lines exhibited lower levels of SA suggesting that flax plants do not require elevated SA expression to display the early flowering phenotype as seen in Arabidopsis species. In addition, SA significantly increased the oxygen consumption rates in wild-type and early flowering plants which further provides evidence for its role as an uncoupling agent. Conclusion: Our findings add to our understanding of the many roles that SA plays in plant physiology. Advantages of SA are well established in the cosmetic and medical communities and investigating its effects on plants can be beneficial. We also looked at the "Uncoupling to Survive Hypothesis" in plants, which helped us get a better grasp of the antioxidant mechanisms that may eventually reduce oxidative stress and lead to senescence.