Antioxidant and chlorophyll dynamics differ between perennial flax (Linum perenne and Linum lewisii) and annual flax (Linum usitatissimum and Linum grandiflorum).

Abstract

Among plants, there is considerable variation in maximum lifespan, with annual species living less than one year and perennial species living as long as 43 600 years. According to the Oxidative Stress Theory of Aging, the maximum lifespan of an organism is partly determined by the rate at which it accumulates oxidative damage to its biomolecules. Consequently, perennial species have likely evolved mechanisms to slow down the accumulation of biomolecular oxidative damage relative to annual species. The present study aimed to evaluate this prediction using annual and perennial flax ( Linum ). While there are several mechanisms by which the accumulation of oxidative damage to biomolecules can be reduced, we focused on the role of antioxidants and biomolecular damage repair. Epicotyl growth and leaf production of annual—but not perennial—species were significantly affected by supplementation with exogenous ascorbic acid or glutathione, suggesting that annuals may have lower levels of endogenous antioxidants than perennials. Furthermore, while rates of chlorophyll degradation in response to exogenous H 2 O 2 did not differ between annual and perennial species, rates of chlorophyll resynthesis following such exposure were 2-fold faster in perennial species, whether assessed via image colour or spectrophotometric analysis, reflecting their greater capacity to repair oxidative damage to chlorophyll compared to annuals. Similarly, when plants were exposed to complete darkness for several days, chlorophyll degradation rates were significantly lower in perennials than annuals, perhaps because annuals quickly redistributed resources from leaves to flowers. When subsequently reintroduced to natural light cycles, chlorophyll resynthesis occurred 2-fold more quickly in perennials than annuals. Overall, our study illuminates that the evolutionary transitions between life history strategies in plants have been accompanied by physiological modifications to antioxidant and chlorophyll dynamics that reflect the need for perennial species to delay the aging process in order to survive for multiple growing seasons.