No signs of physiological deterioration with aging in Borderea pyrenaica, a long-lived perennial herb relict of the Tertiary
There is enormous diversity among the types of perennial plants and among their patterns of aging. Among perennial herbs, the slowest growing species described thus far, Borderea pyrenaica (a small geophyte growing in the Central Pyrenees of northeastern Spain), is also the one with the longest maximum lifespan (350 years). B. pyrenaica is a paleoendemic plant species, a tropical relict from the Tertiary. A subterranean tuber with a strong root system allows the plant to remain anchored to the soil below lime stones of screes of the Central Pyrenees. B. pyrenaicaplants of different ages (ranging between 1 and 170 yr; age was estimated by counting yearly scars left in the tuber) were sampled during spring (June) and summer (September) 2013 in a natural population from the Central Pyrenees. The population studied was located in the Pineta valley (42°41′N, 0°06′E, 2000 m above sea level), where several thousand individuals grow in high densities on a north-facing rocky hillside. Age-related effects on the physiological performance of tubers were examined, considering tuber biomass, hydration, carbon (C) and nitrogen (N) concentrations, the extent of lipid peroxidation, vitamin E concentrations, and jasmonate levels.
Tubers were getting larger and more hydrated up to the plant's maximal age (170 yr) investigated in the present study. By contrast, N concentrations decreased, which might be associated, at least in part, with an increased reproductive effort in mature compared with juvenile plants. It is interesting to note that plants did not stop growing underground, which may help prevent senescence to occur. Malondialdehyde levels, an indicator of lipid peroxidation, decreased as a function of age in tubers, showing a negative correlation with vitamin E levels. Furthermore, levels of jasmonoyl isoleucine, an active jasmonate synthesized when tissues are challenged by insect attack or by herbivores, also decreased with age. It is therefore suggested that B. pyrenaica plants will be less sensitive to biotic stresses with ageing. The present study supports the notion that this plant species shows negligible, or even negative senescence in terms of physiological performance with ageing. Indeed, compared with other plants, B. pyrenaica is unique in its patterns of ageing and mortality. Here, we provide evidence that this plant species has unique physiological features that underlie its distinctive demographic traits, and that the secret to its long life may lie underground.