Review: Aging in plants is not always like aging in animals

Deborah A. Roach and Erin F. Smith

Photo of Plantago lanceolata individual marked for senescence study. By: Deborah A. Roach
Photo of Plantago lanceolata individual marked for senescence study. By: Deborah A. Roach

Aging, also termed senescence, is manifest as declines in function and an increased risk of death as individuals get older.  All living organisms should experience some level of ‘wear and tear’, thus our theoretical expectation has been that all organisms should experience aging. One of our theories of aging, the Disposable Soma Theory, predicts that aging occurs because resources that are allocated to reproduction are at a cost of fewer resources being used to repair ‘wear and tear’ to somatic tissues.  This reduction in repair then leads to an increasing level of damage accumulation, which causes aging declines. The objective of our analysis was to determine whether the predictions of this theory fit our current evidence for aging patterns in plants.

Plants are excellent model systems to study aging because individuals can be marked and their survival and reproduction can thus be easily monitored from birth to death.  For many species it is easy to manipulate resources and reproduction to study the predictions of the disposable soma theory.  Despite these advantages, we found only 22 species have been studied in the wild.  These studies showed all three aging patterns including age-declines, age-improvements and no change with age.  Most species showed an age-dependent decline (aging) in at least one trait, but even within a species the aging patterns varied among traits.  We also evaluated 20 other studies that showed tradeoffs between traits consistent with the allocation of resources between reproduction and survival. 

We found some unique properties of plants that may impact aging and tradeoffs. The Disposable Soma Theory assumes that aging occurs because individuals have finite resources, but some species can increase their acquisition of resources by increasing their rates of photosynthesis.  Some species increase in size as they get older and size, rather than age, may influence senescence declines and tradeoffs.  We also found that species that go through periods of dormancy may be able to slow their aging clock.  Variation across plant species in the dynamics of resource pools, plus the impact of size and the importance of dormancy, may help to explain why aging patterns differ across species.

Read the paper in full here. This paper is part of the Special Feature: An Integrative View of Senescence in Nature.

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