Plant senescence: from paradoxes to evolutive success

To study plant senescence —a type of programmed cell death— is one of the objectives of the research group that Professor Munné-Bosch leads at the University of Barcelona. The group also centres its research activity on plant ecophysiology and agrobiotechnology related to antioxidants (vitamin C and E, flavonoids, etc.), mechanisms of resistance against external factors (water stress, salt stress, etc.) and photo-protection.

The multiple meanings of senescence

Senescence is not a common process in the entire spectrum of life. Some basal metazoans (sponges, cnidarians, etc.) and perennial plants seem to escape the wear and tear of aging. “Senescence so much depends on the level of organization we consider”, emphasizes Sergi Munné-Bosch. “In other words, senescence varies among cells, organisms, individuals and populations. For example, in the case of individuals, senescence increases mortality associated to age-related decline in some organisms. However, this does not always happen, at least in perennial plants”.

“In the case of organs —for instance, in plant leaves— senescence can benefit the whole plant. In this case, it is a programmed process with a biological function: to eliminate cell components, to mobilise plant nutrients, etc. If we consider the plant as a colony of organisms —not like a single life being—, senescence will be a survival strategy: it favours some biological structures to the disadvantage of others that disappear”.

Longevity: the challenge of surviving in the nature

Perennial plants show a great capacity to survive. An indeterminate growth pattern turns these plants into a very valuable scientific model to be used in longevity and senescence studies.

“Itʼs quite easy to find long-lived trees, maybe hundreds or thousands years old. But, this makes a difference in animal physiology. It points out perennial plants own a group of very distinct strategies that enable them to grown indefinitely”. Munné-Bosch stresses that “in plants that are models of long-lived organisms, senescence remains unproved. Senescence is a phenomenon that cannot be observed in the nature. It could be a study methodological limit, but if it really exists, it cannot be detected, so it seems that it is not a relevant process ecologically”. 

Senescence and evolution paradoxes

Many authors question whether senescence is irrelevant in populations. However, in terms of evolution, it seems to be a complex paradox: the successful selection of a process that promotes mortality in organisms. “It is in contradiction to Darwinʼs theory of evolution”, points out Professor Munné-Bosch. “Several articles published by the research team I head and other scientific studies show that senescence is not a relevant process in the nature. Extrinsic factors that influence mortality are much more important”.  

Senescence and growth, explains the author, are opposite processes. “For example, we know well the anti-senescence effects of cytokinins, growth-promoting hormones in plants. However, the antagonism remains unproved at the individual level. When will we be sure that the process is universal? Biological diversity is so high that it is difficult to reach conclusions based on a significant sample”.

Senescence processes also affect plant ecophysiology and, thus, agricultural output. The research team led by Professor Munné-Bosch also studies floral senescence processes, which are of great interest from gardening business. “There is an important business sector behind, so there is an increasing interest in developing products which can delay floral senescence, thus making flowers lasting longer”.

From plant science to preventive medicine

Many advances in biology and biomedicine concerning cell regeneration have been first discovered in plants. To study biological mechanisms of senescence, cell death and longevity in plants will contribute to open new horizons in future regenerative medicine.

“Senescence in humans and mammals is different from plant senescence. We want to find universal mechanisms but reality is very complex. Nevertheless, why donʼt we study perennial plant models and apply them to tissue and organ regeneration in humans? Moreover, it is important to approach plant studies from diverse perspectives and bring closer knowledge obtained in areas like demography, ecology and plant biology, which are much segmented nowadays”, concludes the researcher. 

Article reference:

Munné S. «Senescence: Is it universal or not?». Trends in Plant Science, octubre 2015. DOI: 10.1016/j.tplants.2015.07.009