Seeds and stress

A new stress concept for seeds raises awareness of the challenges scientists face in researching stress associated with changing environments.

11 Apr 2011

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Suaeda maritima seed

Seed of Suaeda maritima, one of the model seeds used to study seed response to salt stress at the Millennium Seed Bank (Image: Charlotte Seal)

Importance of seeds

A recent publication in the prestigious Tansley Reviews series of the journal New Phytologist has addressed a lack of attention given to stress concepts of seeds and plants. The paper was co-authored by Ilse Kranner, Charlotte Seal (Kew), Farida Minibayeva (Kazan Institute of Biochemistry and Biophysics, Russia) and Richard Beckett (University of KwaZulu-Natal, South Africa).

Suaeda maritima habitat

Suaeda maritima in its natural salt marsh habitat at Cuckmere Haven, East Sussex. S. maritima is a halophyte, thriving in saline environments where most other plants cannot grow. Halophytes are an untapped source of food, fibre and bioenergy. (Image: Charlotte Seal)

Like all living organisms, seeds are constantly exposed to stress. However, stresses that impact upon seeds can affect plant reproduction and productivity. Therefore, understanding how seeds cope with stress is an important issue in relation to food security and to the effects of climate change on species biodiversity and agricultural land use.

Understanding stress concepts

The ‘General Adaptation Syndrome’, published in 1936, is still one of the most widely accepted stress concepts in medicine. Considering the recent progress in molecular biology and biochemistry, Kranner et al. have now taken the General Adaptation Syndrome to the molecular level and modified it for seeds, identifying three stages of stress response; alarm, resistance and exhaustion. This modified version of the General Adaptation Syndrome also has relevance to plants generally as many of the causes of stress and response systems are common to both.

The dose and the duration an organism is exposed to a stress factor determine the effects the stress factor exerts. First, in the ‘alarm phase’, a stress factor is perceived. Under continuing stress, the ‘resistance phase’ is reached when protection and repair mechanism maintain seed viability. The third and final ‘exhaustion phase’ is reached if the protection and repair mechanisms fail, ultimately resulting in seed death.

Stress model

General Adaptation Syndrome, modified for seeds (after Kranner et al., 2010).

Stresses are not always negative

Not all stresses are negative, and some even have positive effects, such as seed dormancy alleviation by extreme cold or heat. In the article, analogies with human stress are considered. For example, psychologists often distinguish between ‘eustress’ and ‘distress’. A eustress is a stress that makes us stronger, for example cardiovascular training that stimulates the immune system and strengthens the heart muscle, whereas a ‘distress’ has negative effects such as happens when untrained runners suffer a coronary attack. Therefore, what is a ‘distress’ to one individual is not necessarily so for another. Stresses which effect seeds do not always have the same effect on plants and the impact of stresses differ during the life cycle. In other words, whether or not the environment exerts ‘stress’, depends on the organism, its state of adaptation, dose and duration of the exposure to the stress factor:

“All things are poison and nothing is without poison, only the dose permits something not to be poisonous.” (Paracelsus Phillippus Aureolus Theophrastus Bombastus von Hohenheim, 1493-1541)

It is important to raise awareness of the challenges scientists face in stress research and to provoke discussion on the way in which stress in plants is viewed and researched. By understanding more about the types of stress, common causes of stress, and recommendations on how to quantify stress, we can support successful plant regeneration in changing environments.

Item from Dr. Ilse Kranner (Senior Biochemist, Seed Conservation Department, RBG Kew). Email i.kranner@kew.org.

Article reference: Kranner I, Beckett RP, Minibayeva FV and Seal CE (2010). What is stress? Concepts, definitions and applications in seed science. New Phytologist 188: 655-673 Download a pdf of this article

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