In the case of animal physiology

firstly proposed stress for medical term
1915-1932 research on Fight or flight
1932 SAM (Sympatho‑Adrenal Medullary system) = threat →

activation of the sympathetic nervous system + adrenal medulla

Def. (Cannon) stress = the physiological mobilization that occurs when the organism faces a threat

stress = response (≠ stressor)

stress = the nonspecific response of the body to any demand

to clearly distinguish the stimulus (the stressor) from the response (stress)

1936 a theory of stress (ストレス学説提唱), or general adaptation syndrome (汎適応症候群, GAS)

1. stressor (ストレッサー, ストレス刺激): external-environmental stimuli that induce stresses
   physical stressor: temperature, UV, etc.
   chemical stressor: chemical substance, enzyme, etc.
   biological stressor
2. stress (ストレス, ストレス反応): responses of plants (and animals) induced by stressors

Def. (Selye) stress: any external factor, biotic or abiotic, that disrupts an optimal metabolic balance, leading to physiological changes that may impair growth, development or survival

assumption = nonspecificity, i.e., any stimulus produces essentially the same physiological response - criticized ⇒

= stimulus‑based approaches
≈ the amount of life events ∝ the magnitude of stress

SRRS: cannot capture individual differences in response to the same event

Def. (Holmes & Rahe) stress: essentially the amount of life events a person experienced, with the magnitude of those events assumed to determine the level of stress

What determines stress is not the stimulus itself but how the individual evaluates that stimulus, through primary and secondary appraisal
→ fundamentally cognitive‑based, i.e., the same event produces different levels of stress depending on the person
+ introduced the concept of coping

Def. (Lazarus): a transaction between the person and the environment

Cognition alone cannot explain the cumulative physiological damage caused by chronic stress - criticized ⇒

→ allostatic load (アロスタシス負荷)

Applied to plant physiology

Stress

⇒ plant physiology started to use the term, stress, to express stressor

Advanced: ABA/JA/SA/Ca²⁺/ROS, gene regulatory networks, epigenetic stress memory (ストレス記憶)

• deviation from optimal conditions Ex. water, temperature, light, nutrients
• inducing altered physiological states, e.g., reduced photosynthesis, impaired cell expansion or disrupted hormone signaling
• leading to strain, which is the measurable change in plant structure or function due to stress

→ habitat partitioning

Chilling injury (冷害)

Freezing injury (凍害)

these two injuries are closely related

Snow injury (雪害)

Relationships between broad-leaved trees and coldness

1. Direct effects: Ex. tissue fluid (water) frozen by low temperature → tissue(s) is(are) frozen → freezing injury
2. Indirect effects: Ex. frost drought (in particular the abovegroud organs)
   bark: vessels are clogged up → inhibition of water transportation + evaporation (on the aboveground) → death owing to dehydration

Difficulties in plant establishment in relation to cold tolerance

1. unstable climate in early fall
2. unstable climate in early spring (in particular occurring late frost)
   The frequency of late frosts determines the establihsment of European beech in Europe and Sakhalin fir in Hokkaido

Factors causing drought stress

Physiological changes

A small Asian desert plant that dries into a tight ball and expands when moistened
Often used interchangeably with resurrection plant (s.l)

A fern shriveling during drought and becoming green again after rain
US southeastern forests; also called a resurrection plant (s.l)

Adaptation

Distribution: Atacama Desert, Chile - Annual precipitation = 13 mm
living on the water vapor absorbed from the humid night air

Ex. mangrove trees

seed dormancy