Stress is o normal, physiological reaction in adaptation on exogen and endogen influences.

dear Nikola, i can't understand what you said.

Stress is the enhanced reaction of a creature to requirements. Thats what I know. And I think what  Nikola wanted to express.

Under Stress conditions all organisms are focusing on the main purpose of their existence: Survival of their species. 'Lower' organisms are either focusing on individual or partial survival, 'higher organisms are focusing on their individual survival because there reproduction cycle is to complex to adapt during stress.  So all fluids and elements in their physical existence are adapting to that principal . What is useful to increase under this general principal will increase

What is useful, can be active substances?

The hypothalamic-pituitary-adrenal (HPA) system is activated by a stress caused from fear of unexpected event. Release of Steroid Hormones and the Stress Hormone Cortisol also important to organize the system especially the heart lungs, circulation, metabolism, immune systems, and skin) to deal quickly with the event. It is our body response as an acute or in chronic adaptation to stress. A chronic stress may cause failure to the body system.  

Hello. If all active substances increase in stress conditions? Actually, not. Allow me to explain what I mean. I would say "stress" means external conditions. How the plant reacts to stress depends on its capacity to survive. If certain substances increase due to stress, then you know the plant reacts actively and its capacity to survive is strong. If you have no increase or even decrease, it means there is a passivity, a decline that leads to Programmed Cell Death (PCD). I am not sure what you mean active substances. Allow me an example. If reduced glutathione is increased under stress, you know that stress has crossed the first lines of defense (ascorbic acid) and affected the S cycle. If the oxidized form of glutathione is increased (with no increase in total glutathione), then it doesn't look good for the plant because there is no renewed production of active forms of glutahione. It is even possible that other activated compounds increase and end up inducing PCD. Perhaps it belongs to the strategy of a species to cause the death of an organ, or even a part of a population in order for the species to have available more resources and survive. Important is also that in order to survive stress some species decrease even the whole metabolism and fall into a mode of hibernation or a time when they sleep through drought or frost (stress). That is why I would not be so absolute. The reaction of plants (or all organisms) depends. That does not characterize the stress conditions. It characterizes the organism. Sorry for my intervention. I hope all this is interesting.

I believe so. There are plants that exhibit behavior under "ideal" nutrient and water availability in soil, but if exposed to a lack of water, often do not survive. But if the same species is grown under conditions of low soil fertility, even if there is no water for a long period can survive.

Dear Alexou

I also agree with you. There are some species where initially antioxidants increase with response to stress, thereafter decline when duration of stress prolonged. In some other it decreases from the very beginning. So it cannot be generalized that under stress plant responds negatively or positively.

Stress was till now discussed as unnormal conditions to an organism. But may I give the proposal to extend the term stress also to biochemical processes?

Did someone argue about the stress for functional proteins like enzymes under stress. I know that normal proteins change their binding and shape if being heated or have contact to strong pH acid.

I do not think all active substances (how do you define active substances?) will increase under stress. I worked with several aromatic plants. Biotic (pests and diseases) and abiotic (moisture and temperature) stresses modified the chemical composition of essential oils distilled from aromatic plants. While some components of the essential oils increased others decreased. All these phytochemicals are aromatic in nature and are biologically active (exhibited antimicrobial activities). The stress response differs from species to species and genotype to genotype. For example arid and semi-arid plants grow under moisture stress. They are also subjected to temperature, wind and light stress. Alpine and temperate crops grow under entirely different conditions. The response of these plants certainly differs and we can not generalize issues in biological systems.

Hello,

I am agreed with Mr. Paul Germann's statement, The evolutionary phrase "SURVIVAL OF THE FITTEST"  describing the mechanism of natural selection we should remain these things in our mind. Recent days this phrase is discussed by biologist with various meanings but it should be based on nature and their conditions. Each and every organisms have the ability to survive on favorable as well as unfavorable conditions through secondary metabolite secretion, morphological modifications, arresting and etc. The secondary metabolites produced on stress condition may be or may not be useful for us but that is secreted by the host (plants) for their existence in the environment otherwise it should get impermanence from the environment.     

in our study, irrigation of fenel increase it's essential oil. n- fertilizers increase essential oils in chamomile and thyme, etc. these are some examples.