Chemical stresses are either endogenous or exogenous.

Endogenous Chemical Stress is the one, which are created inside our bodies. They are the result of improper diet or improper food combining.

Toxins from outside the body are referred to as exogenous chemical stress. These are chemicals like food additives, pollution and drugs. They all have some sort of negative effect on our health. Chemical stresses cause damage or irritation to vital organs or sensitive tissues, which result in a reflex to the spine creating spinal imbalances and subluxations.

 

Plant adaptations to toxic trace elements

Some metal ions and other trace elements in excess are highly toxic, including As, Cd, Cu, Ni, Zn and Se (although some of these serve also as essential micronutrients in smaller quantities). Mechanisms of defense include exclusion from the plant and internal tolerance mechanisms. Plants in over 400 taxa can hyperaccumulate potentially toxic elements such as As, Cd, Cr, Hg, Ni, Pb, Se and Zn (usually in the vacuole, where they are bound to organic acids). These hyperaccumulated toxic elements, though safely compartmentalized in the plant, render their shoot toxic to pathogens and insect herbivores and thus serve a protective role. Such plants require not only high internal tolerance and protection against oxidative damage etc. but also powerful scavenging mechanisms and overproduction of transporters to import high amounts of these elements. Chelators such as nicotianamide (which derives from L-methionine) and histidine are also involved in the transport process.

Some of these hyperaccumulator plant capabilities are being studied for exploitation in environmental phytoremediation directed against toxic element contamination. Phytoremediation of contaminated sites generally involve phytoextraction, phytodegradation (detoxification or organic pollutants, chelation, sequestration). Air Pollution

Dusts deposited on leaves block light and PS and can also impair stomatal gas exchanges, even if they are not otherwise toxic.

Chemical pollutants

Polluting chemical or altered levels of atmospheric CO2, CO, SO2, nitrogen oxides (NOx, NO, and NO2, etc. in varying proportions) and C2H4 (ethylene), H2S and HF adversely affect the plant. In some areas, these pollutants attain sufficiently high levels to inhibit plant growth, especially when interacting with other adverse environmental conditions. Photochemical smog includes many of these pollutants, plus other compounds deleterious to plants such as ozone (O3), peroxyacetylnitrate (PAN) and hydrogen peroxide (H2O2).

Inorganic N and S Polluting gases such as SO2 and NOx enter leaves through stomata, following the same diffusion pathway as CO2. NOx dissolves in cells and gives rise to nitrite ions (NO2, which are toxic at high concentrations) and nitrite ions (NO3) that enter into nitrogen metabolism as if they had been absorbed through the roots exposure to SO2 causing stomatal closure.

Mechanical stress

Wind is a huge part of abiotic stress. There is simply no way to stop the wind from blowing. This is definitely a bigger problem in some parts of the world than in others. Barren areas such as deserts are very susceptible to natural wind erosion. These types of areas don‟t have any vegetation to hold the soil particles in place. Once the wind starts to blow the soil around, there is nothing to stop the process. The only chance for the soil to stay in place is if the wind doesn‟t blow which is usually not an option. Plant growth in windblown areas is very limited. Because the soil is constantly moving, there is no opportunity for plants to develop a root system. Soil that blows a lot usually is very dry also. This leaves little nutrients to promote plant growth. Farmland is typically very susceptible to wind erosion. Most farmers do not plant cover crops during the seasons when their main crops are not in the fields. They simply leave the ground open and uncovered. When the soil is dry, the top layer becomes similar to powder. When the wind blows, the powdery top layer of the farmland is picked up and carried for miles. This is the exact scenario that occurred during the Dust Bow in the 1930‟s. The combination of drought and poor farming practices allowed the wind to move thousands of tons of dirt from one area to the next.

 

Soil movement

By simply practicing good farming practice soil movement can be checked. Don’t leave ground bare and without any type of vegetation. During dry seasons it is especially important to have the land covered because dry soil moves much easier than wet soil in the wind. When soil is not blowing due to the wind, conditions are much better for plant growth. Plants cannot grow in a soil that is constantly blowing. Their root systems do not have time to be established. Also, when soil particles are blowing they wear away at the plants that they run into. Plants are essentially “sand blasted”.

 

Air Pollution

Dusts deposited on leaves block light and PS and can also impair stomatal gas exchanges, even if they are not otherwise toxic.

Chemical pollutants Polluting chemical or altered levels of atmospheric CO2, CO, SO2, nitrogen oxides (NOx, NO, and NO2, etc. in varying proportions) and C2H4 (ethylene), H2S and HF adversely affect the plant. In some areas, these pollutants attain sufficiently high levels to inhibit plant growth, especially when interacting with other adverse environmental conditions. Photochemical smog includes many of these pollutants, plus other compounds deleterious to plants such as ozone (O3), peroxyacetylnitrate (PAN) and hydrogen peroxide (H2O2).

Inorganic N and S Polluting gases such as SO2 and NOx enter leaves through stomata, following the same diffusion pathway as CO2. NOx dissolves in cells and gives rise to nitrite ions (NO2, which are toxic at high concentrations) and nitrite ions (NO3) that enter into nitrogen metabolism as if they had been absorbed through the roots exposure to SO2 causing stomatal closure.

 

UV defense mechanism in plants

Plants have complex and dynamic systems of response to stress stimuli which are much more intricate than found in animals despite the absence of an immune system in plants. The paramount reason for this is that plants do not pose the ability to simply move away from the region of stressful stimuli. Multiple stresses or astress and an external potential ameliorant can evoke very complex responses in plants systems. UV-B radiation on plants is one such stress, which is now of major concern to plant biologists. The threat to productivity in global agriculture due to stratospheric ozone depletion cannot be overstated, nor should it be overlooked. Attempts at quantitative and qualitative predictions of expected effects and the search for a suitable ameliorant or a stress alleviant are being met with mixed outcomes. One of the reasons for this is the limitation in controlled-environment studies. Results from greenhouse or growth-chamber studies and field studies on UV-B effects are often conflicting or difficult to interpret, because of unrealistically high UV irradiation levels, inadequate levels of UV-A, low PAR or other technical difficulties. There is a dearth of well designed and replicated experiments in the field owing to difficulties in simulating natural levels of UV-B irradiance in field conditions.