Phenolic compounds are a group of defense compounds synthesized by plants in response to stress from air pollution. When plants are exposed to air pollutants like SO2, NO2, and O3, there is an increase in phenolic compound production. Phenolic compounds accumulate in plant tissues and compartments like vacuoles and cell walls. This accumulation can lead to cell damage and necrosis. The increased production of phenolic compounds helps protect plants from damage by oxidative stress caused by air pollutants.
formation of phenolic compounds in plants during air pollution
1. FORMATION OF PHENOLIC COMPOUNDS
UNDER AIR POLLUTION STRESS
NIHARIKA
M.SC BOTANY 2nd YEAR
BOTANY DEPPT.
SUBMITTED TO :- SALIQ SIR
2. Phenolic Compounds and Pollutant
• Modern industry has provided our environment with an almost
indefinite number of agents.
• The most common of these components are SO2, NO2, CO, HC
(Hydrocarbons), O3 and APM (Atmospheric Particulate Matter).
• Different ions and compounds enter and kill the plant.
• Reactions of a living organism exposed to air pollution under
natural conditions reactions may be used as bioindicators.
• A group of defense compounds synthesized by plants comprises of
phenolic compounds.
3. Continued………
• The concentration of phenolic compounds increases with invasion
by pathogens.
• There is a change in enzyme-gene system due to pollution as they
have genetic capacity to compensate for drastic changes in the
environment.
• Drastic changes are termed as “stress”.
• Adjustment of such stress is done by secondary products ie,
phenolic compounds.
• Air pollution induces qualitative and quantitative changes in
secondary metabolite composition in plants.
4. Cont….
• Phenolic compounds are tissue specific.
• They do not produce the death of the cell which produce them,
but inhibit their growth and multiplication by binding to and
precipitating proteins.
• By binding, phenolic compounds alter the structure and hence the
activity of enzymes and other proteins.
• In order to be non-toxic to the cell producing them, they are
compartmentalized and separated from the cytoplasm and if they
are not isolated by membrane, phenolics would deactivate the
cell’s own cytoplasm.
5. ANTHOCYANINS
• located in ideoblastic cells.
• Their concentrations can change depending on altered environmental
conditions.
TANNINS
• Now known as proanthocyanidins.
• Are wound compounds.
• They are biosynthesized due to wounding.
• Concentrations increase in the tissue surrounding the wound.
• LOCATION : in every cell or in ideoblastic cells.
6. SITE OF LOCALIZATION OF PHENOLIC
COMPOUNDS
• They both separate the outside compartments from the ground
cytoplasm.
• Phenolics are non-toxic to their own cells.
• Cells below the dead cells increase the production of phenolics.
INTERCELLULAR SPACES : separated by
plasmalemma
VACUOLE : separated from
ground cytoplasm by the
membrane tonoplast
7. Example
• The concentration of phenolics increases inside the needle of
pinus, when exposed to air pollution.
• Flavonoids and Coumarins exists on plant surface of Rutaceae,
Umbelliferae, Leguminosae.
• They are embedded in the epicuticular layer and is coated
protecting the whole plant body.
• Cutin and Waxes as well as Intine and Exine in pollen, located
outside the cell isolates the cytoplasm from harsh conditions.
• Furanocoumarins are embedded in wax.
8. MONOTERPENES
• Responsible for communication between the plant and its
environment.
SESQUITERPENES
• Extruded to the surface by trichomes of plants growing in semi
arid conditions.
9. Effect of phenolics on plants
• Destruction of the structure of mesophyll cell occurs as first sign of
damage. There is a thin layer of mesophyll, composed of two rows of
cells between hypodermis and endodermis.
• Mesophyll cells filled first with phenolics and the damage rapidly reaches
the endodermis leading to the damage to central parenchyma quickly.
• Lesions appear in the areas where more phenolics are stored.
• Parenchymatous cells around veins, show effects close to necrosis due to
higher concentration of phenolics.
• Basal part of the needle in pinus reacts the air pollution by blocking
differentiation of some of the cells.
11. Effect on plant tissues….
• There is an increase production of small vacuoles and vesicles
filled with phenolics from E.R, fusion with central vacuole, in
isodiametric cells and in mesophyll cells.
• Central vacuoles are heterogeneous, containing phenolic
compounds which are electron-dense, lipid-like droplets are
found.
• Different size lipid droplets in vacuoles can be observed in the
vacuole due to air pollution stress.
12. Contii..….
• Excess of phenolic compounds may lead to cell lysis resulting in cell death
visible as necrosis.
• Production of phenolics is visible in the tunica of promeristem cells at the
very apex of the shoot.
• Phenolic production increases the influence of other ions and their
mixtures.
• Sulphur dioxide lowers the net photosynthesis, leaf respiration and
transpiration.
• Assimilation rates are lowered by SO2 fumigation.
• Disorganisation of cuticular striation pattern and dissolution of the cell
wall occur.
• Epiphytic lichens become more abundant by SO2.
13. Enzymes responsible for production of
phenolics in response to stress
• PEROXIDASES are stimulated by SO2 .
• glutamate dehydrogenase
• Phosphatases
• Proline
• Isocitrate-glucose-6-phosphate dehydrogenase
• Chalcone synthase
14. Conti…
• Phenol acts as a free radical scavenger to protect plants away
from damage by oxidative stress.
• Total phenols in the leaves of plants growing in the polluted site
were higher compared to the plants growing in unpolluted area.
Increase of the phenolic compound level has also been observed
after the exposure of plants to several toxic pollutants .
• Air pollution influences the accumulation of phenolic content in
the leaves .
15. Effect on pollen grains
• The role of pollen grains in the fertilisation and fertility of plants
is one of the most important biological factors.
• Fertility decreases under different stresses due to the direct and
indirect effects on reproductive apparatus.
• The effects of air pollutants on roots and aerial parts affect
generative apparatus development and plant fertility.
• Pollutants affect pollen structure, germination and pollen tube
growth after anther dehiscence until reaching to stigma.
16. Contii..
• Air pollution caused shrinkage, thinning and fragility of pollen.
• Pollen grains lose their exine when they are in contact to
moisture.
• Indirect effects of air pollution on pollen grains are possible via
the soil. If a plant grows in polluted soil, its physiologic functions
may change and affect properties of the developing pollen.
• Injury of floral organs especially anthers can cause pollen
abnormality and sterility, and consequently malfunction of
fertilisation.
