presentation 19 - copy

8/3/2019 Presentation 19 - Copy

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Global warming and its impact on

productivity


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INDEX

Evolution of atmosphere with respect to different eras

Sequence involved in climate change

Concept of Productivity

Physiological changes in plants under temperature stress

Mitigation strategies to cope climate change


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Aeon Era Duration in

millions of

years

Millions of

years ago

Phanerozo

icCenozoic 65 5

Mesozoic 183 248

Palaeozoic 295 543

Precambrian

Proterozoic Late 357 900

Middle 700 1600Early 900 2500

A

rchaean Late 500 3000

Middle 400 3400

Early 400 3800

Hadean 800 4600

Table 1: Geologic time-scale showing major climatic and evolutionary eventsduring the Precambrian Era

rise of atmospheric oxygen (ice age)


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Elements Theoretical reducingatmosphere

Present oxidizingatmosphere

CarbonMethane (CH4)Carbon Monoxide (CO)

Carbon Dioxide (CO2)

Hydrogen Hydrogen (H2) Water (H2)

NitrogenAmmonia (NH3)Nitrogen (N2)

Nitrogen (N2)

Oxygen Water (H2O) Oxygen (O2)

Table 2. Forms of elements in early and present atmosphere.


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Climate change :

Statistically significant variation in either the mean state of the climate or

in its variability, persisting for an extended period (typically decades or

longer).-----

MOEF.

Global Warming:

Global Warming refers to an average increase in the Earth's temperature,

which in turn causes changes in climate patterns.

Green House Gases:

Carbon dioxide (CO2), Methane (CH4), Nitrous oxide (N2O), Hydro

fluorocarbons (HFCs), Per fluorocarbons (PFCs) ,Sulfur hexafluoride

(SF6)

Green House effect:

The greenhouse effect is an increase in the temperature of a planet as heat

energy from sunlight is trapped by the gaseous atmosphere


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Morphological changes Anatomical changes

Scorching of leaves and twigs Sunburns on leaves, branches

and stems Leaf senescence and abscission

Shoot and root growth inhibition Fruit discoloration

Reduced cell size Closure of stomata and curtailed

water loss Increased stomatal and

trichomatous densities Greater xylem vessels of both

root and shoot Mesophyll cells were damaged

in grapes.


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Physiologicalchanges


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High leaf temperature and water deficit lead to heat stress

CAMplants

Stomataclosed (Day)

No cooling byTranspiration

Re emitted by conductionconvection

Loss of heat

a) Soil water deficit

b) High relative humidity

4 to 5 0C increase leaftemperature

C3 andC4 Plants

Stomataopen (day)

C3 and C4Plants

Stomatapartial closed

Cooling of leaf temperature


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Photosynthesis is inhibited before respiration at hightemperature

At normal condition, rate of photosynthesis is more than rate of

respiration.

Temperature at which rate of photosynthesis equals rate of respiration

is called as compensation point.

At temperatures above compensation point, rate of respiration is more

than the rate of photosynthesis.

Under such condition photosynthesis cannot replace the carbon used

as substrate for respiration.

As a result carbohydrate reserves decline, and fruits and vegetables

lose their sweetness.


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High temperature reduces membrane stability

At high temperature, there is a increase in the fluidity of membrane

lipids which results in loss of physiological function.

High temperature decreases the strength of hydrogen bonds and

electrostatic interaction between the polar groups of proteins within

the aqueous phase of the membrane.

Modification of membrane composition, structure and leakage of

ions.

Inhibition of processes such as photosynthesis and respiration that

depend on the activity of membrane associated electron carriers and

enzymes


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Several adaptation to protect leaves against excessive heating

Plants avoid excessive heating of leaves by lowering the

absorption of solar radiation.

Reflective leaf hairs and leaf waxes.

Leaf rolling orientation and growth of small, highly dissected

leaves.


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At high temperatures plant produce heat shock proteins

Book source :Plant Physiology (Taiz & Zeiger) p 605


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Adaptation to heat stress is mediated through cytosolicCalcium

Book source :Plant Physiology (Taiz & Zeiger) p 606


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Accumulation of

compatible osmolytes

sugars and sugaralcohols (polyols),proline, tertiary andquaternary ammoniumcompounds, andtertiary sulphonium

compounds


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Mitigation strategies for plants to cope up with climate change

To identify the varieties sensitive to high temperature.

Improved thermotolerance using various genetic approaches.

Induction of Thermo tolerance.


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Accumulation of compatible osmolytes:

sugars and sugar alcohols (polyols), proline, tertiary and quaternary

ammonium compounds, and tertiary sulphonium compounds areaccumulated .

Secondary metabolite production:

Increased activity of Phenylalanine ammonia-lyase -main acclimatory

response of cells to heat stress.

Thermal stress induces the biosynthesis of phenolics and suppressestheir oxidation-acclimation to heat stress in watermelon.

anthocyanins serve to decrease leaf osmotic potential -increased uptake

and reduced transpirational loss of water under environmental stressesincluding high temperature


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CONCLUSION

Climate change is a serious concern which canaffect overall productivity of crops plants andnatural vegetation.

Effects of high temperature on plants range frommorphological, anatomical and physiologicalchanges.

It is important to study plants responses to heatstress in order to understand their mechanism to

cope with high temperature.

It is possible to induce thermo tolerance in plantsthrough gradual exposure to heat.


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REFERENCES

Book of Plant Physiology (Taiz & Zeiger)

A. Wahid, S. Gelani a, M. Ashraf a, M.R. Fooladb(2007) , Heat tolerance in plants: An overviewEnvironmental and Experimental Botany 61 199

223.

Jenks M.A and Hasegawa P.M (2005) Plant abioticstress (1th ed) Blackwell Publishing Ltd. Oxford. UK.


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