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NAME : NIDHI S. DARJI.

COURSE : BIOTECHNOLOGY (FY B.sc).

COLLEGE : GOVERNMENT SCIENCE COLLEGE.

INTRODUCTION.

HISTORICAL BACKGROUND.

OVERVIEW OF CAM : A TWO-PART CYCLE.i. DURING THE NIGHT.ii. DURING THE DAY.

BENEFITS.

COMPARISON WITH C4 METABOLISM.

Crassulacean acid metabolism, also

known as CAM photosynthesis, is a

carbon fixation pathway that evolved

in some plants as an adaptation to

arid conditions.

In a plant using full CAM, the stoma inthe leaves remain shut during the day toreduce evapotranspiration, but open atnight to collect carbon dioxide (CO2). TheCO2 is stored as thefourcarbonacid malate, and then usedduring photosynthesis during the day.The pre-collected CO2 is concentratedaround the enzyme RuBisCO, increasingphotosynthetic efficiency.

CAM was first suspected by De Saussure in1804 in his Recherches Chimiques sur laVegetation, confirmed and refined byAubert, E. in 1892 in his Recherchesphysiologiques sur les plantes grasses andexpounded upon by Richards, H. M. 1915in Acidity and Gas Interchange in Cacti,Carnegie Institution.

The term CAM may have been coined by Ranson and Thomas in 1940, but they were not the first to discover this cycle.

It was observed by the botanists Ransonand Thomas, in the Crassulaceae family of succulents (which includes jade plants and Sedum).

Its name refers to acid metabolism in Crassulaceae, not the metabolism of crassulacean acid.

i. DURING THE NIGHT

CAM is an adaptation for increased efficiency in the use of water, and so is typically found in plants growing in arid conditions.

During the night, a plant employing CAM has its stomata open, allowing CO2 to enter and be fixed as organic acids that are stored vacuoles in. During the day the stomata are closed (thus preventing water loss), and the carbon is released to the Calvin cycleso that photosynthesis may take place.

The carbon dioxide is fixed in the cytoplasmof mesophyll cells by a PEP reaction similar to that of C4 pathway. But, unlike theC4mechanism, the resulting organic acids are stored in vacuoles for later use; that is, they are not immediately passed on to the Calvin cycle. The latter cannot operate during the night because the light reactions that provide it with ATP and NADPH cannot take place.

During the day, the CO2-storing organic acids are released from the vacuoles of the mesophyll cells and enter the stroma of the chloroplasts where an enzyme releases the CO2, which then enters into the Calvin cycle

i. DURING THE DAY

CAM photosynthesis- left, at night; right, during the day.

1. chloroplast, 2. vacuole, 3. cytoplasm, 4. Calvin cycle, 5.

stoma, 6. oxaloacetic acid (OAA), 7. PEP carboxylase

(PEPCase), 8. granum (stack of thylakoids), 9. stroma of

chloroplast, 10. malate, 11.malic acid

The most important benefit of CAM to the plant is the ability to leave most leaf stomata closed during the day.

Plants employing CAM are most common in arid environments, where water comes at a premium. Being able to keep stomata closed during the hottest and driest part of the day reduces the loss of water through evapotranspiration, allowing such plants to grow in environments that would otherwise be far too dry.

Plants using only C3 carbon fixation, for example, lose 97% of the water they uptake through the roots to transpiration - a high cost avoided by plants able to employ CAM.

The C4 pathway bears resemblance to CAM; both act to concentrate CO2 around RuBisCO, thereby increasing its efficiency.

CAM concentrates it in time, providing CO2 during the day, and not at night, when respiration is the dominant reaction.

C4 plants, in contrast, concentrate CO2 spatially, with a RuBisCO reaction centre in a "bundle sheathcell" being inundated with CO2.

Due to the inactivity required by the CAM mechanism, C4 carbon fixation has a greater efficiency in terms of PGA synthesis.

Pineapple is a CAM plan.

CAM is named after the

family Crassulaceae, to

which Jade plant belongs

C.Michael Hogan. 2011. Respiration. Encyclopedia of Earth. Eds. Mark McGinley & C.J.cleveland. National council for Science and the Environment. Washington DC

Ranson S. L.; Thomas M (1960). "Crassulacean acid metabolism". Annual Rev Plant Physiol

Herrera, A. (2008), "Crassulacean acid metabolism and fitness under water deficit stress: if not for carbon gain, what is facultative CAM good for?", Annals of Botany 103

Ting, I P (1985). "Crassulacean Acid Metabolism". Annual Review of Plant Physiology 36

Raven, JA; Edwards, D. (2001). "Roots: evolutionary origins and biogeochemical significance". Journal of Experimental Botany 52

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