Calvin --> Photorespiration ---> C4 ---> CAM

CAM or Crassulacean Acid Metabolism:

CAM plants use a similar process as C4 plants except they let CO2 in at night, turn it into malic or aspartic acid and then store it in the vacoules of their photosynthetic cells.

When the sun comes out, they are able to close their stomata and breakdown the malate (malic acid) to keep the internal concentration of CO2 high enough to prevent photorespiration. This enables the plants to keep their stomata closed in order to prevent dessication.

These plants do not exhibit Kranz anatomy. The CAM pathway has evolved in many different families of plants separately.
plant families that use CAM including the:

Agavaceae

agaves, yucca

Cactaceae

cacti

Liliaceae

some of the lilies

Euphorbeace

spurges

Orchidaceae

some orchids

Polypodieace

some ferns

Portulaceae

purslanes

Vitacea

few grapes

Weltiwitschiaceae

our favorite odd gymnosperm of Nabim desert

 

Although some of the plants make sense ( cacti) why should some orchids or grapes have CAM?

(below adapted from:http://www.rrz.uni-hamburg.de/biologie/b_online/e24/24b.htm)

CAM has been detected in more than 1000 angiosperms of 17 different families.

It is usually accompanied by succulence, though not all Crassulaceae, for example, display CAM and succulence is no precondition of CAM.

Mesemryanthemum crystallinum (a plant with succulent leaves) can use the C3 pathway but switches to CAM when growing in saline soils. Under experimental conditions can the shift be achieved by increasing the NaCl concentration of the nutrient medium (K. WINTER and D. J. von WILLERT, 1972).

The degree of the CAM influence in CAM plants regulated mainly by temperature, atmospheric humidity, and salinity. This differs from C4 in which light is the primary consideration..

Both strong and weak CAM plants are known. In weak CAM plants becomes CAM only apparent at certain differences between day and night temperature. CAM plants that store a lot of malate and due to the thus high osmotic value also a lot of water, are usually less frost resistant than C3 plants. Because of the high concentration of acid they are less heat resistant, surprisingly. Species of arid regions are therefore forced to break their pool of malate down during the daytime (R. LÖSCH and H. KAPPEN, Universität Kiel, 1985).

Below adapted from: Koning, Ross E. "Photosynthesis: the Synthesis part". Plant Physiology Website. 1994. http://koning.ecsu.ctstateu.edu/plant_biology/synthpart.html (3/27/99)


 

A final thought....

Vicious global warming cycle predicted Friday, January 15, 1999 By Reuters

Global warming could disrupt the ability of a large portion of the world's oceans to absorb carbon dioxide from the atmosphere, setting off a vicious cycle in which the Earth gets even hotter, researchers said Thursday. Evidence from a new study indicates that some conditions scientists think will occur with global warming may promote the growth of algae in the Southern Ocean that do not absorb carbon dioxide as well as others.

These waters around Antarctica make up 10 percent of the world's oceans and play a significant role in soaking up carbon dioxide, a greenhouse gas seen as one of the main causes of global warming, Kevin Arrigo, a biologist at NASA-Goddard Space Flight Center in Maryland, who led the study, said. "The capacity for the Southern Ocean to take up carbon dioxide might be reduced," Arrigo said in a telephone interview. Since carbon dioxide contributes to global warming, scientists believe a growing buildup of the gas would make the environmental problem increasingly worse. Plants "breathe" carbon dioxide and help control the balance of the gas in the atmosphere. About half the plants that use this gas are in the oceans, Arrigo said. But the earth's rising temperatures create an environment where some phytoplankton, called diatoms, begin to dominate over single-celled algae called Phaeocystis antarctica, which are better at absorbing carbon dioxide. "Given the same amount of nutrients, Phaeocystis antarctica takes up almost two times as much carbon dioxide," Arrigo said. Writing in the journal Science, the researchers said increasing stratification of the Southern Ocean, or differences in water density at different depths, was the change causing diatoms to dominate the environment. Normally there is very little stratification in the Southern Ocean because frequent strong winds keep the waters well mixed, Arrigo said. But the increased precipitation that scientists predict will happen with global warming means more diluted water is sitting on the top, making the waters more difficult to mix. This causes the death of the more efficient carbon-eating phytoplankton.

"If global warming continues with increased precipitation in the Southern Ocean, there will be more stratification and that will favor diatoms," Arrigo said.

The study, which took place during a month-long expedition during the Antarctic summer, was also one of the first to show that some types of algae absorb carbon dioxide better than others. Arrigo said knowing how much atmospheric carbon dioxide the oceans use is important for scientists when trying to predict climate change. "We need to understand the capacity of the world's oceans to take up all this carbon dioxide," he said. "At some point the ocean might reach its limit and shut off."