NEWS
First Report of a Succulent Grass with CAM Photosynthesis
Sejarah Poaceae
The Poaceae as a whole are about equally divided between those that use C3 photosynthesis , and those that have the C4 version of photosynthesis , which is more energetically costly , but which allows the plants to be more productive in hot and arid environments .
In C3 plants , which are the vast majority of plants in the world , CO 2 is directly fixed into a 3-Carbon compound by the enzyme RuBisCo in the Calvin-Benson cycle . Unfortunately , RuBisCo can use both O 2 and CO 2
, and when a C3 plant closes its stomata in order to conserve water in hot dry environments , more O 2 is used , which leads to a let loss of carbon in the plant . In fact , some calculations show that C3 plants could end up wasting up to 40 % of absorbed energy due to photorespiration !
C4 plants solve this problem through a carbon-concentrating mechanism . They have modified leaf anatomy wherein
CO 2 is first fixed onto a 4-carbon compound in outer mesophyll cells by an enzyme not affected by O 2
, before being shunted to inner bundle sheath cells , where it is converted back to CO 2 for use by RuBisCo in those cells .
CAM plants are also adapted to hot and dry environments , and they also initially fix CO 2 into a 4-carbon compound . In their case , they keep their stomata close during the heat of the day , then open them at night . The CO 2 that comes in when the stomata are open is fixed into a 4-carbon compound by the same enzyme used by C4 plants , then shunted into a nearby vacuole , where they remain until needed to complete carbon fixation during the daytime . So in the case of CAM plants , they concentrate carbon by separating the process temporally , instead of spatially like C4 plants do .
The Poaceae recently became one of only 8 families of plants that have members using all 3 different photosynthetic methods , with the single grass species
23 Grassroots Vol 22 No 1 March 2022