C4 Plants Adaptation to High Levels of CO2 and to Drought Environments

摘要: 1.1 General features of the C4 cycle All plants use Photosynthetic Carbon Reduction (PCR or Calvin-Benson) for CO2 fixation in which Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) catalyzes first step producing a three-carbon compound, phosphoglycerate (3-PGA). For this reason process is referred to as C3 cycle. Plants utilizing pathway are often named species. A major problem with that enzyme Rubisco two competing reactions: carboxylation and oxygenation (Portis & Parry, 2007). The reaction directs flow carbon through photorespiratory pathway, can result losses between 25% 30% fixed. Environmental variables such high temperature drought an increase oxygenase reaction. Therefore, reducing has potential assimilation significantly would represent change photosynthesis (up 100% depending on temperature; Long et al., 2006). adaptation overcomes limitation photorespiration, improving photosynthetic efficiency minimizing water loss hot, dry environments (Edwards Walker, 1983). Generally, species originate from warmer climates than (Sage Monson, 1999). Most native tropics warm temperate zones light intensity temperature. Under these conditions, exhibit higher growth rates due gains water, nitrogen uses. Indeed, highest known productivity natural vegetation perennial grass central Amazon, achieves net production 100 t (dry matter) ha-1 year-1 (Piedade 1991; Long, Some world s most productive crops pasture, maize (Zea mays), sugar cane (Saccharum officinarum), sorghum (Sorghum bicolor), amaranth, paspalums (Paspalum notatum P. urvillei), bermudagrass (Cynodon dactylon), blue grama (Bouteloua gracilis) rhodes (Chloris gayana) plants. In addition, troublesome weeds like nutgrass, crabgrass barnyard, also Although only small portion plant species, accounting 3 % vascular plants, they contribute about 20% global primary because highly C4grass-lands (Ehleringer 1997). Approximately half 10,000 sedge have photosynthesis, but fewer 2,000 dicotyledonous