The photosynthetic role of ears in C3 cereals: metabolism, water use efficiency and contribution to grain yield

TAMBUSSI E. A.; BORT J.; GUIAMET J.J.; NOGUÉS S.; ARAUS J.L.

CRITICAL REVIEWS IN PLANT SCIENCES

Año: 2007 p. 1 - 16

0735-2689

The present review will discuss several issues regarding ear photosynthesis and its contribution to grain filling in C3 cereals. Ear photosynthesis appears quantitatively important to grain filling, mainly in dry areas where source (i.e., assimilate) limitations can occur. Compared with the flag leaf, ear photosynthesis shows a higher water stress tolerance. Several peculiarities could be involved in the ear’s ‘drought tolerance’. First, although the presence of some degree of C4 metabolism in ear parts has been reported, current evidence seems to support the existence of a typical C3 metabolism. Second, the recycling of respired CO2 (i.e., refixation) is a well-documented process. This refixation could have considerable impact in the final crop yield, preventing the loss of CO2 respired by the growing grain. Because the refixation of CO2 is independent of atmospheric conditions, water use efficiency (measured as total ear photosynthesis divided by transpiration) could be higher in the ear than in the flag leaf. Moreover, the ear parts (in particular the awns) show higher relative water content, as well as better osmotic adjustment under water stress than does the flag leaf. This capacity, in addition to the persistence of photosynthetic components under drought (delayed senescence), might help the ear to continue fixing CO2 late in the grain filling period.