Effect of Rapid Dehydration on the activity of Rubisco from the C4 grass Paspalum dilatatum

摘要

C4 plants in contrast to their C3 plants counterparts, are usually located in warm-climate areas with high irradiance and some periods of water stress (tropical, sub-tropical and semi-desert areas) (Hatch, 1987). P. dilatatum is a C4-plant sub-typeNADP-ME that forms dense prairies, resistant to mild frosts (Hacker et al.,1974) and to low temperatures (Bernardes da Silva, 1996) and although preferring wet soils, it can stand a high level of water stress as long as it has benefit from rain in part of the year (Pinto da Silva, 1969). In the C4 pathway Rubisco is involved in a secondary re-fixation of CO_2 in the bundle sheath cells, where C4 acid decarboxylation provides, at the level of Calvin cycle, a high CO_2 concentration. The effect of water stress on the enzyme is still a matter of controversy. It has been reported that slowly imposed water stress, in maize plants, leads to a sharp decrease in Rubisco activity whereas the Rubisco protein was affected to a lesser extent (Castrillo and Fernandez, 1990). However in sunflower it has been shown that the effect of water stress was mainly on the Rubisco-protein content (Turner,1981). Also, results from our laboratory, using the C4 gramineae Setaria sphacelata showed a decrease on Rubisco activitywith water stress, whereas its content was kept relatively constant, oscillating around 8 percent of the total soluble protein (Marques da Silva, 1999). However when this plant was subjected to a rapid dehydration the maximal activity did not change withthe stress whereas the inicial activity and Rubisco protein content increased. The aim of this work was the study of rapid dehydration effect on Rubisco activities and activation, using as a model the C4 gramineae Paspalum dilatatum.