Can negligible levels of Rubisco activase be the reason for decreased Rubisco activity levels in guard cells?

摘要

Although Rubisco is a normal and abundant enzyme in mesophyll chloroplasts, its presence and activity in guard cell chloroplasts has been a subject of controversy. Several studies using a variety of techniques have unequivocally confirmed not only the presence of Rubisco in guard cells (Vaughn and Vaughn, 1988), but also found it to be catalytically active (Reckmann et al, 1990). Based on a cell basis, the amount of Rubisco in guard cells is suggested to be in the range of 0.6 to 1.4 percent whereasits activity is reported to be in the range of 0.35 to 0.5 percent, of a mesophyll cell. The absolute physiological significance of Rubisco, however, has still not been clearly understood in these cells.