Abstract
During light induction, the water-water cycle (WWC) functions and leads to ΔpH formation. This activates Rubisco. When WWC is suppressed, cyclic electron flow (CEF-PSI) is engaged and Rubisco is activated. Both low and high temperatures promote CEF-PSI. At cool temperature, since the capacity for linear electron flow (LEF) is sufficient for CO2 assimilation, an additional formation of ΔpH by CEF-PSI maintains a high activation of Rubisco. At high temperature, however, Rubisco activation declines. One reason is heat-lability of Rubisco activase, but another reason is that the activation of CEF-PSI at the expense of LEF leads to a decline in the stromal redox-state. Low N also stimulates CEF-PSI, and leads to a high activation of Rubisco. In the rbcS-antisense lines, the CEF-PSI is also engaged and Rubisco is fully activated. Thus, Rubisco activation is controlled by activase as a result of a limitation in the electron-transport system.
