Signal Integration by ABA in the Blue Light-Induced Acidification of Leaf Pavement Cells in Pea (Pisum sativum L. var. Argenteum).

Leaf pavement cell expansion in light depends on apoplastic acidification by a plasma membrane proton-pumping ATPase, modifying cell wall extensibility and providing the driving force for uptake of osmotically active solutes generating turgor. This paper shows that the plant hormone ABA inhibits light-induced leaf disk growth as well as the blue light-induced pavement cell growth in pea (Pisum sativum L.). In the phytochrome chromophore-deficient mutant pcd2, the effect of ABA on the blue light-induced apoplastic acidification response, which exhibits a high fluence phase via phytochrome and a low fluence phase via an unknown blue light receptor, is still present, indicating an interaction of ABA with the blue light receptor pathway. Furthermore, it is shown that ABA inhibits the blue light-induced apoplastic acidification reversibly. These results indicate that the effect of ABA on apoplastic acidification can provide a mechanism for short term, reversible adjustment of leaf growth rate to environmental change.