Induction of Kranz anatomy and C4-like biochemical characteristics in a submerged amphibious plant by abscisic acid

The amphibious leafless sedge Eleocharis vivipara develops C(4)-like traits as well as Kranz anatomy under terrestrial conditions, but it develops C(3)-like traits without Kranz anatomy under submerged conditions. When submerged plants are exposed to aerial conditions, they rapidly produce new photosynthetic tissues with C(4)-like traits. In this study, experiments were performed to determine whether abscisic acid (ABA), a plant stress hormone, could induce the formation of photosynthetic tissues with Kranz anatomy and C(4)-like biochemical traits under water in the submerged form. When the submerged plants were grown in water containing 5 mu M ABA, they developed new photosynthetic tissues with Kranz anatomy, forming well-developed Kranz (bundle sheath) cells that contained many organelles. The ABA-induced tissues accumulated large amounts of phosphoenolpyruvate carboxylase, pyruvate orthophosphate dikinase, and NAD-malic enzyme at the appropriate cellular sites. The tissues had 3.4 to 3.8 times more C(4) enzyme activity than did tissues of the untreated submerged plants. Carbon-14 pulse and carbon-12 chase experiments revealed that the ABA-induced tissues fixed higher amounts of carbon-14 into C(4) compounds and lower amounts of carbon-14 into C(3) compounds as initial products than did the submerged plants and that they exhibited a C(4)-like pattern of carbon fixation under aqueous conditions of low carbon, indicating enhanced C(4) capacity in the tissues. This report provides an example of the hormonal control of the differentiation of the structural and functional traits required for the C(4) pathway.