-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 m 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.