Abstract
A gray mangrove, Avicennia marina, develops erected pneumatophores which transport O2 from the atmosphere to the roots in an anaerobic and saline muddy soil in the lagoon through the lenticel and the aerenchyma passage and contribute to the root respiration. Recently it became clear that there was a thin green layer just inside the surface of the pneumatophore and that photosynthetic reaction occurred in the layer. Photosynthetically generated O2 in a thin green layers is used for the root respiration. We found that chloroplasts in the green layer were extremely rich in grana stacks as compared with those in the leaf. In addition, the photosynthetic CO2 fixation activity of the chloroplasts in pneumatophore was more than ten times as high as that in the leaf under lighting condition at the PPFD of 210μmol m-2 s-1. The photosynthesis in the green layer chloroplasts could support the efficient O2 generation in the pneumatophore and also could play an important role in the energy supply for the selective ion permeability and osmotic regulation of roots in the saline soil.
