Photosynthetic capacity in seagrass seeds and early-stage seedlings of Zostera marina L

Summary In many terrestrial seeds, photosynthetic activity supplies O2 to the developing plant embryo to sustain aerobic metabolism and enhance biosynthetic activity. However, whether seagrass seeds possess similar photosynthetic capacity to alleviate intra-seed hypoxic stress conditions is unknown. We used a novel combination of microscale variable chlorophyll fluorescence imaging, a custom-made O2 optode microrespirometry system, and planar optode O2 imaging, to determine the O2 microenvironment and photosynthetic activity in developing seeds and seedlings of seagrass (Z. marina L.). Developing, sheath-covered seeds exhibited high O2 concentrations in the photosynthetic active seed sheath and low O2 concentrations in the center of the seed at the position of the embryo. In light, photosynthesis in the seed sheath increased O2 availability in central parts of the seed enabling enhanced respiratory energy generation for biosynthetic activity. Early-stage seedlings also displayed photosynthetic capacity in hypocotyl and cotyledonary tissues, which may be beneficial for seedling establishment. Sheath O2 production is important for alleviating intra-seed hypoxic stress and can increase endosperm storage activity improving the conditions for successful seed maturation and germination.