Chloroplast Encapsulation in Pectin Hydrogel via Thiol-ene Photo-Click Reaction

Bioengineered chloroplast has great potentials in carbon sequestration as well as production of biological molecules. Although plants are preferred in chloroplast engineering, isolated chloroplasts provide benefits in terms of environmental friendliness, abundant resource in nature, and cost effectiveness. For example, the isolated chloroplasts are more efficient than plant in carbon dioxide absorption, because they did not discharge carbon dioxide unlike plants. However, isolated chloroplasts lose their photosynthetic activity quickly. It requires a novel platform for chloroplast incubation as maintaining intactness of chloroplast. Chloroplast encapsulation in biopolymers or synthetic materials has been proposed to prolong the photosynthetic activity. Nevertheless, sufficient photosynthetic activity of encapsulated was not achieved in these attempts. In this study, we fabricated pectin hydrogels as a novel matrix, which mimicked plant cytosol for preservation chloroplast photosynthetic activity. Chloroplast-laden pectin hydrogels were formed via thiol-ene photo-crosslinking with pectin-norbornene and dithiothreitol. As a result of modulus measurement, the network integrity was maintained in incubation medium for 14 days. In pectin hydrogel, the encapsulated chloroplasts showed photosynthetic activity for 7 days, while the depletion of the photosynthetic activity of the chloroplasts suspended in the medium was relatively quick. The use of antioxidant even improved the photosynthetic activity in pectin hydrogel. Importantly, caffeic acid was most effective in preventing chloroplast damage by reactive oxygen species during photosynthesis. In conclusion, photo-crosslinked pectin hydrogel provided a suitable microenvironment for encapsulated chloroplasts, resulting in extended photosynthetic activity.