The present invention relates to agriculture. More particularly, the invention relates to a method of increasing photosynthesis of a plant and more particularly of crop plants. In addition, the invention relates to a method of increasing photosynthesis and/or yield in crop plants, comprising an exposure thereof to lipo-chitooligosaccharides, and compositions therefor. Further, the invention relates to an agricultural composition for enhancing a plant crop photosynthetic rate and/or growth thereof comprising a photosynthetic rate-promoting amount of at least one lipo chitooligosaccharide (LCO) together with an agriculturally suitable carrier and methods using same.