Depending on the presence or absence of chlorophylls in the embryo, angiosperms are divided into chloroembryophytes and leucoembryophytes. Synthesis of chlorophylls (Chl) in the chloroembryos starts in the globular stage, rises as the embryo is formed, and stops in the late phase of seed maturation. The seeds also contain carotenoids that participate in photosynthesis and act as ABA precursors. The chloroembryos contain photochemically active chloroplasts that contain all the main photosynthetic complexes at a necessary stoichiometric ratio. Dark reactions of photosynthesis in developing seeds are notable for the fact that the main source of carbon therein is sucrose arriving from the maternal plant. Therefore, function of chloroplasts mainly aims at production of NADPH and ATP that are spent on conversion of sucrose into acetylCoA and, subsequently, to fatty acids. The CO2 fixation system involving Rubisco and/or phosphoenolpyruvate carboxylase operates in the chloroembryos. In the course of photosynthesis,