Composition and function of plastoglobuli. I. Isolation and purification from chloroplasts and chromoplasts

Plastoglobuli have been isolated and purified from chloroplasts of beech and spinach leaves and from broom flower chromoplasts by a repeated floating-gradient technique. The main components in plastoglobuli isolated from chloroplasts were triacylglycerols and lipophilic prenyl quinones, mainly plastohydroquinone and α-tocopherol. The corresponding oxidized prenyl quinones, plastoquinone (ox), α-tocoquinone, and the phylloquinone vitamin K1, were detected in trace amounts. Plastoglobuli isolated from chromoplasts contained large amounts of carotenoid esters. Triacylglycerols constituted two-thirds of the content of these plastoglobuli. The total prenyl quinone content was low in chromoplast plastoglobuli. Plastoquinone (ox) was the major prenyl quinone constituent. Plastoglobuli contained small amounts of chlorophylls, carotenoids (with the exception of chromoplast plastoglobuli), glycolipids, and proteins due to adsorption phenomena during the isolation process; however, increasing purification of the plastoglobuli fractions resulted in an exponential decline of these components. Adsorption of thylakoid lipids onto the plastoglobuli during the isolation process was demonstrated using an artificial globuli system. Therefore, pigments, glyco- and phospholipids, and proteins were regarded as thylakoid contaminations and not as actual constituents of plastoglobuli.