Experiments to determine the efficacy of different nano-particle systems to deliver nutrients and antimicrobial molecules to citrus leaves: Greenhouse experiments to test the efficacy of nano-particles to deliver Mg to citrus trees are underway. Mg deficient citrus trees were treated with three types of nano-particles containing Mg. The nano-particles being tested are: 1.liposomes, 2. dendrimers, 3. kaolin. As control, we used an aqueous solution of Mg at a concentration commonly used in foliar nutrition programs. Trees are being sampled on a weekly basis for their photosynthetic rates as an indication of the effect of Mg in the reconstitution of the photosynthetic apparatus. Anatomical studies should follow completion of the treatments. Concurrently, polymer based nano-particles and liposomes containing a soluble fluorescent marker have been applied to citrus leaves to study the delivery of antimicrobial substances. Application has been performed on both abaxial and adaxial leaf surfaces. Penetration and movement of the fluorescent probe is being analyzed by fluorescent microscopy and laser scanning confocal microscopy.