title: Rates of foliar penetration of chelated Fe(III): role of light, stomata, species, and leaf age.
abstract: Rates of foliar penetration of Fe(III) chelates of imidodisuccinic acid (IDHA), ligninsulfonic acid (Natrel), and citric acid (ammonium ferric citrate) were studied at 20 degrees C using a leaf disk method. After drying of the donor droplets, the humidity over the donor residues was maintained at 100% because Fe(III) chelates deliquesce only when humidity is higher than 90%. The wetting agent Glucopon 215 CSUP was added at a concentration of 0.2 g L(-1) to all donor solutions. With fully expanded stomatous broad bean leaves, penetration of Fe-IDHA followed first-order kinetics and rate constants of penetration were higher in light (0.073 h(-1)) than in the dark (0.042 h(-1)). Permeability of broad been leaves to CaCl2 was about 8 times higher than to Fe-IDHA. Doubling the Fe-IDHA concentration in the donor from 2.5 to 5 mmol L(-1) decreased rate constants of Fe-IDHA penetration by a factor of 2.2. Adding the silicon surfactant Break Thru S240 at 10 g L(-1) to the donor induced infiltration of open stomata and about 80% of the applied Fe-IDHA penetrated during droplet drying, while with Glucopon 215 CSUP stomatal infiltration was not observed. With broad bean leaves, penetration of Natrel and ammonium ferric citrate also followed first-order kinetics and rate constants were also higher in light than in the dark. Adaxial astomatous surfaces of fully expanded pear, apple, and grapevine leaves were practically impermeable to Fe-IDHA while stomatous abaxial leaf surfaces were permeable, but rate constants of penetration decreased with time and differed greatly among species. Astomatous surfaces of young unfurling grapevine and peach leaves were permeable to Fe-IDHA, but permeability of stomatous surfaces was much higher. The effect of light on permeability of stomatous leaf surfaces is attributed to the presence of aqueous pores in cuticles over guard cells, and it is suggested that permeability of these pores increases as stomata open. Consequences of these results for foliar applications of Fe chelates are discussed.
authors.affiliation: Institute of Biological Production Systems, Fruit Science Division, University of Hannover, Herrenhäuser Strasse 2, 30419 Hannover, Germany.
authors.forename: Thomas K
authors.initials: TK
authors.lastname: Schlegel
authors.forename: Jörg
authors.initials: J
authors.lastname: Schönherr
authors.forename: Lukas
authors.initials: L
authors.lastname: Schreiber
mesh_terms: D002122:Calcium Chloride / Q000378:metabolism; D005290:Ferric Compounds / Q000378:metabolism*; D007502:Iron Chelating Agents / Q000378:metabolism*; D007700:Kinetics; D008027:Light; D027845:Malus; D010539:Permeability; D018515:Plant Leaves / Q000378:metabolism*; D027861:Prunus; D031989:Pyrus; D013045:Species Specificity; D013997:Time Factors; D031307:Vicia faba; D027843:Vitis
chemical_list: D005290:Ferric Compounds; D007502:Iron Chelating Agents; D002122:Calcium Chloride