Foliar applications of thidiazuron and putrescine increase leaf iron and chlorophyll concentrations in iron-deficient pot marigold (Calendula officinalis L.)

The study was aimed to determine the effects of foliar applications of thidiazuron and putrescine, two compounds that may cause iron (Fe) remobilization, in pot marigold (Calendula officinalis L.) grown in controlled conditions under a limited Fe supply. In a first experiment, plants were grown in a greenhouse in a mixture of sand and perlite with pre-growth/growth Fe concentrations ranging from 0 to 20 µM, and treated three consecutive times with foliar sprays of 0 or 45.4 µM thidiazuron. In a second experiment, plants were grown in a greenhouse in hydroponics with pre-growth/growth Fe concentrations in the nutrient solution ranging from 0 to 20 µM, and treated three consecutive times with foliar sprays of 0, 2.27, or 5.67 mM putrescine. Parameters measured included leaf photosynthetic pigments and Fe concentrations, root ferric chelate reductase activities, photosynthesis rates and peroxidase in leaf extracts in the first experiment, and leaf photosynthetic pigments, leaf and root micronutrient concentrations, root ferric chelate reductase activities, and superoxide dismutase and peroxidase activities in leaf extracts in the second experiment. Results indicate that foliar thidiazuron and putrescine treatments in the µM and mM ranges, respectively, improve Fe transport to the leaf under zero or low supply of Fe. This indicates that foliar treatments with thidiazuron and putrescine increase remobilization of pre-existing plant Fe pools. This could be an additional tool for the optimization of Fe nutrition in ornamental plants such as C. officinalis when grown in controlled conditions.