Silicon promotes root development by modulating polar transport of auxin during cutting propagation of poinsettia

Abstract

Silicon (Si) has been found to promote root development in many plant species. However, the underlying mechanism is not clear. In this study, effect of naphthalene acetic acid (NAA) and Si on growth and root development of poinsettia 'Flame' and 'Pink Bell' was investigated. Terminal cuttings stuck in a foam wedge substrate in plug trays were irrigated with either distilled water, a nutrient solution, or a nutrient solution supplemented with 75 mg L-1 Si. They were also treated with either 30 μM NAA, 15 μM L-kynurenine (Kyn, a biosynthesis inhibitor of auxin), or 80 μM N-1-naphthylphthalamic acid (NPA, a polar transport inhibitor of auxin) once a week. The cuttings were kept in a fogged propagation bench set in a glasshouse with 30/25°C day/night temperatures, an average light intensity of 300 μmol m-2 s-1 PPFD coming from the sun, and natural photoperiod of 13 h for 3 weeks. The results showed that the NPA significantly reduced shoot length, number of leaves, length of the longest root, root fresh weight, and root dry weight of the rooted cuttings. However, supplementary Si alleviated the inhibitory effect of NPA, indicating Si might have contributed to the polar transport of auxin. The Kyn and NAA showed limited effects on root development, which might be probably caused by low concentrations used in this study. Therefore, further works should be conducted by increasing the concentration of Kyn and NAA, and also to find out evidence that explains how Si promotes the polar transport of auxin. ? 2020 International Society for Horticultural Science. All rights reserved.