Involvement of naphthalene acetic acid in contractile root formation and the growth of <i>Gladiolus grandiflorus</i> cv. ‘Eurovision’ cormel plants

Abstract

Formation of contractile roots (CRs) in geophyte plants ensures the depth regulation in the soil of the new geophytic organs. The effect of auxin naphthalene acetic acid (NAA) on the development and activity of CRs was studied in Gladiolus grandiflorus cv. 'Eurovision' cormel plants. The following parameters were recorded up to 80-90 days from planting following application of 0.054-1.37 mM NAA to leaves of cormels grown in the phytotron under long day conditions (16 h) at 27/17 °C day/night temperature: production of CRs primordia, root elongation and contraction, leaf morphology, corm production, and downward movement in the soil. NAA treatments increased CRs' primordia formation, but delayed the elongation and contraction processes (onset and rate). The typical sequential formation of CRs in gladiolus cormel plants was not observed in NAA-treated cormels, in which simultaneous CR production was observed. NAA inhibited thickening and downward movement of the daughter-corm in the soil and reduced leaf number, leaf length, and dry weight (DW). Simultaneous production of several CRs resulted in about 50% reduction of CR effectiveness in downward movement of the daughter-corm in the soil. Apparently, the involvement of auxin in CR formation and contraction depends on interaction with other growth regulators and requires further study.