Exogenous Phytohormones Modulate Mycorrhiza-Induced Changes in Root Hair Configuration of Trifoliate Orange

Abstract

Mycorrhizas alter root hair profile, but it is not clear whether exogenous phytohormones regulate the mycorrhizal effects on root hair. Studies were carried out in a two-chambered rootbox separated by 37-μm nylon mesh to establish root+hyphae chamber carrying trifoliate orange [Poncirus trifoliata (L.) Raf.] as the test plant inoculated with Diversispora versiformis and hyphae chamber (without roots). Indole butyric acid (IBA), abscisic acid (ABA), and jasmonic acid (JA) (each at 0.1 μM concentration) were weekly applied into hyphae chamber, in total of six times before plant harvest. Mycorrhization strongly stimulated plant growth performance, and exogenous phytohormones, especially IBA, further magnified the mycorrhizal-stimulated growth responses. Three exogenous phytohormones decreased mycorrhizal colonization in taproot and first-order lateral roots, but increased in second- and third-order lateral roots. These phytohormones also increased hyphal length in nylon mesh and soil, irrespective of root+hyphae or hyphae chamber. Mycorrhizal inoculation significantly increased root hair density of different root classes, and exogenous hormones further strengthened the mycorrhizal effect. Average root hair length was stimulated by mycorrhization, but all exogenous phytohormones weakened the mycorrhizal response. Mycorrhization in combination with exogenous phytohormones showed no response on root hair diameter. Our studies, hence, suggested that application of exogenous phytohormones in hyphae chamber strengthened the D. versiformis-induced changes in average root hair density but weakened in average root hair length in trifofliate orange grown in root+hyphae chamber.