Comparative adventitious root development in pre-etiolated and flooded Arabidopsis hypocotyls exposed to different auxins

Abstract

Adventitious roots (ARs) emerge from stems, leaves or hypocotyls, being strategic for clonal propagation. ARs may develop spontaneously, upon environmental stress or hormonal treatment. Auxins strongly influence AR development (ARD), depending on concentration and kind. However, the role of different types of auxin is rarely compared at the molecular level. Rooting triggered by light exposure and flooding was examined in intact etiolated Arabidopsis thaliana hypocotyls treated with distinct auxin types. Morphological aspects, rooting-related gene expression profiles, and IAA immunolocalization were recorded. NAA and 2,4-D effects were highly dose-dependent; at higher concentrations NAA inhibited root growth and 2,4-D promoted callus formation. NAA yielded the highest number of roots, but inhibited elongation. IAA increased the number of roots with less interference in elongation, yielding the best overall rooting response. IAA was localized close to the tissues of root origin. Auxin stimulated ARD was marked by increased expression of PIN1 and GH3.3. NAA treatment induced expression of CYCB1, GH3.6 and ARF8. These NAA-specific responses may be associated with the development of numerous shorter roots. In contrast, expression of the auxin action inhibitor IAA28 was induced by IAA. Increased PIN1 expression indicated the relevance of auxin efflux transport for focusing in target cells, whereas GH3.3 suggested tight control of auxin homeostasis. IAA28 increased expression during IAA-induced ARD differs from what was previously reported for lateral root development, pointing to yet another possible difference in the molecular programs of these two developmental processes.

The role of auxin transporters and receptors in adventitious rooting of Arabidopsis thaliana pre-etiolated flooded seedlings

“…As previously reported, although it was possible to record the development of some ARs in the hypocotyl of pre-etiolated Col-0 seedlings flooded with medium devoid of auxin, application of IAA stimulated AR development (Fig. 1B) [37].…”

“…Seed sterilization and culture were carried out according to [36,37]. Surface sterilized seeds of Col-0 were placed on medium 0.1x MS supplemented with 2% sucrose and solidified with agar (0.6% w/v) in 24well microplates of 2 mL each.…”

“…Subsequently, 0.5 mL of liquid 0.3% agar medium with or without auxins was aseptically added to each well, covering part of the hypocotyl. The treatment with exogenous auxin was carried out with 57 μM of IAA, a concentration that promotes adventitious rooting without causing major impacts on root length (previously described by [36,37]). Exogenous supply of IAA was used aiming to synchronize and intensify the rooting process, as well as verify if it would recover the wild-type phenotype in the mutants.…”

Comparative transcriptome and metabolome analyses provide new insights into the molecular mechanism underlying taproot thickening in Panax notoginseng

“…Studies have demonstrated that auxin with low concentrations can promote cell elongation and expansion while high concentrations inhibit them. Different plant tissues respond differently to auxin concentration, which mainly depends on the modulation of local biosynthesis and directional intercellular transport [42][43][44][45]. Our study showed that endogenous IAA content and genes involved in IAA signaling including Auxin/Indole-3-Acetic Acid (Aux/IAAs) and auxin response factor (ARFs) were significantly up-regulated in the early stage and down-regulated in the later stage during P.notoginseng taproot thickening (Fig.…”

Effects of auxin and urea derivatives on adventitious rooting in chestnut and oak microshoots

“…For instance, Tereso et al (2008) reported contrasting results for rooting percentages produced in response to different auxins and different exposure times in almond shoots. As observed in Arabidopsis hypocotyls, changes in the auxin concentration also affect callus formation (Da Costa et al 2018). The auxin responsive machinery has the potential to confer quantitatively different responses to varying auxin concentrations and to different auxins (Weijers and Wagner 2016).…”