Ricerc@Sapienza

Developmental and environmental signaling networks often converge during plant growth in response to changing conditions. Stress-induced hormones, such as jasmonates (JAs), can influence growth by crosstalk with other signals like brassinosteroids (BRs) and ethylene (ET). Nevertheless, it is unclear how avoidance of an abiotic stress triggers local changes in development as a response.

Adventitious roots (ARs) are post-embryonic roots formed in planta by tissues of the primary root in secondary vascular structure and by tissues of the aerial organs. Indole-3-acetic acid (IAA), and its natural precursor indole-3-butyric acid (IBA), control AR formation in planta and in vitro, however IBA roles have to be elucidated. Arabidopsis thin cell layers (TCL) consist of stem inflorescence tissue external to the vascular system and 10 microM IBA applied with 0.1microM Kinetin induce AR formation from stem TCL.

Background: Adventitious roots (ARs) are often necessary for plant survival, and essential for successful micropropagation. In Arabidopsis thaliana dark-grown seedlings AR-formation occurs from the hypocotyl and is enhanced by application of indole-3-butyric acid (IBA) combined with kinetin (Kin). The same IBA + Kin-treatment induces AR-formation in thin cell layers (TCLs). Auxin is the main inducer of AR-formation and xylogenesis in numerous species and experimental systems. Xylogenesis is competitive to AR-formation in Arabidopsis hypocotyls and TCLs.

The role of indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) and of the auxin-interacting phytohormone ethylene on xylogenesis is still little known, even if a xylogenic promotion by auxins has been reported. In particular, auxin/ethylene-target tissue(s), modality of the de novo xylary process, and the kind of ectopic elements formed (metaxylem vs. protoxylem) are currently unknown. It is instead widely known that auxins positively affect adventitious root (AR) formation, e.g. in the model plant Arabidopsis thaliana and in in vitro cultured systems of numerous species.

In Arabidopsis basal hypocotyls of dark-grown seedlings, xylary cells may form from the pericycle as an alternative to adventitious roots. Several hormones may induce xylogenesis, as Jasmonic acid (JA), as well as indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) auxins, which also affect xylary identity. Studies with the ethylene (ET)-perception mutant ein3eil1 and the ET-precursor 1-aminocyclopropane-1-carboxylic acid (ACC), also demonstrate ET involvement in IBA-induced ectopic metaxylem.

Auxins induce adventitious roots (ARs) in numerous culture-systems, and indole-3-butyric acid (IBA) is frequently the best AR-inducer. Vitamin requirements vary according to species, explant, and culture-conditions. Arabidopsis thaliana thin cell layers (AtTCLs) are uncapable of AR-formation on hormone-free medium containing thiamine and myo-inositol, whereas ARs are induced when IBA (10 μM), with/without kinetin (Kin, 0.1 μM), is added. The research frst aim was to determine whether a synergism between IBA and myo-inositol and thiamine was necessary for AR-formation.