Adventitious rooting is enhanced by methyl jasmonate in tobacco thin cell layers

Abstract

Adventitious roots (ARs) are induced by auxins. Jasmonic acid (JA) and methyl jasmonate (MeJA) are also plant growth regulators with many effects on development, but their role on ARs needs investigation. To this aim, we analyzed AR formation in tobacco thin cell layers (TCLs) cultured with 0.01-10 microM MeJA, either under root-inductive conditions, i.e., on medium containing 10 microM indole-3-butyric acid (IBA) and 0.1 microM kinetin, or without hormones. The explants were excised from the cultivars Samsun, Xanthii and Petite Havana, and from genotypes with altered AR-forming ability in response to auxin, namely the non-rooting rac mutant and the over-rooting Agrobacterium rhizogenes rolB transgenic line. Results show that NtRNR1 (G1/S) and Ntcyc29 (G2/M) gene activity, cell proliferation and meristemoid formation were stimulated in hormone-cultured TCLs by submicromolar MeJA concentrations. The meristemoids developed either into ARs and xylogenic nodules, or into xylogenic nodules only (rac TCLs). MeJA-induced meristemoid over-production characterized rolB TCLs. No rooting or xylogenesis occurred under hormone-free conditions, independently of MeJA and genotype. Endogenous JA progressively (days 1-4) increased in hormone-cultured TCLs in the absence of MeJA. JA levels were enhanced by 0.1 microM MeJA, on both days 1 and 4. Endogenous IBA was the only auxin detected, both in the free form and as IBA-glucose. Free IBA increased up to day 2, remaining constant thereafter (day 4). Its level was enhanced by 0.1 microM MeJA only on day 1, while IBA conjugation was not affected by MeJA. Taken together, these results show that an interplay between jasmonates and auxins regulates AR formation and xylogenesis in tobacco TCLs.

The Apoplastic Copper AMINE OXIDASE1 Mediates Jasmonic Acid-Induced Protoxylem Differentiation in Arabidopsis Roots

“…Interestingly, an earlier developmental expression pattern occurred after MeJA treatment, as shown by the appearance of GUS staining in a location closest to the root tip, suggesting a role of AtAO1 in MeJA signaling leading to protoxylem differentiation. In a few recent reports, a still quite unexplored role for MeJA in xylem development was suggested (Cenzano et al, 2003;Fattorini et al, 2009). In this regard, exogenous JA and MeJA have been shown to induce early xylem differentiation in potato stolons (Cenzano et al, 2003) and xylogenesis in tobacco thin cell layers (Fattorini et al, 2009), respectively.…”

“…Taking into account the previously suggested involvement of MeJA in xylogenesis (Fattorini et al, 2009) along with the proposed participation of AtAO1 or ZmPAO in root vascular differentiation, respectively, upon nematode invasion or under stress-like conditions (Tisi et al, 2011a(Tisi et al, , 2011b, LSCM analysis was carried out to visualize xylem tissue alteration following MeJA treatment in the wild type and Atao1 mutants. In particular, we focused our attention on protoxylem differentiation timing, considering as a reference event the final step of the secondary cell wallthickening process.…”

“…Of note, previous studies reported that the stress signaling hormone jasmonic acid (JA), while inducing root growth inhibition (Ren et al, 2009), behaves as a promoter of early vascular tissue differentiation (Cenzano et al, 2003) and xylogenesis (Fattorini et al, 2009). The role of JA in vascular tissue differentiation was first revealed in stolons of potato (Solanum tuberosum) during the tuberization process.…”

“…In particular, exogenous JA accelerated potato tuber formation via the induction of both cell expansion and early differentiation of protoxylem vessels with ring-shaped secondary wall thickenings, leading to increased movement of nutrients toward the stolon tip (Cenzano et al, 2003). Moreover, exogenous methyl jasmonate (MeJA) was reported to enhance the formation of adventitious roots and the development of xylogenic nodules in tobacco (Nicotiana tabacum) thin layers under root-inductive hormonal conditions (Fattorini et al, 2009).…”

Auxin Controls Arabidopsis Adventitious Root Initiation by Regulating Jasmonic Acid Homeostasis

“…In addition, methyl jasmonate was shown to inhibit root growth in Arabidopsis (Staswick et al, 1992), and JA transiently accumulated at the base of Petunia hybrida stem cuttings after mechanical wounding but very rapidly returned to its basal level before adventitious root formation took place (Ahkami et al, 2009). Fattorini et al (2009) showed that submicromolar amounts of methyl jasmonate promoted adventitious root development from thin cell layers of tobacco (Nicotiana tabacum). This information (A) Average number of adventitious roots (AR) in two independent knockout alleles for gh3.3, gh3.5, and gh3.6 single mutants, in the double mutants gh3.3-1gh3.5-2 and gh3.3-1gh3.6-1, and the triple mutant gh3.3-1gh3.5-2gh3.6-1.…”