Stress resistance of Escherichia coli and Bacillus subtilis is modulated by auxins.

Two bacterial species, Gram-negative Escherichia coli and Gram-positive Bacillus subtilis, were exposed to different auxins to examine possible effects of these substances on bacterial stress tolerance. Bacterial resistance to UV irradiation, heat shock, and streptomycin was assessed with and without previous exposure to the following auxins: indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), and 1-naphthalene acetic acid (NAA). Escherichia coli and B. subtilis cultures pretreated with any of the 3 auxins survived UV irradiation better than the untreated cultures. Also, B. subtilis cultures pretreated with IBA or NAA survived prolonged heat exposure better than the untreated cultures, while IAA pretreatment had no effect on heat shock survival. In contrast, auxin pretreatment rendered E. coli more sensitive to heat shock. Escherichia coli cultures pretreated with auxins were also more sensitive to streptomycin, while auxin pretreatment had no effect on sensitivity of B. subtilis to streptomycin. These results show that auxins may either enhance or reduce bacterial tolerance to different stressors, depending on the bacterial species and the type and level of the stress. Auxins usually had similar effects on the same bacterial species in cases when the same type and level of stress were applied.

Biochemical and epigenetic changes in phytoplasma-recovered periwinkle after indole-3-butyric acid treatment.

AIM: To elucidate the possible mechanism of phytoplasma elimination from periwinkle shoots caused by indole-3-butyric acid (IBA) treatment. METHODS AND RESULTS: It has been shown that a transfer of in vitro-grown phytoplasma-infected Catharanthus roseus (periwinkle) plantlets from medium supplemented with 6-benzylaminopurine (BA) to one supplemented with IBA can induce remission of symptoms and even permanent elimination of 'Candidatus Phytoplasma asteris' reference strain HYDB. Endogenous auxin levels and general methylation levels in noninfected periwinkles, periwinkles infected with two 'Candidatus Phytoplasma' species and phytoplasma-recovered periwinkles were measured and compared. After the transfer from cytokinin- to auxin-containing media, healthy shoots maintained their phenotype, methylation levels and hormone concentrations. Phytoplasma infection caused a change in the endogenous indole-3-acetic acid to IBA ratio in periwinkle shoots infected with two 'Candidatus Phytoplasma' species, but general methylation was significantly changed only in shoots infected with 'Ca. P. asteris', which resulted in the only phytoplasma species eliminated from shoots after transfer to IBA-containing medium. Both phytoplasma infection and treatment with plant growth regulators influenced callose deposition in phloem tissue, concentrations of photosynthetic pigments and soluble proteins, H(2) O(2) levels and activities of catalase (CAT) and ascorbate peroxidase (APX). CONCLUSION: Lower level of host genome methylation in 'Ca. P. asteris'-infected periwinkles on medium supplemented with BA was significantly elevated after IBA treatment, while IBA treatment had no effect on cytosine methylation in periwinkles infected with 'Candidatus Phytoplasma ulmi' strain EY-C. SIGNIFICANCE AND IMPACT OF THE STUDY: Hormone-dependent recovery is a distinct phenomenon from natural recovery. As opposed to spontaneously recovered plants in which elevated peroxide levels and differential expression of peroxide-related enzymes were observed, in hormone-dependent recovery changes in global host genome, methylation coincide with the presence/absence of phytoplasma.

Auxin-treatment induces recovery of phytoplasma-infected periwinkle.

AIMS: To test the effect of auxin-treatment on plant pathogenic phytoplasmas and phytoplasma-infected host. METHODS AND RESULTS: In vitro grown periwinkle shoots infected with different 'Candidatus Phytoplasma' species were treated with indole-3-acetic acid (IAA) or indole-3-butyric acid (IBA). Both auxins induced recovery of phytoplasma-infected periwinkle shoots, but IBA was more effective. The time period and concentration of the auxin needed to induce recovery was dependent on the 'Candidatus Phytoplasma' species and the type of auxin. Two 'Candidatus Phytoplasma' species, 'Ca. P. pruni' (strain KVI, clover phyllody from Italy) and 'Ca. P. asteris' (strain HYDB, hydrangea phyllody), were susceptible to auxin-treatment and undetected by nested PCR or detected only in the second nested PCR in the host tissue. 'Ca. P. solani' (strain SA-I, grapevine yellows) persisted in the host tissue despite the obvious recovery of the host plant and was always detected in the direct PCR. CONCLUSIONS: Both auxins induced recovery of phytoplasma-infected plants and affected tested 'Candidatus Phytoplasma' species in the same manner, implying that the mechanism involved in phytoplasma elimination/survival is common to both, IAA and IBA. SIGNIFICANCE AND IMPACT OF THE STUDY: The results imply that in the case of some 'Candidatus Phytoplasma' species, IBA-treatment could be used to eliminate phytoplasmas from in vitro grown Catharanthus roseus shoots.