Luteibacter rhizovicinus MIMR1 promotes root development in barley (Hordeum vulgare L.) under laboratory conditions.

In order to preserve environmental quality, alternative strategies to chemical-intensive agriculture are strongly needed. In this study, we characterized in vitro the potential plant growth promoting (PGP) properties of a gamma-proteobacterium, named MIMR1, originally isolated from apple shoots in micropropagation. The analysis of the 16S rRNA gene sequence allowed the taxonomic identification of MIMR1 as Luteibacter rhizovicinus. The PGP properties of MIMR1 were compared to Pseudomonas chlororaphis subsp. aurantiaca DSM 19603(T), which was selected as a reference PGP bacterium. By means of in vitro experiments, we showed that L. rhizovicinus MIMR1 and P. chlororaphis DSM 19603(T) have the ability to produce molecules able to chelate ferric ions and solubilize monocalcium phosphate. On the contrary, both strains were apparently unable to solubilize tricalcium phosphate. Furthermore, the ability to produce 3-indol acetic acid by MIMR1 was approximately three times higher than that of DSM 19603(T). By using fluorescent recombinants of strains MIMR1 and DSM 19603(T), we also demonstrated that both bacteria are able to abundantly proliferate and colonize the barley rhizosphere, preferentially localizing on root tips and in the rhizoplane. Finally, we observed a negative effect of DSM 19603(T) on barley seed germination and plant growth, whereas MIMR1, compared to the control, determined a significant increase of the weight of aerial part (+22 %), and the weight and length of roots (+53 and +32 %, respectively). The results obtained in this work make L. rhizovicinus MIMR1 a good candidate for possible use in the formulation of bio-fertilizers.

Adaptive responses to iron-deficiency in callus cultures of two cultivars of Vitis spp.

The correlation between iron chlorosis resistance and induction of adaptive mechanisms in grapevine calli belonging to cultivars with different susceptibility to iron chlorosis has been investigated. Fe(III)-chelate reductase was clearly linked to the Fe-efficiency status of the genotype. When growing on iron deprived medium (-Fe) calli of the Fe-efficient genotype "Cabernet sauvignon" showed a remarkable increase in enzyme activity, up to five times higher, with respect to +Fe cultures. Moreover, 31P-NMR revealed that in -Fe medium the increase of vacuolar Pi content of the Fe-efficient cultures was more pronounced than that recorded for the Fe-inefficient Vitis riparia. Furthermore, Fe starvation also enhanced the production of phenolic compounds in calli of "Cabernet sauvignon" with respect to those of Vitis riparia. The role of H(+)-ATPase as a marker of Fe-efficiency in tissue culture remains ambiguous in the case of grapevines.