Extensive communication occurs between plants and microorganisms during different stages of plant development in which signaling molecules from the two partners play an important role. Volatile organic compounds (VOCs) emission by certain plant-growth promoting rhizobacteria (PGPR) has been found to be involved in plant growth. However, little is known about the role of bacterial VOCs in plant developmental processes. In this work, we investigated the effects of inoculation with twelve bacterial strains isolated from the rhizosphere of lemon plants (Citrus aurantifolia) on growth and development of Arabidopsis thaliana seedlings. Several bacterial strains showed a plant growth promoting effect stimulating biomass production, which was related to differential modulation of root-system architecture. The isolates L263, L266, and L272a stimulated primary root growth and lateral root development, while L254, L265a and L265b did not significantly alter primary root growth but strongly promoted lateral root formation. VOC emission analysis by SPME-GC-MS identified aldehydes, ketones and alcohols as the most abundant compounds common to most rhizobacteria. Other VOCs, including 1-octen-3-ol and butyrolactone were strain specific. Characterization of L254, L266 and L272a bacterial isolates by 16S rDNA analysis revealed the identity of these strains as Bacillus cereus, Bacillus simplex and Bacillus sp, respectively. Taken together, our data suggest that rhizospheric bacterial strains can modulate both plant growth promotion and root-system architecture by differential VOC emission.

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Plant growth-promoting rhizobacteria stimulate plant growth and development via different mechanisms. In this study, we characterized the effect of volatiles from Bacillus methylotrophicus M4-96 isolated from the maize rhizosphere on root and shoot development, and auxin homeostasis in Arabidopsis thaliana. Phytostimulation occurred after 4 days of interaction between M4-96 and Arabidopsis grown on opposite sides of divided Petri plates, as revealed by enhanced primary root growth, root branching, leaf formation, and shoot biomass accumulation. Analysis of indole-3-acetic acid content revealed two- and threefold higher accumulation in the shoot and root of bacterized seedlings, respectively, compared to uninoculated plants, which was correlated with increased expression of the auxin response marker DR5::GUS. The auxin transport inhibitor 1-naphthylphthalamic acid inhibited primary root growth and lateral root formation in axenically grown seedlings and antagonized the plant growth-promoting effects of M4-96. Analysis of bacterial volatile compounds revealed the presence of four classes of compounds, including ten ketones, eight alcohols, one aldehyde, and two hydrocarbons. However, the abundance of ketones and alcohols represented 88.73 and 8.05%, respectively, of all airborne signals detected, with acetoin being the main compound produced. Application of acetoin had a different effect from application of volatiles, suggesting that either the entire pool or acetoin acting in concert with another unidentified compound underlies the strong phytostimulatory response. Taken together, our results show that B. methylotrophicus M4-96 generates bioactive volatiles that increase the active auxin pool of plants, stimulate the growth and formation of new organs, and reprogram root morphogenesis.

Studies on Rhizobium-legume symbiosis show that trehalose content in nodules under drought stress correlates positively with an increase in plant tolerance to this stress. Fewer reports describe trehalose accumulation in mycorrhiza where, in contrast with rhizobia, there is no flux of carbohydrates from the microsymbiont to the plant. However, the trehalose dynamics in the Mycorrhiza-Rhizobium-Legume tripartite symbiosis is unknown. The present study explores the role of this tripartite symbiosis in the trehalose content of nodules grown under contrasting moisture conditions. Three wild genotypes (P. filiformis, P. acutifolis and P. vulgaris) and two commercial genotypes of Phaseolus vulgaris (Pinto villa and Flor de Mayo) were used. Co-inoculation treatments were conducted with Glomus intraradices and a mixture of seven native rhizobial strains, and trehalose content was determined by GC/MS. The results showed a negative effect of mycorrhizal inoculation on nodule development, as mycorrhized plants showed fewer nodules and lower nodule dry weight compared to plants inoculated only with Rhizobium. Mycorrhizal colonization was also higher in plants inoculated only with Glomus as compared to plants co-inoculated with both microsymbionts. In regard to trehalose, co-inoculation negatively affects its accumulation in the nodules of each genotype tested. However, the correlation analysis showed a significantly positive correlation between mycorrhizal colonization and nodule trehalose content.

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The first direct synthesis of β-unsubstituted meso-decamethylcalix [5]pyrrole from pyrrole and acetone, with moderate yield, is described. The results showed that a bismuth salt was necessary to obtain calix [5]pyrrole, with the best results obtained using Bi(NO 3 ) 3 .Page 1 of (page number not for citation purposes) 3 Results and DiscussionCalix[n]pyrroles have attracted attention because of their ability to recognize anions [1,2]. To date, the calix[4]pyrroles have been studied the most, in part due to the ease with which the macrocycle can be obtained by the condensation of pyrrole with a ketone catalyzed by a Brønsted-Lowry acid such as HCl or methanesulfonic acid, or a Lewis acid such as zeolites with aluminium or cobalt, BF 3 or a bismuth salt [2][3][4][5]. The synthesis of calix[n]pyrroles where n > 4 has been reported for n = 5 or 6. The latter compounds have been synthesized via two routes: a) from the sterically hindered diaryldi(pyrrol-2-yl)methane with 25% yield; and b) through the conversion of a calix [6]furan into the corresponding calix [6]pyrrole by an opening process of the six heterocycles, a selective reduction of the double bond and then a Paal-Knorr condensation with ammonium acetate with 40% yield [6,7]. On the other hand, β-unsubstituted calix[5]pyrroles have been obtained by two routes: a) from the corresponding meso-decamethylcalix [5]furan, via a method analogous to that reported for calix[6]pyrroles, with 1% yield; and b) directly when the macrocycle is covalently bound to a calix[5]arene, with 10% yield [8,9]. However, these approaches afford calix[5]pyrroles in low yield, which has limited the study of these compounds as anion receptors.One explanation for why it is difficult to obtain calix[5]pyrroles via direct condensation of a pyrrole and the corresponding ketone is that the five heterocycle system is unstable: it opens and loses a pyrrole-isopropyl fragment to give the calix[4]pyrrole [8,10]. While studying the role of bismuth as a Lewis acid in the synthesis of calix[4]pyrroles, we found that at low catalyst concentrations some additional products were formed, as observed by 1 H NMR spectroscopy. These byproducts exhibited 1 H NMR, 13 C NMR and MS data consistent with those reported for calix[n]pyrroles with n = 4, 5 and 6 (compounds 1-3, respectively) and 5,5-dimethyldipyrromethane (4); see Experimental section [5,6,8]. The relative proportions of these four products obtained using different catalyst equivalents are listed in Table 1. Compounds 1 and 2 were almost indistinguishable on TLC because of their similar R f values, and recrystallization from ethanol, as reported in other works, was not satisfactory to give the pure compounds. However, it was possible to separate 1 and 2 by HPLC, to obtain 2 in 25% yield (using the conditions specified in Table 1, entry 12). Compound 2 was found to be unstable, which probably decreased the yield.To determine whether the reaction proceeds with other Lewis acids, we explored the use of MgCl 2 , CuCl 2 , ZnCl 2 , AlCl 3 , BiCl...

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