Plant-Growth Endophytic Bacteria Improve Nutrient Use Efficiency and Modulate Foliar N-Metabolites in Sugarcane Seedling.

Beneficial plant-microbe interactions lead to physiological and biochemical changes that may result in plant-growth promotion. This study evaluated the effect of the interaction between sugarcane and endophytic bacterial strains on plant physiological and biochemical responses under two levels of nitrogen (N) fertilization. Six strains of endophytic bacteria, previously selected as plant growth-promoting bacteria (PGPB), were used to inoculate sugarcane mini stalks, with and without N fertilization. After 45 days, biomass production; shoot nutrient concentrations; foliar polyamine and free amino acid profiles; activities of nitrate reductase and glutamine synthase; and the relative transcript levels of the GS1, GS2, and SHR5 genes in sugarcane leaves were determined. All six endophytic strains promoted sugarcane growth, increasing shoot and root biomass, plant nutritional status, and the use efficiency of most nutrients. The inoculation-induced changes at the biochemical level altered the foliar free amino acid and polyamine profiles, mainly regarding the relative concentrations of citrulline, putrescine, glycine, alanine, glutamate, glutamine, proline, and aspartate. The transcription of GS1, GS2, and SHR5 was higher in the N fertilized seedlings, and almost not altered by endophytic bacterial strains. The endophytic strains promoted sugarcane seedlings growth mainly by improving nutrient efficiency. This improvement could not be explained by their ability to induce the production of amino acid and polyamine composts, or GS1, GS2, and SHR5, showing that complex interactions may be associated with enhancement of the sugarcane seedlings' performance by endophytic bacteria. The strains demonstrated biotechnological potential for sugarcane seedling production.

The Role of Non-Mycorrhizal Fungi in Germination of the Mycoheterotrophic Orchid Pogoniopsis schenckii Cogn.

Endophytic fungi are those that inhabit within organs and tissues without causing damage, while mycorrhizal fungi develop hyphal complexes called pelotons within cortical cells of orchid roots. Although abundant and frequent in all plant organs, the role of endophytic fungi has been neglected in relation to orchid's early development. Pogoniopsis schenckii Cogn. is an aclorophyllated and mycoheterotrophic (MH) orchid. This study aimed at i) investigating the endophytic fungal community in organs of P. schenckii and its mycorrhizal fungi associated; ii) evaluating the ability of isolated fungus in the in vitro germination of the seeds of the species, and iii) describing the development of P. schenckii protocorm, analyzing the ultrastructure of the infected cells. Six genera of fungi were isolated and identified through the partial sequencing of the internal transcribed spacer region, all belonging to the phylum Ascomycota. Also, Tulasnellaceae was identified through uncultured technique as potentially mycorrhizal in this MH orchid. Some isolates of the genera Trichoderma, Fusarium, and especially Clonostachys presented germinative potential on P. schenckii seeds, causing rupture of the external tegument. The protocorms showed complete absence of peloton formation, but fungal hyphae were clearly observed within living cells. This is the first report of germination of a MH and aclorophyllated orchid species stimulated by the presence of non-mycorrhizal endophytic fungi isolated from fruits and roots of the same species.

Photosynthesis is induced in rice plants that associate with arbuscular mycorrhizal fungi and are grown under arsenate and arsenite stress.

The metalloid arsenic (As) increases in agricultural soils because of anthropogenic activities and may have phytotoxic effects depending on the available concentrations. Plant performance can be improved by arbuscular mycorrhiza (AM) association under challenging conditions, such as those caused by excessive soil As levels. In this study, the influence of AM on CO2 assimilation, chlorophyll a fluorescence, SPAD-chlorophyll contents and plant growth was investigated in rice plants exposed to arsenate (AsV) or arsenite (AsIII) and inoculated or not with Rhizophagus irregularis. Under AsV and AsIII exposure, AM rice plants had greater biomass accumulation and relative chlorophyll content, increased water-use efficiency, higher carbon assimilation rate and higher stomatal conductance and transpiration rates than non-AM rice plants did. Chlorophyll a fluorescence analysis revealed significant differences in the response of AM-associated and -non-associated plants to As. Mycorrhization increased the maximum and actual quantum yields of photosystem II and the electron transport rate, maintaining higher values even under As exposure. Apart from the negative effects of AsV and AsIII on the photosynthetic rates and PSII efficiency in rice leaves, taken together, these results indicate that AM is able to sustain higher rice photosynthesis efficiency even under elevated As concentrations, especially when As is present as AsV.

Evaluation of mycorrhizal influence on the development and phytoremediation potential of Canavalia gladiata in Pb-contaminated soils.

Soil contamination by heavy metals is a serious problem to humans due to its high level of toxicity. The heavy metal lead (Pb) is commonly used in industries and if the disposal of residues that contain this element is not done properly may result in tragic consequences to the organisms. In this experiment we assessed the potential of a forrage leguminous, Canavalia gladiata, to phytoremediate lead-contaminated soil under mycorrhizal influence. The experimental design was composed of 4 Pb doses (0, 250, 500, and 1000 mg kg(-1) of soil) and the plants were inoculated or uninoculated with arbuscular mycorrhizal fungi (AMF). We observed that the nodulation was severely affected by the presence of Pb independently of the mycorrhizal status; most of the elements analyzed were affected independently of the mycorrhizal status with exception of P. The mycorrhizal colonization was able to restrict the entrance of Pb in plants under high concentrations of Pb but promoted it's accumulation in both organs under intermediate concentrations of this element. Besides the mycorrhization did not promote plant growth under Pb stress, the use of this plant may be considered to be used for phytostabilization purposes.

Cadmium accumulation in sunflower plants influenced by arbuscular mycorrhiza.

In order to investigate the cadmium (Cd) accumulation patterns and possible alleviation of Cd stress by mycorrhization, sunflower plants (Helianthus annuus L.) were grown in the presence or absence of Cd (20 micromol L(-1)) and inoculated or not inoculated with the arbuscular mycorrhizal fungus (AMF) Glomus intraradices. No visual symptoms of Cd phytotoxicity were observed; nevertheless, in non-mycorrhizal plants the presence of Cd decreased plant growth. The addition of Cd had no significant effect on either mycorrhizal colonization or the amount of extra-radical mycelia that was produced by the AMF. Cd accumulated mainly in roots; only 22% of the total Cd absorbed was translocated to the shoots, where it accumulated to an average of 228 mg Cd kg(-1). Although the shoot-to-root ratio of Cd was similar in both the AMF inoculated and non-inoculated plants, the total absorbed Cd was 23% higher in mycorrhizal plants. Cd concentration in AMF extra-radical mycelium was 728 microg g(-1) dry weight. Despite the greater absorption of Cd, mycorrhizal plants showed higher photosynthetic pigment concentrations and shoot P contents. Cd also influenced mineral nutrition, leading to decreased Ca and Cu shoot concentrations; N, Fe and Cu shoot contents; and increased S and K shoot concentrations. Cd induced guaiacol peroxidase activity in roots in both mycorrhizal and non-mycorrhizal plants, but this increase was much more accentuated in non-mycorrhizal roots. In conclusion, sunflower plants associated with G. intraradices were less sensitive to Cd stress than non-mycorrhizal plants. Mycorrhizal sunflowers showed enhanced Cd accumulation and some tolerance to excessive Cd concentrations in plant tissues.