Diminution of arsenic accumulation in rice seedlings co-cultured with Anabaena sp.: Modulation in the expression of lower silicon transporters, two nitrogen dependent genes and lowering of antioxidants activity

Bacillus and microalgae biofertilizers improved quality and biomass of Salvia miltiorrhiza by altering microbial communities

Objective

Biofertilizers are reliable alternatives to chemical fertilizers due to various advantages. However, the effect of biofertilizers on Salvia miltiorrhiza yield and quality and the possible mechanisms remain little known. Here, an experiment was conducted in S. miltiorrhiza field treated with two kinds of biofertilizers including Bacillus and microalgae.

Methods

A field experiment was conducted on S. miltiorrhiza of one year old. The biofertilizers were applied at six treatments: (i) control check, CK; (ii) microalgae, VZ; (iii) Bacillus, TTB; (iv) microalgae + Bacillus (1:1), VTA; (v) microalgae + Bacillus (0.5:1), VTB; (vi) microalgae + Bacillus (1:0.5), VTC. Here, high-throughput sequencing, ICP-MS and UPLC were employed to systematically characterize changes of microbial diversity and structure composition, heavy metals content and bioactive compounds, respectively.

Results

Compared to CK, root biomass increased by 29.31%-60.39% (P < 0.001). Meanwhile, bioactive compounds were higher than CK after the application of the biofertilizers, peculiarly in TTB and VTB. However, the content of Pb contents in roots significantly reduced by 46.03% and 37.58% respectively in VTC and TTB (P < 0.05). VTA application notably increased the available nitrogen content by 53.03% (P < 0.05), indicating the improvement of soil fertility. Significantly, bacterial and fungal Chao I diversity indices showed an increasing trend with biofertilizer application (P < 0.05), and biofertilizer amendment enriched the rhizosphere soil with beneficial microorganisms that have abilities on promoting plant growth (Achromobacter and Penicillium), adsorbing heavy metal (Achromobacter and Beauveria), controlling plant pathogen (Plectosphaerella, Lechevalieria, Sorangium, Phlebiopsis and Beauveria) and promoting the accumulation of metabolites (Beauveria and Phoma).

Conclusion

Bacillus and microalgae biofertilizers improved the quality and biomass of S. miltiorrhiza by altering microbial communities in soil.

Comparison of Silicon-Evoked Responses on Arsenic Stress between Different Dular Rice Genotypes

Arsenic is one of the most hazardous metalloids in nature, and due to its high water solubility, it is one of the most important causes of pollution. However, silicon reduces the uptake and transport of arsenic in rice. This study investigates the interaction of different arsenic and silicon levels on dry weight, protein content, and concentrations of arsenic and silicon in two different rice shoots and roots of Dular wild-type (DU-WT) and Dular Lsi1-overexpressed (DU-OE) rice. It should be noted that all seedlings were subjected to four different treatments. For RNA-seq and qPCR, the DU-WT genotype was selected as the control and DU-OE as the treatment. With the addition of silicone treatment, dry weight and protein content in the shoots and roots of both rice lines were increased, while the concentration of arsenic in these two organs was decreased. When seedlings were exposed to arsenic treatments, protein content, silicon concentration, and dry weight were decreased in both roots and shoots, while arsenic concentration was increased in both rice genotypes. The RNA-seq in DU-OE showed 5823 differentially expressed genes (DEGs), of which 2604 were up-regulated and 3219 down-regulated. Treatment of rice by arsenic and silicon has changed the expression of genes encoding cytokinin-responsive GATA transcription factor 1, protein IN2-1 homolog B, calcium-binding EGF domain-containing protein, Os01g0369700 protein, probable glutathione S-transferase GSTU1, glutathione S-transferase protein, Os09g0367700 protein, isocitrate dehydrogenase (NADP), and Os08g0522400 protein in the root of DU-OE. The present study’s findings showed that in the presence of silicon, the transgenic genotype is much more resistant to arsenic than the wild genotype of Dular rice.

Chlorella sp. modulates the glutathione mediated detoxification and S-adenosylmethionine dependent methyltransferase to counter arsenic toxicity in Oryza sativa L

The present study investigates the role of Chlorella sp. in the mitigation of arsenic (iAs) induced toxicity in Oryza sativa L. The study shows, co-culture of rice seedlings with Chlorella sp. reduced the iAs accumulation, simultaneously improving the growth of seedlings under iAs treatments. While treatment with As^(III) and As^(V) (60 µM) alone, inflicted toxicity in rice seedlings, manifested as significant enhancement in stress markers levels (TBRAS and H₂O₂), this coincided with the shifting of cellular reduced state to oxidized state (reduced GSH/GSSG ratio). Contrarily, co-culturing rice seedlings with Chlorella sp. under iAs toxicity, reduced these stress markers and recovered the GSH/GSSG ratio. The GSH dependent antioxidant enzymes i.e. GR and GPX activities also exhibited significant enhancement upon co-culturing rice seedlings with Chlorella sp. against iAs stress. Simultaneously, the expression of four thiol dependent GRX genes, i.e. GRX13950, GRX35340, GRX12190 and GRX07950 were enhanced against As^(III) and As^(V) (60 µM), which reduced upon co-culturing with Chlorella sp. A similar trend was also observed with the expression of GST genes, where the co-culture with Chlorella sp. significantly reduced the genes expression of two isoforms (GST 38600 and GST 38610). On the contrary, the expression of S-adenosylmethionine dependent methyltransferases (SAMT) gene in rice seedlings was enhanced upon co-culturing with the Chlorella sp. against iAs stress. Overall, the results demonstrate that the rice seedlings when co-culture with Chlorella sp. ameliorates iAs toxicity through GSH dependent detoxification pathway, evident from the enhanced expression of GRX, GST, SAMT genes and activity of GSH dependent antioxidant enzymes (GR and GPX) in the rice seedlings.

Evaluation of uptake, translocation, and accumulation of arsenic species by six different Brazilian rice (Oryza sativa L.) cultivars

Rice is a significant source of arsenic (As) exposure. The accumulation of the plant depends on several factors, including environmental conditions and genetic factors. The differences in As uptake, translocation, and grains filling in different cultivars are a focus on studies to mitigate the grains contamination. This study assessed the pattern of As species accumulation in different Brazilian rice cultivars (Oryza sativa L.). Thus, pot experiments were conducted with 6 different cultivars (white rice: EPAGRI 109, EPAGRI 108, BRS Tiotaka SCS, and SCS 114 Andosan and red rice: Maranhão and Cáqui) cultivated in soils at low (As-) (0.65 mg kg^-1) and high (As+) (12.1 mg kg^-1) As levels. All cultivars in As+ group presented total As (t-As) in grains more elevated than the maximum limit of inorganic arsenic (i-As) recommended by Codex Alimentarius Commission. The As speciation disclose that Maranhão, Caqui, and SCS 114 Andosan cultivars presented the lowest % i-As (27%, 25% and 31%, respectively) at the highest As exposure condition. On the other hand, higher i-As concentration and % i-As (91%) were observed in EPAGRI 108. Moreover, EPAGRI 108 and EPAGRI 109 had the highest transference factor soil-to-grain (TFsoil-grain = 0.22 and 0.20, respectively). Interestingly, for the cultivars EPAGRI 108 and Maranhão, the levels of some essential elements (Co and Mn) in grains were modulated by the levels of As in the soil. This study shows that levels of i-As were modulated by the type of Brazilian rice cultivar, the range of As levels in soil, As phytotoxicity and the transference factor of As from soil to root straw and grains. Moreover, SCS 114 Andosan is the promising cultivar that exhibits low t-As and % i-As in grains and low TF soil-grain.