5-Aminolevulinic acid promotes low-light tolerance by regulating chloroplast ultrastructure, photosynthesis, and antioxidant capacity in tall fescue

5-Aminolevulinic acid mitigates the chromium-induced changes in Helianthus annuus L. as revealed by plant defense system enhancement

Chromium (Cr) in the soil is one of the major pollutants for agricultural production. This study examined the efficiency of sunflower plants to remediate Cr-contaminated soils using a plant growth regulator, 5-aminolevolinic acid (ALA). At six leaf stage, sunflower plants were exposed to soil-applied Cr (0.15 g kg^-1), manganese (Mn, 0.3 g kg^-1) and trisodium (S,S)-ethylenediamine-N,N'-disuccinic acid (EDDS, 2.5 mmol kg^-1), ALA (10 mg L^-1) was sprayed. After ALA treatment, the plants were harvested for further biochemical analyses. Results showed that EDDS and Mn improved the Cr accumulation but restrained plant growth. Conversely, ALA improved the growth of Cr-stressed plants by promoting chlorophyll concentration in the top fully expanded leaves. The bioaccumulation quantity and removal efficiency of sunflowers treated by Cr + EDDS + ALA was improved by 47.92% and 47.94%, respectively, as compared to the Cr treatment. This was further supported by qRT-PCR analysis, where the expression of heavy metal transport genes such as ZIP6 and NRAMP6 and subsequently Cr accumulation in sunflower tissues increased by EDDS, Mn, and ALA application. However, compared with other treatments, ALA ameliorated cellular injury from Cr-stress by uptake or movement of Cr prevention, modulation of antioxidant enzymes, and elimination of reactive oxygen species. Our study suggested that ALA as an ideal option for the phytoremediation of Cr-contaminated soils.

Physio-biochemical and transcriptomic analysis reveals that the mechanism of Bacillus cereus G2 alleviated oxidative stress of salt-stressed Glycyrrhiza uralensis Fisch. seedlings

Salt stress severely affects the growth and productivity of Glycyrrhiza uralensis. Our previous research found that the endophyte Bacillus cereus G2 alleviated the osmotic and oxidative stress in G. uralensis exposed to salinity. However, the mechanism is still unclear. Here, a pot experiment was conducted to analyse the change in parameters related to osmotic adjustment and antioxidant metabolism by G2 in salt-stressed G. uralensis at the physio-biochemistry and transcriptome levels. The results showed that G2 significantly increased proline content by 48 %, glycine betaine content by 75 % due to activated expression of BADH1, and soluble sugar content by 77 % due to upregulated expression of α-glucosidase and SS, which might help to decrease the cell osmotic potential, enable the cell to absorb water, and stabilize the cell's protein and membrane structure, thereby alleviating osmotic stress. Regarding antioxidant metabolism, G2 significantly decreased malondialdehyde (MDA) content by 27 %, which might be ascribed to the increase in superoxide dismutase (SOD) activity that facilitated the decrease in the superoxide radical (O₂^‾) production rate; it also increased the activities of catalase (CAT), ascorbate peroxidase (APX) and glutathione peroxidase (GPX), which helped stabilize the normal level of hydrogen peroxide (H₂O₂). G2 also increased glutathione (GSH) content by 65 % due to increased glutathione reductase (GR) activity and GSH/GSSG ratio, but G2 decreased oxidized glutathione (GSSG) content by 13 % due to decreased activity of dehydroascorbate reductase (DHAR), which could provide sufficient substrates for the ascorbate-glutathione (AsA-GSH) cycle to eliminate excess H₂O₂ that was not cleared in a timely manner by the antioxidant enzyme system. Taken together, G2 alleviated osmotic stress by increasing proline, soluble sugar, and glycine betaine contents and alleviated oxidative stress by the synergistic effect of antioxidant enzymes and the AsA-GSH cycle. Therefore, the results may be useful for explaining the mechanism by which endophyte inoculation regulates the salt tolerance of crops.