Ascorbic acid and salicylic acid mitigate nacl stress in Caralluma tuberculata Calli

Humic acids enhance salt stress tolerance associated with pyrroline 5-carboxylate synthetase gene expression and hormonal alteration in perennial ryegrass (Lolium perenne L.)

Humic acid (HA) has been used as an important component in biostimulant formulations to enhance plant tolerance to salt stress, but the mechanisms underlying are not fully understood. This study was to investigate the physiological and molecular mechanisms of HA's impact on salt stress tolerance in perennial ryegrass (Lolium perenne L.). The two types of HA were extracted from weathered coal samples collected from Wutai County (WTH) and Jingle County (JLH) of Shanxi Province, China. The grass seedlings subjected to salt stress (250 mM NaCl) were treated with HA solutions containing 0.01% WTH (W/V) or 0.05% JLH (W/V), respectively. The HA treatments improved leaf photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) and reduced leaf oxidative injury (lower malondialdehyde content) and Pro and intercellular CO2 concentrations in salt-stressed perennial ryegrass. The HA treatments also reversed the decline in antioxidative enzymes ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) activity and improved growth and anti-senescence hormones indole-3-acetic acid (IAA) and brassinosteroid (BR). The HA treatments reduced the relative expression of P5CS and its downstream products proline (Pro) and the stress defense hormones abscisic acid (ABA), salicylic acid (SA), jasmonic acid (JA), and polyamines (PA). The results of this study indicate that the application of HAs may improve salt stress tolerance by regulating P5CS gene expression related to osmotic adjustment and increasing the activity of antioxidant enzymes and anti-senescence hormones in perennial ryegrass.

The carbonate concentration mechanism of Pyropia yezoensis (Rhodophyta): evidence from transcriptomics and biochemical data

BACKGROUND

Pyropia yezoensis (Rhodophyta) is widely cultivated in East Asia and plays important economic, ecological and research roles. Although inorganic carbon utilization of P. yezoensis has been investigated from a physiological aspect, the carbon concentration mechanism (CCM) of P. yezoensis remains unclear. To explore the CCM of P. yezoensis, especially during its different life stages, we tracked changes in the transcriptome, photosynthetic efficiency and in key enzyme activities under different inorganic carbon concentrations.

RESULTS

Photosynthetic efficiency demonstrated that sporophytes were more sensitive to low carbon (LC) than gametophytes, with increased photosynthesis rate during both life stages under high carbon (HC) compared to normal carbon (NC) conditions. The amount of starch and number of plastoglobuli in cells corresponded with the growth reaction to different inorganic carbon (Ci) concentrations. We constructed 18 cDNA libraries from 18 samples (three biological replicates per Ci treatment at two life cycles stages) and sequenced these using the Illumina platform. De novo assembly generated 182,564 unigenes, including approximately 275 unigenes related to CCM. Most genes encoding internal carbonic anhydrase (CA) and bicarbonate transporters involved in the biophysical CCM pathway were induced under LC in comparison with NC, with transcript abundance of some PyCAs in gametophytes typically higher than that in sporophytes. We identified all key genes participating in the C4 pathway and showed that their RNA abundances changed with varying Ci conditions. High decarboxylating activity of PEPCKase and low PEPCase activity were observed in P. yezoensis. Activities of other key enzymes involved in the C4-like pathway were higher under HC than under the other two conditions. Pyruvate carboxylase (PYC) showed higher carboxylation activity than PEPC under these Ci conditions. Isocitrate lyase (ICL) showed high activity, but the activity of malate synthase (MS) was very low.

CONCLUSION

We elucidated the CCM of P. yezoensis from transcriptome and enzyme activity levels. All results indicated at least two types of CCM in P. yezoensis, one involving CA and an anion exchanger (transporter), and a second, C4-like pathway belonging to the PEPCK subtype. PYC may play the main carboxylation role in this C4-like pathway, which functions in both the sporophyte and gametophyte life cycles.

Regulation of Ascorbate-Glutathione Pathway in Mitigating Oxidative Damage in Plants under Abiotic Stress

Reactive oxygen species (ROS) generation is a usual phenomenon in a plant both under a normal and stressed condition. However, under unfavorable or adverse conditions, ROS production exceeds the capacity of the antioxidant defense system. Both non-enzymatic and enzymatic components of the antioxidant defense system either detoxify or scavenge ROS and mitigate their deleterious effects. The Ascorbate-Glutathione (AsA-GSH) pathway, also known as Asada-Halliwell pathway comprises of AsA, GSH, and four enzymes viz. ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase, play a vital role in detoxifying ROS. Apart from ROS detoxification, they also interact with other defense systems in plants and protect the plants from various abiotic stress-induced damages. Several plant studies revealed that the upregulation or overexpression of AsA-GSH pathway enzymes and the enhancement of the AsA and GSH levels conferred plants better tolerance to abiotic stresses by reducing the ROS. In this review, we summarize the recent progress of the research on AsA-GSH pathway in terms of oxidative stress tolerance in plants. We also focus on the defense mechanisms as well as molecular interactions.