LSD3 mediates the oxidative stress response through fine-tuning APX2 activity and the NF-YC15-GSTs module in cassava.

Reactive oxygen species (ROS) overproduction leads to oxidative damage under almost all stress conditions. Lesion-Simulating Disease (LSD), a zinc finger protein, is an important negative regulator of ROS accumulation and cell death in plants. However, the in vivo role of LSD in cassava (Manihot esculenta) and the underlying molecular mechanisms remain elusive. Here, we found that MeLSD3 is essential for the oxidative stress response in cassava. MeLSD3 physically interacted with ascorbate peroxidase 2 (MeAPX2), thereby promoting its enzymatic activity. In addition, MeLSD3 also interacted with the nuclear factor YC15 (MeNF-YC15), which also interacted with nuclear factor YA2/4 (MeNF-YA2/4) and nuclear factor YB18 (MeNF-YB18) to form an MeNF-YC15-MeNF-YA2/4-MeNF-YB18 complex. Notably, MeLSD3 positively modulated the transcriptional activation of the MeNF-YC15-MeNF-YA2/4-MeNF-YB18 complex by interacting with the CCAAT boxes of the promoters of glutathione S-transferases U37/U39 (MeGST-U37/U39), activating their transcription. When one or both of MeLSD3 and the MeNF-YC15-MeNF-YA2/4-MeNF-YB18 complex were co-silenced, cassava showed decreased oxidative stress resistance, while overexpression of MeGST-U37/U39 alleviated the oxidative stress-sensitive phenotype of these silenced plants. This study illustrates the dual roles of MeLSD3 in promoting MeAPX2 activity and MeNF-YC15-MeGST-U37/U39 regulation, which underlie the oxidative stress response in cassava.

Physiological mechanisms of exogenous calcium on alleviating salinity-induced stress in rice (Oryza sativa L.).

Being more sensitive to salt stress among the cereals, growth of rice (Oryza sativa L.) has been habitually affected by salinity. Although, several practices have evolved to sustain the growth of rice under salinity, the enormous role of calcium (Ca2+) as a signalling molecule in salt stress mitigation is still arcane. Considering this fact, an experiment was performed aiming to explicate the mechanism of salt-induced growth inhibition in rice and its alleviation by exogenous Ca2+. At germination stage, 10 mM and 15 mM CaCl2 primed rice (cv. Binadhan-10 & Binadhan-7) seeds were grown in petri dishes for 9 days under 100 mM NaCl stress. At seedling stage, 9-day-old rice seedlings grown on sand were exposed to 100 mM NaCl alone and combined with 10 mM and 15 mM CaCl2 for 15 days. This research revealed that salinity radically slowed down growth of rice seedlings and Ca2+ treatment noticeably improved growth performances. At germination stage, 10 mM CaCl2 treatment significantly increased the final germination percentage, germination rate index (in Binadhan-7), shoot, root length (89.20, 67.58% in Bindhan-10 & 84.72, 31.15% in Bindhan-7) and biomass production under salinity. Similarly, at seedling stage, 10 mM CaCl2 supplementation in salt-stressed plants enhanced shoot length (42.17, 28.76%) and shoot dry weight (339.52, 396.20%) significantly in Binadhan-10 & Binadhan-7, respectively, but enhanced root dry weight (36.76%) only in Binadhan-10. In addition, 10 mM CaCl2 supplementation on salt-stressed seedlings increased the chlorophyll and proline content, and oppressed the accretion of reactive oxygen species thus protecting from oxidative damage more pronouncedly in Binadhan-10 than Binadhan-7 as reflected by the elevated levels of catalase and ascorbate peroxidase activity. The 15 mM CaCl2 somehow also enhanced some growth parameters but overall was less effective than 10 mM CaCl2 to alleviate salt stress, and sometimes showed negative effect. Therefore, supplementary application of calcium-rich fertilizers in saline prone soils can be an effective approach to acclimatize salt stress and cultivate rice successfully.

Effects of humic acids derived from lignite and cattle manure on antioxidant enzymatic activities of barley root.

To investigate the effects of humic acids (HAs) on the ability of plants to defend themselves against oxidative stress, barley was hydroponically cultured in the absence and presence of HAs, and the antioxidant enzymatic activities (catalase, superoxide dismutase, ascorbate and glutathione peroxidases) of root tissue were evaluated. Auxin-like structures in HAs, which were extracted from an oxidation product of lignite (LHA) and compost derived from cattle manure (CHA), were identified by pyrolysis-gas chromatography/mass spectrometry (GC/MS) with tetramethylammonium hydroxide. The LHA, which had the lower molecular weight, was more effective in promoting the growth of barley root than CHA. However, the amounts of auxin-like structures in the CHA were much higher than those for LHA. The antioxidant enzymatic activities were initially decreased in the presence of LHA and CHA at the first day after refreshing the culture solution, but were significantly increased on the second day. The CHA sample, which contained relatively high levels of phenolic acids that contained auxin-like structures, was effective in increasing four types of enzymatic activities, while the activities of catalase and ascorbate peroxidase were increased in the presence of LHA, which contains naphthalene derivatives. These results indicate that using HAs as a supplement can be effective in enhancing antioxidation enzymatic activities, while the appearance of the effects is retarded because of the decomposition and release of auxin-like compounds from HAs by organic acids from the plant roots.

Effect of light intensity on nitrogen transformation, enzymatic activity, antioxidant system and transcriptional response of Chlorella pyrenoidosa during treating mariculture wastewater.

The nitrogen transformation, enzymatic activity, antioxidant ability and transcriptional response of Chlorella pyrenoidosa (C. pyrenoidosa) treating mariculture wastewater were compared under different light intensities. The microalgal growth, chlorophyll synthesis and nitrogen removal ability of C. pyrenoidosa increased with the light intensity from 3000 to 7000 Lux, whereas they slightly decreased under 9000 and 11,000 Lux. The nitrogen metabolism enzymatic activities displayed obvious differences under different light intensities and affected the nitrogen transformation process. The reactive oxygen species (ROS) production increased with the increase of operational time, whereas it had distinct differences under different light intensities. The changes of antioxidant enzymatic activities were positively correlated with the ROS production. The transcriptional response of C. pyrenoidosa was in accordance with the variation of the photosynthesis, nitrogen assimilation and antioxidant system under different light intensities. This study provides theoretical basis and technical support to select suitable light intensity for algae treating mariculture wastewater.

Quinoa Response to Application of Phosphogypsum and Plant Growth-Promoting Rhizobacteria under Water Stress Associated with Salt-Affected Soil.

The aim of the study was to estimate the impact of soil amendments (i.e., phosphogypsum and plant growth-promoting rhizobacteria (PGPR)) separately or their combination on exchangeable sodium percentage (ESP), soil enzymes' activity (urease and dehydrogenase), pigment content, relative water content (RWC), antioxidant enzymatic activity, oxidative stress, productivity, and quality of quinoa under deficient irrigation conditions in two field experiments during the 2019-2020 and 2020-2021 seasons under salt-affected soil. Results revealed that ESP, soil urease activity, soil dehydrogenase activity, leaf chlorophyll a, b, and carotenoids, leaf K content, RWC, SOD (superoxide dismutase), CAT (catalase), and POD (peroxidase) activities were declined, resulting in overproduction of leaf Na content, proline content, and oxidative stress indicators (H2O2, malondialdehyde (MDA) and electrolyte leakage) under water stress and soil salinity, which negatively influence yield-related traits, productivity, and seed quality of quinoa. However, amendment of salt-affected soil with combined phosphogypsum and seed inoculation with PGPR under deficient irrigation conditions was more effective than singular application and control plots in ameliorating the harmful effects of water stress and soil salinity. Additionally, combined application limited Na uptake in leaves and increased K uptake and leaf chlorophyll a, b, and carotenoids as well as improved SOD, CAT, and POD activities to ameliorate oxidative stress indicators (H2O2, MDA, and electrolyte leakage), which eventually positively reflected on productivity and quality in quinoa. We conclude that the potential utilization of phosphogypsum and PGPR are very promising as sustainable eco-friendly strategies to improve quinoa tolerance to water stress under soil salinity.

CsCYT75B1, a Citrus CYTOCHROME P450 Gene, Is Involved in Accumulation of Antioxidant Flavonoids and Induces Drought Tolerance in Transgenic Arabidopsis.

CYTOCHROME P450s genes are a large gene family in the plant kingdom. Our earlier transcriptome data revealed that a CYTOCHROME P450 gene of Citrus sinensis (CsCYT75B1) was associated with flavonoid metabolism and was highly induced after drought stress. Here, we characterized the function of CsCYT75B1 in drought tolerance by overexpressing it in Arabidopsis thaliana. Our results demonstrated that the overexpression of the CsCYT75B1 gene significantly enhanced the total flavonoid contents with increased antioxidant activity in transgenic Arabidopsis. The gene expression results showed that several genes that are responsible for the biosynthesis of antioxidant flavonoids were induced by 2-12 fold in transgenic Arabidopsis lines. After 14 days of drought stress, all transgenic lines displayed an enhanced tolerance to drought stress along with accumulating antioxidant flavonoids with lower superoxide radicals and reactive oxygen species (ROS) than wild type plants. In addition, drought-stressed transgenic lines possessed higher antioxidant enzymatic activities than wild type transgenic lines. Moreover, the stressed transgenic lines had significantly lower levels of electrolytic leakage than wild type transgenic lines. These results demonstrate that the CsCYT75B1 gene of sweet orange functions in the metabolism of antioxidant flavonoid and contributes to drought tolerance by elevating ROS scavenging activities.