Effect of exogenous taurine on pea (Pisum sativum L.) plants under salinity and iron deficiency stress.

Soil salinity and Fe deficiency affect plant growth and survival by changing nutrient availability and disrupting water balance. Natural and human activities, such as evaporation and deforestation, can intensify these soil conditions. Taurine, a novel growth regulator, holds promise in mediating plant defense responses. Its effects on defense responses are still unclear. Previously, taurine showed potential in improving clover tolerance to alkaline stress and manganese toxicity. Taurine impact on plant growth under Fe deficiency and salinity stress remains uninvestigated. A pot experiment was conducted to evaluate the effects of taurine on pea plant growth, ion uptake, and defense strategies in response to salt stress and Fe deficiency. Iron deficiency was established by substituting 0.1 mM FeSO4 for 0.1 mM Fe-EDTA in the nutrient solution. Salinity stress was induced by incorporating a mixture of NaCl, MgCl2, KCl, Na2SO4, Na2CO3, NaHCO3 and CaCl2 in a 1:1:1:1:1:1:1 ratio to produce a salinity concentration of 100 mM. The simultaneous imposition of salinity and Fe deficiency significantly exacerbated oxidative stress, as evidenced by elevated levels of relative membrane permeability, hydrogen peroxide (H2O2), superoxide radical (O2•-), methylglyoxal (MG), malondialdehyde (MDA), and increased activity of lipoxygenase (LOX). Salinity stress alone and the combination of salinity and Fe deficiency resulted in substantial accumulation of Na+ ions that impeded acquisition of essential nutrients. Taurine (100 and 200 mg L-1) notably improved osmotic adjustment and oxidative defense to diminish water imbalance and oxidative injury in plants under stress. These results suggest that exogenous taurine may serve as a promising means of mitigating the detrimental effects of salt stress and Fe deficiency in plants.

Individual and combinatorial effects of SNP and NaHS on morpho-physio-biochemical attributes and phytoextraction of chromium through Cr-stressed spinach (Spinacia oleracea L.).

Chromium (Cr) is a toxic heavy metal that contaminates soil and water resources after its discharge from different industries. A pot experiment was conducted to determine the effects of single and/or combined application of sodium nitroprusside (SNP) (250 µM) and sodium hydrogen sulfide (NaHS) (1 mM) on growth, photosynthetic pigments, gas exchange characteristics, oxidative stress biomarkers, antioxidant machinery (enzymatic and non-enzymatic antioxidants), ion uptake, organic acid exudation, and Cr uptake of spinach (Spinacia oleracea L.) exposed to severe Cr stress [Cr: 0 (no Cr), 150, and 300 µM]. Our results depicted that Cr addition to the soil significantly (P < 0.05) decreased plant growth and biomass, gas exchange attributes, and mineral uptake by S. oleracea when compared to the plants grown without the addition of Cr. However, Cr toxicity boosted the production of reactive oxygen species (ROS) by increasing the content of malondialdehyde (MDA), which is the indication of oxidative stress in S. oleracea, and was also manifested by hydrogen peroxide (H2O2) content and electrolyte leakage to the membrane-bound organelles. The results showed that the activities of various antioxidative enzymes, such as superoxidase dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX), and the content of non-enzymatic antioxidants, such as phenolic, flavonoid, ascorbic acid, and anthocyanin, initially increased with an increase in the Cr concentration in the soil. The results also revealed that the levels of soluble sugar, reducing sugar, and non-reducing sugar were decreased in plants grown under elevating Cr levels, but the accumulation of the metal in the roots and shoots of S. oleracea, was found to be increased, and the values of bioaccumulation factor were <1 in all the Cr treatments. The negative impacts of Cr injury were reduced by the application of SNP and NaHS (individually or combined), which increased plant growth and biomass, improved photosynthetic apparatus, antioxidant enzymes, and mineral uptake, as well as diminished the exudation of organic acids and oxidative stress indicators in roots of S. oleracea by decreasing Cr toxicity. Here, we conclude that the application of SNP and NaHS under the exposure to Cr stress significantly improved plant growth and biomass, photosynthetic pigments, and gas exchange characteristics; regulated antioxidant defense system and essential nutrient uptake; and balanced organic acid exudation pattern in S. oleracea.

Organic chelates decrease phytotoxic effects and enhance chromium uptake by regulating chromium-speciation in castor bean (Ricinus communis L.).

There is limited information available on changes in the uptake of essential nutrients and secondary metabolites accumulation in castor bean under Cr toxicity. Besides, the role of organic chelates (EDTA and citric acid) mediated improvement in Cr uptake by castor bean is mostly unknown. Three independent experiments (sand, hydroponics, and soil) were executed to determine the Cr phytoextraction potential of Ricinus communis L. In the sand experiment, optimum doses of organic chelates (EDTA and citric acid) were selected. These optimum doses of chelates were used in the hydroponics and soil experiments. The results of hydroponics and soil experiments manifested a significant decrease in growth characteristics and leaf pigments in response to Cr stress applied as K2Cr2O7 (a source of Cr6+). The application of organic chelates (2.5 and 5 mM) showed a noticeable improvement in oxidative defense and secondary metabolites accumulation that might have decreased oxidative injury reflected as lower hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents. Moreover, chelates improved the uptake of essential nutrients (K+, Ca2+, Mg2+, Fe2+ and P) alongside significant enhancement in total Cr contents of plants. Our results advocated that chelates application resulted in greater endogenous levels of Cr3+ in plants compared with Cr6+ which is more toxic. In nutshell, organic chelates improved growth by regulating Cr species, ion homeostasis and secondary metabolites accumulation in Ricinus communis L.