Table_1_Individual and combinatorial effects of SNP and NaHS on morpho-physio-biochemical attributes and phytoextraction of chromium through Cr-stressed spinach (Spinacia oleracea L.).DOCX

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.

铬（Chromium, Cr）是一种有毒重金属，经不同工业排放后会污染土壤与水资源。本研究通过盆栽试验，探究了硝普钠（sodium nitroprusside, SNP，250 μM）与硫氢化钠（sodium hydrogen sulfide, NaHS，1 mM）单独或复合施用，对遭受重度铬胁迫[Cr浓度设置为0（无铬对照）、150 μM和300 μM]的菠菜（Spinacia oleracea L.）的生长、光合色素、气体交换特性、氧化应激生物标志物、抗氧化系统（酶促与非酶促抗氧化剂）、离子吸收、有机酸分泌以及铬吸收的影响。
研究结果显示，与未添加铬的对照组相比，土壤中添加铬会显著（P < 0.05）降低菠菜的生长与生物量、气体交换参数以及矿质元素吸收量。铬胁迫会通过提升丙二醛（malondialdehyde, MDA）含量促进活性氧（reactive oxygen species, ROS）的生成——MDA是菠菜氧化应激的典型指示物；同时过氧化氢（hydrogen peroxide, H₂O₂）含量升高与膜结合细胞器的电解质渗漏现象，也印证了菠菜体内氧化应激的发生。结果表明，随着土壤铬浓度升高，超氧化物歧化酶（superoxidase dismutase, SOD）、过氧化物酶（peroxidase, POD）、过氧化氢酶（catalase, CAT）与抗坏血酸过氧化物酶（ascorbate peroxidase, APX）等多种抗氧化酶的活性，以及酚类、类黄酮、抗坏血酸、花青素等非酶促抗氧化物质的含量均呈初始上升趋势。此外，随着铬胁迫程度加剧，菠菜体内可溶性糖、还原糖与非还原糖含量均有所下降，但菠菜根、地上部的铬积累量却随之升高，且所有铬处理组的生物富集因子值均小于1。
单独或复合施用硝普钠（SNP）与硫氢化钠（NaHS），可缓解铬胁迫带来的负面影响：其可提升菠菜的生长与生物量，改善光合系统功能、抗氧化酶活性与矿质元素吸收能力，同时通过降低铬毒性，减少菠菜根系的有机酸分泌量与氧化应激指标水平。
综上，在铬胁迫条件下施用硝普钠（SNP）与硫氢化钠（NaHS），可显著改善菠菜的生长与生物量、光合色素及气体交换特性，调控抗氧化防御系统与必需养分吸收，并平衡菠菜的有机酸分泌模式。