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Soil contamination with nickel (Ni) is a persistent threat to crop production worldwide. The present study examined the putative roles of jasmonic acid (JA) in improving Ni tolerance in soybean. Our findings showed that priming of soybean seeds with JA significantly improved the growth performance of soybean when grown under excessive Ni. The enhanced Ni tolerance of soybean prompted by JA could be ascribed to its ability to regulate Ni uptake and accumulation, and to decrease Ni-induced membrane damage as evidenced by reduced levels of reactive oxygen species (ROS), malondialdehyde, lipoxygenase activity, and electrolyte leakage in Ni-stressed plants. JA also boosted redox states and antioxidant capacity in Ni-stressed plants by maintaining increased levels of ascorbate and glutathione, and enhanced activities of ROS-detoxifying enzymes compared with Ni-stressed alone plants. Additionally, methylglyoxal detoxification system was significantly upregulated in JA-primed and “JA-primed + Ni-stressed” plants, indicating an alleviating effect of JA on Ni-induced methylglyoxal toxicity. Our results conclude that JA-mediated regulation of Ni uptake and accumulation, and enhanced ROS metabolism by activating antioxidant defense and glyoxalase systems contributed to improved performance of soybean under excessive Ni, thereby suggesting JA as an effective stress regulator in mitigating Ni toxicity in economically important soybean, and perhaps in other crops.

This study was undertaken to investigate the possible involvement of the antioxidant defense and glyoxalase systems in protecting rice seedlings from heat-induced damage in the presence of spermidine (Spd). Hydroponically grown 14-day-old seedlings were subjected to foliar spray with Spd (1 mM, 24 h) prior to heat stress (42 °C, 48 h) followed by subsequent recovery (27 °C, 48 h). Lipoxygenase activity, malondialdehyde (MDA), hydrogen peroxide (H₂O₂) and proline (Pro) content increased significantly whereas fresh weight (FW) and chlorophyll (Chl) content decreased during heat stress and after recovery, indicating unrecoverable damage to rice seedlings. Heat-induced damage was also evident in decreased levels of ascorbate (AsA), glutathione (GSH), and AsA and GSH redox ratios. Superoxide dismutase (SOD) and catalase (CAT) activities increased during heat stress but declined after recovery. Activities of glutathione peroxidase (GPX), ascorbate peroxidase (APX), monodehydroascorbate reductase, dehydroascorbate reductase (DHAR) and glutathione reductase (GR) decreased during heat stress but an opposite trend for most of these enzymes was observed after recovery. Heat stress also resulted in significant increases in the activities of glyoxalase enzymes (Gly I and Gly II). In contrast, exogenous Spd protected rice seedlings from heat-induced damage as marked by lower levels of MDA, H₂O₂, and Pro content coupled with increased levels of AsA, GSH, FW, Chl, and AsA and GSH redox status. After recovery, Spd-pretreated heat-exposed seedlings displayed higher activities of SOD, CAT, GPX, GST APX, DHAR and GR as well as of Gly I and Gly II. In addition, polyamine analysis revealed that exogenously applied Spd significantly elevated the levels of free and soluble conjugated Spd. Therefore, we conclude from our results that heat exposure provoked an oxidative burden while enhancement of the antioxidative and glyoxalase systems by Spd rendered rice seedlings more tolerant to heat stress. Further, co-induction of the antioxidative and glyoxalase systems was closely associated with Spd mediated enhanced level of GSH.

Key messageLipoxygenases mediate important biological processes. Through comparative genomics, domain-scan analysis, sequence analysis, phylogenetic analysis, homology modelling and transcriptional analysis the lipoxygenase gene family of pepper (Capsicum annuum) has been identified.Lipoxygenases (LOXs) are non-heme, iron-containing dioxygenases playing a pivotal role in diverse biological processes in plants, including defence and development. Here, we exploited the recent sequencing of the pepper genome to investigate the LOX gene family in pepper. Two LOX classes are recognized, the 9- and 13-LOXs that oxygenate lipids at the 9th and 13th carbon atom, respectively. Using two main in-silico approaches, we identified a total of eight LOXs in pepper. Phylogenetic analysis classified four LOXs (CaLOX1, CaLOX3, CaLOX4 and CaLOX5) as 9-LOXs and four (CaLOX2, CaLOX6, CaLOX7 and CaLOX8) as 13-LOXs. Furthermore, sequence similarity/identity and subcellular localization analysis strengthen the classification predicted by phylogenetic analysis. Pivotal amino acids together with all domains and motifs are highly conserved in all pepper LOXs. Expression of 13-LOXs appeared to be more dynamic compared to 9-LOXs both in response to exogenous JA application and to thrips feeding. Bioinformatic and expression analyses predict the putative functions of two 13-LOXs, CaLOX6 and CaLOX7, in the biosynthesis of Green Leaf Volatiles, involved in indirect defence. The data are discussed in the context of LOX families in solanaceous plants and plants of other families.

Background Understanding the mechanisms involved in climacteric fruit ripening is key to improve fruit harvest quality and postharvest performance. Kiwifruit ( Actinidia deliciosa cv. ‘Hayward’) ripening involves a series of metabolic changes regulated by ethylene. Although 1-methylcyclopropene (1-MCP, inhibitor of ethylene action) or ozone (O 3 ) exposure suppresses ethylene-related kiwifruit ripening, how these molecules interact during ripening is unknown. Results Harvested ‘Hayward’ kiwifruits were treated with 1-MCP and exposed to ethylene-free cold storage (0 °C, RH 95%) with ambient atmosphere (control) or atmosphere enriched with O 3 (0.3 μL L − 1 ) for up to 6 months. Their subsequent ripening performance at 20 °C (90% RH) was characterized. Treatment with either 1-MCP or O 3 inhibited endogenous ethylene biosynthesis and delayed fruit ripening at 20 °C. 1-MCP and O 3 in combination severely inhibited kiwifruit ripening, significantly extending fruit storage potential. To characterize ethylene sensitivity of kiwifruit following 1-MCP and O 3 treatments, fruit were exposed to exogenous ethylene (100 μL L − 1 , 24 h) upon transfer to 20 °C following 4 and 6 months of cold storage. Exogenous ethylene treatment restored ethylene biosynthesis in fruit previously exposed in an O 3 -enriched atmosphere. Comparative proteomics analysis showed separate kiwifruit ripening responses, unraveled common 1-MCP- and O 3 -dependent metabolic pathways and identified specific proteins associated with these different ripening behaviors. Protein components that were differentially expressed following exogenous ethylene exposure after 1-MCP or O 3 treatment were identified and their protein-protein interaction networks were determined. The expression of several kiwifruit ripening related genes, such as 1-aminocyclopropane-1-carboxylic acid oxidase ( ACO1 ), ethylene receptor ( ETR1 ) , lipoxygenase ( LOX1 ), geranylgeranyl diphosphate synthase ( GGP1 ), and expansin ( EXP2 ), was strongly affected by O 3 , 1-MCP, their combination, and exogenously applied ethylene. Conclusions Our findings suggest that the combination of 1-MCP and O 3 functions as a robust repressive modulator of kiwifruit ripening and provide new insight into the metabolic events underlying ethylene-induced and ethylene-independent ripening outcomes.

Nitric oxide (NO) and glutathione (GSH) regulate a variety of physiological processes and stress responses; however, their involvement in mitigating Cu toxicity in plants has not been extensively studied. This study investigated the interactive effect of exogenous sodium nitroprusside (SNP) and GSH on Cu homeostasis and Cu-induced oxidative damage in rice seedlings. Hydroponically grown 12-day-old seedlings were subjected to 100 μM CuSO 4 alone and in combination with 200 μM SNP (an NO donor) and 200 μM GSH. Cu exposure for 48 h resulted in toxicity symptoms such as stunted growth, chlorosis, and rolling in leaves. Cu toxicity was also manifested by a sharp increase in lipoxygenase (LOX) activity, lipid peroxidation (MDA), hydrogen peroxide (H 2 O 2 ), proline (Pro) content, and rapid reductions in biomass, chlorophyll (Chl), and relative water content (RWC). Cu-caused oxidative stress was evident by overaccumulation of reactive oxygen species (ROS; superoxide (O 2 •– ) and H 2 O 2 ). Ascorbate (AsA) content decreased while GSH and phytochelatin (PC) content increased significantly in Cu-stressed seedlings. Exogenous SNP, GSH, or SNP + GSH decreased toxicity symptoms and diminished a Cu-induced increase in LOX activity, O 2 •– , H 2 O 2 , MDA, and Pro content. They also counteracted a Cu-induced increase in superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), and glyoxalase I and glyoxalase II activities, which paralleled changes in ROS and MDA levels. These seedlings also showed a significant increase in catalase (CAT), glutathione peroxidase (GPX), dehydroascorbate reductase (DHAR), glutathione S -transferase (GST) activities, and AsA and PC content compared with the seedlings stressed with Cu alone. Cu analysis revealed that SNP and GSH restricted the accumulation of Cu in the roots and leaves of Cu-stressed seedlings. Our results suggest that Cu exposure provoked an oxidative burden while reduced Cu uptake and modulating the antioxidant defense and glyoxalase systems by adding SNP and GSH play an important role in alleviating Cu toxicity. Furthermore, the protective action of GSH and SNP + GSH was more efficient than SNP alone.

Postharvest browning is the primary cause of a decrease in the shelf life of the white button mushroom ( Agaricus bisporus ). This study investigated the effect of postharvest brassinolide (BL) treatment on metabolism in relation to browning of the white button mushroom. Each harvested mushroom was dipped into one of three solutions containing 0, 1, or 3 μM BL for 5 min and stored in darkness at 4 °C for 16 days. Our results indicated that treatment with BL restrains browning development and reduces the total phenolic content and polyphenol oxidase activity. In addition, BL treatment maintains lower weight loss, electrolyte leakage, and malondialdehyde content and inhibits any increase in lipoxygenase activity compared with those of the control mushrooms. Furthermore, BL treatment significantly decreases the accumulation of reactive oxygen species (ROS) and induces the antioxidant enzyme system. Compared with 1 μM BL, treatment with 3 μM BL is more effective in reducing cap browning. The reduction of membrane oxidative damage and ROS levels induced by BL inhibits enzymatic browning reaction in the white button mushroom. These findings suggest that treatment with BL could have the potential of inhibiting browning and thus maintaining the mushroom’s commercial value.

Sex determination in maize is controlled by a developmental cascade leading to the formation of unisexual florets derived from an initially bisexual floral meristem. Abortion of pistil primordia in staminate florets is controlled by a tasselseed-mediated cell death process. We positionally cloned and characterized the function of the sex determination gene tasselseed1 (ts1). The TS1 protein encodes a plastid-targeted lipoxygenase with predicted 13-lipoxygenase specificity, which suggests that TS1 may be involved in the biosynthesis of the plant hormone jasmonic acid. In the absence of a functional ts1 gene, lipoxygenase activity was missing and endogenous jasmonic acid concentrations were reduced in developing inflorescences. Application of jasmonic acid to developing inflorescences rescued stamen development in mutant ts1 and ts2 inflorescences, revealing a role for jasmonic acid in male flower development in maize.

We investigated the roles of exogenously applied Spd (0.3 mM spermidine) in alleviating Al (AlCl 3 , 0.5 mM, 48 and 72 h)- induced injury in mung bean seedlings ( Vigna radiata L. cv. BARI Mung-2). Aluminum toxicity induced oxidative damage overproducing reactive oxygen species (ROS; H 2 O 2 and O 2 •− ), increasing lipoxygenase activity and membrane lipid peroxidation. The toxic compound methylglyoxal (MG) also overproduced under Al stress. In order to circumvent Al-induced oxidative stress, enzymatic and non-enzymatic antioxidant defense were activated by the application of exogenous Spd. Exogenous Spd increased ascorbate (AsA) and glutathione (GSH) content, AsA/dehydroascorbate (DHA) ratio, GSH/ glutathione disulfide (GSSG) ratio, activity of ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), glutathione reductase (GR) and catalase (CAT) which reduced ROS production and oxidative stress under Al stress. Spd-induced improvement of GSH pool and Gly II activity alleviated injurious effects of MG. Exogenous Spd positively modulated the endogenous PAs level. Regulating the osmoprotectant molecule (proline), Spd improved plant water status under Al stress. Exogenous Spd was potent to prevent breakdown of Al-induced photosynthetic pigment and to improve growth performances under Al stress. The mechanism by which Spd enhances antioxidant and glyoxalase components might be studied extensively. Spermidine-induced protection of photosynthetic pigment from damages and growth enhancement were remarkable and recommended for further detailed study to understand the mechanism.

Salinity in the form of abiotic stress adversely effects plant growth, development, and productivity. Various osmoprotectants are involved in regulating plant responses to salinity; however, the precise role of trehalose (Tre) in this process remains to be further elucidated. The present study investigated the regulatory role of Tre in alleviating salt-induced oxidative stress in hydroponically grown rice seedlings. Salt stress (150 and 250 mM NaCl) for 72 h resulted in toxicity symptoms such as stunted growth, severe yellowing, and leaf rolling, particularly at 250 mM NaCl. Histochemical observation of reactive oxygen species (ROS; O 2 ∙− and H 2 O 2 ) indicated evident oxidative stress in salt-stressed seedlings. In these seedlings, the levels of lipoxygenase (LOX) activity, malondialdehyde (MDA), H 2 O 2 , and proline (Pro) increased significantly whereas total chlorophyll (Chl) and relative water content (RWC) decreased. Salt stress caused an imbalance in non-enzymatic antioxidants, i.e., ascorbic acid (AsA) content, AsA/DHA ratio, and GSH/GSSG ratio decreased but glutathione (GSH) content increased significantly. In contrast, Tre pretreatment (10 mM, 48 h) significantly addressed salt-induced toxicity symptoms and dramatically depressed LOX activity, ROS, MDA, and Pro accumulation whereas AsA, GSH, RWC, Chl contents, and redox status improved considerably. Salt stress stimulated the activities of SOD, GPX, APX, MDHAR, DHAR, and GR but decreased the activities of CAT and GST. However, Tre-pretreated salt-stressed seedlings counteracted SOD and MDHAR activities, elevated CAT and GST activities, further enhanced APX and DHAR activities, and maintained GPX and GR activities similar to the seedlings stressed with salt alone. In addition, Tre pretreatment enhanced the activities of methylglyoxal detoxifying enzymes (Gly I and Gly II) more efficiently in salt-stressed seedlings. Our results suggest a role for Tre in protecting against salt-induced oxidative damage attributed to reduced ROS accumulation, elevation of non-enzymatic antioxidants, and co-activation of the antioxidative and glyoxalase systems.

Chromium (Cr) toxicity is hazardous to the seed germination, growth, and development of plants. γ-aminobutyric acid (GABA) is a non-protein amino acid and is involved in stress tolerance in plants. To investigate the effects of GABA in alleviating Cr toxicity, we treated eight-d-old mustard ( Brassica juncea L.) seedlings with Cr (0.15 and 0.3 mM K 2 CrO 4 , 5 days) alone and in combination with GABA (125 µM) in a semi-hydroponic medium. The roots and shoots of the seedlings accumulated Cr in a dose-dependent manner, which led to an increase in oxidative damage [lipid peroxidation; hydrogen peroxide (H 2 O 2 ) content; superoxide (O 2 •− ) generation; lipoxygenase (LOX) activity], methylglyoxal (MG) content, and disrupted antioxidant defense and glyoxalase systems. Chromium stress also reduced growth, leaf relative water content (RWC), and chlorophyll (chl) content but increased phytochelatin (PC) and proline (Pro) content. Furthermore, supplementing the Cr-treated seedlings with GABA reduced Cr uptake and upregulated the non-enzymatic antioxidants (ascorbate, AsA; glutathione, GSH) and the activities of the enzymatic antioxidants including ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), glutathione peroxidase (GPX), superoxide dismutase (SOD), catalase (CAT), glyoxalase I (Gly I), and glyoxalase II (Gly II), and finally reduced oxidative damage. Adding GABA also increased leaf RWC and chl content, decreased Pro and PC content, and restored plant growth. These findings shed light on the effect of GABA in improving the physiological mechanisms of mustard seedlings in response to Cr stress.