Photosynthetic Characteristics and Chloroplast Ultrastructure Responses of Citrus Leaves to Copper Toxicity Induced by Bordeaux Mixture in Greenhouse

Effects of Nitrogen Deficiency on the Photosynthesis, Chlorophyll a Fluorescence, Antioxidant System, and Sulfur Compounds in Oryza sativa

Decreasing nitrogen (N) supply affected the normal growth of Oryza sativa (O. sativa) seedlings, reducing CO2 assimilation, stomatal conductance (gs), the contents of chlorophylls (Chl) and the ratio of Chl a/Chl b, but increasing the intercellular CO2 concentration. Polyphasic chlorophyll a fluorescence transient and relative fluorescence parameters (JIP test) results indicated that N deficiency increased Fo, but decreased the maximum quantum yield of primary photochemistry (Fv/Fm) and the maximum of the IPphase, implying that N-limiting condition impaired the whole photo electron transport chain from the donor side of photosystem II (PSII) to the end acceptor side of PSI in O. sativa. N deficiency enhanced the activities of the antioxidant enzymes, such as ascorbate peroxidase (APX), guaiacol peroxidase (GuPX), dehydro-ascorbate reductase (DHAR), superoxide dismutase (SOD), glutathione peroxidase (GlPX), glutathione reductase (GR), glutathione S-transferase (GST) and O-acetylserine (thiol) lyase (OASTL), and the contents of antioxidant compounds including reduced glutathione (GSH), total glutathione (GSH+GSSG) and non-protein thiol compounds in O. sativa leaves. In contrast, the enhanced activities of catalase (CAT), DHAR, GR, GST and OASTL, the enhanced ASC-GSH cycle and content of sulfur-containing compounds might provide protective roles against oxidative stress in O. sativa roots under N-limiting conditions. Quantitative real-time PCR (qRT-PCR) analysis indicated that 70% of the enzymes have a consistence between the gene expression pattern and the dynamic of enzyme activity in O. sativa leaves under different N supplies, whereas only 60% of the enzymes have a consistence in O. sativa roots. Our results suggested that the antioxidant system and sulfur metabolism take part in the response of N limiting condition in O. sativa, and this response was different between leaves and roots. Future work should focus on the responsive mechanisms underlying the metabolism of sulfur-containing compounds in O. sativa under nutrient deficient especially N-limiting conditions.

Resin Acid Copper Salt, an Interesting Chemical Pesticide, Controls Rice Bacterial Leaf Blight by Regulating Bacterial Biofilm, Motility, and Extracellular Enzymes

Bacterial virulence plays an important role in infection. Antibacterial virulence factors are effective for preventing crop bacterial diseases. Resin acid copper salt as an effective inhibitor exhibited excellent anti-Xanthomonas oryzae pv. oryzae (Xoo) activity with an EC50 of 50.0 μg mL-1. Resin acid copper salt (RACS) can reduce extracellular polysaccharides' (EPS's) biosynthesis by down-regulating gumB relative expression. RACS can also effectively inhibit the bio-mass of Xoo biofilm. It can reduce the activity of Xoo extracellular amylase at a concentration of 100 μg mL-1. Meanwhile, the results of virtual computing suggested that RACS is an enzyme inhibitor. RACS displayed good curative activity with a control effect of 38.5%. Furthermore, the result of the phytotoxicity assessment revealed that RACS exhibited slight toxicity compared with the control at a concentration of 200 μg mL-1. The curative effect was increased to 45.0% using an additional antimicrobial agent like orange peel essential oil. RACS markedly inhibited bacterial pathogenicity at a concentration of 100 μg mL-1 in vivo.

Molecular Mechanisms of Plant Responses to Copper: From Deficiency to Excess

Copper (Cu) is an essential nutrient for plant growth and development. This metal serves as a constituent element or enzyme cofactor that participates in many biochemical pathways and plays a key role in photosynthesis, respiration, ethylene sensing, and antioxidant systems. The physiological significance of Cu uptake and compartmentalization in plants has been underestimated, despite the importance of Cu in cellular metabolic processes. As a micronutrient, Cu has low cellular requirements in plants. However, its bioavailability may be significantly reduced in alkaline or organic matter-rich soils. Cu deficiency is a severe and widespread nutritional disorder that affects plants. In contrast, excessive levels of available Cu in soil can inhibit plant photosynthesis and induce cellular oxidative stress. This can affect plant productivity and potentially pose serious health risks to humans via bioaccumulation in the food chain. Plants have evolved mechanisms to strictly regulate Cu uptake, transport, and cellular homeostasis during long-term environmental adaptation. This review provides a comprehensive overview of the diverse functions of Cu chelators, chaperones, and transporters involved in Cu homeostasis and their regulatory mechanisms in plant responses to varying Cu availability conditions. Finally, we identified that future research needs to enhance our understanding of the mechanisms regulating Cu deficiency or stress in plants. This will pave the way for improving the Cu utilization efficiency and/or Cu tolerance of crops grown in alkaline or Cu-contaminated soils.

Stress Physiology and Molecular Biology of Fruit Crops

Fruit crops provide various kinds of fruit commodities that are of significant nutritional benefit and economic value to humans [...].

Application of the Aliivibrio fischeri bacterium bioassay for assessing single and mixture effects of antibiotics and copper

The Aliivibrio fischeri bioassay was successfully applied in order to evaluate the acute effect of sulfamethoxazole (SMX), ciprofloxacin (CIP), chlortetracycline (CTC) and copper (Cu), alone or in binary, ternary, and overall mixture. The toxicity results are reported in terms of both effective concentrations, which inhibited 50% of the bacterium bioluminescence (EC50%), and in Toxic Units (TUs). The TUs were compared with predicted values obtained using the Concentration Addition model (CA). Finally, the toxicity of water extracts from a soil contaminated by the three antibiotics (7 mg Kg-1 each) in the presence/absence of copper (30 mg Kg-1) was also evaluated. Copper was the most toxic chemical (EC50: 0.78 mg L-1), followed by CTC (EC50: 3.64 mg L-1), CIP (96 mg L-1) and SMX (196 mg L-1). Comparing the TU and CA values of the mixtures, additive effects were generally found. However, a synergic action was recorded in the case of the CIP+Cu co-presence and antagonistic effects in the case of CTC+Cu and the ternary mixture (containing each antibiotic at 0.7 mg L-1), were identified. Soil water extracts did not show any toxicity, demonstrating the buffering ability of the soil to immobilize these chemicals.

The adaptation of root cell wall pectin to copper toxicity in two citrus species differing in copper tolerance: remodeling and responding

Citrus species are prone to suffer from copper (Cu) toxicity because of improper application of Cu-based agrochemicals. Copper immobilization mediated by pectin methylesterase (PME) in the root cell wall (CW) is effective for Cu detoxification. However, the underlying mechanisms of the structural modification and stress responses of citrus root CW pectin to Cu toxicity have been less discussed. In the present study, seedlings of 'Shatian pummelo' (Citrus grandis L. Osbeck) and 'Xuegan' (Citrus sinensis L. Osbeck), which differ in Cu tolerance, were irrigated with nutrient solution containing 0.5 (as control), 100, 300 or 500 μM Cu for 18 weeks in sandy culture or 24 h in hydroponics. At the end of treatments in the 18-week sandy culture, Cu toxicity on CW pectin content, Cu distribution, degree of pectin methylesterification (DPM) and the PME enzyme activity were discussed. At the genome-wide level, PME gene family was identified from the two citrus species, and qRT-PCR array of citrus PMEs under control and 300 μM Cu stress for 18 weeks were performed to screen the Cu-responsive PME genes. Moreover, the candidate genes that responded to Cu toxicity were further examined within 24 h. The results showed that Cu toxicity increased the root CW pectin content. The root CW pectin under Cu toxicity was remodeled by upregulation of the expression of the Cu-responsive PME genes followed by increasing PME activity, which mainly promoted low methylesterased pectin level and the Cu content on root CW pectin. Compared with C. sinensis, C. grandis root CW had a lower DPM and higher Cu content on the Cu-stressed root CW pectin, contributing to its higher Cu tolerance. Our present study provided theoretical evidence for root CW pectin remodeling in response to Cu toxicity of citrus species.

Identification of Photosynthesis Characteristics and Chlorophyll Metabolism in Leaves of Citrus Cultivar (Harumi) with Varying Degrees of Chlorosis

In autumn and spring, citrus leaves with a Ponkan (Citrus reticulata Blanco cv. Ponkan) genetic background (Harumi, Daya, etc.) are prone to abnormal physiological chlorosis. The effects of different degrees of chlorosis (normal, mild, moderate and severe) on photosynthesis and the chlorophyll metabolism of leaves of Citrus cultivar (Harumi) were studied via field experiment. Compared with severe chlorotic leaves, the results showed that chlorosis could break leaf metabolism balance, including reduced chlorophyll content, photosynthetic parameters, antioxidant enzyme activity and enzyme activity related to chlorophyll synthesis, increased catalase and decreased enzyme activity. In addition, the content of chlorophyll synthesis precursors showed an overall downward trend expected for uroporphyrinogen III. Furthermore, the relative expression of genes for chlorophyll synthesis (HEMA1, HEME2, HEMG1 and CHLH) was down-regulated to some extent and chlorophyll degradation (CAO, CLH, PPH, PAO and SGR) showed the opposite trend with increased chlorosis. Changes in degradation were more significant. In general, the chlorosis of Harumi leaves might be related to the blocked transformation of uroporphyrinogen III (Urogen III) to coproporphyrinogen III (Coprogen III), the weakening of antioxidant enzyme system activity, the weakening of chlorophyll synthesis and the enhancement in degradation.