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Limited data are available on copper (Cu)–pH interaction-responsive genes and/or metabolites in plant roots. Citrus sinensis seedlings were treated with 300 μM (Cu toxicity) or 0.5 μM (control) CuCl2 at pH 3.0 or 4.8 for 17 weeks. Thereafter, gene expression and metabolite profiles were obtained using RNA-Seq and widely targeted metabolome, respectively. Additionally, several related physiological parameters were measured in roots. The results indicated that elevating the pH decreased the toxic effects of Cu on the abundances of secondary metabolites and primary metabolites in roots. This difference was related to the following several factors: (a) elevating the pH increased the capacity of Cu-toxic roots to maintain Cu homeostasis by reducing Cu uptake and Cu translocation to young leaves; (b) elevating the pH alleviated Cu toxicity-triggered oxidative damage by decreasing reactive oxygen species (ROS) formation and free fatty acid abundances and increasing the ability to detoxify ROS and maintain cell redox homeostasis in roots; and (c) increasing the pH prevented root senescence and cell wall (CW) metabolism impairments caused by Cu toxicity by lowering Cu levels in roots and root CWs, thus improving root growth. There were some differences and similarities in Cu–pH interaction-responsive genes and metabolites between leaves and roots. [ABSTRACT FROM AUTHOR]

Some citrus orchards in China often experience nitrogen (N) deficiency. For the first time, targeted metabolomics was used to examine N-deficient effects on hormones in sweet orange (Citrus sinensis (L.) Osbeck cv. Xuegan) leaves and roots. The purpose was to validate the hypothesis that hormones play a role in N deficiency tolerance by regulating root/shoot dry weight ratio (R/S), root system architecture (RSA), and leaf and root senescence. N deficiency-induced decreases in gibberellins and indole-3-acetic acid (IAA) levels and increases in cis(+)-12-oxophytodienoic acid (OPDA) levels, ethylene production, and salicylic acid (SA) biosynthesis might contribute to reduced growth and accelerated senescence in leaves. The increased ethylene formation in N-deficient leaves might be caused by increased 1-aminocyclopropanecarboxylic acid and OPDA and decreased abscisic acid (ABA). N deficiency increased R/S, altered RSA, and delayed root senescence by lowering cytokinins, jasmonic acid, OPDA, and ABA levels and ethylene and SA biosynthesis, increasing 5-deoxystrigol levels, and maintaining IAA and gibberellin homeostasis. The unchanged IAA concentration in N-deficient roots involved increased leaf-to-root IAA transport. The different responses of leaf and root hormones to N deficiency might be involved in the regulation of R/S, RSA, and leaf and root senescence, thus improving N use efficiency, N remobilization efficiency, and the ability to acquire N, and hence conferring N deficiency tolerance. [ABSTRACT FROM AUTHOR]

Hole mobility is critical to the power conversion efficiencies of perovskite solar cells (PSCs). Organic small‐molecule hole‐transporting materials (HTMs) have attracted considerable interest in PSCs due to their structural flexibility and operational durability, but they suffer from modest hole mobility. On the other hand, inorganic HTMs with good hole mobility are inflexible in structural variation and exhibit unsatisfactory cell efficiency. In this study, a ligand BT28 and its zinc‐based coordination complex BTZ30 were synthesized, characterized, and investigated as HTMs for PSC applications. The mixed‐halide perovskites can be grown uniformly with large crystalline grains on both HTMs, which exhibit similar optical and electrochemical properties. However, it was discovered that the BTZ30‐based solar cell exhibited an open‐circuit voltage of 1.0817 V and a high short‐circuit current density of 23.1392 mA cm−2 with a champion power conversion efficiency of close to 20 %. The performance difference between the two HTMs can be attributed to the difference in their hole mobilities, which is 63.31 % higher for BTZ30 than BT28. The comparison of non‐metal and metal HTMs revealed the importance of considering hybrid structures to overcome some shortcomings associated with organic and inorganic HTMs and achieve high‐performance PSCs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Citrus sinensis (L.) Osbeck seedlings were fertigated with nutrient solution containing 2 [magnesium (Mg)-sufficiency] or 0 mM (Mg-deficiency) Mg(NO 3 ) 2 for 16 weeks. Thereafter, RNA-Seq was used to investigate Mg-deficiency-responsive genes in the veins of upper and lower leaves in order to understand the molecular mechanisms for Mg-deficiency-induced vein lignification, enlargement and cracking, which appeared only in the lower leaves. In this study, 3065 upregulated and 1220 downregulated, and 1390 upregulated and 375 downregulated genes were identified in Mg-deficiency veins of lower leaves (MDVLL) vs Mg-sufficiency veins of lower leaves (MSVLL) and Mg-deficiency veins of upper leaves (MDVUL) vs Mg-sufficiency veins of upper leaves (MSVUL), respectively. There were 1473 common differentially expressed genes (DEGs) between MDVLL vs MSVLL and MDVUL vs MSVUL, 1463 of which displayed the same expression trend. Magnesium-deficiency-induced lignification, enlargement and cracking in veins of lower leaves might be related to the following factors: (i) numerous transciption factors and genes involved in lignin biosynthesis pathways, regulation of cell cycle and cell wall metabolism were upregulated; and (ii) reactive oxygen species, phytohormone and cell wall integrity signalings were activated. Conjoint analysis of proteome and transcriptome indicated that there were 287 and 56 common elements between DEGs and differentially abundant proteins (DAPs) identified in MDVLL vs MSVLL and MDVUL vs MSVUL, respectively, and that among these common elements, the abundances of 198 and 55 DAPs matched well with the transcript levels of the corresponding DEGs in MDVLL vs MSVLL and MDVUL vs MSVUL, respectively, indicating the existence of concordances between protein and transcript levels. [ABSTRACT FROM AUTHOR]

Citrus sinensis seedlings were irrigated with nutrient solution at a concentration of 0 (Mg-deficiency) or 2 (Mg-sufficiency) mM Mg (NO3)2 for 16 weeks. Mg-deficiency-induced interveinal chlorosis, vein enlargement and corkiness, and alterations of gas exchange, pigments, chlorophyll a fluorescence (OJIP) transients and related parameters were observed in middle and lower leaves, especially in the latter, but not in upper leaves. Mg-deficiency might impair the whole photosynthetic electron transport, including structural damage to thylakoids, ungrouping of photosystem II (PSII), inactivation of oxygen-evolving complex (OEC) and reaction centers (RCs), increased reduction of primary quinone electron acceptor (QA) and plastoquinone pool at PSII acceptor side and oxidation of PSI end-electron acceptors, thus lowering energy transfer and absorption efficiency and the transfer of electrons to the dark reactions, hence, the rate of CO2 assimilation in Mg-deficiency middle and lower leaves. Although potassium, Mg, manganese and zinc concentration in blades displayed a significant and positive relationship with the corresponding element concentration in veins, respectively, great differences existed in Mg-deficiency-induced alterations of nutrient concentrations between leaf blades and veins. For example, Mg-deficiency increased boron level in the blades of upper leaves, decreased boron level in the blades of lower leaves, but did not affect boron level in the blades of middle leaves and veins of upper, middle and lower leaves. To conclude, Mg-deficiency-induced interveinal chlorosis, vein enlargement, and corkiness, and alterations to photosynthesis and related parameters increased with increasing leaf age. Mg-deficiency-induced enlargement and corkiness of veins were not caused by Mg-deficiency-induced boron-starvation. [ABSTRACT FROM AUTHOR]