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Isoprenoid metabolism and its derivatives took part in photosynthesis, growth regulation, signal transduction, and plant defense to biotic and abiotic stresses. However, how aluminum (Al) stress affects the isoprenoid metabolism and whether isoprenoid metabolism plays a vital role in the Citrus plants in coping with Al stress remain unclear. In this study, we reported that Al–treatment–induced alternation in the volatilization rate of monoterpenes (α–pinene, β–pinene, limonene, α–terpinene, γ–terpinene and 3–carene) and isoprene were different between Citrus sinensis (Al-tolerant) and C. grandis (Al-sensitive) leaves. The Al-induced decrease of CO 2 assimilation, maximum quantum yield of primary PSII photochemistry (F v /F m), the lower contents of glucose and starch, and the lowered activities of enzymes involved in the mevalonic acid (MVA) pathway and 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway might account for the different volatilization rate of isoprenoids. Furthermore, the altered transcript levels of genes related to isoprenoid precursors and/or derivatives metabolism, such as geranyl diphosphate (GPP) synthase (GPPS) in GPP biosynthesis, geranylgeranyl diphosphate synthase (GGPPS), chlorophyll synthase (CHS) and GGPP reductase (GGPPR) in chlorophyll biosynthesis, limonene synthase (LS) and α-pinene synthase (APS) in limonene and α–pinene synthesis, respectively, might be responsible for the different contents of corresponding products in C. grandis and C. sinensis. Our data suggested that isoprenoid metabolism was involved in Al tolerance response in Citrus , and the alternation of some branches of isoprenoid metabolism could confer different Al-tolerance to Citrus species. [Display omitted] • The emission rate of volatile isoprenoids varied in C. grandis and C. sinensis. • Al treatment downregulated both MVA and MEP pathways in C. grandis leaves. • Al treatment upregulated MEP pathway in C. sinensis leaves. • Isoprenoid metabolism was involved in Al tolerance response in Citrus plants. [ABSTRACT FROM AUTHOR]

'Xuegan' (Citrus sinensis) seedlings were fertilized 6 times weekly for 24 weeks with 0.5 or 350 μM CuCl 2 and 2.5, 10 or 25 μM H 3 BO 3. Cu-toxicity increased Cu uptake per plant (UPP) and Cu concentrations in leaves, stems and roots, decreased water uptake and phosphorus, nitrogen, calcium, magnesium, potassium, sulfur, boron and iron UPP, and increased the ratios of magnesium, potassium, calcium and sulfur UPP to phosphorus UPP and the ratios of leaf magnesium, potassium and calcium concentrations to leaf phosphorus concentration. Many decaying and dead fibrous roots occurred in Cu-toxic seedlings. Cu-toxicity-induced alterations of these parameters and root damage decreased with the increase of boron supply. These results demonstrated that B supplementation lowered Cu uptake and its concentrations in leaves, stems and roots and subsequently alleviated Cu-toxicity-induced damage to root growth and function, thus improving plant nutrient (decreased Cu uptake and efficient maintenance of the other nutrient homeostasis and balance) and water status. Further analysis indicated that the improved nutrition and water status contributed to the boron-mediated amelioration of Cu-toxicity-induced inhibition of seedlings, decline of leaf pigments, large reduction of leaf CO 2 assimilation and impairment of leaf photosynthetic electron transport chain revealed by greatly altered chlorophyll a fluorescence (OJIP) transients, reduced maximum quantum yield of primary photochemistry (F v /F m), quantum yield for electron transport (ET o /ABS) and total performance index (PI abs,total), and elevated dissipated energy per reaction center (DI o /RC). To conclude, our findings corroborate the hypothesis that B-mediated amelioration of Cu-toxicity involved reduced damage to roots and improved nutrient and water status. Principal component analysis showed that Cu-toxicity-induced changes of above physiological parameters generally decreased with the increase of B supply and that B supply-induced alterations of above physiological parameters was greater in 350 μM Cu-treated than in 0.5 μM Cu-treated seedlings. B and Cu had a significant interactive influence on C. sinensis seedlings. • B supply lowered Cu uptake and Cu level in C. sinensis leaves, stems and roots. • Cu-toxicity-induced root damage decreased with the increase of B supply. • B supply improved nutrition and water status of Cu-toxic seedlings. • B and Cu had a significant and interactive influence on C. sinensis seedlings. [ABSTRACT FROM AUTHOR]

Limited data are available on metabolic responses of plants to copper (Cu)-toxicity. Firstly, we investigated Cu-toxic effects on metabolomics, the levels of free amino acids, NH 4 +-N, NO 3 --N, total nitrogen, total soluble proteins, total phenolics, lignin, reduced glutathione (GSH) and malondialdehyde, and the activities of nitrogen-assimilatory enzymes in 'Shatian' pummelo (Citrus grandis) leaves. Then, a conjoint analysis of metabolomics, physiology and transcriptomics was performed. Herein, 59 upregulated [30 primary metabolites (PMs) and 29 secondary metabolites (SMs)] and 52 downregulated (31 PMs and 21 SMs) metabolites were identified in Cu-toxic leaves. The toxicity of Cu to leaves was related to the Cu-induced accumulation of NH 4 + and decrease of nitrogen assimilation. Metabolomics combined with physiology and transcriptomics revealed some adaptive responses of C. grandis leaves to Cu-toxicity, including (a) enhancing tryptophan metabolism and the levels of some amino acids and derivatives (tryptophan, phenylalanine, 5-hydroxy- l -tryptophan, 5-oxoproline and GSH); (b) increasing the accumulation of carbohydrates and alcohols and upregulating tricarboxylic acid cycle and the levels of some organic acids and derivatives (chlorogenic acid, quinic acid, d -tartaric acid and gallic acid o -hexoside); (c) reducing phospholipid (lysophosphatidylcholine and lysophosphatidylethanolamine) levels, increasing non-phosphate containing lipid [monoacylglycerol ester (acyl 18:2) isomer 1] levels, and inducing low-phosphate-responsive gene expression; and (d) triggering the biosynthesis of some chelators (total phenolics, lignin, l -trytamine, indole, eriodictyol C-hexoside, quercetin 5-O-malonylhexosyl-hexoside, N-caffeoyl agmatine, N′-p-coumaroyl agmatine, hydroxy-methoxycinnamate and protocatechuic acid o -glucoside) and vitamins and derivatives (nicotinic acid-hexoside, B 1 and methyl nicotinate). Cu-induced upregulation of many antioxidants could not protect Cu-toxic leaves from oxidative damage. To conclude, our findings corroborated the hypothesis that extensive reprogramming of metabolites was carried out in Cu-toxic C. grandis leaves in order to cope with Cu-toxicity. [Display omitted] • Citrus leaves underwent extensive metabolic reprograming under Cu-toxicity. • Cu impaired N assimilation in leaves, thus lowering Cu-tolerance. • Cu increased carbohydrates and alcohols levels and upregulated TCA cycle in leaves. • Cu triggered the biosynthesis of some chelators, vitamins and derivatives in leaves. • MDA accumulated in Cu-toxic leaves despite increased levels of some antioxidants. [ABSTRACT FROM AUTHOR]

Waste classification is regarded as one of the most important strategies for waste management, and its success depends on the active participation of the public. Based on the theory of planned behavior (TPB) and attitude-behavior-condition (A-B-C) theory, this research investigated the key factors affecting residents' domestic waste classification intention (WCI) and waste classification behavior (WCB), and explored the moderating effects of three external factors including infrastructure (INF), government publicity (GP), and incentive measures (IM) on the intention-behavior relationship. The valid data were collected from 584 residents via conducting a face-to-face interview in Chengdu, a pilot city of waste classification in China, and analyzed by using the structural equation model (SEM). Results showed that residents' WCI and WCB had a significant discrepancy with the average values of 4.07 and 2.81, respectively. Attitude (AT), perceived behavior control (PBC) and classification knowledge (CK) were significantly related to residents' WCI, with AT (β = 0.65, P < 0.001) having the greatest direct impact. Meanwhile, CK and INF had a stronger impact on the WCB than WCI. GP indirectly affected WCB through the intermediary effect of CK. In addition, INF and GP had a positively moderating effect on residents' waste classification intention-behavior relationship and can facilitate the intention-behavior conversion. By contrast, IM failed to promote the conversion of residents' classification intention into behavior, and had no direct significant influence on residents' WCB. Finally, some relevant policy suggestions were put forward for the new pilot cities of waste classification in China. • Key factors affecting residents' WCI and WCB were investigated. • Moderating effects of external factors on intention-behavior relation was explored. • Attitude had the greatest direct influence on residents' WCI. • CK and Infrastructure had a stronger impact on WCB than WCI. • Infrastructure and GP can strengthen the intention-behavior conversion. [ABSTRACT FROM AUTHOR]