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The effects of increasing concentrations of lead (Pb) on malondialdehyde (MDA) content, soluble protein, Pb accumulation, nutrients, polyamines (PAs) and proline metabolism were investigated in sterilized seedlings of Potamogeton crispus L. after 5 d exposure. Significant oxidative stress was not caused, indicated by a little induction of MDA content and soluble proteins. Pb accumulation increased in a concentration-dependent manner and most of Pb was stored in the cell wall. Total P, Mg, Na and Zn rose and total Fe fell; total Ca increased at 25 μM Pb but then declined. The nutrients in cell wall fraction changed in the same pattern as total nutrients, whereas those in soluble and organelle fraction declined. Total putrescine (Put) decreased markedly, while total spermidine (Spd), spermine (Spm) and (Spd + Spm)/Put ratio increased progressively but then declined. The trends for free, perchloric acid soluble conjugated (PS-conjugated) and perchloric acid insoluble bound (PIS-bound) PAs were similar to those on total PAs, except that PIS-bound Spm increased significantly. Arginine decarboxylase (ADC) and ornithine decarboxylase (ODC) activities rose gradually, while diamine oxidase (DAO) initially increased but then declined. Proline content increased initially only to decline later, due to the increase of r -glutamyl kinase (GK) activity. Meanwhile, ornithine-d-aminotransferase (OAT) activity gradually reduced, while no significant change was observed in proline dehydrogenase (PDH) activity. Our results indicated that the tolerance of P . crispus to Pb stress was based on cell wall compartmentalization combined with increase of nutrients, alterations of PAs, and induction of proline. [ABSTRACT FROM AUTHOR]

The plastidic thioredoxin F-type (TrxF) protein plays an important role in plant carbohydrate metabolism and starch biosynthesis. In this work, a TrxF gene from maize, named ZmTrxF , was isolated and transformed into Arabidopsis . Constitutive expression of ZmTrxF significantly increased starch accumulation in transgenic plants. Real-time quantitative PCR (qRT-PCR) analyses showed that the transcript levels of starch biosynthetic genes, including those encoding sucrose synthase ( AtSUS ), phosphoglucomutase ( AtPGM ), ADP-glucose pyrophosphorylase ( AtAGPase-S1 , AtAGPase-S2 , AtAGPase-L1 and AtAGPase-L2 ), granule-bound starch synthase ( AtGBSS I and AtGBSS II ), soluble starch synthase ( AtSSS I , AtSSS II , AtSSS III and AtSSS IV ) and starch branching enzyme ( AtSBE I and AtSBE II ), were increased in transgenic plants. In contrast, there was no signifcant difference in the expression levels of α-amylase ( AtAMY3 ) and β-amylase ( AtBAM1 , AtBAM3 and AtBAM4 ) genes. Meanwhile, the activity of the major enzymes such as AGPase, GBSS, SSS and SBE involved in starch biosynthesis was higher in transgenic plants compared to that in the wild-type (WT). Furthermore, soluble sugar content was also increased in transgenic plants. All these results suggest that ZmTrxF could be used as a candidate gene for developing high starch-accumulating plants as alternative energy crops. [ABSTRACT FROM AUTHOR]

Ion homeostasis is maintained in plant cells by specialized transporters. However, functional studies on Mn transporters in apple trees have not been reported. MdMTP11.1 , which encodes a putative Mn-MTP transporter in Malus domestica , was expressed highly in leaves and induced by Mn stress. Subcellular localization analysis of the MdMTP11.1 -GFP fusion protein indicated that MdMTP11.1 was targeted to the Golgi. Meanwhile, overexpression of MdMTP11.1 in Arabidopsis thaliana conferred increased resistance to plants under toxic Mn levels, as evidenced by increased biomass of whole plant and length of primary root. Analysis of Mn bioaccumulation indicated that overexpression of MdMTP11.1 effectively reduced the content of Mn in every subcellular component and chemical forms when the plants were subjected with Mn stress. The majority of Mn of action were bound to cell wall and combined with un-dissolved phosphate. Besides, contents of malondialdehyde (MDA), proline and hydrogen peroxide (H 2 O 2) were significantly lower, while content of chlorophyll and activities of CAT, SOD, POD and APX were significantly higher in MdMTP11.1 -over-expressing plants compared with that in wild type plants under Mn stress. Taken together, these results suggest that MdMTP11.1 is a Mn specific transporter localized to the Golgi can maintain the phenotype, reduce the Mn accumulation and alleviate damage of oxidative stress, conferring the positive role of Mn tolerance. • MdMTP11.1 was induced by Mn stress and located in Golgi. • MdMTP11.1 enhanced plant phenotype under Mn stress. • MdMTP11.1 modified the subcellular distribution and chemical forms of Mn, thus reducing Mn bioaccumulation. • MdMTP11.1 alleviates oxidative stress damage induced by Mn stress. [ABSTRACT FROM AUTHOR]

Manganese (Mn) toxicity in soil is a widely observed phenomenon, which seriously restricts growth, quality, and yield of various crops and fruits including apples. However, mechanisms underlying the regulation of polyamines (PAs) by brassinosteroids (BRs) to improve tolerance to Mn stress are still unclear. In this study, we investigated the effects of 2,4-epibrassinolide (EBL; a BR) on the expression of genes involved in BR signaling pathway, Mn accumulation, PAs-mediated responses (PA precursor levels, metabolic enzymes, and genes), and growth parameters in Mn-stressed Malus robusta Rehd. EBL application significantly modulated the expressions of genes related to BR signaling (MdBRI , MdBSK , etc.) and reduced Mn accumulation, along with improving the rate of increase in root length and plant height, relative water content, chlorophyll content, maximum photochemical efficiency of PSII (Fv/Fm), and actual photochemical efficiency (Φ PSII) and decreasing electrical conductivity. Furthermore, EBL application significantly reduced putrescine (Put) accumulation and increased spermine (Spm) content and (Spd + Spm)/Put ratio. EBL weakened ornithine (Orn) pathway, decreased ornithine decarboxylase (ODC) activity, and increased biosynthesis of Spm from Put via elevating the PA oxidase (PAO) activity and expression of MdSPDS , MdSPMS , and MdPAO. The trends for free, PS-conjugated, and PIS-bound PAs were similar to that of total PAs, except that no significant change was observed in free Spm, PS-conjugated Spd, and Spm, as well as PIS-bound Spd. This study revealed that BR-regulated PAs help in mitigating Mn toxicity and clarified the mechanisms of regulation of PAs by BRs in apple trees. • EBL application significantly activated the expressions of genes related to BR signaling. • Mn accumulation was significantly reduced after EBL application. • EBL application improved growth parameters and physiological indexes in M. robusta under Mn toxicity. • The strategy to overcome Mn stress was highly associated with the stimulation of PAs profile by BRs. • The mechanism of regulation of PAs by BRs against Mn stress was provided. [ABSTRACT FROM AUTHOR]

The growth and production of fruit trees are adversely affected by heavy metal pollution in orchard lands. Plant metal homeostasis and resistance are regulated by metal tolerance proteins (MTP), which function as divalent cation transporters. To understand the possible role of MTPs in fruit trees, we identified 20 MdMTPs in the apple genome. Phylogenetic and collinear relationship analyses revealed that they belonged to Zn-MTP, Fe/Zn-MTP and Mn-MTP subfamilies, and have gone through two tandem and six segmental duplication events under purifying selection. All MdMTPs were predicted to form homodimer, with each monocase containing a conserved cation efflux domain (CED), the typical structural feature of MTP family, and one or two HXXXD or DXXXD residues. Further spatiotemporal expression analyses indicated that all MdMTP genes were ubiquitously expressed, and most of them were induced by at least three heavy metal ions, in roots, stems or leaves. Yeast and Arabidopsis mutant complementation experiments verified the function of MdMTP11.1 in response to heavy metal stress. Our findings provide an important genetic foundation for the functional elucidation of MdMTP genes, which can be used as the potential gene candidates for the breeding of new fruit tree cultivars with improved tolerance to heavy metal stress. • A total number of 20 metal tolerance protein (MTP) genes were identified in apple. • All MdMTP proteins contained a cation efflux domain to work for metal ion efflux. • Tandem and segmental duplication events occurred in MdMTPs under purifying selection. • Most of MdMTPs were induced by at least three heavy metal ions in various organs. [ABSTRACT FROM AUTHOR]