Effects of boron toxicity on root and leaf anatomy in two Citrus species differing in boron tolerance

Key message

Typical toxic symptom only occurred in B-toxic C. grandis leaves. B-toxicity induced PCD of C. grandis leaf phloem tissue. The lower leaf free B might contribute to the higher B-tolerance of C. sinensis.

Abstract

Seedlings of ‘Xuegan’ (Citrus sinensis) and ‘Sour pummelo’ (Citrus grandis) differing in boron (B)-tolerance were irrigated with nutrient solution containing 10 (control) or 400 (B-toxic) μM H₃BO₃ for 15 weeks. Thereafter, the effects of B-toxicity on leaf photosynthesis, chlorophyll, plant B absorption and distribution, root and leaf anatomy were investigated to elucidate the possible B-tolerant mechanisms of Citrus plants. Typical toxic symptom only occurred in B-toxic C. grandis leaves. Similarly, B-toxicity only affected C. grandis photosynthesis and chlorophyll. Although total B concentration in B-toxic roots and leaves was similar between the two species, leaves from B-toxic C. grandis plant middle had higher free B and lower bound B as compared with those from C. sinensis. Effects of B-toxicity on leaf structure were mainly limited to the mesophyll cells and the phloem of leaf veins. Although irregular cell wall thickening was observed in leaf cortex cells and phloem tissue of B-toxic C. grandis and C. sinensis leaves, exocytosis only occurred in the companion cells and the parenchyma cells of B-toxic C. sinensis leaf phloem. Also, B-toxicity induced cell death of phloem tissue through autophagy in C. grandis leaf veins. B-toxicity caused death of root epidermal cells of the two Citrus species. B-toxicity restrained degradation of middle lamella, but did not alter ultrastructure of Golgi apparatus and mitochondria in root elongating zone cells. In conclusion, C. sinensis was more tolerant to B-toxicity than C. grandis. The lower leaf free B and higher bound B might contribute to the higher B-tolerance of C. sinensis.     

Proteomic profile of <Emphasis Type="Italic">Citrus grandis</Emphasis> roots under long-term boron-deficiency revealed by iTRAQ

Key message

Eighty-six differentially abundant proteins were identified in Citrus grandis roots in response to boron-deficiency using the iTRAQ technique and possible mechanism underlying boron-deficiency tolerance of citrus plants was identified.

Abstract

Boron (B) is an essential element for plant growth and development and adequate B supply is an important determinant of good quality and high yield of crops. B-deficiency is a worldwide problem in agricultural production including citrus. However, little is known about the molecular mechanism of plant tolerance to B-deficiency. Using the iTRAQ technique, 86 differentially abundant proteins were identified from B-deficient Citrus grandis roots. The adaptive strategy of C. grandis roots under B-deficiency was summarized as follows: (1) enhancement of alternative splicing of mRNA and DNA methylation; (2) up-regulation of post-translation modification (PTM) and turnover of proteins; (3) reinforcement of cellular transport; (4) enhancement of antioxidant system and signal transduction. In general, these results increase our understanding of molecular mechanisms underlining the resistance of citrus plant under B-deficiency. Further studies should focus on how do roots perceive B deficiency in the rhizosphere and which pathway or proteins react to this adverse condition in the first place and then stimulates the downstream responses in Citrus plants.

     

New taxa in Pectis (Compositae: Pectidinae) from Mexico and the southwestern United States

Pectis minutiflora,P. papposa var.grandis, andP. purpurea var.sonorae are described as new. A new combination,P. purpurea var.lancifolia also is included. Chromosome counts (n = 12) are reported forP. papposa var.grandis andP. purpurea var.sonorae.     

Salicylic acid induces physiological and biochemical changes in Torreya grandis cv. Merrillii seedlings under drought stress

Key message

SA treatment effectively ameliorated the negative effect of moderate drought stress on T. grandis Seedlings through increasing the water content, Pn, proline content, antioxidant enzymes activity and reducing MDA.

Abstract

Water availability is one of the most critical factors that limits the growth and development of plants. Salicylic acid (SA) is an important signal molecule that modulates plant responses to abiotic stress. To elucidate the regulating mechanism of exogenous SA on Torreya grandis cv. Merrillii under different water stresses, a pot experiment was conducted in a greenhouse. Exposure of T. grandis seedlings to drought conditions resulted in reduced growth rate that was associated with a decline in water content and CO₂ assimilation. Foliar application of SA effectively increased the water content, net CO₂ assimilation rate, proline content and antioxidant enzymes activity in the plants, which helped T. grandis to acclimate to moderate drought stress and increase the shoot dry matter. However, when the plants were under severe drought stress, the relative water content and CO₂ assimilation in the SA-treated plants were significantly lower than those in the control plants. Therefore, our results indicated that SA can effectively ameliorate the negative effect of moderate drought stress on T. grandis seedling growth.     

Rubiacearum Americanarum Magna Hama Pars XXXII. New Species and a New Combination in Coussarea (Coussareeae) from Western South America

The Neotropical genus Coussarea is species-rich and widely distributed but not well known. Seven new species are described here, documented mainly by recent botanical exploration: C. acrensis is found in western Brazil, C. boliviensis and C. mexiae in the mountains of northwestern Bolivia, and C. camposiana, C. maranonensis, C. pseudopilosula, and C. vasqueziana in Peru. The new combination C. insolita is based on Rudgea insolita from Colombia.     

Overexpression of Camellia sinensis H1 histone gene confers abiotic stress tolerance in transgenic tobacco

Key message

Overexpression of CsHis in tobacco promoted chromatin condensation, but did not affect the phenotype. It also conferred tolerance to low-temperature, high-salinity, ABA, drought and oxidative stress in transgenic tobacco.

Abstract

H1 histone, as a major structural protein of higher-order chromatin, is associated with stress responses in plants. Here, we describe the functions of the Camellia sinensis H1 Histone gene (CsHis) to illustrate its roles in plant responses to stresses. Subcellular localization and prokaryotic expression assays showed that the CsHis protein is localized in the nucleus, and its molecular size is approximately 22.5 kD. The expression levels of CsHis in C. sinensis leaves under various conditions were investigated by qRT-PCR, and the results indicated that CsHis was strongly induced by various abiotic stresses such as low-temperature, high-salinity, ABA, drought and oxidative stress. Overexpression of CsHis in tobacco (Nicotiana tabacum) promoted chromatin condensation, while there were almost no changes in the growth and development of transgenic tobacco plants. Phylogenetic analysis showed that CsHis belongs to the H1C and H1D variants of H1 histones, which are stress-induced variants and not the key variants required for growth and development. Stress tolerance analysis indicated that the transgenic tobacco plants exhibited higher tolerance than the WT plants upon exposure to various abiotic stresses; the transgenic plants displayed reduced wilting and senescence and exhibited greater net photosynthetic rate (Pn), stomatal conductance (Gs) and maximal photochemical efficiency (Fv/Fm) values. All the above results suggest that CsHis is a stress-induced gene and that its overexpression improves the tolerance to various abiotic stresses in the transgenic tobacco plants, possibly through the maintenance of photosynthetic efficiency.     

Influence of carbohydrate source on xanthone content in root cultures of Gentiana dinarica Beck

The effects of different types and concentrations of sugars on root growth and xanthone production in root culture of Gentiana dinarica were investigated. The results showed that sucrose, glucose and fructose all supported root growth, and sucrose was superior in terms of growth index, dry mass and fresh/dry mass ratio then fructose or glucose at the same concentrations. However, considering equimolar concentration of sugars, their contribution to the root growth was similar. The HPLC analysis of roots indicated the presence of xanthone compounds, and the contents of norswertianin-1-O-primeveroside (1), norswertianin-1-O-glucoside (2), gentioside (3) and norswertianin (4) were evaluated. In all samples, norswertianin-1-O-primeveroside (1) was present in highest concentration, followed by norswertianin-1-O-glucoside (2), whereas gentioside (3) and norswertianin (4) were present in lower amounts. The production of xanthones was affected by both type and concentration of sugar. In general, roots growing in media supplemented with sucrose contained higher levels of xanthones. The amounts of xanthone primeveroses (1) and (3) increased with the increase of concentrations of all types of sugars, whereas higher sugar concentrations resulted in reduction of the contents of norswertianin-1-O-glucoside (2) and aglycone norswertianin (4). The roots were also evaluated regarding the content of total phenolics and higher accumulation of total phenolic compounds was observed in roots grown in fructose-containing medium. Antioxidant activity was determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay, and high correlation between total phenolic content and antiradical activity was observed (r = ?0.83).     

A new subspecies and new combinations in Comarostaphylis (Ericaceae)

Comarostaphylis spinulosa subsp.glandulifera is described from the mountains of Oaxaca and Puebla, Mexico. Four new combinations inComarostaphylis are also made:C. arbutoides subsp.costaricensis, C. discolor subsp.rupestris, C. polifolia subsp.minor, andC. spinulosa.Arctostaphylos glabrata, A. rupestris, andA. spinulosa are lectotypified and the status ofC. polifolia is discussed.     

A new name and new combinations in Campomanesia and Pimenta (Myrtaceae)

One new name is proposed and eleven new combinations are made inCampomanesia andPimenta. Lectotypes are selected forC. eugenioides var.desertorum, C. phaea, andP. racemosa var.hispaniolensis, var.ouza, and var.terebinthina.     

Combination of 1,4-naphthoquinone with benzothiazoles had selective algicidal effects against harmful algae

A series of naphthoquinone-benzothiazole conjugates were synthesized as algicides, and their efficacies against harmful algal blooming species, such as Chattonella marina, Heterosigma akashiwo and Cochlodinium polykrikoides, were examined. The introduction of substituted benzothiazole at the C2 position of 1,4-naphthoquinone (compounds 1–9) resulted in higher algicidal activity against C. polykrikoides than the C6 conjugates (compounds 10–20). On the other hand, of the C6 conjugates, compounds 11 and 12 exhibited better algicidal activity against H. akashiwo, C. marina, and C. polykrikoides than the C2 conjugates. Further structure-activity analysis indicated that a replacement of the methoxy groups with hydroxyl groups (compounds 21–26) decreased the algicidal activity significantly. Among the various synthetic naphthoquinonebezothiazole conjugates tested, compound 12 was found to affect the most significant decrease in the level of C. polykrikoides growth, with an IC₅₀ of 0.19 μM. Compound 11 was found to be the most potent inhibitor against H. akashiwo and C. polykrikoides, with IC₅₀ values of 0.32 and 0.12 μM, respectively. Overall, these results highlight a possible method for controlling and inhibiting red tide forming algae using NQ derivatives.     

New combinations in Hawaiian Chamaesyce (Euphorbiaceae)

Chamaesyce is accepted at the genus level for the Hawaiian taxa. The following new combinations are made:C. celastroides var.laehiensis, C. celastroides var.tomentella, C. rockii var.grandifolia, C. skottsbergii var.vaccinioides, andC. sparsiflora.     

Cytotoxic metabolites from the cultures of endophytic fungi from Panax ginseng

Two strains of endophytic fungi, Penicillium melinii Yuan-25 and Penicillium janthinellum Yuan-27, with strong anti-Pyricularia oryzae activity, were obtained from the roots of Panax ginseng. Based on bioactivity-oriented isolation, a new benzaldehyde derivative, ginsenocin (1), together with six known compounds, methyl 2,4-dihydroxy-3,5,6-trimethylbenzoate (2), 3,4,5-trimethyl-1,2-benzenediol (3), penicillic acid (4), mannitol (5), ergosterol (6), and ergosterol peroxide (7), were separated from the EtOAc extract of Yuan-25 culture, while brefeldin A (8) was isolated as the major constituent from the EtOAc extract of Yuan-27 culture. The chemical structures were determined based on spectroscopic methods. All the isolated compounds 1–8 were evaluated for their cytotoxicity against six human cancer cell lines. Brefeldin A (8) was the most cytotoxic constituent against all the tested cell lines with IC₅₀ values <0.12 μg/ml, while ginsenocin (1) and penicillic acid (4) also exhibited potent cytotoxicity with IC₅₀ values ranging from 0.49 to 7.46 μg/ml. Our results suggest that endophytic fungi isolated from P. ginseng are a promising natural source of potential anticancer agents.