Graft copolymers with a large number of side chains chemically attached onto a linear backbone are endowed with unusual properties thanks to their confined and compact structures, including wormlike conformation, compact molecular dimensions and notable chain end effects. Growing attention has been paid to these interesting macromolecules due to their importance in understanding the correlation between architectures and properties, as well as their potential applications. To date, the synthesis and properties of graft copolymers in both solution and bulk have been extensively investigated, along with their applications. In this tutorial review, recent advances in synthetic approaches towards the construction of well-defined graft copolymers are discussed in detail and applications of these interesting macromolecules are highlighted by selected examples.

A series of well-defined asymmetric centipede-like copolymers, containing polyacrylate backbone, hydrophilic poly(ethylene glycol), and hydrophobic polystyrene side chains, was synthesized by successive atom transfer radical polymerization. The grafting-through strategy was first employed for the preparation of poly-[poly(ethylene glycol) methyl ether acrylate] comb copolymer. The grafting-from route was used following for the synthesis of the final amphiphilic centipede-like copolymer, poly[poly(ethylene glycol) methyl ether acrylate]g-polystyrene. At each grafting point, two different chains are connected and the spacing between the grafting points is constant. Polystyrene side chains were connected to the polyacrylate backbone through stable C-C bonds instead of ester connections. The molecular weights of both the backbone and the side chains were controllable. The molecular weight distributions were in the range of 1.24-1.38. The critical micelle concentrations of these amphiphilic centipede-like graft copolymers in water were determined by fluorescence probe technique. The morphologies of the micelles formed from these centipede-like graft copolymers were preliminarily explored by TEM and were found to be spheres.

Salicylic acid (SA) is a potent signaling molecule in plants and is involved in eliciting specific responses to biotic and abiotic stresses. The aim of this study is to investigate whether the exogenous application of SA can improve cadmium (Cd) induced inhibition of photosynthesis in castor bean (Ricinus communis L.) plants. The effects of SA and Cd on plant growth, spectral reflectance, pigment contents, chlorophyll fluorescence and gas exchange were examined in a hydroponic cultivation system. Results indicate that Cd exposure significantly decreased the dry biomass, photosynthetic rate (P n ), stomatal conductance (G s ), intercellular CO 2 concentration (C i ), pigment contents, quantum yield of PS II photochemistry (F v /F m ), and effective quantum yield of PS II (ΦPS II) in the plants. Pretreatment with SA alone reduced the biomass and P n in castor bean plants, whereas pigment contents, F v /F m and ΦPS II remained unaffected. Reduced G s , C i and E, as well as increased stomatal limitation (L s ) and water use efficiency (WUE), were observed in plants pretreated with 500 μM SA alone, whereas plants treated with 250 μM SA were unaffected. Under Cd stress, SA pretreatment led to a significant decrease in P n , G s , E, C i , and chlorophyll contents (Chl a, Chl b, Chl a+b, Car, Chl a/b), and an increase in L s and WUE. Cd exposure enhanced spectral reflectance in the range 550-680 nm and 750-1,050 nm. It also decreased the normalized difference vegetation index ( chl NDI), the modified red edge simple ratio index (mSR 705 ), the red edge position (REP), water band index, and red/ green ratio, whereas the structure independent pigment index (SIPI) was increased. Significant correlations (P<0.01) between spectral indices (mSR 705 , chl NDI, REP, red/green ratio) and pigment contents. SA significantly worsened plant growth and photosynthesis in Cd-stressed castor bean plants, in which a stomatal limitation was involved. The leaf spectral reflectance is a sensitive indicator in determining Cd toxicity in plants.

We report a transcriptome assembly and expression profiles from RNA-Seq data and identify genes responsible for culm gall formation in Zizania latifolia induced by Ustilago esculenta. The smut fungus Ustilago esculenta can induce culm gall in Zizania latifolia, which is used as a vegetable in Asian countries. However, the underlying molecular mechanism of culm gall formation is still unclear. To characterize the processes underlying this host-fungus association, we performed transcriptomic and expression profiling analyses of culms from Z. latifolia infected by the fungus U. esculenta. Transcriptomic analysis detected U. esculenta induced differential expression of 19,033 and 17,669 genes in Jiaobai (JB) and Huijiao (HJ) type of gall, respectively. Additionally, to detect the potential gall inducing genes, expression profiles of infected culms collected at -7, 1 and 10 DAS of culm gall development were  analyzed. Compared to control, we detected 8089 genes (4389 up-regulated, 3700 down-regulated) and 5251 genes (3121 up-regulated, 2130 down-regulated) were differentially expressed in JB and HJ, respectively. And we identified 376 host and 187 fungal candidate genes that showed stage-specific expression pattern, which are  possibly responsible for gall formation at the initial and later phases, respectively. Our results indicated that cytokinins play more prominent roles in regulating gall formation than do auxins. Together, our work provides general implications for the understanding of gene regulatory networks for culm gall development in Z. latifolia, and potential targets for genetic manipulation to improve the future yield   of  this crop.

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Self-assembly behavior of a double-bond-based amphiphilic graft copolymer consisting of hydrophobic polyallene backbone and hydrophilic poly(ethylene glycol) side chains in tetrahydrofuran (THF)/water was investigated. Polyallene backbone was first prepared via living coordination polymerization of 6-methyl-1,2-heptadien-4-ol (MHDO) initiated by [(η 3 -allyl)NiOCOCF 3 ] 2 . The targeted amphiphilic graft copolymer with relative narrow molecular weight distribution (M w /M n = 1.22) was synthesized by the coupling reaction between the pendant hydroxyls of the backbone and acyl chloride end group of poly (ethylene glycol) via the grafting-onto approach. The critical micelle concentration (cmc) was determined by the fluorescence probe technique. Micelle morphologies could be well tuned by water content, initial copolymer content, and ion strength. In particular, this kind of achiral copolymer could aggregate to form chiral helical nanostructures under given conditions.

A novel amphiphilic graft copolymer consisting of hydrophilic poly(acrylic acid) backbones and hydrophobic poly(butyl methacrylate) side chains was synthesized by successive atom transfer radical polymerization followed by hydrolysis of poly‐(methoxymethyl acrylate) backbone. A grafting‐from strategy was employed for the synthesis of graft copolymers with narrow molecular weight distributions (polydispersity index < 1.40). Hydrophobic side chains were connected to the backbone through stable CC bonds instead of ester connections. Poly(methoxymethyl acrylate) backbone was easily hydrolyzed to poly(acrylic acid) backbone with HCl without affecting the hydrophobic side chains. The amphiphilic graft copolymer could form stable micelles in water. The critical micelle concentration in water was determined by a fluorescence probe technique. The morphology of the micelles was preliminarily explored with transmission electron microscopy and was found to be spheres. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6857–6868, 2006

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