Lignification of developing maize ( Zea mays L.) endosperm transfer cells and starchy endosperm cells

Glutaraldehyde possesses unique characteristics that render it one of the most effective protein crosslinking reagents. It can be present in at least 13 different forms depending on solution conditions such as pH, concentration, temperature, etc. Substantial literature is found concerning the use of glutaraldehyde for protein immobilization, yet there is no agreement about the main reactive species that participates in the crosslinking process because monomeric and polymeric forms are in equilibrium. Glutaraldehyde may react with proteins by several means such as aldol condensation or Michael-type addition, and we show here 8 different reactions for various aqueous forms of this reagent. As a result of these discrepancies and the unique characteristics of each enzyme, crosslinking procedures using glutaraldehyde are largely developed through empirical observation. The choice of the enzyme-glutaraldehyde ratio, as well as their final concentration, is critical because insolubilization of the enzyme must result in minimal distortion of its structure in order to retain catalytic activity. The purpose of this paper is to give an overview of glutaraldehyde as a crosslinking reagent by describing its structure and chemical properties in aqueous solution in an attempt to explain its high reactivity toward proteins, particularly as applied to the production of insoluble enzymes.

The incompatible pathosystem between resistant cotton (Gossypium barbadense cv. 7124) and Verticillium dahliae strain V991 was used to study the cotton transcriptome changes after pathogen inoculation by RNA-Seq. Of 32 774 genes detected by mapping the tags to assembly cotton contigs, 3442 defence-responsive genes were identified. Gene cluster analyses and functional assignments of differentially expressed genes indicated a significant transcriptional complexity. Quantitative real-time PCR (qPCR) was performed on selected genes with different expression levels and functional assignments to demonstrate the utility of RNA-Seq for gene expression profiles during the cotton defence response. Detailed elucidation of responses of leucine-rich repeat receptor-like kinases (LRR-RLKs), phytohormone signalling-related genes, and transcription factors described the interplay of signals that allowed the plant to fine-tune defence responses. On the basis of global gene regulation of phenylpropanoid metabolism-related genes, phenylpropanoid metabolism was deduced to be involved in the cotton defence response. A closer look at the expression of these genes, enzyme activity, and lignin levels revealed differences between resistant and susceptible cotton plants. Both types of plants showed an increased level of expression of lignin synthesis-related genes and increased phenylalanine-ammonia lyase (PAL) and peroxidase (POD) enzyme activity after inoculation with V. dahliae, but the increase was greater and faster in the resistant line. Histochemical analysis of lignin revealed that the resistant cotton not only retains its vascular structure, but also accumulates high levels of lignin. Furthermore, quantitative analysis demonstrated increased lignification and cross-linking of lignin in resistant cotton stems. Overall, a critical role for lignin was believed to contribute to the resistance of cotton to disease.

This review discuses the ultrastructural aspects of cell wall lignification and lignin topochemistry. Lignification results from the enzyme mediated polymerization of monolignols initiated by unknown factors (initiation sites) located at the corners of cells and in the middle lamella. Lignification results in the filling of pores within the carbohydrate matrix following a sequence from the outer regions of the wall towards the lumen. The amount and chemical characteristics of lignin vary across the cell wall, with the presence of reaction wood, and among cell types.