The impact of Covid-19 on education equity: A view from Barbados and Jamaica.

The outbreak of Covid-19 worldwide has presented an unprecedented challenge for the equity-in-education agenda, especially in developing countries of the Global South (e.g., the English-speaking Caribbean). This article examines the impact school closures have had in Jamaica and Barbados, and highlights the emerging disparities the global pandemic has had on education. The central organizing questions are as follows: Who was affected by school closures in Barbados and Jamaica? How did the Ministries of Education (MOEs) support curriculum and instruction during the pandemic? What challenges does Covid-19 present for MOEs? What are the implications for education after Covid-19? School closure data suggest a gender disparity, with more males than females out of school due to Covid-19 from preprimary to secondary school in Barbados and Jamaica. MOEs in the region responded to school closures primarily by increasing access to technology to facilitate remote learning. Some of the challenges with continuing education for students during Covid-19 were due to a lack of infrastructure and amenities to support remote learning. Implications for education post-Covid-19 are considered.

Differential expression of cell-wall-related genes during the formation of tracheary elements in the Zinnia mesophyll cell system.

Plants, animals and some fungi undergo processes of cell specialization such that specific groups of cells are adapted to carry out particular functions. One of the more remarkable examples of cellular development in higher plants is the formation of water-conducting cells that are capable of supporting a column of water from the roots to tens of metres in the air for some trees. The Zinnia mesophyll cell system is a remarkable tool with which to study this entire developmental pathway in vitro. We have recently applied an RNA fingerprinting technology, to allow the detection of DNA fragments derived from RNA using cDNA synthesis and subsequent PCR-amplified fragment length polymorphisms (cDNA-AFLP), to systematically characterize hundreds of the genes involved in the process of tracheary element formation. Building hoops of secondary wall material is the key structural event in forming functional tracheary elements and we have identified over 50 partial sequences related to cell walls out of 600 differentially expressed cDNA fragments. The Zinnia system is an engine of gene discovery which is allowing us to identify and characterize candidate genes involved in cell wall biosynthesis and assembly.

Approaches to understanding the functional architecture of the plant cell wall.

Cell wall polysaccharides are some of the most complex biopolymers known, and yet their functions remain largely mysterious. Advances in imaging methods permit direct visualisation of the molecular architecture of cell walls and the modifications that occur to polymers during growth and development. To address the structural and functional relationships of individual cell wall components, we need to better characterise a broad range of structural and architectural alterations in cell walls, appearing as a consequence of developmental regulation, environmental adaptation or genetic modification. We have developed a rapid method to screen large numbers of plants for a broad range of cell wall phenotypes using Fourier transform infrared microspectroscopy and Principal Component Analysis. We are using model systems to uncover the genes that encode some of the cell-wall-related biosynthetic and hydrolytic enzymes, and structural proteins.

A pectate lyase from Zinnia elegans is auxin inducible.

The Zinnia mesophyll cell system consists of isolated leaf mesophyll cells in culture that can be induced, by auxin and cytokinin, to reproducibly trans-differentiate into tracheary elements (TE) after 96 h, while in the presence of auxin alone the cells simply elongate. In a search for genes involved in modifications to cell-wall architecture before any overt signs of cell differentiation, a differential hybridization of a 72-h cDNA library with probes from mRNA at time-points of 24 h and 72 h was done revealing a number of transcripts up-regulated between these times. One of these cDNAs shows homology to pectate lyase, a pectin-degrading enzyme. The complete cDNA sequence (ZePel) corresponds to a translated protein of 44 kDa with an N-terminal signal peptide of about 2 kDa, and one potential N-glycosylation site. Northern analysis confirms that the strong expression of this gene during TE induction occurs at a very early stage of the process and is due solely to the presence of auxin in the induction medium. In situ hybridization studies in young Zinnia stems show that ZePel expression is associated with vascular bundles and shoot primordia. Recombinant protein made in Escherichia coli possesses calcium-dependent pectate lyase activity. Pectate lyase activity is detected in elongating and differentiating in vitro cell populations. The role of this enzyme in remodelling the cell wall during cell elongation and differentiation is discussed.

Orientation of macromolecules in the walls of elongating carrot cells.

When round cells from a carrot cell suspension culture are diluted into fresh medium without auxin, the cells elongate to almost 50 times their original diameter within three days. This process of elongation is accompanied by changes in both the composition and the orientation of cell wall polymers. We have obtained information on the orientation of wall polymers in elongating cells by two complementary techniques, one using microscopy and one spectroscopy. Images obtained by the fast-freeze, deep-etch, rotary-shadowed replica technique show that walls of round carrot cells have no net orientation of cellulose microfibrils, and that many thin fibres can be seen cross-linking microfibrils. Walls of elongated carrot cells, in contrast, show a marked net orientation of microfibrils at right angles to the axis of elongation. Fourier Transform Infrared (FTIR) spectra obtained from defined areas of single cell walls show that walls of round carrot cells contain more protein, esters and phenolics in a given area (10 microns x 10 microns) than walls of elongated carrot cells, that contain proportionally more carbohydrate. The orientation of particular functional groups, with respect to the direction of elongation of the cell, can be determined by inserting a polariser into the path of the infrared beam, before it passes through a cell wall sample mounted on the stage of the microscope accessory. In the walls of elongated cells, ester bands, amide bands characteristic of proteins, and stretching frequencies in the carbohydrate region of the spectrum all show a net orientation transverse to the long axis of the cells. In the walls of round carrot cells, however, there is no such net orientation of polymers. Spectra obtained from 25 microns-thick fresh sections of the etiolated stem of a carrot seedling show that different wall components are polarised in different tissue types. These techniques have therefore enabled us to define differences in both the composition and the architecture of walls of elongating cells at the level of a single cell, and to suggest that polymers not previously thought to be ordered, such as pectin and protein, are strictly oriented in some wall types.

Patterns of expression of the JIM4 arabinogalactan-protein epitope in cell cultures and during somatic embryogenesis in Daucus carota L.

Spatiotemporal patterns of expression of the cell-surface arabinogalactan-protein epitope defined by monoclonal antibody JIM4 (J.P. Knox et al., 1989, Development 106, 47-56) have been characterized by indirect immunofluorescence during the process of somatic embryogenesis in Daucus carota L. The JIM 4 epitope (J4e) occurred on cells established in culture from hypocotyl explants which appeared to derive, at least in part, from the epidermal cells of the hypocotyl. Cultures maintained in the presence of 2,4-dichlorophenoxyacetic acid developed proembryogenic masses of which only infrequent cells at the surface expressed J4e. Sub-culture at a low cell density and withdrawl of the synthetic auxin resulted in an increase in J4e expression in most surface cells and most abundantly in surface layers of cells at the future shoot end of developing embryos. The transition to heart-shaped embryos occurred concurrently with the expression of J4e by groups of cells beneath the developing cotyledons, at the junction of the future root and shoot. At this stage, J4e was also expressed by a single well-defined layer of cells at the surface of the embryos. Advancement to the mature torpedo stage was accompanied by the expression of the epitope on cells forming two regions of the future stele and of cells associated with the cotyledonary provascular tissue characteristic of the carrot seedling. At this stage there was substantially less expression of the marker antigen by epidermal cells, although infrequent expression by isolated cells of the epidermis was maintained. The correlation of J4e expression with the development and distinction of plant tissue patterns during somatic embryogenesis indicates a role for plasma-membrane arabinogalactan proteins in these processes.

Replication of wheat dwarf virus DNA in protoplasts and analysis of coat protein mutants in protoplasts and plants.

The replication of wheat dwarf virus (WDV) in protoplasts derived from a Triticum monococcum suspension cell system was investigated. The production of circular viral double-stranded DNA (dsDNA) forms consistent with the replication of the viral genome was observed. In comparison to whole plants, the production of viral single-stranded DNA (ssDNA) was reduced, possibly due to only low levels of viral coat protein being produced in the protoplasts. Mutations introduced into the viral coat protein open reading frame (ORF) did not affect the ability of the viral DNA to replicate, and a deletion of ca. 400 bp was tolerated. However, these mutations abolished the infectivity of the viral genome when agroinoculated onto wheat plants, providing evidence that, contrary to the case for the bipartite geminiviruses, the coat protein is essential for infection by WDV.

Inoculation of protoplasts with viruses by electroporation.

Optimal conditions for electroporation have been determined using inoculation of brome mosaic virus (BMV) and cowpea chlorotic mottle virus (CCMV) and its RNA into protoplasts of Nicotiana tabacum and N. plumbaginifolia. The most satisfactory medium was 0.5-0.7 M mannitol; calcium ions were toxic and other electrolytes were not helpful during electroporation. Brief pulses (ca. 10 microsec) were less destructive to the protoplasts than longer ones (ca. 10 msec) and gave high percentage infections with CCMV RNA. RNA entered the protoplasts only if present during the voltage pulse. Optimal voltage depended on the sample size, interelectrode distance, and pulse duration. A 50-nF capacitor discharging a 5- to 10-microsec pulse through a 1-ml sample in 0.7 M mannitol with a 4-mm interelectrode distance gave maximum infection with minimal protoplast damage at 2.5 kV/cm. A single pulse was sufficient; multiple pulses slightly increased infection. Electroporation of viral RNA was at least as effective as inoculation in the presence of polyethylene glycol. Positively charged BMV also infected readily but negatively charged CCMV only poorly.