Plant Cuttings

Time for some carbs, now

Carbohydrates and plants means more than just sucrose, starch and cellulose.
Image: Wikimedia Commons.
Image: Wikimedia Commons.

When carbohydrates [organic compounds consisting only of carbon, hydrogen and water, usually with a H:O ratio of 2:1, and with the empirical formula of Cm(H2O)n; e.g. glucose] and plants are mentioned, the botanically inclined amongst you should – in suitable pavlovian manner – think instantly of saccharides (a general synonym for sugars, and including mono-, di-, oligo-, and polysaccharides) such as sucrose, starch and cellulose. Well, this piece will make no further mention of sucrose (a disaccharide of glucose and fructose that is the main form in which photosynthetically fixed carbon is transported long-distance in many plants) nor of starch (a medium- to long-term polysaccharide store of fixed carbon/energy, often deposited in storage organs, e.g. tubers of potato). Cellulose does feature, but let’s build-up to that (yes, pun intended!).

First, a tale of trehalose, a disaccharide that is famously linked to feats of desiccation-tolerance in the resurrection plant Selaginella, but which – especially in its phosphorylated form trehalose-6-phosphae (T6P) – participates in a variety of roles connecting plant metabolism and development. To its list of accomplishments we now need to add a role in flowering, since loss of TREHALOSE-6-PHOSPHATE SYNTHASE 1 (which enzyme adds the phosphate group to trehalose to make T6P) causes Arabidopsis thaliana to flower extremely late – even under otherwise inductive environmental conditions. Want to find out more? Then go to the article by Vanessa Wahl et al. or either of the two summary/interpretative commentaries – by Jonas Danielson and Wolf Frommer or by Pamela Hines).

From a new role for a disaccharide to a new spin on a long-standing application of the polysaccharide cellulose. Although probably better known as the main structural component of plant cell walls in vivo, cellulose – a polysaccharide with the formula (C6H10O5)n, consisting of a linear chain of several hundred to more than ten thousand β(1→4) linked D-glucose units – is also commercially important in the walls of fibres (e.g. hemp) and hairs (e.g. cotton) that are extracted from plants and used as a variety of textiles, etc. Extending the uses of such natural materials in humankind’s age-old war against microbes, a team at KTH Royal Institute of Technology (Denmark) have developed an antibacterial polymer that attaches stably to cellulose in textiles, nappies, bandages, etc. Whilst antibacterial chemicals are not new, a danger inherent in their use is that they may ‘escape’ into the environment, creating selection pressure that encourages the development and spread of antibiotic-resistant bacteria. However, the Danish product is so tightly bonded to the cellulose that it does not leak, thereby minimising such dangers and concerns. Furthermore, the positively charged polymer actually draws the negatively charged bacteria to itself! Now, that is attractive, and reminds me somewhat of Ning Liu et al.’s work on ‘self-cleaning cotton’. Incorporating photosensitive 2-anthraquinone carboxylic acid (2-AQC) onto cellulose fibres, those workers demonstrated decomposition of 90 % aldicarb (an insecticide and nematicide, implicated in affecting human health) in 3 hours of UVA exposure, and inactivation of over 99 % of both Escherichia coli and Staphylococcus aureus (bacteria that are well-known human pathogens) with 1 hour of light exposure. In this instance, the self-cleaning functions result from formation of reactive oxygen species (ROS) upon light irradiation of the 2-AQC-treated cotton. Talking of ROS… Oops, out of space for this item!

[For an update on progress on photo-induced antimicrobial and decontaminating agents in polymer and textile applications, see this review by Gang Sun and Kyung Hwa Hong  – Ed.]