Light‐activated plant defence

Abstract

summary Sunlight provides the energy required for all biochemical, physiological and developmental processes necessary for plant growth, reproduction and survival. The role of light in photosynthesis and photomorphogenesis has been appreciated for some time; however, the role of light in plant defence is a comparatively recent realization. Between 75–100 photosensitizers or phototoxins, molecules that become toxic in the presence of light, have been extracted from higher plant tissues. These biologically‐active compounds have diverse biosynthetic origins and belong to at least 15 different phytochemical classes (i.e. acetophenones, acetylenes, benzophenanthrenes, β‐carbolines, coumarins, extended quinones, furanochromones, furanocoumarins, furanoquinolines, isoquinolines, lignans, pterocarpans, quinolines, sesquiterpenes and thiophenes). Of more than 100 angiosperm families assayed, phototoxins and/or phototoxic activity have been reported in c. 40 families representing 32 orders and 8 subclasses of the Magnoliophyta. Most of these allelochemicals are acute toxins with little organism‐specificity. As such, they are effective biocides capable of killing a wide‐range of potentially harmful organisms including: viruses, pathogenic bacteria and fungi, nematodes and herbivorous insects, as well as competing plant species. This review focuses on the phytochemistry, taxonomic occurrence and toxicological consequences of phototoxic metabolites in flowering plants. The available information suggests that phototoxic phytochemicals: (i) are broad‐spectrum allelochemicals capable of protecting plants against a variety of detrimental organisms in nature, (ii) represent a successful defensive strategy in both primitive and advanced plant taxa, and (iii) may be an effective defence under a variety of photoenvironmental conditions.

The effects of ultraviolet‐B (UV‐B: 290–320 nm) radiation on blister blight disease of tea (Camellia sinensis)

“…There is some evidence that sunlight can influence pathogens by causing accumulation of phytoalexins or protective pigments in plant tissues (Downum, 1992). UV-B had no or little effect on the expansion of translucent spots or sporulation of the fungus.…”

Actividad antifúngica de tres extractos de plantas chilenas en Botrytis cinerea

“…It is also discussed that these compounds interfere in the electron transport, the nutrient absorption, the fatty acid synthesis, the adenosine triphosphatase activity, and other metabolic processes of the cell, probably due to the interaction with the enzymes responsible of those processes (Feng and Zheng, 2007). When interfering with the molecular compounds present in various microorganisms, these compounds have a large range of action, but in general a low level of toxicity (Downum, 1992;VanEtten et al, 1994).…”

“…All the compounds determined with the HPLC method are reported in literature as antibiotic and fungistatic (Clarke, 1972;San Francisco and Cooper-Driver, 1984;Downum, 1992;Zadernowski et al, 2005;Ruelas et al, 2006;Vermerris and Nicholson, 2006;Feng and Zheng, 2007). For example, a combination of the following acids p-coumaric, ferulic, caffeic, and p-hydroxybenzoic at a concentration of 500 ppm inhibits the mycelial growth of Botrytis cinerea model, where the two first compounds had the more powerful antifungal effect (San Francisco and Cooper-Driver, 1984).…”

“…The following compounds were found in the different samples analyzed: chlorogenic acid, cinnamic acid, p-coumaric acid, ferulic acid, vanillin, vanillic acid, rutin, caffeic acid, 3, 4-hydroxybenzoic acid (veratric acid), 3, 4-dimethoxycinnamic acid (caffeic acid dimethyl ester), and protocatechuic acid. All these compounds have been described as metabolic antimicrobial compounds (Clarke, 1972;Downum, 1992;Zadernowski et al, 2005;Ruelas et al, 2006;Vermerris and Nicholson, 2006;Feng and Zheng, 2007).…”

Regeneration of Rhizophora mangle in a Caribbean mangrove forest: interacting effects of canopy disturbance and a stem-boring beetle

“…However, some form of light-activated, toxic secondary metabolite, or phototoxin, could be involved (L. Bjostad, personal communication). Such compounds are rapidly excited by absorption of light, accumulate relatively quickly under high light conditions, and can effectively defend against insect herbivores (Berenbaum 1987;Downum 1992). To our knowledge, phototoxins have not been looked for in Rhizophora, but have been found in more than 40 families of plants (Downum and Wen 1995;K.…”