Epidermal Lignin Deposition in Quinoa Cotyledons in Response to UV-B Radiation¶

Abstract

UV-B radiation (280-320 nm) is harmful to living organisms and has detrimental effects on plant growth, development and physiology. In this work we examined some mechanisms involved in plant responses to UV-B radiation. Seedlings of quinoa (Chenopodium quinoa Willd.) were exposed to variable numbers of UV-B radiation doses, and the effect on cotyledons was studied. We analyzed (1) cotyledons anatomy and chloroplasts ultrastructure; (2) peroxidase activity involved in the lignification processes; and (3) content of photosynthetic pigments, phenolic compounds and carbohydrates. Exposure to two UV-B doses induced an increase in the wall thickness of epidermal cells, which was associated with lignin deposition and higher activity of the peroxidase. The chloroplast ultrastructure showed an appearance typical of plants under shade conditions, likely in response to reduced light penetration into the mesophyll cells due to the screening effect of epidermal lignin deposition. Exposure to UV-B radiation also led to (1) enhancement in the level of phenolics, which may serve a protective function; (2) strong increase in the fructose content, a fact that might be related to higher requirement of erythrose-4P as a substrate for the synthesis of lignin and phenolics; and (3) reduction in the chlorophyll concentration, evidencing alteration in the photosynthetic system. We propose that the observed lignin deposition in epidermal tissues of quinoa is a resistance mechanism against UV-B radiation, which allows growing of this species in Andean highlands.

Differential expression of 10 sweetpotato peroxidases in response to sulfur dioxide, ozone, and ultraviolet radiation

“…UV radiation generates H 2 O 2 for the synthesis of secondary metabolites such as lignin. POD activity and lignin contents increase during exposure to UV radiation in quinoa seedlings [9]. POD activity in plants can increase in response to a variety of stresses, including air pollutants and UV radiation, and POD activities have been suggested to be involved in cell wall cross-linking, diferulic bonds, extensin, lignification, suberization, and in responses to abiotic and biotic stresses [23].…”

Lignin: Characterization of a Multifaceted Crop Component

“…There is consensus that UV-B or UV-C radiation stimulated the phenylpropanoid pathway leading to enhanced lignification in grasses [88], tomato fruits [89], cucumber seedlings [90], and quinoa seedlings [91], representing a resistance mechanism against oxidative stress. In a study on soybeans [92], high UV-B radiation only increased the level of soluble phenolics but not that of lignin polymers.…”

UV-B radiation escalate allelopathic effect of benzoic acid on Solanum lycopersicum L.

“…UV-B radiation and BA decreased the sugar content of the Solanum seedlings. The changes in sugar content under the abiotic stresses may be due to upsetting the structure of chloroplast and blocking of chloroplast electron transport (Day and Neale, 2002;Hilal et al, 2004). The decreased chlorophyll contents may be one of the factors for low level of sugar contents.…”