[D-Leu1]MC-LR and MC-LR: A Small–Large Difference: Significantly Different Effects on Phaseolus vulgaris L. (Fabaceae) Growth and Phototropic Response after Single Contact during Imbibition with Each of These Microcystin Variants

Abstract

[D-Leu1]MC-LR and MC-LR, two microcystins differing in one amino acid, constitute a sanitary and environmental problem owing to their frequent and concomitant presence in water bodies of the Americas and their association with human intoxication during recreational exposure to cyanobacterial bloom. Present in reservoirs used for irrigation as well, they can generate problems in the development of crops such as Phaseolus vulgaris, of nutritional and economic interest to the region. Although numerous works address the toxic effects of MC-LR, information on the toxicity of [D-Leu1]MC-LR is limited. Our objective was to study the toxic effects of [D-Leu1]MC-LR and MC-LR (3.5 µg/ml) on P. vulgaris after a single contact at the imbibition stage. Our findings indicate that 10 days post treatment, [D-Leu1]MC-LR generates morphological and physiological alterations more pronounced than those caused by MC-LR. In addition to the alterations produced by [D-Leu1]MC-LR in the development of seedlings and the structure of the leaves, roots and stems, we also found alterations in leaf stomatal density and conductivity, a longer delay in the phototropic response and a decrease in the maximum curvature angles achieved with respect to that observed for MC-LR. Our findings indicate that these alterations are linked to the greater inhibition of phosphatase activity generated by [D-Leu1]MC-LR, rather than to oxidative damage. We observed that 30 days after treatment with MC-LR, plants presented better development and recovery than those treated with [D-Leu1]MC-LR. Further studies are required on [D-Leu1]MC-LR and MC-LR toxicity and their underlying mechanisms of action.

Impacts of Microcystins on Morphological and Physiological Parameters of Agricultural Plants: A Review

“…Small variations in the chemical structure of MCs were shown recently to have a significant impact on phytotoxicity. The variant (D-Leu1) MC-LR, found, for example, in La Plata Basin blooms in Argentina, proved to be more toxic than MC-LR to common bean ( Phaseolus vulgaris L.) [ 27 ]. Malaissi et al (2020) [ 27 ] reported the inhibition of germination after a single contact in the imbibition stage and delay in the development of common bean seedlings.…”

“…The variant (D-Leu1) MC-LR, found, for example, in La Plata Basin blooms in Argentina, proved to be more toxic than MC-LR to common bean ( Phaseolus vulgaris L.) [ 27 ]. Malaissi et al (2020) [ 27 ] reported the inhibition of germination after a single contact in the imbibition stage and delay in the development of common bean seedlings. Alterations in the structure of the leaves (alteration in the size, color and shape), roots (smaller root area) and stems (shorter stem lengths), as well as alterations in leaf stomatal density and conductivity were also reported ( Table 1 ).…”

“…Some of these effects induced by (D-Leu1) MC-LR persisted over time, 30 days after a single contact with the toxin. Histological analysis showed significant alterations in the root tissues affecting the pericycle and endodermis and, for instance, an increase in the number of stomata on the abaxial side of P. vulgaris exposed to (D-Leu1) MC-LR [ 27 ]. Both MC variants induced lipid peroxidation and inhibited total phosphatase activity [ 27 , 28 ].…”

The 6th Iberian and 2nd Ibero-American Cyanotoxin Congress CIC2019

“…Some fairly rare toxins may abound locally and may represent important hazards that affect people, animals, and even crops. Anabaenopeptins (A, B, C, and F) and Oscilamide Y were detected at unusually high concentrations in a reservoir system in NE Spain [ 11 ] and [D-Leu 1 ]MC-LR is more frequent than MC-LR in some South American countries [ 12 ]. The detection of some of these compounds may pose a challenge, and Flores and Caixach [ 11 ] recommend taking a suspect screening approach based on High-Resolution Mass Spectrometry (HRMS) for the cyanobacterial peptides that are not often monitored by target strategies.…”

“…[D-Leu1] MC-LR is frequently reported in water bodies throughout America and shows clear toxic potency differences with MC-LR, with greater phosphatase activity inhibition in both animal and plant models. The effects on plants ( Phaseolus vulgaris ) can be observed from germination at fairly low concentrations [ 12 , 13 ]. This may be a warning for not only managers to be aware of most minority compounds that challenge the accuracy of methods, but also for researchers to study the potential toxic effects of Anabaenopeptins and Oscilamide, among others.…”