Abstract
We evaluated the effect of crude extracts of the microcystin-producing (MC+) cyanobacteria Microcystis aeruginosa on seed germination and initial development of lettuce and arugula, at concentrations between 0.5 μg.L(-1) and 100 μg.L(-1) of MC-LR equivalent, and compared it to crude extracts of the same species without the toxin (MC-). Crude extracts of the cyanobacteria with MC (+) and without MC (-) caused different effects on seed germination and initial development of the salad green seedlings, lettuce being more sensitive to both extracts when compared to arugula. Crude extracts of M. aeruginosa (MC+) caused more evident effects on seed germination and initial development of both species of salad greens than MC-. Concentrations of 75 μg.L(-1) and 100 μg.L(-1) of MC-LR equivalent induced a greater occurrence of abnormal seedlings in lettuce, due to necrosis of the radicle and shortening of this organ in normal seedlings, as well as the reduction in total chlorophyll content and increase in the activity of the antioxidant enzyme peroxidase (POD). The MC- extract caused no harmful effects to seed germination and initial development of seedlings of arugula. However, in lettuce, it caused elevation of POD enzyme activity, decrease in seed germination at concentrations of 75 μg.L(-1) (MC-75) and 100 μg.L(-1) (MC-100), and shortening of the radicle length, suggesting that other compounds present in the cyanobacteria extracts contributed to this result. Crude extracts of M. aeruginosa (MC-) may contain other compounds, besides the cyanotoxins, capable of causing inhibitory or stimulatory effects on seed germination and initial development of salad green seedlings. Arugula was more sensitive to the crude extracts of M. aeruginosa (MC+) and (MC-) and to other possible compounds produced by the cyanobacteria.
Highlights
Salad green consumption in Brazil has increased over the last decade due to the adoption of healthier eating habits
The effects of the extracts were significantly different depending on the sensitivity of each salad green species tested, being lettuce the most affected in the presence of MC–LR equivalent
There was a high incidence (~ 85%) of seedlings with radicle necrosis (Figure 2), a symptom observed when cultivated in crude extracts with 75 μg.L–1 (MC–75) and 100 μg.L–1 (MC–100), but at lower percentages, 48.8% and 56%, respectively
Summary
Salad green consumption in Brazil has increased over the last decade due to the adoption of healthier eating habits. Several substances present in irrigation water, such as quantity of salts (Rhoades and Loveday, 1990), copper (Ahsan et al, 2007) and chromium (Prakash et al, 2004), can reduce the germination and development of seedlings, hampering production. Among these substances, the cyanotoxin microcystin (MC), a hepatotoxin that causes serious poisoning in animals, including humans (Carmichael, 1992; Yuan et al, 2006), can be included. In a previous study, Hereman and Bittencourt-Oliveira (2012), found in adult plants of lettuce accumulation concentrations of microcystin-LR equivalent above the recommended to the tolerable daily intake (TDI) for human consumption (0.04 μg.Kg–1) (WHO, 1998) when irrigated with crude extracts of toxic M. aeruginosa strain
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