20-Hydroxyecdysone protects wheat seedlings (Triticum aestivum L.) against lead stress.

20-Hydroxyecdysone (20E) is the most abundant phytoecdysteroid (PE) produced by plants, where it represents a protective molecule against insect attack. The aim of the present study was to assess the effects of 20E on the growth, metabolic enzymes and antioxidant systems of wheat seedlings under lead stress induced by Pb(NO3)2 (3 mM). Pre-treatment concentrations (0, 1, 3 and 5 µM) of 20E were applied for two days, then wheat seedlings were transferred for 5 days to a treatment solution containing lead nitrate. When plants were grown without pre-treatment, germination and growth were impaired, while signs of oxidative stress were observed. 20E pre-treatment (3 or 5 µM) was able to efficiently protect seedlings from Pb toxicity by reducing Pb uptake and Pb-induced oxidative stress, as well by enhancing Pb excretion. Thus, 20E pre-treatment maintains normal germination, elongation, biomass, and metabolism in spite of the presence of Pb. Our results show that 20E protects oxidative balance and enhances the anti-oxidative systems, and more specifically the ascorbate-glutathione system. To our knowledge, this study shows for the first time that 20E treatment induces metabolic changes that allow the plants to resist heavy metal stress.

Effect of lead stress on mineral content and growth of wheat (Triticum aestivum) and spinach (Spinacia oleracea) seedlings.

Lead (Pb) is the most common heavy metal contaminant in the environment. Pb is not an essential element for plants, but they absorb it when it is present in their environment, especially in rural areas when the soil is polluted by automotive exhaust and in fields contaminated with fertilizers containing heavy metal impurities. To investigate lead effects on nutrient uptake and metabolism, two plant species, spinach (Spinacia oleracea) and wheat (Triticum aestivum), were grown under hydroponic conditions and stressed with lead nitrate, Pb(NO3)2, at three concentrations (1.5, 3, and 15 mM). Lead is accumulated in a dose-dependent manner in both plant species, which results in reduced growth and lower uptake of all mineral ions tested. Total amounts and concentrations of most mineral ions (Na, K, Ca, P, Mg, Fe, Cu and Zn) are reduced, although Mn concentrations are increased, as its uptake is reduced less relative to the whole plant's growth. The deficiency of mineral nutrients correlates in a strong decrease in the contents of chlorophylls a and b and proline in both species, but these effects are less pronounced in spinach than in wheat. By contrast, the effects of lead on soluble proteins differ between species; they are reduced in wheat at all lead concentrations, whereas they are increased in spinach, where their value peaks at 3 mM Pb. The relative lead uptake by spinach and wheat, and the different susceptibility of these two species to lead treatment are discussed.

Protective role of a methanolic extract of spinach (Spinacia oleracea L.) against Pb toxicity in wheat (Triticum aestivum L.) seedlings: beneficial effects for a plant of a nutraceutical used with animals.

Spinach extracts contain powerful natural antioxidants and have been used to improve the response of animal cells to various stress factors. The aim of the present study was to assess the effects of a methanolic extract of spinach (SE) used at two concentrations (21.7 and 217 ppm) on the growth, certain enzymes and antioxidant systems in wheat seedlings under lead stress. When wheat seedlings were grown for 7 days in a solution containing Pb(NO3)2 (3 mM), germination and growth were impaired, while signs of oxidative stress were observed. SE (217 ppm) pretreatment was able to protect seedlings from Pb toxicity by both reducing Pb uptake and Pb-induced oxidative stress. As a consequence, almost normal germination, elongation, biomass and α-amylase activity were restored by SE (217 ppm) pretreatment of wheat seedlings, in spite of the presence of Pb. Our results support the protective role and the antioxidant effect of SE against Pb. These results show an amazing similarity to the effects of SE in animals, which suggests that providing "nutraceuticals" to plants could improve their "health" status.

Dietary effects of harmine, a ß-carboline alkaloid, on development, energy reserves and α-amylase activity of Plodia interpunctella Hübner (Lepidoptera: Pyralidae).

The physiological and developmental effects of harmine, a ß-carboline alkaloid, on the insect pest Plodia interpunctella have been analyzed. When added at the larval diet, harmine induced a strong reduction of larvae weight, cannibalism between larvae, in addition to significant mortality. On the other hand, it caused a remarkable development disruption, manifested by both delay and reduction of pupation and adult emergence. Using spectrophotometric assays, we have shown that harmine ingestion provoked a severe reduction in protein, glycogen and lipid contents. Beside, when larvae fed harmine, the activity of the digestive enzyme α-amylase was strongly reduced. In conclusion, our experiments clearly show the susceptibility of P. interpunctella to harmine ingestion revealing the potent bioinsecticidal effect of harmine.

Lead phytotoxicity on wheat (Triticum aestivum L.) seed germination and seedlings growth.

Lead (Pb) is an environmental pollutant extremely toxic to plants and other living organisms including humans. To assess Pb phytotoxicity, experiments focusing on germination of wheat seeds were germinated in a solution containing Pb (NO(3))(2) (0.05; 0.1; 0.5; 1g/L) during 6 days. Lead accumulation in seedlings was positively correlated with the external concentrations, and negatively correlated with morphological parameters of plant growth. Lead increased lipid peroxidation, enhanced soluble protein concentrations and induced a significant accumulation of proline in roots. Esterase activity was enhanced in the presence of lead, whereas α-amylase activity was significantly inhibited. Antioxidant enzymes activities, such as, ascorbate peroxidase, peroxidase, superoxide dismutase, catalase and glutathione S-transferase were generally significantly increased in the presence of lead in a dose-dependent manner. The present results thus provide a model system to screen for natural compounds able to counteract the deleterious effects of lead.