Different mechanisms of the metalliferous Zygophyllum fabago shoots and roots to cope with Pb toxicity.

Lead (Pb) remains classified as a priority pollutant. Zygophyllum fabago is considered an early colonizer of heavy metal-polluted soils under semiarid conditions, but physiological mechanisms underlying this colonizing capacity remain unclear. In order to characterize Z. fabago plants' performance on Pb-contaminated soils, we evaluated how Pb influenced root and shoot growth, carbon metabolism, and oxidative status. For that, 30-day-old seedlings from one population colonizing a mine tailing ("Mercader") at Murcia (southeast Spain) were exposed to 500-µM Pb(NO3)2 for 1 week. Results showed that this high dose of Pb induced no plant mortality nor senescence, though promoting plant nanism. Besides the efficiency of roots to accumulate Pb, shoots also demonstrate a high efficiency to translocate and accumulate this metal. Pb exposure decreased Zn uptake to the aerial part and reduced net photosynthetic rate (A), RuBisCO activity, chlorophyll, and soluble sugar contents in shoots. Moreover, in shoots, Pb exposure increased the levels of O2- and decreased antioxidant capacity, culminating with a loss of cell membrane integrity (electrolyte leakage) and increased protein oxidation. Compared to controls, exposed roots had less Mn and Zn levels, and despite the rise in H2O2 levels, they were able to modulate non-protein thiols presenting a robust defense capacity. This capacity may support the roots' ability to maintain cell membrane integrity (electrolyte leakage) with regard to control. Principal component analysis (PCA) contributed to elucidate how this species adjusts physiological mechanisms to cope with Pb toxicity, showing that roots and shoots evolved different antioxidant defenses, which demonstrates the importance of organ specificity in the response of Z. fabago to heavy metals.

Heavy metal stress reduces the deposition of calcium oxalate crystals in leaves of Phaseolus vulgaris.

Calcium oxalate (CaOx) crystals in plants may serve as a sink for the absorption of excess calcium, and they could play an important role in heavy metal detoxification. In this study, the effect of heavy metals and different calcium concentrations on the growth of calcium oxalate crystals in leaves of Phaseolus vulgaris was investigated. Different analytical techniques were used to determine the influence of exogenous lead and zinc on CaOx deposition and to detect a presence of these metals in CaOx crystals. We found a positive correlation between the calcium concentration in the nutrient medium and the production of calcium oxalate crystals in leaves of hydroponically grown plants. On the other hand, addition of the heavy metals to the nutrient medium decreased the number of crystals. Energy dispersive X-ray spectrometry did not detect the inclusion of heavy metals inside the CaOx crystals. Our investigation suggests that CaOx crystals do not play a major role in heavy metal detoxification in P. vulgaris but do play an important role in bulk calcium regulation.

Changes in phenol content during strawberry (Fragariaxananassa, cv. Chandler) callus culture.

Total soluble phenols, soluble flavanols, (+)-catechin, ferulic acid and 1-O-feruloyl-beta-d-glucose were analyzed during the development of a strawberry (Fragariaxananassa, cv. Chandler) callus culture. The time-course changes of the different phenols assayed were well correlated with callus growth and morphology. The changes in polyphenol oxidase (EC 1.10.3.1-2) and beta-glucosidase (EC 3.2.1.21) activities in the callus were also examined. The total phenol, soluble flavanols and (+)-catechin contents were high during the preexponential and exponential phases of growth. The subsequent decrease in (+)-catechin concentration coincided with high levels of polyphenol oxidase activity. The 1-O-feruloyl-beta-d-glucose content was highest as callus growth ceased, and its subsequent decrease was accompanied by the increased production of ferulic acid. This increase in ferulic acid was accompanied by an increase in beta-glucosidase activity. The ferulic acid content decreased at the end of culture, when callus growth had stopped and showed clear symptoms of senescence. This decrease in the ferulic acid concentration was accompanied by an increase in the levels of ferulic acid bound to cell wall components.

Enhancement of phytosterols, taraxasterol and induction of extracellular pathogenesis-related proteins in cell cultures of Solanum lycopersicum cv Micro-Tom elicited with cyclodextrins and methyl jasmonate.

Suspension-cultured cells of Solanum lycopersicum cv Micro-Tom were used to evaluate the effect of methyl jasmonate and cyclodextrins, separately or in combination, on the induction of defense responses. An extracellular accumulation of two sterols (isofucosterol and ß-sitosterol) and taraxasterol, a common tomato fruit cuticular triterpene, were observed. Their levels were higher in Micro-Tom tomato suspension cultured cells elicited with cyclodextrins than in control and methyl jasmonate-treated cells. Also, their accumulation profiles during the cell growth phase were markedly different. The most striking feature in response to cyclodextrin treatments was the observed enhancement of taraxasterol accumulation. Likewise, the exogenous application of methyl jasmonate and cyclodextrins induced the accumulation of pathogenesis-related proteins. Analysis of the extracellular proteome showed the presence of amino acid sequences homologous to pathogenesis-related 1 and 5 proteins, a cationic peroxidase and a biotic cell death-associated protein, which suggests that methyl jasmonate and cyclodextrins could play a role in mediating defense-related gene product expression in S. lycopersicum cv Micro-Tom.

Induction of sesquiterpenes, phytoesterols and extracellular pathogenesis-related proteins in elicited cell cultures of Capsicum annuum.

Capsicum annuum suspension cell cultures were used to evaluate the effect of cyclodextrins and methyl jasmonate as elicitors of defence responses. The induced defence responses included the accumulation of sesquiterpenes and phytosterols and the activation of pathogenesis-related proteins, leading to reinforcement and modification of the cell wall architecture during elicitation and protection cells against biotic stress. The results showed that the addition of both cyclodextrins and methyl jasmonate induced the biosynthesis of two sesquiterpenes, aromadendrene and solavetivone. This response was clearly synergistic since the increase in the levels of these compounds was much greater in the presence of both elicitors than when they were used separately. The biosynthesis of phytosterols was also induced in the combined treatment, as the result of an additive effect. Likewise, the exogenous application of methyl jasmonate induced the accumulation of pathogenesis-related proteins. The analysis of the extracellular proteome showed the presence of amino acid sequences homologous to PR1 and 4, NtPRp27-like proteins and class I chitinases, peroxidases and the hydrolytic enzymes LEXYL1 and 2, arabinosidases, pectinases, nectarin IV and leucin-rich repeat protein, which suggests that methyl jasmonate plays a role in mediating defence-related gene product expression in C. annuum. Apart from these methyl jamonate-induced proteins, other PR proteins were found in both the control and elicited cell cultures of C. annuum. These included class IV chitinases, beta-1,3-glucanases, thaumatin-like proteins and peroxidases, suggesting that their expression is mainly constitutive since they are involved in growth, development and defence processes.