Contrasting effects of Miocene and Anthropocene levels of atmospheric CO 2 on silicon accumulation in a model grass

Grasses are hyper-accumulators of silicon (Si), which they acquire from the soil and deposit in tissues to resist environmental stresses. Given the high metabolic costs of herbivore defensive chemicals and structural constituents (e.g. cellulose), grasses may substitute Si for these components when carbon is limited. Indeed, high Si uptake grasses evolved in the Miocene when atmospheric CO 2 concentration was much lower than present levels. It is, however, unknown how pre-industrial CO 2 concentrations affect Si accumulation in grasses. Using Brachypodium distachyon , we hydroponically manipulated Si-supply (0.0, 0.5, 1, 1.5, 2 mM) and grew plants under Miocene (200 ppm) and Anthropocene levels of CO 2 comprising ambient (410 ppm) and elevated (640 ppm) CO 2 concentrations. We showed that regardless of Si treatments, the Miocene CO 2 levels increased foliar Si concentrations by 47% and 56% relative to plants grown under ambient and elevated CO 2 , respectively. This is owing to higher accumulation overall, but also the reallocation of Si from the roots into the shoots. Our results suggest that grasses may accumulate high Si concentrations in foliage when carbon is less available (i.e. pre-industrial CO 2 levels) but this is likely to decline under future climate change scenarios, potentially leaving grasses more susceptible to environmental stresses.

Nickel phytoremediation potential of some plant species of the Lower Dir, Khyber Pakhtunkhwa, Pakistan

Nickel is a known hepatotoxic, haemotoxic, pulmonary toxic, nephrotoxic, reproductive toxic, carcinogenic, phytotoxic and neurotoxic agent. The adverse ecological impacts from unnecessary heavy metals include contamination of water and soil which pose serious threats to human health. This study was conducted to screen plants for the phytoremediation of nickel from sixty-one sites of the Lower Dir. Nickel-metal was analyzed in the soil, roots and shoots of plants. The total concentration of nickel in soil, roots and shoots was found to be in the range of 1.03-18.98, 12.63-540.73 and 12.00-295.86 mg kg–1 dry weight basis (DW) respectively. The highest nickel contents were present in the roots of Xanthium strumarium (540.73) and shoots of Bryophyllum daigremontianum (295.86). None of the plant species were identified as hyper accumulators for nickel but based on BCF, TF and BAC values most of the species showed feasibility for its phytoextraction and phytostabilization. Xanthium strumarium, Filago hurdwarica, Ranunculus arvensis, Medicago lupulina, Cannabis sativa, Geranium rotundifolium and Cerastium glomeratum are suggested for the phytostabilization of nickel whereas Bryophyllum daigremontianum, Rosularia adenotricha, Iris germanica, Asplenium dalhousiae and Isatis tinctoria for the phytoextraction of soil contaminated with nickel.

Silicon is an inducible and effective herbivore defence against Helicoverpa punctigera (Lepidoptera: Noctuidae) in soybean

The role of silicon (Si) in alleviating the effects of biotic and abiotic stresses, including defence against insect herbivores, in plants is widely reported. Si defence against insect herbivores is overwhelmingly studied in grasses (especially the cereals), many of which are hyper-accumulators of Si. Despite being neglected, legumes such as soybean (Glycine max) have the capacity to control Si accumulation and benefit from increased Si supply. We tested how Si supplementation via potassium, sodium or calcium silicate affected a soybean pest, the native budworm Helicoverpa punctigera Wallengren (Lepidoptera: Noctuidae). Herbivory reduced leaf biomass similarly in Si-supplemented (+Si) and non-supplemented (–Si) plants (c. 29 and 23%, respectively) relative to herbivore-free plants. Both Si supplementation and herbivory increased leaf Si concentrations. In relative terms, herbivores induced Si uptake by c. 19% in both +Si and –Si plants. All Si treatments reduced H. punctigera relative growth rates (RGR) to a similar extent for potassium (−41%), sodium (−49%) and calcium (−48%) silicate. Moreover, there was a strong negative correlation between Si accumulation in leaves and herbivore RGR. To our knowledge, this is only the second report of Si-based herbivore defence in soybean; the rapid increase in leaf Si following herbivory being indicative of an induced defence. Taken together with the other benefits of Si supplementation of legumes, Si could prove an effective herbivore defence in legumes as well as grasses.

Molecular Overview of Heavy Metal Phytoremediation

Metal toxification has remained one of the problems with the advent of industrial revolution. Plant based remediation are showing increasing promise for use in soils contaminated with organic and inorganic pollutants. A large number of plant families has been identified which has shown significant result in detoxification of heavy metals. Hyperaccumulator plant is capable of sequestering heavy metals in their shoot tissues. High tolerance to HM toxicity is dependent on a reduced metal uptake or increased internal sequestration, which depends on plant and environmental condition. Recent progresses on understanding cellular/molecular mechanisms of metal tolerance by plants are reviewed. This chapter aims to focus on molecular mechanism involved in heavy metal detoxification and tolerance by plants. A different method by which plant effectively converts toxic metal in less toxic compounds has been explained in this chapter. Further, mode of accumulation and sequestration of metals have been explained which are utilized by hyper accumulators.

Evaluation of localization of lead and nickel in plant cells of Amaranthus sp. and Brassica sp. absorbed from mine spoil waste

A detailed survey was undertaken in the sewage water contaminated areas of Coimbatore to select the natural hyper accumulators to rehabilitate the contaminated mine spoils. From this experiment the Pb and Ni accumulators, Amaranthus sp. and Brassica sp. were selected for further studies towards remediating the metal contaminated mine spoils. Microtomy of root, stem and leaf of Amaranthus sp. and Brassica sp. showed that the colour development in the plant species is evidence for accumulation of metals in different parts of plants and also tolerance mechanism employed by plant species under metal stress condition. The accumulation of heavy metals from soil to plant did not follow any particular pattern and varied with respect to metals, species and plant parts. However, the maximum Pb localization took place in root portion than in aerial parts. But the Ni accumulation was almost equal or higher in aerial parts (leaf and stem) compared to roots. This study revealed that the Amaranthus sp and Brassica sp stored lead and nickel in roots, leaves and stems. The roots showed more localization of metals followed by leaves and stems.