Chromium toxicity in plants.

Bacteria with ACC deaminase can promote plant growth and help to feed the world

Root-secreted chemicals mediate multi-partite interactions in the rhizosphere, where plant roots continually respond to and alter their immediate environment. Increasing evidence suggests that root exudates initiate and modulate dialogue between roots and soil microbes. For example, root exudates serve as signals that initiate symbiosis with rhizobia and mycorrhizal fungi. In addition, root exudates maintain and support a highly specific diversity of microbes in the rhizosphere of a given particular plant species, thus suggesting a close evolutionary link. In this review, we focus mainly on compiling the information available on the regulation and mechanisms of root exudation processes, and provide some ideas related to the evolutionary role of root exudates in shaping soil microbial communities.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3040.2009.01926.x

Regulation and function of root exudates.

plants capable of accumulating uncommonly high Zn levels. In 1935, Byers documented the accumulation of Remediation of sites contaminated with toxic metals is particularly selenium in Astragalus spp. One decade later, Minguzzi challenging. Unlike organic compounds, metals cannot be degraded, and the cleanup usually requires their removal. However, this energy- and Vergnano (1948) identified plants capable of hyperintensive approach can be prohibitively expensive. In addition, the accumulating up to 1% Ni in shoots. Following the idenmetal removing process often employs stringent physicochemical tification of these and other hyperaccumulator species, agents which can dramatically inhibit soil fertility with subsequent a great deal of research has been conducted to elucidate negative impacts on the ecosystem. Phytoremediation has been pro- the physiology and biochemistry of metal hyperaccumuposed as a cost-effective, environmental-friendly alternative technol- lation in plants. Significant results have been obtained, ogy. A great deal of research indicates that plants have the genetic and the understanding of metal accumulating mechapotential to remove many toxic metals from the soil. Despite this nisms substantially advanced. However, a better undpotential, phytoremediation is yet to become a commercially available erstanding of the biological processes is needed if phytechnology. Progress in the field is hindered by a lack of understanding toextraction is to become a reliable, commercially of complex interactions in the rhizosphere and plant-based mechanisms which allow metal translocation and accumulation in plants. In available technology. this paper, four research areas relevant to metal phytoextraction from The success of phytoextraction, as an environmental contaminated soil are reviewed. The review concludes with an assess- cleanup technology, depends on several factors includment of the current status of technology deployment and suggestions ing the extent of soil contamination, metal availability for future phytoremediation research. for uptake into roots (bioavailability), and plant ability to intercept, absorb, and accumulate metals in shoots (Ernst, 1996). Ultimately, the potential for phytoextracP hytoremediation, the use of plants for environmen- tion depends on the interaction between soil, metal, and tal restoration, is an emerging cleanup technology. plant. The complexity of this interaction, controlled by To exploit plant potential to remediate soil and water climatic conditions, argues against generic and in favor contaminated with a variety of compounds, several tech- of a site specific phytoremediating approach. This undernological subsets have been proposed. Phytoextraction lines the importance of understanding the mechanisms is the use of higher plants to remove inorganic contami- and processes that govern metal uptake and accumulanants, primarily metals, from polluted soil. In this ap- tion in plants. In this review, four research areas, releproach, plants capable of accumulating high levels of vant to soil and plant interaction as it relates to metal metals are grown in contaminated soil. At maturity, phytoextraction, have been identified. The significance metal-enriched aboveground biomass is harvested and of these areas is briefly discussed below.

https://clu-in.org/download/remed/lasat_article.pdf

Phytoextraction of toxic metals: a review of biological mechanisms.

as a consequence of industrial development, the environment is increasingly polluted with heavy met - als.�Plantspossesshomeostaticmechanismsthatallowthemtokeepcorrectconcentrationsofessential� metalionsincellularcompartmentsandtominimizethedamagingeffectsofanexcessofnonessential� ones. one of their adverse effects on plants is the generation of harmful active oxygen species, leading to oxidativestress.�Besidesthewell-studiedantioxidantsystemsconsistingoflow-molecularantioxidantsand� specific enzymes, recent works have begun to highlight the potential role of flavonoids, phenylopropanoids andphenolicacidsaseffectiveantioxidants.� Duringheavymetalstressphenoliccompoundscanactas� metalchelatorsandontheotherhandphenolicscandirectlyscavengemolecularspeciesofactiveoxygen.�� phenolics, especially flavonoids and phenylopropanoids, are oxidized by peroxidase, and act in h 2 O 2 - scavenging, phenolic/asc/poX system. their antioxidant action resides mainly in their chemical struc -

Phenolic compounds and their antioxidant activity in plants growing under heavy metal stress

http://clemkuek.com/papers/heavymetalreview.pdf

Role of plants, mycorrhizae and phytochelators in heavy metal contaminated land remediation.

The effects of acetaldehyde, benzaldehyde, cinnamaldehyde, ethanol, benzyl alcohol, nerolidol, 2-nonanone, beta-ionone, and ethyl formate vapors on the growth of Rhizopus stolonifer, Penicillium digitatum, Colletotrichum musae, Erwinia carotovora, and Pseudomonas aeruginosa on agar medium were evaluated. The aldehydes were found to be the strongest growth inhibitors and the most lethal to the fungal spores and mycelia and bacterial cells. The average minimum inhibitory concentrations (MICs) of aldehydes that were germicidal to decay microorganisms were 0.28, 0.49, and 0.88 mmol per Petri dish, for cinnamaldehyde, benzaldehyde, and acetaldehyde, respectively. Ethanol also inhibited growth completely, but the MIC, which was 14.6 mmol per Petri dish, was significantly higher than those of the aldehydes. Ethanol can be considered germistatic because the alcohol does not inhibit germination of spores completely; it completely controlled only mycelial growth. The ketones tended to be effective only on P. digitatum and C. musae, whereas ethyl formate was not effective except on P. digitatum. The concentration of a volatile compound in the headspace of the Petri dish and its diffusion into the medium largely determined its efficacy against decay microorganisms.

In vitro efficacy of plant volatiles for inhibiting the growth of fruit and vegetable decay microorganisms.

http://www.clemkuek.com/papers/P17column.pdf

Continuous degradation of phenol at low concentration using immobilized Pseudomonas putida

Alginate concentrations between 2 and 4% had little effect on the degradation rate of phenol by alginate-immobilized Pseudomonas putida Ten-degree shifts from 25°C resulted in approximately 30% slower degradation Maximal degradation rates were favored at pH 55–60 The response of degradation rate to increased air flow in the bubble column used was almost linear and an optimal higher than 16 vol vol−1 was indicated, although free cells appeared in the reaction medium above 12 vol vol−1 When the initial phenol concentration was raised, degradation rate was not significantly affected until levels higher than 1200 mg ml−1 where performance was markedly reduced Increasing the ratio of total bead volume to medium volume gave progressively smaller increases in degradation rate At a medium volume to total bead volume ratio of 5:1, the maximum degradation rate was 250 mg L−1 h−1

/pdf/aerobic-batch-degradation-of-phenol-using-immobilized-mgn10kg117.pdf

Aerobic batch degradation of phenol using immobilized Pseudomonas putida

The effects of mycorrhizae on growth and uptake of N,P, Zn, andPbby plantswere investigatedinagreenhousetrial using vetiver grass (Vetiveria zizanioides)ashost.Inoculation of the host plants with arbuscular mycor-rhizal fungi (AMF), Glomus mosseae and G. intraradi-ces spores, signiﬁcantly increased the growth and Puptake. Mycorrhizal colonization increased Pb and Znuptake by plants under low soil metal concentrations (at0 and 10 mg/kg of Pb or Zn), whereas under higher con-centrations (at 100 and 1,000 mg/kg of Pb or Zn), itdecreased Pb and Zn uptake. P concentration in soil wasnegatively correlated with mycorrhizal colonizationas well as Zn or Pb concentrations. The results showedthat inoculation of the host plants with AMF protectsthem from the potential toxicity caused by increaseduptake of Pb and Zn, but the degree of protection variedaccording to the fungus and host plant combination. Thepotential of arbuscular mycorrhizae in phytoremediationof the Zn- or the Pb-contaminated soils is discussed inthis article.Key words: arbuscular mycorrhiza, lead, nitrogen, phos-phorus, vetiver grass, zinc.IntroductionPhytoremediation technology is emerging as a promisingenvironmentally friendly method for large-scale cleanupof contaminated waters and soil (Brooks 1998; Chaudhryet al. 1998). It is important to select an appropriate pio-neer plant species for successful site reclamation and inphytoremediation efforts to ensure a self-sustainable vege-tative cover. Recently, Shu et al. (2002) showed successfulestablishment and colonization of vetiver grass as pioneer-ing plant species on Pb/Zn mine spoils in China and con-cluded that this plant should be considered as one of theplants to be used for mine site revegetation. The vetiverplant (Vetiveria zizanioides L. Nansh), a common wetlandgrass species from the tribe Andropogonaeae native totropical and subtropical areas, has been cultivated com-mercially for many industrial applications and for the pro-duction of the medicinally valued volatile essential oil thatcan be distilled from its roots (Maffei 2002). Once estab-lished, it is not affected by droughts or ﬂoods. It is alsohighly tolerant to frost, heat, extreme soil pH, sodicity,salinity, and alkalinity as well as to a range of potentialtoxic elements such as As, Cd, Cu, Cr, Pb, Se, Zn, Ni, Al,and Mn in the soil (Truong & Claridge 1996). Due to itsunique physiological and morphological characteristicssuch as higher biomass; fast growth; higher metal toler-ance, uptake, and accumulation; and strong ecologicaladaptability, the vetiver plant can play an important rolein all subsets of phytoremediation of heavy metal–contam-inated soils and water, that is, phytostabilization, phytoex-traction, and phytoﬁltration of heavy metal contaminants(Mucciarelli et al. 1998; Khan et al. 2000; Lavania & Lavania2000; Shu et al. 2002). Another beneﬁt of using vetivergrass for phytoremediation is its foliage, which can beused as a mulch to improve soil physical properties.Many plants growing on metal-contaminated soils pos-sess mycorrhizae (Chaudhry et al. 1998), indicating thatthese fungi have evolved a tolerance to heavy metals andthat they play an important role in the phytoremediation ofcontaminated soils (Khan et al. 2000; Khan 2001). There-fore, metal-tolerant mycorrhizal inoculants are promisingfor the phytoremediation of metal-contaminated soils.Arbuscular mycorrhizal fungi (AMF) are known toimprove plant growth on nutrient-poor soils and enhancetheir uptake of P, Cu, Ni, Pb, and Zn (Khan et al. 2000;Zhu et al. 2001). Despite the importance of the role thatAMF play in plant interactions with the soil environmentin general, and heavy metals in particular, relatively fewstudies have focused on their effect on metal-remediationefforts. Previous phytoremediation studies have focusedon the predominantly nonmycorrhizal plant families, e.g.,Brassicaceae or Caryophyllaceae, and arbuscular mycor-rhizae (AM) have not been considered as importantcomponent of phytoremediation practices (Pawlowska et al.

Clem Kuek

Papers

Role of plants, mycorrhizae and phytochelators in heavy metal contaminated land remediation.

In vitro efficacy of plant volatiles for inhibiting the growth of fruit and vegetable decay microorganisms.

Continuous degradation of phenol at low concentration using immobilized Pseudomonas putida

Aerobic batch degradation of phenol using immobilized Pseudomonas putida

The role of mycorrhizae associated with vetiver grown in Pb-/ Zn-contaminated soils: Greenhouse study