ABSTRACT
The adaptations of tall fescue (Festuca arundinacea) arising from growth in naphthalene-contaminated sand (0.8 g kg(-1) sand dry weight (dw)) were investigated in the contexts of xenobiotic stress and water stress. The transfer of polycyclic aromatic hydrocarbons (PAHs) across the root endodermis was investigated using the hydrophobic Nile red stain as a PAH homologue. Nile red was applied to the epidermis of a living root to visualise uptake into the root through the transpiration stream, and the distance travelled by the stain into the root tissues was investigated using epi-fluorescence microscopy (Nikon Eclipse 90i). The results showed that the Nile red applied to the roots grown in naphthalene-contaminated sand was unable to penetrate the roots beyond the endodermis, whereas those grown in 'clean' sand showed evidence of uptake into the xylem vessels beyond the endodermis. Furthermore, partial collapse was observed in the cortex of naphthalene-treated roots, suggesting drought stress. Interestingly, the treated plants showed visual resilience to drought stress whilst the leaves of the control plants showed signs of wilting.
Subject(s)
Festuca/growth & development , Naphthalenes/metabolism , Soil Pollutants/metabolism , Water/analysis , Droughts , Festuca/chemistry , Festuca/metabolism , Plant Leaves/chemistry , Plant Leaves/growth & development , Plant Leaves/metabolism , Plant Roots/chemistry , Plant Roots/growth & development , Plant Roots/metabolism , Silicon Dioxide/analysis , Soil Pollutants/analysis , Water/metabolismABSTRACT
The hydrophilic metabolome of tall fescue (Festuca arundinacea) adapted to grow in naphthalene-treated sand (0.8 g kg(-1) sand dw) was analysed using gas chromatography-mass spectrometry, and peaks corresponding to the more abundant compounds were tentatively identified from analysis of their mass spectral features and reference to the NIST Mass Spectral Database. Particular attention was paid to sugars as they are known to play important roles as stress regulators in plants. The results showed that the abundance of sugars was greater in the roots but lesser in the shoots of treated plants when compared to their control counterparts. The results for indole acetic acid (IAA) were notable: IAA was prominently less in the treated roots compared to shoots, and in treated shoots, IAA was particularly subdued compared to untreated shoots consistent with IAA degradation in treated plant tissues. The differences in the molecular phenotype between control and treated plants were expressed in root structural differences. The treated roots were modified to have greater suberisation, enhanced thickening in the endodermis and distortions in the cortical zone as demonstrated through scanning electron and epi-fluorescence microscopy.
Subject(s)
Festuca/metabolism , Monosaccharides/metabolism , Naphthalenes/pharmacology , Soil Pollutants/pharmacology , Carbohydrate Metabolism/drug effects , Festuca/drug effects , Festuca/growth & development , Festuca/ultrastructure , Naphthalenes/chemistry , Plant Leaves/drug effects , Plant Leaves/growth & development , Plant Leaves/metabolism , Plant Roots/drug effects , Plant Roots/growth & development , Plant Roots/metabolism , Plant Roots/ultrastructure , Plant Shoots/drug effects , Plant Shoots/growth & development , Plant Shoots/metabolism , Silicon Dioxide/chemistry , Soil Pollutants/chemistry , Sucrose/metabolism , Trehalose/metabolismABSTRACT
The choice of plant for phytoremediation success requires knowledge of how plants respond to contaminant exposure, especially their roots which are instrumental in supporting rhizosphere activity. In this study, we investigated the responses of plants with different architectures represented by beetroot (Beta vulgaris), a eudicot with a central taproot and many narrower lateral roots, and tall fescue (Festuca arundinacea), a monocot possessing a mass of threadlike fibrous roots to grow in crude oil-treated sand. In this paper, scanning electron microscopy was used to investigate modifications to plant root structure caused by growth in crude oil-contaminated sand. Root structural disorders were evident and included enhanced thickening in the endodermis, increased width of the root cortical zone and smaller diameter of xylem vessels. Inhibition in the rate of root elongation correlated with the increase in cell wall thickening and was dramatically pronounced in beetroot compared to the roots of treated fescue. The latter possessed significantly fewer (p < 0.001) and significantly shorter (p < 0.001) root hairs compared to control plants. Possibly, root hairs that absorb the hydrophobic contaminants may prevent contaminant absorption into the main root and concomitant axile root thickening by being sloughed off from roots. Tall fescue exhibited greater root morphological adaptability to growth in crude oil-treated sand than beetroot and, thus, a potential for long-term phytoremediation.
