Indicator Of Plant Stress Research Articles

Small Variations over Large Scales: Fluctuating Asymmetry over the Range of Two Oak Species

Fluctuating asymmetry (FA) represents small, random variation from symmetry, and it has been used as an indicator of plant stress at relatively local scales. In this study, variation in FA was examined at the landscape scale across the whole distributional range of the two oak species Quercus myrtifolia and Quercus chapmanii in Florida. Oak leaf morphology was evaluated in 40 sites covering ∼170,000 km2. Plants growing on coastal/edge sites exhibited significantly higher levels of FA than did plants inhabiting inland/center sites. For myrtle oaks, levels of FA were also spatially structured, and sites were positively spatially autocorrelated at small distances, indicating that sites that were closer exhibited similar levels of environmental stress and FA. Our results have shown that FA, a reliable measurement of plant stress at local scales, can also be used as a biological tool for monitoring the quality of the environment at larger spatial scales, increasing its usefulness in studies across the full ran...

Localization of eIF4A-III in the nucleolus and splicing speckles is an indicator of plant stress

The mechanisms of long-term adaptation to low oxygen environment are quite well studied, but little is known about the sensing of oxygen shortage, the signal transduction and the short-term effects of hypoxia in plant cells. We have found that an RNA helicase eIF4A-III, a putative component of the Exon Junction Complex, rapidly changes its pattern of localisation in the plant nucleus under hypoxic conditions. In normal cell growth conditions GFP- eIF4A-III was mainly nucleoplasmic, but in hypoxia stress conditions it moved to the nucleolus and splicing speckles. This transition occurred within 15-20 min in Arabidopsis culture cells and seedling root cells, but took more than 2 h in tobacco BY-2 culture cells. Inhibition of respiration, transcription or phosphorylation in cells and ethanol treatment had similar effects to hypoxia. The most likely consequence is that a certain mRNA population will remain bound to the eIF4A-III and other mRNA processing proteins, rather than being transported from the nucleus to the cytoplasm, and thus its translation will be suspended.

Cadmium availability in soil and retention in oak roots: Potential for phytostabilization

Afforestation of contaminated land by trees is considered as a feasible strategy for the extensive stabilization of contaminants. In this work, we studied the patterns of metal availability (Cd, Cu, Pb and Zn) in a contaminated and afforested area. Specifically, we observed the response of Holm oak ( Quercus ilex subsp. ballota) leaves to changes in the availability of metals under field conditions, focusing on Cd. Under controlled conditions we studied the performance of oak seedlings exposed to high levels of Cd, with the aim of analyzing the patterns of translocation and tolerance of the seedlings. Cadmium was the most available metal, in relative terms; 15% of the total Cd in the soil was extracted with NH 4NO 3. The availabilities of Cd, Cu and Zn showed exponential relationships with soil pH (pH values ranged from 2.4 to 8.4). Cadmium accumulation in the leaves was not related to the changes in Cd availability. Greenhouse studies showed that seedlings had a high Cd retention capacity in fine roots (up to 7 g kg −1) and low rates of Cd translocation to the leaves (transfer coefficients below 0.03). Root biomass and thickness was altered by exposure to Cd. In spite of this, the chlorophyll fluorescence measurements (an indicator of plant stress) only differed slightly from the control treatment at a Cd dose of 200 mg L −1. Due to the relatively high tolerance to Cd and the capacity of roots to retain this metal, Holm oak may be useful for the phytostabilization of soils contaminated by Cd.

Physiological Stress caused by Salinity in Cordyline fruticosa and Its Indicators

Crop plants are usually nonhalophytes that tolerate only moderate saline concentrations; under salinity, they accumulate salt in their aboveground organs and, to a smaller extent, in roots. Enhanced synthesis of determined secondary metabolites (such as proline, phenolics, or malondyaldehide) under stressful conditions is believed to protect the cellular structures from oxidative damage, in addition to the osmotic advantage for the plants. The aim of this work is to study the influence of the fertigation water salinity on osmoprotectant content in Cordyline fruticosa var. ‘Red Edge.’ Four nutrient solutions with different electrical conductivity levels were applied: EC1.5 (1.5 dS m−1), EC2.5 (2.5 dS m−1), EC3.5 (3.5 dS m−1), and EC4.5 (4.5 dS m−1), obtained by the addition of different quantities of sodium chloride (NaCl) to a basic nutrient solution (EC 1.5 dS m−1), followed by stirring to dissolve the salt and make the solution homogeneous. The results show that malondialdehyde (MDA) content is not a good indicator of plant stress, as levels in EC1.5 and EC4.5 are similar, but flavonoids, phenols and sugars contents are more useful indicators, because the highest values in leaves are found with the more saline treatment. Proline plays an osmoregulatory role, increasing in roots when NaCl concentration in the nutrient solution is too high but also when it is too low.

Can PAHs influence Cu accumulation by salt marsh plants?

The presence of polycyclic aromatic hydrocarbons (PAHs) may change the mechanisms of metal uptake, thus influencing kinetics and extent of metal phytoextraction. Studies on the subject are scarce, particularly for salt marsh plants. The aim of this work was to investigate the effect of PAHs on the uptake of Cu by Halimione portulacoides, a plant commonly found in salt marshes. Experiments were carried out in the laboratory, either in hydroponics (sediment elutriate) or in sediment soaked in elutriate, which were prepared with sediment and water from a salt marsh of the Cavado river estuary (NW Portugal). Groups of H. portulacoides (grown in a greenhouse) were exposed to those media during six days. Cu 2+ (as Cu(NO 3) 2), 10 2 and 10 4 μg l −1, was added to the media as well as 1.6 μg l −1 of the sixteen EPA priority PAHs (0.1 μg l −1 of each PAHs). Cu was assayed in solutions, sediments and different plant tissues before and after experiments. After exposure, photosynthetic efficiency and levels of chlorophylls were also measured, indicating that plant stress indicators were identical in all plants independently of the media to which the plants were exposed. PAHs influenced both the soluble Cu fraction and Cu uptake by plants. The amounts of metal accumulated in both roots and stems were significantly higher when the 10 4 μg l −1 of Cu enriched elutriate was amended with PAHs. Thus, results suggest that PAHs may modify Cu solubility, the Cu sorption by plants and/or the passive penetration of Cu into the root cells. Therefore, the combined effects of different types of pollutants should be taken in consideration when studying the remediation potential of plants, namely in terms of phytoextraction.

Assessing Steady-state Fluorescence and PRI from Hyperspectral Proximal Sensing as Early Indicators of Plant Stress: The Case of Ozone Exposure.

High spectral resolution spectrometers were used to detect optical signals ofongoing plant stress in potted white clover canopies subjected to ozone fumigation. Thecase of ozone stress is used in this manuscript as a paradigm of oxidative stress. Steadystatefluorescence (Fs) and the Photochemical Reflectance Index (PRI) were investigatedas advanced hyperspectral remote sensing techniques able to sense variations in the excessenergy dissipation pathways occurring when photosynthesis declines in plants exposed to astress agent. Fs and PRI were monitored in control and ozone fumigated canopies during a21-day experiment together with the traditional Normalized Difference Vegetation Index(NDVI) and physiological measurements commonly employed by physiologists to describestress development (i.e. net CO₂ assimilation, active fluorimetry, chlorophyll concentrationand visible injuries). It is shown that remote detection of an ongoing stress through Fs andPRI can be achieved in an early phase, characterized by the decline of photosynthesis. Onthe contrary, NDVI was able to detect the stress only when damage occurred. These resultsopen up new possibilities for assessment of plant stress by means of hyperspectral remotesensing.

Terpene emission in tissue culture

Tissue cultured plants’ vessel headspace is subject to changes during subculture, and the analysis of its variation offers a non-destructive approach for monitoring plant physiology. Among the volatile organic compounds (VOCs) that can be released by plants and be potentially recovered in the airspace of plant tissue cultures, terpenes are very important since they can offer a snapshot of the physiological status of the plant under in vitro cultivation. Terpenes are synthesized from carbon directly shunted from the photosynthetic carbon fixation cycle and their emission is under genetic and environmental control. The experiments described in this paper propose the evaluation of the plant terpene profile in the culture’s headspace as an early indicator of plant stress through the characterization of plant terpene production. Monitoring of terpene emission as a plant response to mechanical stress such as plant wounding showed an increased isoprene and monoterpene emission rates in the first hour after cutting. The comparison of headspace composition of cultures of two fruit rootstocks, Colt and GF677, showed the former having higher emissions of isoprene, α-pinene and limonene than the latter. A decreasing emission trend was observed during subculture, apparently as a result of culture aging. The in vitro headspace analysis of different myrtle (Myrtus communis L.) clones showed a specific and distinctive terpene emission profile. VOC monitoring of in vitro culture headspace is discussed as a non-destructive approach useful for its relation with major physiological activities of culture and for the determination of the potential production of terpenes.

Phylloxera-infested grapevines have reduced chlorophyll and increased photoprotective pigment content - can leaf pigment composition aid pest detection?

Grape phylloxera (Daktulosphaira vitifoliae Fitch) is a root-feeding pest of grapevines. In Australia, phylloxera-infested vineyards are subjected to quarantine restrictions and early detection remains vital for the timely implementation of post-outbreak quarantine protocols. Current detection methods rely on time-consuming ground surveying, which involves detailed examination of grapevine (Vitis vinifera L.) root systems. Leaf pigment composition is often a sensitive indicator of plant stress. The increasing popularity of remote sensing systems, which exploit those changes in pigments observed with plant stress, offers a real possibility for the development of a phylloxera-specific remote detection system. Our objective was to investigate changes in grapevine leaf pigments associated with phylloxera infestation and to relate any changes to appropriate reflectance indices. This was achieved with a glasshouse experiment in which the responses of two vine cultivars (Cabernet Sauvignon and Shiraz) to phylloxera infestation were compared with their responses to water and nitrogen deficiencies. The responses of leaf pigments to phylloxera infestation were also investigated in Pinot Noir and Cabernet Sauvignon grapevines grown under field conditions. A reduction in the leaf chlorophyll content and an increase in photoprotective pigment concentrations were observed in leaves of phylloxera-infested grapevines compared with uninfested vines. The photochemical reflectance index (PRI) was found to be most closely associated with the ratio of total carotenoid to chlorophyll in these vines.

Translational asymmetry as a sensitive indicator of cadmium stress in plants: a laboratory test with wild-type and mutant Arabidopsis thaliana.

• Translational and bilateral asymmetry have been proposed as sensitive measures of stress in plants, but few studies have addressed the asymmetry-stress association for individuals grown under strictly defined conditions. Here, we assess the impact of cadmium (Cd) stress on various asymmetry measures in a wild-type and mutant strain of Arabidopsis thaliana. • Fitness measures (fresh weight, pod count and shoot length) and developmental stability (DS) measures (bilateral asymmetry and translational asymmetry (TA)) were compared between plants grown under different cadmium concentrations. • Cadmium stress sharply increased TA in both strains but had inconsistent effects on bilateral asymmetry. The TA effects were detected at a Cd concentration when effects on growth and reproduction were not yet evident. • Translational asymmetry, but not bilateral asymmetry, may therefore act as a sensitive indicator of cadmium stress and could be used to assess soil contamination in transplanted A. thaliana.

Toxicity of copper to Quercus robur (English Oak) seedlings from a copper-rich soil

Wisniewski, L. and Dickinson, N.M. Toxicity of copper to Quercus robur (English Oak) seedlings. ––Acorns were germinated after collection from a mature Q. robur woodland at an historic copper mine site in Cheshire, England, and from an uncontaminated reference site. Hydroponic screening trials of seedlings using 0.5 mg Cu l −1 in 25% Hoagland's solution found no growth differences between sites of origin that indicated tolerance. Copper accumulated in the roots, with restricted transport to foliage. Prolonged exposure caused gross perturbations of root morphology, reduced root and shoot growth, and leaf chlorosis. Pre-exposure of seedlings to low levels of copper and repeated exposure provided little evidence for acclimation to the metal. Damage to photosynthetic systems was reflected in altered chlorophyll ratios and carotenoid pigments, including those related to the xanthophyll cycle. Zeaxanthin biosynthesis was not a particularly sensitive or reliable indicator of plant stress. It is concluded that survival of oak seedlings in the field is related to soil or rhizosphere processes mediating copper mobility, rather than to physiological tolerance or plant acclimation.

Effects of Pb-EDTA and EDTA on oxidative stress reactions and mineral uptake in Phaseolus vulgaris.

Sequestration of Pb by synthetic chelates has been reported to increase bioavailability, uptake, and translocation of this metal in plants. In this work the potential phytotoxic effects of Pb-EDTA were investigated in Phaseolus vulgaris L. cv. Limburgse vroege plants grown on hydroponics. Addition of 50 microM Pb-EDTA to the nutrient solution caused a significant induction of syringaldazine peroxidase (SPOD; EC 1.11.1.7) in roots and primary leaves and guaiacol peroxidase (GPOD; EC 1.11.1.7) in leaves. Addition of 100 microM Pb-EDTA further exacerbated ascorbate peroxidase (APOD; EC 1.11.1.11), GPOD, dehydroascorbate reductase (DHAR; EC 1.8.5.1), glutathione reductase (GR; EC 1.6.4.2) and malic enzyme (ME; EC 1.1.1.40) in roots and APOD and ME in primary leaves. Addition of 200 microM Pb-EDTA also induced DHAR in leaves. This induction of peroxidases (SPOD, GPOD, APOD), enzymes of the ascorbate-glutathione cycle (DHAR, GR in roots) and of an NADP+ reducing enzyme in roots and primary leaves indicates that oxidative stress has been initiated. At 200 microM Pb-EDTA, chlorophyll a and b content in leaves was significantly reduced while visible effects on root morphology and shoot length were observed, while no significant morphological effects were found in the leaves, confirming the sensitive character of the measured enzymes as plant stress indicators. Elevation of the Pb-EDTA concentration in the growth medium significantly reduced the content of Ca, Fe, Mn and Zn taken up by plants, probably due to ion leakage as a result of observed toxicity. Addition of up to 200 microM EDTA increased chelation of divalent cations in nutrient solution resulting in reduced plant uptake of Zn, Cu, Fe and Mn. This did not result in phytotoxicity.

Assessing salt marsh health: A test of the utility of five potential indicators

We examined the utility of five measures of salt marsh function, focusing on angiosperms and microbes, as potential indicators of salt marsh health. We studied twelve salt marsh creeks around Charleston Harbor, South Carolina, USA, six of which were polluted with metals and/or organic compounds and six of which were relatively pristine. Physical variables (sediment clay-silt content, creek water salinity) did not differ between impacted and reference sites. Microtox toxicity measures (expressed as wet or dry units) did not differ between impacted and reference sites. Photosynthesis and transpiration rates of creekbank Spartina alterniflora did not differ between impacted and reference sites, nor did measures of peroxidase activity in S. alterniflora. The glutathione concentration of S. alterniflora was lower at impacted sites than at reference sites; however, glutathione concentration did not respond to pollution in an earlier study in Georgia, likely because glutathione responds differently to particular chemicals rather than being a generic indicator of plant stress. Overall, these measures showed little promise as rapid indicators of salt marsh health. Other methods, such as quantifying benthic invertebrate taxa, may be more reliable for assessing ecosystem health in salt marsh systems.

592 Use of Infrared Thermometry and Heat-pulse Technique for Detection of Water Stress in Apple Trees

The recent development of small portable infrared thermometers has made canopy temperature an easily measured characteristc in the field. Our objective was to correlate a reduction of soil water with foliage temperature and to compare it with other indicators of plant stress (Pn, E, gs, leaf expansion, sap flow). During Summer 1998, we evaluated the responses of potted apple rootstocks (cultivars Budagowski 9, M9, and Mark) to soil water deficit. Irrigation was withheld for 7 days, and the canopy temperature (Tc) was measured daily with an infrared camera. Tc was always higher than air temperature (Ta). Tc between control and stress plants began to differentiate from day 3. In Mark, this difference was maintained until the end of the experiment. However, gas exchange in Mark seemed to be less affected by the stress than in the other two cultivars. At day 7, midday stomatal conductance (gs) was 38.0, 32.3, and 72.0 mmol·m–2·s–1 in Budagowski 9, M9, and Mark, respectively (control values varied between 161.6 and 164.3 mmol·m–2·s–1 for all the cultivars). Heat-pulse sapflow sensors installed on Mark indicated that the speed of the xylem sap was affected by the stress from day 4 (19-26 cm/h for the controls vs. 15–21 cm/h for the stressed plants). Specific details on the physiological data will be presented.

Monitoring plant physiological characteristics to evaluate mine site revegetation: A case study from the wet-dry tropics of northern Australia

Biologically driven markers or monitors were used to evaluate plant and ecosystem health of uranium-mining affected sites. Plant water, nitrogen (N) and phosphorus (P) status were used to measure physiological characteristics of tree and shrub species at sites perturbed by mining activities (waste rock dumps: WRD 1, WRD 2; mine wastewater irrigated woodland) and of species at undisturbed woodland (tropical savanna). Plant water status was evaluated by measuring leaf relative water content (RWC) and carbon isotope discrimination (δ13C). Leaf RWC varied significantly (P<0.0001) between wet and dry season in species at the woodland sites with higher RWC in the wet season compared to the dry season. No seasonal differences were observed in RWC in species at the WRDs. Leaf δ13C was similar in species at woodland sites and WRD 2 (−28.8 to −28.1‰) but was significantly (P<0.05) lower in species at WRD 1 (−27.6‰). This suggests that species at WRD 1 had a lower water availability and/or lower water use compared to species at all other sites. WRD substrate had an up to 4-orders of magnitude greater availability of inorganic phosphate (Pi) compared to woodland soil as determined using in situ ion exchange resin. Pi concentrations in xylem sap of species at WRDs were 2- to 3-fold higher compared to species at woodland sites. Plant nitrate reductase (NR) activity was low in most species at woodland and WRD 1. In contrast, Eucalyptus and Acacia species had high NR activities of up to 300–700 pkat g-1 fw at WRD 2 indicating that these species had greater nitrate use than species at all other sites. Nitrate availability in the top five cm of the profile, as determined using in situ ion exchange resins, increased at all sites in the wet season, but no significant differences were observed between sites using this method. However, traditional soil analysis revealed that WRD substrate had a 2-times higher nitrate content (0 to 1000 mm depth) compared to woodland soil. Thus, it is likely that plants at WRD2 accessed nitrate from deeper parts of the profile. Proline, an indicator of plant stress, was found in appreciable quantities in leaves of herbaceous species but not in woody species. Soil and leaf δ15N were measured to investigate N-cycling and the contribution of diazotrophic N2 fixation to plant N nutrition. Soil δ15N values were highest and most variable at WRD 2 (6.2‰) compared to all other sites (irrigated woodland 3.1‰, undisturbed woodland 2.5‰, WRD 1 0.9‰). This may indicate that N-turnover and nitrification was greatest at WRD 2 leading to greater 15N enrichment of soil N. At all sites, Acacia species were nodulated and putatively fixing N2. With the exception of WRD 2 where leaf δ15N of Acacia species averaged 0.9‰, Acacia species had 15N depleted values characteristic of species that receive N derived from N2 fixation (−0.8 to −0.6‰).

Assessment and monitoring of decline and dieback of forest eucalypts in relation to ecologically sustainable forest management: a review with a case study

Summary In this paper techniques for assessing and monitoring the decline and dieback of forest eucalypts are reviewed in relation to ecologically sustainable forest management. The concept of ecologically sustainable management is a guiding philosophy being adopted for the management of all Australian native forests. An integral component of this strategy will be the ability to monitor forest health. This requires assessment of both the appearance of trees (canopy condition) and their underlying physiological status. However, visual assessment of eucalypt canopies can be misleading because of their opportunistic leafing phenology and epicormic regrowth characteristics. Several forest health assessment programs outside Australia now use multispectral imagery obtained by remote sensing. Such programs depend on relating spectral features with plant physiological properties such as chlorophyll content of the foliage. More recently chlorophyll fluorescence spectra have been related to the functioning of the photosynthetic apparatus and have been shown to be highly sensitive indicators of plant stress. Both reflectance and fluorescence spectral properties should be included in the development of future health monitoring programs for eucalypt forests. A form of forest eucalypt dieback associated with bell miners (Manorina melanophrys) was selected to test the correlation between canopy dieback and leaf-based chlorophyll fluorescence measurements. In addition, a conceptual model of this form of eucalypt dieback is presented in order to demonstrate the complex interrelationships between the poor health of individual tree canopies and overall declining health of the forest ecosystem. Such a model is critical to the correct interpretation of remote sensing imagery.

Effect of Root Severance on Growth of Field-grown Sugar Maple

This study addresses the growth limits imposed on large landscape trees by root severance at harvest and tests the effect of rootball size on stress following root severance. Two rootball sizes and a nontreated control treatment were randomly assigned to Acer saccharum Marsh. (sugar maple) trees in four adjacent nursery rows at Waynesboro Nurseries, near Waynesboro, Va. One rootball size (75 cm in diameter) corresponded to the American Association of Nurserymen standards, and the other was 90 cm in diameter. Trees were dug with intact rootballs before bud swell. Height growth of root-severed trees was 19%, trunk diameter increase 10%, and twig extension 18% of control trees 2 years after root severance. Total stem nonstructural carbohydrate content was higher on controls than on root-severed trees. Leaf nitrogen content was greater for root-severed trees, presumably due to lack of a dilution effect. Although growth was severely curtailed by root severance, no effect on growth or measured plant stress indicators resulted from the use of a 90-cm vs. a 75-cm-diameter rootball.

ANALYSIS OF LASER‐INDUCED FLUORESCENCE LINE SHAPE OF INTACT LEAVES: APPLICATION TO UV STRESS DETECTION

Abstract— In vivo laser‐induced fluorescence spectra of intact leaves of healthy and UV‐irradiated Salvia splendens plants excited at 337 nm by a nitrogen laser were recorded using an optical multichannel analyzer system. The spectra showed the typical fluorescence bands centered around 450, 530, 685 and 730 nm. Exposure to UV radiation changed the relative intensity values of these bands and their peak positions. The analysis of the acquired spectra in terms of a linear combination of Gaussian bands was carried out to determine accurately the peak positions and the relative intensity contribution of the various bands to the laser‐induced fluorescence spectra on healthy and UV‐treated plants of different age.The results indicate that a curve‐fitting analysis of the measured fluorescence spectra is a useful and sensitive method to discriminate the various band contribution to the whole leaf fluorescence spectrum. The comparison among blue‐green and red‐far‐red fluorescence of leaves was also confirmed as an effective indicator of UV stress in plants.

Applications of Chlorophyll Fluorescence to Forest Ecology

Functioning of photosystem II (PSII) is the most sensitive indicator of environmental stress in plants. Changes in PSII activity can be assayed rapidly and non-destructively by measurement of chlorophyll fluorescence. While there have been many laboratory studies of chlorophyll fluorescence, fluorescence techniques have seldom been applied to questions in forest ecology. Most studies have emphasised the fluorescence parameter, Fv/Fm, which is well correlated with the quantum efficiency of photosynthetic carbon dioxide assimilation or oxygen evolution. This parameter reveals information which can be related to diurnal and seasonal variation in photosynthesis, plant growth and community dynamics. Thus, fluorescence techniques provide a powerful means of linking photosynthesis with higher levels of plant functioning and have great potential for research in forest ecology.

Ratios of leaf reflectances in narrow wavebands as indicators of plant stress

Abstract Ratios of leaf reflectances that were measured within narrow wavebands (2nm) were evaluated as indicators of plant stress. Wavebands used in ratio computation were based on earlier studies that determined the wavelength regions in which reflectance was most affected by 8 stress agents among 6 plant species. Several ratios, such as reflectance at 695 nm divided by reflectance at 670 nm (R695/R670), were affected by some but not all stress agents. However, R695/R420, R605/R760, R695/R760 and R710/R760 were significantly greater (p≤0·05) in stressed compared with non-stressed leaves for all stress agents. The ratios that most strongly indicated plant stress were reflectance at 695 nm divided by reflectance at 420 nm or 760 nm.

Putrescine (1,4-Diaminobutane) as an Indicator of Pollution-Induced Stress in Higher Plants: Barley and Rape Stressed with Cr(III) or Cr(VI)

The performance of the free polyamines as plant stress indicators is studied in barley and rape plants grown in nutrient culture, by exposure to Cr(VI) or Cr(lIl) in concentrations ranging from 0 to 100 ppm. Putrescine levels are elevated up to 10 times in the leaves of stressed plants compared to those of control plants, but neither spermidine nor spermine show any consistent reactions on the stress. Cr(VI) is more toxic than Cr(lIl) and induces putrescine accumulation quicker than Cr(llI). Chromium concentrations in leaves reach 3000-5000 ppm (dry wt) after exposure to 100 ppm Cr(VI) and 300-400 ppm (dry wt) following exposure to 100 ppm Cr(III). Simultaneously with, or following shortly after the putrescine induction, reductions in root growth, chlorosis, induction of leaf chitinase activity, and, later, reduced shoot growth and lowered water content in leaves are observed. The pattern of the effects indicates that the basal toxicity mechanism of the two chromium species is connected to disturbance of the normal function of the root. Putrescine induction is an integrated part of the response mechanism of the stressed plants, appearing as an early sign of stress. However, the chromium concentration of the leaves as a warning of chromium-induced stress is judged to be an even more sensitive indicator.