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Journal of Plant Nutrition
ISSN: 0190-4167 (Print) 1532-4087 (Online) Journal homepage: http://www.tandfonline.com/loi/lpla20
Effect of excess lead, cadmium, copper, and zinc on water relations in sunflower R. Kastori , M. Petrović & N. Petrović To cite this article: R. Kastori , M. Petrović & N. Petrović (1992) Effect of excess lead, cadmium, copper, and zinc on water relations in sunflower, Journal of Plant Nutrition, 15:11, 2427-2439, DOI: 10.1080/01904169209364485 To link to this article: http://dx.doi.org/10.1080/01904169209364485
Published online: 21 Nov 2008.
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Date: 03 May 2017, At: 19:06
JOURNAL OF PLANT NUTRITION, 15(11), 2427-2439 (1992)
EFFECT OF EXCESS LEAD, CADMIUM, COPPER, AND ZINC ON WATER RELATIONS IN SUNFLOWER R. Kastori, M. Petrovic, and N. Petrovic Institute of Field and Vegetable Crops, Faculty of Agriculture, 21000 Novi Sad, Yugoslavia
ABSTRACT:
The effect of excess concentrations of lead (Pb), cadmium (Cd),
copper (Cu), and zinc (Zn) on water relations in young sunflower (Helianthus annuus L.) plants was studied in water culture under greenhouse conditions. The accumulation of the heavy metals was more intensive in the root than in the shoot. The rates of heavy metal accumulation in root were arranged in the following decreasing order: Cu, Cd, Zn, and Pb. Their transport into the above-ground parts followed the order: Zn, Cu, Pb, and Cd. Transpiration and relative water content were significantly decreased by excess concentrations of the heavy metals. The number of stomata per unit leaf area was increased while the size of the stomata was decreased. The concentration of free proline significantly increased in the leaves of intact plants as well as in leaf discs incubated in the presence of heavy metals. The concentration of soluble proteins decreased as well, particularly when plants were exposed to high concentrations of the heavy metals. It was concluded that excess concentrations of the heavy metals significantly affected plant water status, causing water deficit and subsequent changes in the plants. The most intensive effect on the plants was exerted by Cd, less intensive by Cu and Zn and the least intensive by Pb. INTRODUCTION Heavy metal availability in soil depends on natural processes, particularly lithogenic and pedogenic, as well as on anthropogenic factors (7). 2427 Copyright © 1992 by Maicel Dekker, Inc.
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KASTORI, PETROVIC, AND PETROVlC
Anthropogenic factors such as industrial activity and mining, sewage disposal, traffic, etc., are mainly responsible for the increase in the concentration of heavy metals in soil most often. Furthermore, soil acidification by acid rains increases heavy metal availability to plants, posing an important problem in agriculture and forestry. Heavy metal stress causes multiple direct and indirect effects on practically all physiological processes in plants (29). The primary toxicity mechanisms of heavy metals alter the catalytic function of enzymes (24,18), damage cellular membranes (22), and inhibit root growth (30). These changes cause numerous secondary effects such as inhibitions in photosynthesis (20) and mineral nutrient uptake (16), hormonal imbalance and water stress (1), changes in photoassimilate accumulation (10), structural and ultrastructural changes (25), etc. In investigating metal toxicity in plants, it is very difficult to distinguish between the primary effects and the secondary changes. Up to now, greater attention has been paid to the effect of heavy metal stress on photosynthesis and mineral nutrition than to water relations in plants (3). Metals such as Zn 2+ , Cd2+, and Cu 2+ have similar electron characteristics, but different chemical properties, ion radius, and affinities for biological ligands. Therefore, it can be assumed that their physiological effects differ as well. This investigation compared the effect of various concentrations of Pb, Cu, Zn, and Cd on the water relations in sunflower. MATERIALS AND METHODS Plant Material and Culture Conditions:
In this experiment, we used intact
plants and leaf discs of the sunflower (Helianthus annum L.) hybrid NS-H-26RM. The plants were grown on Hoagland's liquid nutrient medium under greenhouse conditions for 25 days. Thereafter, the plants were exposed to heavy metals stress. A certain number of plants was transferred to solutions which contained the following molar concentrations of heavy metals: 10 6 and 10^* Pb, 10"6 and 10"4 Cd, 1 0 6 and 10"4 Cu, and 1 0 6 and 10"4 Zn. Lead was applied as Pb(NO3)2, Cd as CdCl2-H2O, Zn as ZnSO4-7H2O, and Cu as CuSO4-5H2O. The plants were exposed to the heavy metals for 48 hours and then analyzed.
WATER RELATIONS IN SUNFLOWER
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Plant Analysis: Round 8-mm discs cut out from the second pair of leaves from that bottom of the control plants were put in the above mentioned solutions of heavy metals plus 0.5% glucose (1 g in 100 mL). The discs were treated for 12 hours at 25°C and 10,000 lx light intensity. The second pair of leaves from the bottom was used for all analyses, except for transpiration intensity which was examined in intact plants. Transpiration intensity was determined gravimetrically from 9 a.m. to 1 p.m. at 25°C. The measurements were replicated six times, with eight plants in each replicate. To determine the relative water content (RWC), one-gram leaf discs (1 cm in diameter) were weighed and then floated on distilled water for 4 h at 25°C. The discs were blotted dry and weighed prior to oven drying at 80°C for 24 h. RWC was calculated as follows (4): , RWC = (Fresh weight - Dry weight) / (Turgid weight - Dry weight) x 100 In the period from 8 to 9 a.m., we took stomata impressions from the upper and lower leaf surfaces with colorless lacquer and a transparent adhesive tape. The length and width of stomata were measured with a micrometer at their longest and widest part, respectively. The results in Table 2 represent the average values for four replications with 10 ocular areas per each replication. The concentration of the heavy metals was assessed in plant material dried at 80°C. The dried samples were digested with a mixture of concentrated nitric and perchloric acids. Total Pb, Cd, Cu, and Zn in the plant digests were determined by standard atomic absorption spectroscopy. The concentration of free proline was determined in fresh plant matter after its extraction with 3% sulfosalicylic acid and coloring with acid ninhydrin reagent in the presence of glacial acetic acid. Spectrophotometric readings were done at 520 nm (5). The soluble protein content in leaves was determined by the method of Iowry et al. (14). The results were statistically processed calculating the least significant difference and the standard errors. RESULTS AND DISCUSSION The uptake of the tested heavy metals was more intensive than their transport from roots to shoot. The rates of heavy metal accumulation in roots were arranged
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KASTORI, PETROVIC, AND PETROVIC
TABLE 1
Effects of Different Levels of Pb, Cd, Cu, and Zn on their Concentration in individual Parts of Young Sunflower Plants
Concentration
Roots
M
Stem
Leaves
ftmol/100 g DW Pb.
Pb 10^ 10^
6.3 ± 0.50 300.4 + 17.90
1.8 ± 0.03 10.1 + 0.06
1.2 ± 0.04 1.8 ± 0.04
Cd 10^ 1O4
114.0 + 7.10 2664.4 + 158.40
2.7 + 0.21 18.4 + 1.50
0.4 + 0.01 1.2 ± 0.05
£u Cu 10* 10^
430.0+ 29.00 3256.2 +163.20
12.1 + 1.80 51.5 ± 5.04
11.8 + 0.83 13.4 + 0.98
Zn 6
Zn 10" 10^
57.8 + 3.60 1576.9 +102.00
27.1 ± 2.04 214.7+18.30
29.8 ± 2.15 35.6 + 2.72
Averages of three replications ± SE
in the following decreasing order: Cu, Cd, Zn, and Pb (Table 1). Their transport into the above-ground parts followed the order: Zn, Cu, Pb, and Cd. Differences in the intensity of uptake and transport of heavy metals have been observed by other authors too. According to Oberlander and Roth (16), Cu and Zn accumulated in barley roots most and least intensively, respectively. Zinc was transported into the barley shoot most intensively, while Cu and Cd were transported less intensively. The meager transport of Cd from root into the above-ground parts may perhaps be due to mechanisms which restrict the movement of Cd through plants (12). The deposition of Cd in roots may be considered as a form of detoxification.
WATER RELATIONS IN SUNFLOWER
2431
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