Effects of heavy metals (Cd, Cu, Pb, Hg) on pollen germination and tube growth of quince (Cydonia oblonga M.) and plum (Prunus domestica L.)

Fresenius Environmental Bulletin

EFFECTS

OF HEAVY

METALS (Cd, Cu,

Pb, Hg)

ON POLLEN GERMINATION AND TUBE

GROWTH OF

QUINCE (Cydonia oblonga M.) AND

PLUM (Prunus domestica L.)

Nazmi Giir and Aykut Topdemir

Firat University, Department of Biology, Elazig, 23169, Turkey

SUMMARY

Pollen germination and tube elongation rate have fre-quently been used as indicators for air pollution with heavy metals. The tubes of quince and plum pollen were germinated in a culture medium containing the heavy metals Cd, Cu, Hg and Pb. According to the results obtained, these heavy metals led to a significant decrease in pollen germination and tube growth. It was found that there was a parallelism between the concentration of heavy metal salts, and pollen germination and tube growth. While Cd had the most inhibiting effect on pollen germination and tube growth of plums, Cu had the least. Mercury showed the highest toxicity, whereas pollen germination and tube growth rate was less affected by copper in quince plants. As a result, all heavy metals examined negatively affected pollen germination and tube growth in quince and plum plants, but their toxicity levels varied.

KEYWORDS: pollen germination, pollen tube growth, heavy metals, quince, plum.

affect animals and plants [2]. Heavy metals have received the attention of researchers all over the world, mainly due to their harmful effects on plants, especially those on vegetative and generative parts of the plants [3-10]. There are also findings indicating that they cause cytogenic anomalies in plants, such as inhibition of mitosis division, decrease in the mitotic index (cell

division frequency), and

chromosomal anomalies [11]. The generative plant parts can be affected by heavy metals [12]. It has recently been shown that trace amounts of various air pollutants inhibited pollen germination and tube elongation [13]. Pollen germination and tube growth was reduced by SO2 [14, 15] and tube elongation was decreased by inorganic components in acid rain [16-18]. Pollen germination and tube elongation have been prevented or reduced, when treated with insecticides, pesticides [13, 19-22], and heavy metals [9, 10, 23-26]. Therefore, the effects of Cd, Cu, Hg and Pb on pollen germination and tube length of quince (Cydonia oblonga M.) and plum (Prunus domestica L.) plants were investigated in this study.

INTRODUCTION

The term 'heavy metal' is often used to cover a diverse range of elements, which constitute an important class of pollutants. With the industrial development, the production and emission of heavy metals have increased. Some metals, e.g., Mn, Cu, Zn, Mo and Ni, are essential or beneficial micronutrients for microorganisms, plants, and animals, but at high concentrations all these metals have strong toxic effects and pose an environmental threat [1].

Heavy metal pollution can be defined as an undesirable change in the physical, chemical or biological characteristics of land, water and air that may or will harmfully

MATERIALS AND

METHODS _______________________________

Pollens of quince and plum flowers were obtained from Koparusagi village of Elazig in the eastern part of Turkey. The flowers were placed in polyethylene containers and the experiments were carried out without any delay. Flowers from the same tree were used in every sequence of the experiments. Standard solutions of each metal (30, 60, 90,120 and 240 ^M) were prepared with distilled water using CuCl2, PbCl2, HgCl2 and CdCl2

The pollen samples were germinated in Brewbaker and Kwack [27] culture solution. Sterile 3 micro-slides were prepared for each heavy metal solution (2 for experimental group, 1 for control group). A 50 JX\

culture solution aliquot was dripped to 2 various areas on each slide. Then 50 fi\ heavy metal solutions (experimental 36 © by PSP Volume 14 - No 1. 2005 Fresenius Environm ental Bulletin

groups) and 50 /*! deionized water (control group, CG) were added onto the slides. Pollens on anther were homogeneously cultivated in the culture medium using a sterile syringe under a stereomicroscope [27]. Petri dishes (15 cm diameter) with a moist filter paper lining the lower plate served as an improvised humidity chamber. Two glass rods were placed parallel, about 4 cm apart, on the moist filter paper to facilitate the handling of the pollen cultures. Then, the petri dishes were settled in the incubator at 22 ± 2 °C. Each germination medium was fixed with 10 % ethanol after 3 hours [27] to close the lamella. Germina-tion percentages and tube lengths of the pollens were determined under the light microscope by the method of Shivanna and Rangaswamy [27].

Mean and standard deviations were calculated for pollen germination and tube length in each treatment and control of each species. Multiple range tests (Duncan) were used to determine significant differences among the means (P<0.05) in either pollen germination or pollen tube length.

RESULTS _______________________________

The effects of Cu, Pb, Hg and Cd chlorides on pollen germination and tube lengths of quince and plum plants are given in Tables 1 and 2.

TABLE 1 The effects of Cd, Pb, Hg and Cu, respectively, on pollen germination and pollen tube lenght in quince (Cydonia oblonga M.).

CdCl2.H2O PbCl2

Treatment Pollen germ. (%) Tube length (u) Treatment Pollen germ. (%) Tube length (u)

Control 94.7a 281.9a Control 94.7a 281.9a

30 73.1b 157.5b 30 76.0b 199.3b

60 54.4c 59.9c 60 62.8c 137.5c

90 32.2d 44.6cd 90 47.6d 127.6c

120 23.7e 27.2de 120 39.7e 80.2d

240 13.4f 10.4e 240 16.6f 29.8e

HgCl2 CuCl2

Treatment Pollen germ. (%) Tube length (u) Treatment Pollen germ. (%) Tube length (u)

Control 94.7a 281.9a Control 94.7a 281.9a

30 63.5b 155.8b 30 82.8b 218.8b

60 40.3c 123.0c 60 59.6c 141.9c

90 34.0d 107.6c 90 43.2d 117.4d

120 22.3e 72.7d 120 37.0e 102.7d

240 10.6f 26.7e 240 28.5f 59.9e

Note. Significant differences (P<0.05) are indicated by different letters according to multiple range test (Duncan).

TABLE 2 The effects of Cd, Pb, Hg and Cu, respectively, on pollen germination and polen tube lenght in plum (Prunus domestica L.).

HgCl2 CuCl2

Treatment Polen germ. (%) Tube lenght (u) Treatment Pollen germ. (%) Tube lenght (u)

Control 94.3a 151.9a Control 94.3a 151.9a

30 47.2b 68.9b 30 53.5b 84.9b

60 27.7c 31.3c 60 45.4c 64.3c

90 20.3d 25.2cd 90 32.2d 59.20c

120 11.6e 14.7de 120 24.5e 35.0d

240 7.7f 9.3e 240 19.2f 16.9e

CdCl2.H2O PbCl2

Treatment Polen germ. (%) Tube lenght (u) Treatment Pollen germ. (%) Tube lenght (u,)

Control 94.3a 151.9a Control 94.3a 151.9a

30 13.4b 16.5b 30 43.4b 81.45b

60 8.6c 11.8b 60 24.9c 36.7c

90 6.1d 9.6b 90 23.9d 29.9c .

120 4.7e 6.7b 120 14.2e 13.7d

240 2.1f 5.3b 240 9.1f 12.7d

Note. Significant differences (P<0.05) are indicated by different letters according to multiple range test (Duncan)

37

■ © by PSP volume 14 - No 1. 2005

Fresenius Environmental Bulletin

As can be seen, germination rate and tube elongation of pollen decreased with the application of heavy metal solutions. Quince pollen germination was mostly inhibited by Hg, but only weakly by Cu. Significant differences (P<0.05) are observed between all heavy metal concentrations on quince pollen germination. Pollen germination of plum plants is significantly different (P<0.05) at all heavy metal concentrations. Also pollen germination of plum plants was weakly affected by Cu, but mostly by Cd.

Pollen tube lengths of both plants were increasingly affected with the concentrations of the heavy metals applied. Significant differences (P<0.05) on plum pollen tube length are not observed between the treatments with Cu or Pb at 60 and 90 |iM. In addition, no statistically significant differences were found between all concentra-tions of Cd on pollen tube length of plum plants. In contrast, the pollen tube length of quince is not statistically different at 120 and 240 (iM Cd concentration. Pollen tube growth in quince (Cydonia

domestica L) was mostly inhibited

by Cd.

DISCUSSION _____________________________ Addition of heavy metal salts

(CuCl2, PbCl2, HgCl2 and CdCl2) inhibited both in vitro germination and tube growth of quince and plum pollens. Some of the heavy metals are essential micronutrients for the plants at low doses, but in higher doses they may cause metabolic disorders and growth inhibition for most of the plant species [28, 29]. Munzuroglu and Geckil [30] showed that the seed germination, root elongation and coleoptile and hypocotyl growth of wheat and cucumber was inhibited by heavy metals (Hg, Cd, Co, Cu, Pb and Zn). Cheng and Zhou [31] and Song et al. [32] found in their studies on the toxicity of heavy metals (Cd, Cu, Pb and Zn) to wheat that the inhibitory rate of root elongation was higher than that of germination rate at the same concentration of pollutants.

It has been suggested that the inhibitory effects of air pollutants on pollen germination and tube growth may influence plant reproduction [12]. For example, both pollen germination and tube growth are inhibited in apples

(Malus sylvestris Miller cv.

Golden) exposed to simulated acid rain [18]. Tuna et al. [10] showed that the most toxic effect on tobacco pollen germination was ob-servable with the application of Cu, Ni and Hg, but, on other hand, a similar tendency was determined with the applications of Hg, Cd and Ni on pollen tube length. In our study, pollen germination of plum plants was mostly affected by Cd, which also caused the highest toxic effects on pollen tube growth in Cydonia oblonga M. and Prunus

domestica L.

In conclusion, the results proved that all heavy metals have negative effects on pollen germination and tube

growth of the economically important Cydonia oblonga M. and

Prunus domestica L. plants.

However, the damage to pollen varies with the dose. Heavy metals are generally considered to be readily available by the plants from both air and soil sources. Soils and plants are usually subjected to heavy metal contamination from traffic [26]. This will be realized better, when the information that dust and gas particles reach a distance of 20 to 100 km and contain heavy metals at different rates are taken into consideration [33].

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environmental Science and Technology. Elsevier, Amsterdam, 516 pp. Receiv ed: April 28, 2004 Accept ed: August 28, 2004 CORRESPONDING AUTHOR Nazmi Giir Firat Universit y Departme nt of Biology Elazig, 23169-TURKEY e-mail: n2ur@firat.edu.tr FEB/Vol 14/No 1/2005-pages 36-39 9