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Relative phytotoxicity of an allelochemical hydroquinone to coontail (Ceratophyllum demersum L.) and rice (Oryza sativa L. var. Kranti)

D. K. Pandey and N. Mishra

Physiology Section, National Research Center for Weed Science, ICAR, Maharajpur, Jabalpur (M.P.) 402004, India. E-mail: dayapandey@hotmail.com , dkpandey54@yahoo.com

Abstract

Relative toxicity of hydroquinone on rice (Oryza sativa L. var. Kranti) and associated submerged aquatic weed coontail (Ceratophyllum demersum L.) was investigated for exploring possible use of the phytotoxin as herbicide in management of the weed. The hydroquinone was lethal to rice at and above 5mM. It was phytotoxic to coontail at as low as 0.01 mM and lethal at 0.075-0.10 mM. The toxicity symptoms on the weed were dull green appearance followed by loss of biomass, and bleaching and fragmentation of the plant resulting in death in 3-12 days. The treated plants showed an excessive leakage of cellular constituents from coontail reflecting loss of cellular membrane integrity. There was a loss of photosynthetic pigments with the advancement of the treatment and concomitant accumulation of oxidative stress as reflected by initial spurt of activity of some of the enzymes of the oxidative stress. Relatively higher toxicity of hydroquinone, a phytotoxin, to coontail than to rice appeared to be due to capability of the latter to withstand excessive accumulation of the chemical in the roots and inability of the chemical to reach the shoots. The phytotoxin appears to have killed the weed by causing massive damage to cellular membrane integrity, loss of metabolic activities and macromolecules, accompanied by associated starvation and accumulation of oxidative stress. Such a differential toxicity of a phytotoxin, which is short lived in the environment, to a crop and associated weed may have potential of weed management under certain circumstances.

Media summary

Hydroquinone was found to be more toxic to the aquatic weed coontail than rice and may have potential as a weed management tool in rice paddies

Key Words

Hydroquinone; coontail; Ceratophyllum demersum L.; rice; Oryza sativa L.; enzymes of oxidative stress; solute leakage; aquatic weed; photosynthetic pigments

Introduction

Several plant species have been reported to show allelopathic interactions in aquatic ecosystems (Gopal and Goel 1993). The findings imply that at high density such plants in aquatic ecosystems may exert chemical regulation on the growth of other plants. Dead and decomposition of plant and plant parts, and macrophytes and aquatic-terrestrial plant interactions may also interact with species dynamics in aquatic ecosystems (Gopal and Goel 1993). Thus, the allelochemicals and other phytotoxic plant constituents have potential for use as such and/or after chemical modification to more bioactive molecules for use as environment-friendly herbicides. Several plant materials and their constituents have been reported to have phytotoxic potential enough to act as natural herbicides (Duke et al. 2000; Pandey 1996) in aquatic ecosystems and possibly for the management of aquatic weeds. It appears from the scientific literature that herbicidal potential of a large number of plant constituents has not been studied adequately. Therefore it would be relevant to study herbicidal property of hydroquinone, a phytotoxic plant constituent, on a representative submerged aquatic weed and rice. This may facilitate exploration and exploitation of the chemical for an environment-friendly weed management. The natural occurrence of hydroquinone has been observed in many products.

Hydroquinone is considered to be the most important component of the allelopathic interaction between the perennial weed leafy spurge (Euphorbia esula) and the small everlasting (Antennaria microphylla). A differential ability to detoxify hydroquinone in the two species was observed in tissue cultures (Hogan and Manners 1990, 1991). Hydroquinone has been found in plant-derived food products (e.g., wheat germ), in brewed coffee, and in teas prepared from the leaves of some berries, where the concentration sometimes exceeds 1%. Hydroquinone occurs in a variety of forms as a natural product from plants and animals. It has been found in non-volatile extracts of coffee beans (Hogel 1958) and other foods, and as arbutin (a glucoside of hydroquinone) in the leaves of blueberry, cranberry, cowberry and bearberry plants (Varagnat 1981). Hydroquinone formation from arbutin in Pyrus spp. is involved in fire blight resistance (Smale and Keil, 1966; Hildebrand et al., 1969). However, adequate information is not available on relative toxicity of the phytotoxin on rice and its aquatic weeds.

The contain coontail (Ceratophyllum demersum L.) is a cosmopolitan quickly and densely growing usually free floating submerged weed occurring in shallow and deep water, growing in both cool and warm water, infesting ponds, irrigation channels and rice fields. The species has tolerance to environmental extremes. The species is one of the prominent and noxious weeds in the rice fields and paddies of the tropics and subtropics competing with the crop for resources and reducing the crop yields (Vongsarog, 1996).

The present investigation was undertaken to evaluate phytotoxicity of hydroquinone on rice and associated common submerged weed coontail to explore possible use of the phytotoxin for management of the weed in aquatic ecosystem. It was also planned to study the mechanism of phytotoxicity of the natural product on the weed.

Methods

Plant materials

The submerged weed coontail (Ceratophyllum demersum L.) maintained in the collection of the Physiology Section of the National Research Center, and rice (Oryza sativa L. var. Kranti) was used in the experiments.

Evaluation of phytotoxicity of hydroquinone to coontail

The hydroquinone solutions were prepared in water containing a quarter strength (Pandey, 1996) of the nutrient medium (Einhellig et al., 1985). Preweighed floating and submerged weeds were placed in the solution (2 L) in plastic bucket and allowed to grow outdoors. Plants placed in nutrient medium similarly comprised controls. Evaporative loss of water was replenished twice daily. Toxicity symptoms and biomass of the weeds were monitored. Similar experiments were conducted in plastic tubs (20 L) for verification of the results.

Mechanism of phytotoxicity of hydroquinone on coontail

The mechanisms of phytotoxicity of hydroquinone on coontail have been described in detail in our earlier communication (Pandey et al. 2005). Sugars, starch, amino acids, phenolics, crude protein, N, P, and K, chlorophyll and carotenoids were estimated in the plants subjected to treatment for different durations. Leakage of solutes was also monitored from the plants. The effect of hydroquinone on protein and enzymes of oxidative stress, phytotoxicity of hydroquinone to rice, effect of hydroquinone on germination and seedling growth of rice, effect of hydroquinone on seedling growth of rice in solution culture outdoors were investigated.

Results

Hydroquinone inhibited growth of coontail at as low as 0.01 mM, and lethal concentration of the phytotoxin was 0.075-0.10 mM (Table 1). The weed was killed in about 3-6 days outdoors. The symptoms of hydroquinone toxicity appeared as early as a few hours from initiation of the treatment. The hydroquinone was not inhibitory to rice seed germination up to the highest concentration (10 mM) tried in the study (Table 2). The seedling growth was inhibited by hydroquinone especially at 5-10 mM. Early seedling (25 days after sowing) growth of rice outdoors was inhibited by hydroquinone marginally at 1.0 mM and was lethal at 5 mM (Table 3).

Table 1. Phytotoxicity of hydroquinone on submerged aquatic weed coontail

Treatment
(mM)

Change in biomass (%) - days after initiation of the treatment

3

6

9

12

Control

6.53.2a

13.25.7a

15.515.5a

18.55.6a

0.05

2.91.5a

4.71.9a

7.32.4a

9.54.9a

0.075

-2.41.6a

-6.22.3a

-19.58.9a

-41.96.6a

0.10

-100.0

-100.0

-100.0

-100.0

LSD at P=0.05

4.46

7.45

12.90

11.50

Values are means of three replications SD. a, Data included in statistical analyses. Minus 100% reduction in biomass denotes death of the treated plants.

Table 2. Phytotoxicity of hydroquinone on germination (16 days after initiation of imbibition) and seedling growth (8 days after initiation of imibition of rice (Oryza sativa L. var. Kranti) seeds at 25C in the dark.

Treatment
(mM)

Germination (%)

Seedling growth

Length (cm)

Fresh weight (mg)

Root

Shoot

Root

Shoot

Control

97.62.30

5.70.05

3.60.25

17.51.55

71.48.46

0.01

97.01.00

5.80.05

2.90.26

17.40.77

73.45.56

0.05

96.02.64

5.40.18

3.00.15

18.71.75

66.310.37

0.10

97.31.52

5.10.30

2.70.36

16.50.95

54.58.35

0.50

97.01.00

4.60.80

2.930.35

16.91.81

56.03.85

1.00

96.31.15

3.30.26

2.50.05

12.41.15

52.82.61

5.00

96.02.64

2.30.15

2.260.25

12.21.20

53.61.92

10.00

96.31.50

0.40.03

1.10.20

0.80.15

21.94.94

LSD at P=0.05

NS

0.57

0.43

2.20

11.13

Values are means of three replications SD.

Table 3. Phytotoxicity of hydroquinone on rice (Oryza sativa L. var. Kranti) (25 days old) seedlings outdoors in aquaculture.

Treatment
(mM)

% Change in biomass over original value days after initiation of the treatment

3

6

9

12

Control

2.01.0a

33.412.6a

35.522.3a

38.47.6a

0.05

7.00.7a

79.226.1a

103.033.8a

116.431.7a

0.075

7.21.1a

11.72.1a

30.610.8a

29.810.3a

0.10

5.42.7a

21.07.0a

39.616.5a

40.215.5a

1.00

4.61.9a

8.48.2a

28.626.5a

18.24.4a

5.00

-13.55.3a

-100.0

-100.0

-100.0

10.00

-19.51.5a

-100.0

-100.0

-100.0

LSD at P=0.05

3.97

24.11

44.5

34.2

Values are means of three replications SD. a, Data included in the LSD calculations. Minus 100% reduction in biomass denotes death of the treated plants.

Table 4. The effect of lethal concentration of hydroquinone (0.10 mM) on sugar, starch, amino acids, phenolics, P and K contents (mg g-1 dry weight) in coontail

Attribute

Values for days after initiation of the treatment

1

2

3

Control

Treatment

Control

Treatment

Control

Treatment

Sugar

26.11.2

17.71.4

25.60.6

12.70.8

20.00.4

5.30.7

LSD at P 0.05

1.72

Starch

137.83.5

102.35.2

133.33.6

93.18.4

121.96.1

70.64.3

LSD at P 0.05

9.76

Amino acids

3.40.2

2.30.2

3.80.4

1.90.2

3.50.3

1.20.1

LSD at P 0.05

0.52

Phenolics

0.940.05

0.800.03

1.000.10

0.660.05

1.070.15

0.260.03

LSD at P 0.05

0.15

Phosphorus

0.970.12

0.870.02

0.980.11

0.810.10

1.300.05

0.400.05

LSD at P 0.05

0.15

Potassium

32.22.2

33.82.5

39.76.1

10.30.4

29.60.4

6.70.5

LSD at P 0.05

5.08

Values are means of three replications SD.

Table 5. The effect of lethal dose of hydroquinone (0.10 mM) on photosynthetic pigments in coontail

Attribute

Chlorophyll and carotenoids (mg g-1 dry weight) days after initiation of the treatment

1

2

3

Control

Treatment

Control

Treatment

Control

Treatment

Chlorophyll a

4.20.5

3.80.4

3.80.4

2.10.7

4.40.6

1.30.1

LSD at P 0.05

0.86

Chlorophyll b

2.00.3

1.70.2

1.80.2

1.40.1

1.90.3

0.90.1

LSD at P 0.05

0.42

Total chlorophyll

6.20.8

5.60.6

5.70.6

3.80.1

6.30.9

2.20.2

LSD at P 0.05

1.13

Carotenoids

2.20.3

1.50.2

2.10.2

0.80.05

2.30.3

0.40.04

LSD at P 0.05

0.37

Values are means of three replications SD.

Table 6. The leakage of solutes (g-1 dry weight) into soak water from coontail plants in response to treatment at lethal concentration of hydroquinone (0.1 mM) outdoors

Attribute

Values for days after initiation of the treatment

1

2

3

Control

Treatment

Control

Treatment

Control

Treatment

EC (μ S)

8717.7

26171.5

6714.7

591110.1

684.9

622122.7

LSD at P 0.05

131.6

OD at 264 nm

10.31.3

161.34.0

12.40.4

244.642.4

10.11.4

341.39.8

LSD at P 0.05

31.78

K (mg)

0.0450.003

11.1502.900

0.0640.006

14.5401.370

0.0810.007

26.6505.050

LSD at P 0.05

4.350

P (mg)

0.150.030

0.3480.088

0.1340.005

0.6660.190

0.1390.016

1.0300.081

LSD at P 0.05

0.168

Sugar (mg)

0.940.47

6.810.62

1.020.36

14.122.05

0.560.004

24.900.56

LSD at P 0.05

1.673

EC (μS), Leakage of electrolytes measured as electrical conductivity. OD at 264 nm, Leakage of UV absorbing substances (units; 0.01 OD at 264 nm = 1 unit). Values are means of three determinations SD.

Table 7. Effect of hydroquinone at lethal concentration 0.1 mM) on enzymes of oxidative stress in coontail

Attribute

Values for days after initiation of the treatment

1

2

3

Control

Treatment

Control

Treatment

Control

Treatment

Catalase

87.19.7

5.50.27

100.17.62

5.81.16

118.96.14

7.20.43

LSD at P 0.05

10.05

Ascorbate peroxidase

2374.0

943.4

2548.0

1418.6

2455.5

11917.0

LSD at P 0.05

16.01

Pyrogallol peroxidase

2953.0

3807.5

3123.0

7115.5

2734.0

7388.6

LSD at P 0.05

10.17

Guaiacol peroxidase

2387.0

2628.6

2299.6

35732.6

2223.5

33231.2

LSD at P 0.05

34.64

Glutathione reductase

8.30.6

18.30.3

12.00.1

34.81.3

6.90.3

37.20.3

LSD at P 0.05

1.14

Glutathione S-transferase

4.60.6

3.10.01

5.350.5

3.870.14

6.80.37

3.20.25

LSD at P 0.05

0.68

The values are means of three replications SD.

Among the first visual symptoms of toxicity was dull green appearance of the plants. Acquisition of flaccid texture, loss of pigments and fragmentation of plants followed this. There was reduction in sugar, starch, amino acids, phenolics, phosphorus and potassium (Table 4), chlorophyll a, chlorophyll b, total chlorophyll and carotenoids in the plants with treatment duration (Table 5). The P and K contents also showed a decline especially with increased duration of the treatment (Table 4). The treated plants leaked into the soak water much more electrolytes, UV absorbing substances (probably including amino acids, polypeptides, nucleotides and nucleic acids, phenolics and other metabolites), K, P and sugars (Table 6).

Activity of antioxidative enzymes in coontail over a short period in response to lethal concentration of hydroquinone (Table 7) showed various responses. There was reduction in the activity of catalase, ascorbate peroxidase and glutathione S-transferases with time. The activity of pyrogallol peroxidase showed initial strong increase followed by subsequent decline. While guaiacol peroxidase and glutathione reductase increased with time.

Conclusion

In the present study hydroquinone was more phytotoxic to coontail than to rice. The seed germination in rice in the dark was not inhibited by the phytotoxin upto 10 mM, the highest concentration tried in the study. Seedling growth in the dark was inhibited at higher concentrations. The seedling growth in the dark may reflect manifestations of the reserve food mobilization from the seed (Bewley and Black, 1985). Thus, it appears that hydroquinone did not have profound effect on the reserve food mobilization in rice. Similarly, early seedling growth of rice had relatively much lower sensitivity to hydroquinone toxicity.

The present study clearly showed that hydroquinone, a phytotoxin, is less phytotoxic to rice than to its associated submerged weed coontail. Such a differential toxicity of a phytotoxin, which is short lived in the environment, to a crop and associated weed may have potential of weed management under certain circumstances.

References

Bewley JD and Black M (1985). Seeds - physiology of development and germination. Plenum Press, New York.

Duke SO, Fedayan FE, Romagni JG, and Rimando AM (2000). Natural products as sources of herbicides: current status and future trends. Weed Research 40, 99-111.

Einhellig FA, Leather GR, Hoffs LL (1985) Use of Lemna minor L. as a bioassay in allelopathy. Journal of Chemical Ecology 11, 65-72.

Gopal B, Goel U (1993) Competition and allelopathy in aquatic plant communities. Botanical Review 59, 155-210.

Hildebrand DC, Powell CC Jr, Schroth MN (1969) Fire blight resistance in Pyrus: Localization of arbutin and -glucosidase. Phytopathology 59, 1534-1539.

Hogan ME, Manners GD (1990) Allelopathy of small everlasting (Antennaria microphylla). Phytotoxicity to leafy spurge (Euphorbia esula) in tissue culture. Journal of Chemical Ecology 16, 931-939.

Hogan ME, Manners GD (1991) Differential allelochemical detoxification mechanism in tissue cultures of Antennaria microphylla and Euphorbia esula. Journal of Chemical Ecology 17, 167-174.

Hgl O (1958) [Some non-volatile extracts of coffee.] Mitt Geb Lebensm Hyg, 49, 433-441 (in German).

Pandey DK (1996) Phytotoxicity of sesquiterpene lactone parthenin on aquatic weeds. Journal of Chemical Ecology 22, 151-160.

Pandey DK, Mishra N, Singh P (2005) Relative phytotoxicity of allelochemical hydroquinone on rice (Oryza sativa L.) and associated aquatic weed green musk chara (Chara zeylanica Willd.). Pesticide Biochemistry and Physiology (In press).

Smale BC, Keil HL (1966) A biochemical study of the intervarietal resistance of Pyrus communis to fire blight. Phytochemistry 5, 1113-1120.

Varagnat J (1981) Hydroquinone, resorcinol, and catechol. In: Grayson M ed. Kirk-Othmer encyclopedia of chemical technology, 3rd ed. New York, John Wiley and Sons, pp 39-69.

Vongsarog P (1996) Weed management in deep water rice, in Weed management in rice, FAO Plant Production and Protection Paper (Rome) 139, 113-122.

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