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Effect of Adaptive Metabolites on Water Relations of Doubled Haploid Wheat Lines at Different Water Levels

E. Nabizadeh1, H. Heidari Sharifabad2, E. Majidi Heravan3 and G. Nourmohammadi4

1 Member of Scientific Council, Islamic Azad University of Mahabad, Esmaeil_nabizadeh@yahoo.com
2
Associated Professor of Plant Physiology, Research Institute of Forests and Rangelands, Tehran, Iran
3
Professor of Crop Physiology, Research Institute of Agricultural Biotechnology, Karaj, Iran
4
Professor of Crop Production, Islamic Azad University, Science and Research Branch, Tehran, Iran

Abstract

Plants that are exposed to environmental stresses, especially water deficit, can respond by altering the osmotic potential of the cells. To study the effects of changes in osmotic potential, the response to water deficit in 8 doubled-haploid lines of wheat was compared with 2 commercial lines (Azar2 and Zarrin). Plants were grown at 100%, 75%, 50% or 25% of soil field capacity. The doubled haploid lines were chosen on the basis of their tolerance to water stress in previous studies. The results showed that decreasing the soil available water caused the leaf water potential and RWC to decrease. The smallest decreases in RWC and water potential under restricted moisture were observed in the lines Azar2 and DH15 and the greatest decreases were observed in the lines Zarrin and DH36. The decrease in plant water potential and RWC was associated with an increase in the concentration of proline and soluble carbohydrates, but these accumulated at different rates between the genotypes. The genotypes considered tolerant to water stress accumulated more soluble sugars as the RWC fell compared to less tolerant genotypes. The highest accumulation of soluble carbohydrates occurred in the line Azar2 and the least belonged to the doubled-haploid DH36.

Media summary

The effects of water deficit on the production of compatible solutes were studied in 8 pure doubled haploid lines of wheat and two commercial varieties.

Key Words

Wheat, drought tolerance, RWC, compatible solutes.

Introduction

Water deficit is one of the most important agronomic problems in the arid and semi-arid areas in the world (Begg and Turner, 1976). Developing genotypes that are tolerance to water deficit is one means to improve yields (Christians and Charles, 1982). Understanding the physiological responses to stress is needed to identify the appropriate traits required to develop lines tolerant to drought (Martin, 1993).

One of the most common reactions of plants to water stress is osmotic adjustment (Mattioni et al., 1997; Bohnert and Shen, 1999) which helps to maintain cell turgidity and decrease the loss of cell water under moisture stress. Accumulation of proline and soluble sugars occur under stress and are associated with the maintenance of physiological process like photosynthesis, respiration and tolerance to stress (Paleg and Aspinall, 1981; Williams et al., 1992; McKersie, 1994). This experiment was conducted to examine the response to water stress within a group of doubled haploid lines of wheat derived from parents differing in their adaptation to rainfed conditions.

Methods

To study the effect of compatibility metabolites on water relations of wheat, eight doubled haploid lines and two commercial lines (Azar2 which was bred for cold non-irrigated regions, and Zarrin which was developed for well-watered environments) were grown under different levels of water deficit. The doubled haploid lines were selected from previous trials in which the lines showed different levels of tolerance to water stress (DH15 and DH28, tolerant; DH21, DH17 and DH19, intermediate tolerance; DH14, DH16 and DH36, sensitive). The experiment was conducted in pots as a factorial RCBD (10 genotypes x 4 water deficit treatments) with 3 replications. Plant were grown until the four leaf stage and then subjected to four water deficit treatments - 100% FC, 75% FC, 50% FC and 25% FC for 15 days. At the end of the treatment period, leaf water potential was measured using a pressure chamber and relative water content (RWC) was measured using the method of Irigoyen et al (1992) and Haidarisharifabad (2001). Proline was measured by the ninhydrin method and soluble carbohydrates were measured by the anthrone method described by Irigoyen et al. (1992).

Results

There was a significant difference among genotypes in their response to drought (Table 1). The reduction in available water significantly reduced plant water potential, RWC and increased the concentration of proline and soluble carbohydrates. The mean leaf water potential of the doubled haploid lines did not differ significantly from that of the commercial varieties in the control and the 75% FC treatment, but as the amount of available water declined there was a significant difference in the leaf water potential among the genotypes. Under the higher soil water deficit (25% FC), the leaf water potential in the doubled haploid line, DH14, reached –2.4 MPa, which was significantly different from the lines DH15, DH21, DH17, DH28 and the variety Azar2, but it was not significantly different from the rest. At these conditions the highest leaf water potential occurred in the variety Azar2 (-1.4 MPa) and the DH 15 (-1.5 MPa). Changes of RWC more or less mirrored the differences in leaf water potential. When plants were watered to 25% FC the highest RWC was measured in the variety Azar2 (64%), and the doubled haploid lines DH15 (63%) and DH21 (55%). These genotypes were significantly different to the other doubled haploid lines and the variety Zarrin.

Increasing levels of water stress caused the concentrations of proline and soluble carbohydrates to increase. In the control treatment (100%FC) there was no significant difference among genotypes. When watered at 25% FC the highest concentration of proline occurred in DH16 (227 μmole/g leaf FW). This was not significantly different to the concentration in DH36 and the variety Zarrin, but it was significantly higher than the rest. The least amount of proline accumulation occurred in the variety Azar2 (144 μmole/g leaf FW) and the lines DH15 (148 μmole/g leaf FW) and DH28 (152 μmole/g leaf FW).

Soluble carbohydrates concentrations in the control treatment ranged from 149 μmole /g leaf FW in DH16 to 98 μmole/g leaf FW in DH17 but there was not any significant difference among the genotypes. The concentration of soluble carbohydrates increased considerably as the water deficit increased and a significant difference was observed among the genotypes when watered to 25% FC. The highest concentration occurred in the variety Azar2 (390 μmole/g leaf FW) although it was not significantly different from the doubled haploid line DH15. The smallest accumulation of carbohydrates in the leaf occurred in DH14 (204 μmole/g leaf FW).

There were significant correlations between the concentration of proline, soluble carbohydrates and plant water status (leaf water potential and RWC), but the sensitivity in the accumulation of proline and soluble carbohydrates under increasing water deficits varied between genotypes. The increase in proline for each % decline in RWC varied between 1.82 μmole/g leaf FW in DH28 up to 2.68 μmole/g leaf FW in DH15. Soluble carbohydrate concentration increased by 1.45 μmole/g leaf FW and 1.74 μmole/g leaf FW in the intolerant doubled haploid lines DH14 and DH36, respectively. In contrast, the increase in the two tolerant lines, DH15 and DH28 were 6.10 μmole/g leaf FW and 4.02 μmole/g leaf FW respectively, and it was 8.74 μmole/g leaf FW in Azar 2. It is seemed that although both proline and soluble carbohydrates increased under water stress, the ability to accumulate soluble carbohydrates in particular was associated with tolerance to water stress.

Conclusion

One of the most common reactions of plants against water deficit is osmotic adjustment that is performed by the way of aggregation of compatibility metabolites. The variety Azar2 and the line DH15 had relatively high RWC and maintained their growth under stress. This was associated with an accumulation of soluble carbohydrates, which enabled plants to tolerate water deficit stress better.

Acknowledgment

I acknowledge my deepest gratitude to Dr. Mohammad Majdi, the ex-dean of Mahabad Islamic Azad University and also Dr. Abdollah Jasebi the present dean of Islamic Azad University of Iran for granting scholarship to me. Last but not least I thank Mr. K. Pirouti for his critical revision and Mr. Mr. Y. Rabihi for his editing of this article.

Table 1. Leaf water potential, relative water content and the concentrations of proline and soluble carbohydrates in doubled haploid wheat lines and commercial varieties grown under different levels of moisture deficits. Means followed by the same letter are not significantly different based on Duncan’s multiple range test.

Genotype

Moisture Level
(%FC)

Water Potential
(MPa)

RWC
(%)

Proline
(μmole/g FW)

Soluble carbohydrates
(μmole /gFW)

15

100

-1.0a

93.4a

66a

131a

75

-1,2bc

81.7ab

110c

127a

50

-1.3cd

73.8a

130e

178ab

25

-1.5cd

62.6a

149d

319b

21

100

-1.2a

95.3a

68a

148a

75

-1.4ab

81.6ab

152bc

144a

50

-1.6ac

74.2a

152ce

158ab

25

-2.1b

55.3ab

162cd

210cd

14

100

-1.1a

95.4a

64a

135a

75

-1.3ac

78.8ab

143ac

132a

50

-1.6ab

62.0bc

143de

167ab

25

-2.4a

44.6bd

194b

204cd

Azar2

100

-0.9a

95.5a

53a

127a

75

-1.1c

86.6a

126c

124a

50

-1.2d

77.7a

126e

207a

25

-1.4d

64.0a

144d

390a

19

100

-1.1a

96.7a

55a

122a

75

-1.3ac

73.7b

172ac

120a

50

-1.7ab

54.6c

172ac

172ab

25

-2.3ab

47.3bd

182bc

239c

17

100

-1.0a

92.6a

57a

98a

75

-1.3ac

80.6ab

132c

88a

50

-1.4bd

59.17c

132e

140b

25

-1.7c

43.5bd

185bc

183d

Zarrin

100

-1.1a

95.10a

62a

146a

75

-1.2c

83.1ab

166ac

148a

50

-1.7a

60.83c

166bd

190ab

25

-2.4a

40.4cd

206ab

256bc

16

100

-1.1a

94.4a

72a

149a

75

-1.5a

82.5ab

187ab

144a

50

-1.8a

55.1c

187ab

152ab

25

-2.3ab

46.8bd

227a

251bc

28

100

-1.0a

93.9a

50a

127a

75

-1.2ac

83.8ab

138ac

132a

50

-1.7ab

72.7ab

138de

158ab

25

-2.1b

49.7de

150ab

297b

36

100

-1.1a

96.0a

64a

149a

75

-1.3ac

83.1ab

195a

152a

50

-1.6ac

51.3c

195a

205a

25

-2.3ab

36.2d

229a

253bc

References

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