Table Of ContentsNext Page

Effect of Water Deficit on Seedling, Plantlets and Compatible Solutes of Forage Sorghum cv. Speedfeed

Masoud Sinaki Jafar 1, Ghorban Nourmohammadi2 Abbas Maleki3

1 Ph.D Student of Crop Physiology, College of Agriculture & Natural Resources, Science & Research Unit, Islamic Azad. Univ,
Tehran, IRAN m_sinaki2003@yahoo.com
2 Prof of Agronomy, College of Agriculture & Natural Resoures, Science & Research Unit, IA. Univ, Tehran, IRAN
ghnour@yahoo.com

3 Ph.D Student of Crop Physiology, Dept of Agronomy, College of Agriculture IA Univ, Ilam Unit, IRAN,
mrhshadi@yahoo.com
* Corresponding author, Email: m_sinaki2003@yahoo.com

Abstract

Water stress restricts crops yields in the arid and semiarid zones of the world. Water stress is associated with low available water as well as with osmotic effects associated with salinity. Plants adapt to water deficits by many different mechanisms including changes in morphology, altered patterns of development as well as a range of physiological and biochemical processes. A number of these adaptive responses are associated with the accumulation of osmolytes like sugars and proline. Two experiments were conducted with forage sorghum (Sorghum bicolor cv. Speedfeed) to examine the response to water stress during germination and seedling growth and the response in some of these traits. In the first experiment seeds were germinated in Petri dishes at 12 levels of water stress (-0.1, -0.2, -0.3, -0.4, -0.5, -0.6, -0.7, -0.8, -0.9, -1, -1.1, -1.2, MPa) which were generated using solutions of PEG 6000 at different concentrations. Water deficit decreased the percent and speed of seed germination, length of shoot and weight of the plants. Seedling root growth was less sensitive to osmotic stress than shoot growth. In the second experiment the effects of 4 periods of water deficit (3, 6, 9 and 12 day) on the growth of 15 day-old seedlings were examined. Water potential, relative water content, root and shoot growth declined with the severity of the water deficit. Chlorophyll concentration decreased but carotene concentration increased with water stress, as did total soluble sugars and proline concentration of the plants.

Media summary

The effects of water deficit on Sorghum bicolor cv.Speedfeed were studied. Complex physiological changes such as osmotic adjustments are involved in the early inhibition of growth in expanding plant tissues exposed to osmotic stress.

Keyword

Water deficit, germination, seedling, compatible solutes, forage sorghum.

Abbreviations

PEG – Polyethylene glycol, RWC – Relative Water Content, WSD – Water Saturation deficit, TSS – Total Soluble Sugar

Introduction

Plants have many adaptive strategies to cope with high salt, soil water deficits and osmotic stress (Sharma et al., 2001; Yancey et al., 1982; Neumann 1997; Epstein et al., 1980). The relationship between tolerance to a number of these stresses and the concentration of osmolytes such as proline, and pigments and antioxidants such as carotene and peroxidase, has been reported previously (Aspinall et al., 1981; Irigoyen et al., 1992; Singh et al., 1995). The accumulation of osmolytes allows the leaves to maintain turgor under decreasing water potential (Christine et al., 1996). Under more prolonged water stress, dehydration of plant tissue can result in an increase in oxidative stress which causes a deterioration in chloroplast structure and an associated loss in of chlorophyll. This leads to a decrease in the photosynthetic activity. This experiment examined the response to water stress in forage sorghum and examined the changes in proline and sugar concentrations under varying water deficits.

Methods

Two experiments were conducted using forage sorghum cv. Speedfeed. The first experiment was conducted in a growth room at 25C and a 14h/10h (light/dark) photoperiod. Seeds were germinated in Petri dishes at 12 levels of water stress (-0.1, -0.2, -0.3, -0.4, -0.5, -0.6, -0.7, -0.8, -0.9, -1, -1.1, -1.2, MPa) which were generated using solutions of PEG 6000 at different concentrations. The experimental design was a completely random design (CRD) with 4 replicates. Sorghum seeds were sterilized with 1% (w/v) Mercuric Chloride and 70% Ethanol. Samples of 100 seeds were germinated between filter paper soaked with the appropriate PEG solution. The number of seeds germinated were counted regularly and after final germination the germination percentage and the speed of germination were estimated. The length and weight of root and shoot of seedling were measured and the roots and shoots were oven-dried at 750C for 48 h.

The second experiment examined the effect of 4 periods of water stress (3, 6, 9 and 12 day) on the growth of seedlings. Twenty seeds, which were treated with fungicide, were sown at a depth of 2 cm into 2 L pots containing 500g of quartz. The seedlings were irrigated every day with 200 mL Hoagland solution for 8 weeks. The experimental design was a CRD with 4 levels of water stress and 4 replicates.

The water potential and relative water potential (RWC) of shoots were measured at the completion of each water stress treatment. Water potential was measured using a thermocouple dew point psychrometer (model HR 33T, Wescor, USA). Water saturation deficit WSD (WSD(%) = 100-RWC) was calculated (Irigoyen et al., 1992). Chlorophyll and carotene concentrations were measured using the a modification of the method described by Arnon (Ando & Oguchi., 1990). Proline and total soluble sugars (TSS) were measured in samples of young leaf tissue (0.5 g), extracted in 5 mL ethanol (70% w/v) and washed twice ethanol. Proline concentration was measured using the ninhydrin method of Irigoyen et al. (1992) and TSS concentration was estimated using the anthrone method (Irigoyen et al., 1992) using glucose as the standard. Proline and TSS concentrations were expressed on a fresh weight (FW) basis. All the data were analysed by analysis of variance. Means were separated by using Duncan’s multiple range method.

Results

Experiment 1

All measured traits were significantly different at the 1% level of probability. Final germination percentage declined and the speed of germination slowed at water potentials greater than –0.2 MPa (Table 1). Seedling root elongation and root dry weight were unaffected until a water potential of –0.4 MPa to -0.5 MPa. Shoot elongation and dry weight were more sensitive to water stress than root growth, with significant reductions in growth occurring at high water potentials. There was very little shoot growth at water potentials less than –0.9 MPa.

Table 1. Effect of PEG6000 treatments on final germination, speed of germination and the root and shoot length, root and shoot dry weight and final leaf number after 15 days of seedlings of forage sorghum cv. Speedfeed. Data are meansSE of ten seedlings

Water
Potential
(MPa)

Germination
(%)

Speed of
germination

Root
length
(cm)

Shoot
length
(cm)

Root dry
weight
(mg)

Shoot dry
weight
(mg)

Final leaf
number

-0.1

89.8

19.4

10.7 1.1

14.3 0.6

25.5 0.02

60.0 0.02

4.25

-0.2

88.8

18.5

9.1 0.5

8.9 0.9

23.5 0.03

56.8 0.01

3.50

-0.3

73.5

16.4

8.6 0.2

7.6 1.0

21.3 0.02

43.0 0.03

3.00

-0.4

75.0

16.6

10.5 0.9

7.8 0.2

20.8 0.01

22.5 0.02

3.00

-0.5

65.0

14.6

10.1 0.7

4.2 0.3

11.8 0.04

40.0 0.03

2.50

-0.6

60.0

11.6

7.1 1.2

4.3 1.1

4.8 0.01

25.8 0.01

2.50

-0.7

63.8

10.5

9.4 1.0

3.5 0.7

7.5 0.01

22.0 0.04

2.00

-0.8

53.8

8.1

6.3 1.1

3.1 0.5

4.8 0.02

12.5 0.02

1.00

-0.9

53.8

7.8

3.9 0.3

1.9 0.4

1.8 0.03

1.3 0.01

1.00

-1.0

35.0

7.2

3.2 0.2

1.2 0.9

1.2 0.02

0.8 0.01

0.50

-1.1

26.3

5.3

2.2 0.7

1.3 0.7

0.6 0.02

0.8 0.02

0.00

-1.2

9.0

2.9

1.1 0.6

0.9 0.6

0.2 0.04

0.0020.02

0.00

CV (%)

1.05

1.05

1.48

1.08

2.92

3.21

2.02

Experiment 2

Increasing the length of the period of water stress affected root and shoot growth differently (Table 2). Root length increased and root dry weight was not affected by increased severity of water stress, while there were significant reductions in shoot height and dry weight. Leaf appearance was greatly reduced with more than 6 days of water stress.

Table 2- Effect of water Period treatments on root and shoot length, root and shoot dry weight and final leaf number of forage sorghum cv. Speedfeed. Data are means SE of 10 plants

Length of water stress
(day)

Root length
(cm)

Shoot height
(cm/plant)

Root dry weight
(mg/plant)

Shoot dry weight
(mg/plant)

Final leaf number

3

18.3 1.2

35.0 0.8

55.3 0.9

98.5 1.9

17.8

6

19.0 1.1

33.3 0.9

54.5 1.1

96.0 1.3

17.0

9

20.8 1.4

30.5 1.1

55.8 1.1

77.0 1.6

10.8

12

23.8 0.95

27.3 0.7

54.5 1.4

51.8 1.4

4.0

CV(%)

2.08

2.89

0.85

1.54

2.96

Water potential and RWC fell with increasing stress (Table 3). The chlorophyll concentration and the ratio of chlorophyll a: chlorophyll b also declined. WSD, TSS and shoot proline concentration all increased with the length of the period of water deficit (Table 3). The highest amount of carotene in the plants was produced after 9 days of stress.

Table 3. Effects of water Period treatments on leaf water potential, RWC, WSD, and the concentrations of chlorophyll carotene, TSS and proline in forage sorghum cv. Speedfeed. Data are means SE of 10 plants

Length of
water stress

Leaf water
potential

RWC

WSD

Chlorophyll concentration

Carotene

Total
soluble
sugars

Proline

Chl a

Chl b

Chl a: b

(day)

(MPa)

(%)

(%)

(mg/g FW)

(mg/g FW)

(mg/g FW)

(mol/g.FW)

3

-0.88

59.3

40.7

0.58

0.14

4.1

1.58

56.5

7.3 18.1

6

-2.78

58.3

41.7

0.59

0.16

3.7

6.08

109.5

16.8 22.0

9

-3.03

42.3

57.7

0.18

0.09

2.0

28.32

185.4

21.2 19.2

12

-3.43

35.5

64.5

0.17

0.08

2.1

7.80

298.4

23.4 11.7

CV (%)

2.29

1.12

2.11

2.68

3.00

2.73

1.78

2.57

1.63

Discussion

Sorghum is a major crop of temperate areas with high tolerance against drought. Water stress often occurs during crop establishment and seedling growth either directly from low available soil moisture of from osmotic effects associated with salinity. Studies are therefore needed to improve our understanding of the effect of water and salt stresses during these important periods of growth. Imposing drought at the seedling stage significantly reduced root and shoot dry matter, RWC, water potential and chlorophyll concentration. Water stress induced carotene, TSS and proline accumulation. These changes were related to the severity of the stress, which indicates that the changes were associated with adaptation of plants to water deficit. Genetic variation in some of these adaptive traits may enable lines that are tolerant to water deficit to be developed.

Studies on the response to salinity have identified an initial phase related to osmotic stress (Phase 1) before the toxic effects of salt reduce growth (Munns et al. 1995). There are reports of genetic diversity in response to osmotic stress in a wide variety of plant species, which seems at variance with a central tenet of the two-phase hypothesis of salinity resistance (Munns, 1993; Munns et al. 1995). Thus, in addition to attempting to reduce salt accumulation, there should be some efforts to increase capacity to maintain growth under moderate osmotic stress. Rapid screening tests, based on indentifying early differences in growth responses to salinity or PEG, should be useful for this purpose (Blum, 1988). An increased capacity to maintain growth under osmotic stress could be especially beneficial for high-input crops grown under intermittent irrigation with moderately saline water or under dryland conditions where the level of salinity is low or transient.

Acknowledgement

Financial assistance for this work was provided by the Department of Crop Production and Biotechnology, Government of IRAN.

References

Archbold, HK., (1940) Fructosans in the monocotyledons. Review. New Phytologist, 39, 185-219.

Aronson, J. A., 1985. Economic halophytes. In: A global review, plant for arid lans. Eds. S. Wichen, J. R. Gooding, D. V. G. Efields. George Allen and Unwin, London, 177-188.

Aspinall, D., K. V. M. Paramaswaran, R. D. Graham, 1983. Proline accumulation in grains, floral organs and flag leaves of wheat and barley in response to variation in water and nitrogen supply. Irrigation Sci., 4, 157-166.

Barlow, E. W., R. G. R. Donovan, J. W. Lee, 1983. Water relations and composition of wheat ears, growth in liquid culture. Effect of Carbon and Nitrogen. Aust. J. Plant Physiol., 10, 99-108.

Bewlay, J. D., M. Black, 1994. Seeds. Physiology of developmental and germination. 2nd edition, Plenum Press, New York.

Bhatia K. N., A. N. Parashar, 1990. Plant Physiology. Truemann Book Company, Jalandhar, India.

Top Of PageNext Page