2 nd international e-conference on agricultural biosciences 2009 conference website:

2nd International e-Conference on Agricultural Biosciences 2009Conference website: http://www.e-conference.elewa.org/agriculture3

Drought is one of the major ecological factors limiting crop

production and food quality globally, especially in the arid and

semi-arid areas of the world.

Among crop plants, wheat (Triticum aestivum), which often

experiences water-limited conditions, is an attractive study

system because of the natural genetic variation in traits

related to drought tolerance (Loggini et al., 1999).

2nd International e-Conference on Agricultural Biosciences 2009Conference website: http://www.e-conference.elewa.org/agriculture

4

Extreme environmental conditions that induce oxidative stress

have been associated to an increased carbonyl groups content

and to an induction in protease activity.

6 04/19/23

Objective:

The objective of the present study was to investigate mechanisms

responsible for acclimatization to drought in two wheat cultivars, Veery

(drought tolerant) and Sids-1 (drought susceptible) subjected to two

drought phases interrupted by 2d re-watering period.

2nd International e-Conference on Agricultural Biosciences 2009Conference website: http://www.e-conference.elewa.org/agriculture

7

For these purposes the glutathione system of the tissue and its

relation to protein synthesis was investigated in both cultivars

upon dehydration and rehydration. Also to understand the

role of proteolysis in the response to drought stress.

2nd International e-Conference on Agricultural Biosciences 2009Conference website: http://www.e-conference.elewa.org/agriculture

04/19/238

2nd International e-Conference on Agricultural Biosciences 2009Conference website: http://www.e-conference.elewa.org/agriculture

9 04/19/23

Estimation of Relative Water Content (RWC)

Determination of Oxidative stress indices (protein oxidation)

Glutathione determination

Glutathione reductase (GR) assay

Measurement of azocaseinolytic activity

Two wheat (T. aestivum L.) cultivars, namely Veery (drought tolerant) and Sids-1 (drought susceptible) were used in this study for:

2nd International e-Conference on Agricultural Biosciences 2009Conference website: http://www.e-conference.elewa.org/agriculture

Fig. (1): relative water content (%) (A) and Carbonyl group content (B) of well watered and drought stressed wheat cultivars CV Sids-1 (sensitive) and CV Veery (Tolerant) subjected to two drought phases interrupted by 2d re-watering. Each value represents the mean ±SE of five replicates. Cont. Sids-1 = Control of sensitive cultivar; cv Sids-1= drought stressed sensitive cultivar, Cont. Veery; Control of tolerant cultivar, Cv Veery; drought stressed tolerant cultivar, 2 Rew; 2 days rewatring. Significant differences (P<0.05) between treatments according to LSD test are shown by an asterisk.

Fig. (1 ):

Rela

tive w

ate

r conte

nt

(%)

ACarb

onyl gro

up c

ont e

nt (%

)

B

Treatments (d)

*

**

**

*

*

*

*

First drought phase Second drought phase

0 4 8 2 Rew 4 8 120

50

100

150

200

0

20

40

60

80

100Cont. Sids Cv Sids 1 Cont. Veery Cv Veery

A

*

* *

**

**

**

*

**

*

**

**

**

*

04/19/2311

2nd International e-Conference on Agricultural Biosciences 2009Conference website: http://www.e-conference.elewa.org/agriculture

Fig. (2) Changes in glutathione status, GSH,

GSSG and GSG/GSSG ratio in wheat cultivars

cv sids-1 and cv Veery exposed to two

drought cycles interrupted by 2d re-watering

(2Rew). Each value represents the mean ±SE

of five replicates. Cont. Sids-1; Control of

sensitive cultivar, cv Sids-1; drought stressed

sensitive cultivar, Cont. Veery; Control of

tolerant cultivar, Cv Veery; drought stressed

tolerant cultivar, 2 Rew; 2 days re-watering.

Significant differences (P<0.05) between

treatments according to LSD test are shown

by an asterisk.

12

2nd International e-Conference on Agricultural Biosciences 2009Conference website: http://www.e-conference.elewa.org/agriculture

Fig. 3 : Glutathione reductase (GR) activity of well watered and drought stressed wheat cultivars CvSids-1 and

Cv Veery subjected to two drought phases interrupted by 2d re-watering. Each value represents the mean ±SE of five replicates. Cont. Sids-1; Control of sensitive cultivar, cv Sids-1; drought stressed sensitive cultivar, Cont. Veery; Control of tolerant cultivar, Cv Veery; drought stressed tolerant cultivar, 2 Rew; 2 days rewatring. Significant differences (P<0.05) between treatments according to LSD test are shown by an asterisk.

2 4 8 2 Rew 4 8 120

5

10

15

20

25

*

*

*

*

**

***

GR

(U/m

g pro tein

)

Fig. (3): Glutathione reductase activity of w ell w atered and droughted w heat cltivars Cv sids and Cv veery subjected to tw o drought phases interrupted by 2d rew atering. Each value represents the mean ±SE of f ive replicates. Signif icant differences (P<0.05) betw een treatments according to LSD test are show n by an asterisk.

*

Treatments (d)

First drought phase Second drought phase

**

13

2nd International e-Conference on Agricultural Biosciences 2009Conference website: http://www.e-conference.elewa.org/agriculture

Fig. (4): Total protein content (A) and Azocaseinolytic activity (B) of well watered and drought stressed wheat cultivars CV Sids-1 (sensitive)

and CV Veery (tolerant) subjected to

two drought phases interrupted by 2d re-watering. Each value represents the mean ±SE of five replicates. Cont. Sids-1; Control of sensitive cultivar, cv Sids-1; drought stressed sensitive cultivar, Cont. Veery; Control of tolerant cultivar, Cv

Veery; drought stressed tolerant cultivar, 2 Rew; 2 days rewatring. Significant differences (P<0.05) between treatments according to

LSD test are shown by an asterisk .

Fig. (3): Total protein content (A) and Azocasinolytic activity (B) of well watered and drought stressed wheat cltivars CV sids (sensitive) and CV veery ( Tolerant) subjected to two drought phases interrupted by 2d rewatering. Each value represents the mean ±SE of five replicates. Significant differences (P<0.05)between treatments according to LSD test are shown by an asterisk.

To

tal s

ol u

bl e

pro

tein

mg

g-1

DW

A

Az o

c asi

no

lytic

act

i vity

un

itsm

g -1

pr o

tein

h-1

B

Treatments (d)

**

*

*

*

First drought phase Second drought phase

**

*

*

*

0

20

40

60

80

100

Cont. Sids Cv Sids 1 Cont. Veery Cv Veery

*

**

*

*

*

*

**

**

**

2 4 8 2 Rew 4 8 120

2

4

6

8

10

* **

*

*

*

*

*

*

*

A

14

2nd International e-Conference on Agricultural Biosciences 2009Conference website: http://www.e-conference.elewa.org/agriculture

15

2nd International e-Conference on Agricultural Biosciences 2009Conference website: http://www.e-conference.elewa.org/agriculture

A significant increase of carbonyl concentration in response to drought

stress in both cultivars tested and after prolonged drought stress,

indicating the presence of oxidized protein which are selectively

recognized and degraded by proteolytic enzymes (Fig.1B)

The ratio of GSH to GSSG was directly related to the level of drought

stress, however, after 2d re-watering, the acclimatized wheat leaves

for both cultivars showed higher values at the end of the second

drought phase when compared to the results obtained after the

completion of the first drought phase (Fig. 2C).

04/19/2316

2nd International e-Conference on Agricultural Biosciences 2009Conference website: http://www.e-conference.elewa.org/agriculture

The high activity of GR, especially during the first drought phase,

maintained glutathione pool in its reduced status. This is

confirmed by the different behavior of cultivars, in which a relative

low GR activity, also at high degree of drought, was associated

with low GSH and high GSSG levels (Fig. 2 A, B and Fig. 3).

2nd International e-Conference on Agricultural Biosciences 2009Conference website: http://www.e-conference.elewa.org/agriculture

17

Lower azocaseinolytic activity was referred to cultivar type in

order of increasing drought stress and associated with a distinct

reduction of soluble protein content in the wheat leaves.

Drought has been associated with decreased protein levels,

increased proteolytic activity, and the up-regulation of cysteine

protease genes (reviewed in Beers et al., 2004).

2nd International e-Conference on Agricultural Biosciences 2009Conference website: http://www.e-conference.elewa.org/agriculture

18

The recent literature confirms a central role of glutathione metabolism in

plant responses to environmental stress.

The results showed that antioxidant protection in both cultivars are

mainly due to the enzymes and molecules involved in glutathione

metabolism and re-watering regulates the timing of drought effect in

part by delaying the increased proteolytic activity and subsequent

protein degradation.

2nd International e-Conference on Agricultural Biosciences 2009Conference website: http://www.e-conference.elewa.org/agriculture20

Genetic, Physiological and Biochemical responses

of some plants to interactive biotic and abiotic

stress.

Effect of some cumulative stress on the ultra-

structure and antioxidant isozymes of some

economically important plants.

21 04/19/23

2nd International e-Conference on Agricultural Biosciences 2009Conference website: http://www.e-conference.elewa.org/agriculture

04/19/23

This research was supported through the research center of Teachers

College at King Saud University, project no. 12/1427. The author would

also like to thank Dr. Salah Barakat, Professor of Plant Physiology,

Botany Dept., Faculty of Science, Alexandria University for his

comments and revision on the manuscript.

22

2nd International e-Conference on Agricultural Biosciences 2009Conference website: http://www.e-conference.elewa.org/agriculture