Eco-physiological responses of desert and riverain legume plant species to extreme environmental stress

Eco-physiological responses of desert and riverain legume plant species to extreme environmental stress

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Journal Pre-proof Eco-physiological responses of desert and riverain legume plant species to extreme environmental stress Zainab G. Ahmed, Usama Radwan, Magdi A. El-Sayed PII:

S1878-8181(19)30321-4

DOI:

https://doi.org/10.1016/j.bcab.2020.101531

Reference:

BCAB 101531

To appear in:

Biocatalysis and Agricultural Biotechnology

Received Date: 16 March 2019 Revised Date:

4 February 2020

Accepted Date: 5 February 2020

Please cite this article as: Ahmed, Z.G., Radwan, U., El-Sayed, M.A., Eco-physiological responses of desert and riverain legume plant species to extreme environmental stress, Biocatalysis and Agricultural Biotechnology (2020), doi: https://doi.org/10.1016/j.bcab.2020.101531. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier Ltd.

authorship contribution statement Zainab G. Ahmed: Methodology, Investigation, Validation, Writing - original draft. Usama Radwan: IRGA instrument. Magdi El-Sayed, Conceptualization, Data curation, Visualization, Supervision, Writing – review and editing.

Eco-physiological responses of desert and riverain legume plant species to extreme environmental stress

1 2 3

Zainab G. Ahmed, Usama Radwan and Magdi A. El-Sayeda*

4

Botany Department, Faculty of Sciences, Aswan University, Aswan 81528, Egypt

5

a

Unit of Environmental Studies and Development, Aswan University, Aswan 81528, Egypt

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*Corresponding authors: M. El-Sayed

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E-mail address: [email protected]

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Abstract

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Drought and heat events frequency and severity are expected to increase in the near

11

future as responses to global warming, influencing crops productivity and human diet

12

as result in the increasing soil aridity and area affected by drought. It is becoming

13

increasingly important to find new crop plants or genotypes of crops that have

14

adaptation strategies to water loss at extreme arid conditions. It was hypothesized that

15

growth and development of plants are affected differently by drought stress, depending

16

on their nature habitats whether desert or riverain.

In this current research, we

17

compared the changes in physiological behavior between desert and riverain legume

18

plants, as response to drought stress at two levels of water regimes. Rates of

19

transpiration were highly correlated to radiation. Transpiration increases with the

20

increase in photosynthetic active radiation (PAR) at both levels of water regimes.

21

Highest photosynthesis (pn) and transpiration (E) were achieved in R. minima at both

22

low water regime and high PAR (1250). The super oxide dismutase (SOD), catalase

23

(CAT), phenyl ammonia lyase (PAL) and peroxidase activities were higher in

24

Rhynchosia minima. Drought stress induced significant accumulation of total sugars,

25

flavonoids, saponins, proteins and phenolics. The higher photosynthesis rate, higher

26

flavonoids and phenolics content and stronger activity of protective enzymes were the

27

important physiological reasons for the drought resistance of Rhynchosia minima.

28 29

Keywords: Drought stress, Photosynthesis, R. minima, Lablab purpureus, Antioxidant

30

enzymes, Transpiration, Chlorophyll fluorescence.

31

1

32 33

1.

Introduction

34

Climatic changes in extreme arid environment were significantly impact on water

35

availability on agriculture activities (Confalonieri et al., 2007). Drought resistance and

36

productivity of many crops play an important role in sustainable development of

37

agricultural activities in arid environments (Shekoofa et al., 2015). Several

38

environmental challenges such as drought, salinity, heat, flooding and heavy metal

39

stresses, in single or in combination can affect plants (Kokila et al., 2014).Drought

40

stress is a common adverse factor affecting plant growth, productivity, and survival.

41

Physiological and biochemical processes are altered by drought, such as water relation,

42

gas exchange, photosynthesis and the metabolism of carbohydrates, protein, amino

43

acids and other organic compounds (Kokila et al., 2014). Studies of (O’toole et al.,

44

1977) concluded that water stress mediated stomatal closure is generally accepted as

45

the primary factor associated with decreased net photosynthesis and transpiration.

46

Another factor that also affecting photosynthesis and related processes is the high

47

temperature resulted in decreasing viable leaf area and chlorophyll content (Shah and

48

Paulsen, 2003). In addition, heat stress induces the accumulation of reactive oxygen

49

species (ROS), leading to the destruction of plant lipids, proteins, and carbohydrates.

50

Thus, plants have evolved antioxidant defense systems which include non-enzymatic

51

(flavonoids, ascorbic acid, and glutathione) and enzymatic antioxidants to scavenge

52

the excess level of ROS and maintain cell ROS homeostasis (Ali et al., 2017). Drought

53

and high temperature often occur simultaneously. Their effects on plants were studied

54

individually but combined effect of the interaction between the two stresses deserves

55

more studies (shah and Paulsen 2003). There have been studies on understanding the

56

use of chlorophyll fluorescence in plant science. Chlorophyll is one of the major

57

chloroplast components for photosynthesis, and relative chlorophyll content has an

58

important role in detecting the influence of water deficit conditions on plant (Guo et

59

al., 2008). Chlorophyll fluorescence parameters are considered as ideal method, gives

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an insight into the health of the photosynthetic systems within the leaf in rapid and

61

sensitive way (Li et al., 2015; Li et al., 2013).

62

2

Lablab purpureus (L.) Sweet (synonyms: Dolichos purpureus, Dolichos lablab (NCBI

63

taxonomy)) in the Fabaceae family named locally as kashrangeeg in Nubia, Egypt.

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The plant is used as a forage for grazing cattle, sheep, goats and pigs .Leaves and pods

65

are also used in popular medicine (Abd-elwahab et al., 2002). Lablab purpureus is a

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drought-tolerant legume widely grown as a high-protein grain food in India and

67

similar climatic areas of Asia and Africa. The herbaceous plant is perennial and occurs

68

as bushy, semi-erect and prostate growth habit type (Guretzki et al., 2013).

69

Rhynchosia minima is a legume of indeterminate growth, annual or biennial, as

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determined by environmental conditions. Our interest in studying this species is due to

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its potential for use as a food and feed legume as it is readily consumed by herds in its

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desert environment (Madueño et al., 2014), and it contained essential oils, tannins,

73

flavonoids, and triterpene steroids based on Jia et al. (2015). Therefore, how these

74

different environmentally legume related plants respond to drought stress. The

75

objective of this study is to evaluate the physiological responses of R. minima and L.

76

purpureus under heat and drought stresses and determine their potentialities as adapted

77

newly crops to extreme arid environmental condition prevailing in sub-tropical desert.

78

2.

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Materials and methods

Seeds of Hyacinth Bean (L. purpureus) procured from Aswan’s market and R. minima

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collected from Wadi Agag in south eastern desert. Seeds were surface sterilized with

81

0.1% HgCl2 for 10 seconds and washed repeatedly with distilled water. Seed of R.

82

minima was scarified for 10 minutes

in a sulfuric acid solution (4N) to break

83

dormancy before sowing in a mix of sand and vermiculite (1:1 w/w), the plant were

84

cultured in pots and watered every 24 h in green house conditions, at 25°C, 16 h light

85

and 8 h dark photoperiod. Plants were grown for three weeks before transferring into

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nursery at Research Unit for Studying plants of Arid Lands (RUSPAL) under stressed

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climatic conditions in which the temperature reached 45°C. Two moisture levels were

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utilized including 12% for control well-watered plants and 2% of the maximum

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capacity for water retention which applied for stressed plants. Watering regime levels

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were carried out by watering 12-week old plants as eighteen homogenous plants of

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each species were selected (nine plants for each level of water regime). Full expanded

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leaf samples were collected at time of measurement for enzymatic and metabolic

93

analyses.

94

2.1.

Measurement of transpiration and photosynthesis parameters 3

95

Measurements of the maximum quantum efficiency of PSII photochemistry,

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photosynthesis rate, transpiration rate, leaf intercellular CO2 concentration and

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chlorophyll fluorescence were performed by using infrared gas analyzer (IRGA, CI

98

340) photosynthesis system (CID Bio-Science, Inc.). Three individual plants were

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selected from each measurement of well-watered control and stressed Plants.

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Measurements were done on the 5th to 7th leaf. Measurement of light level was set to

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PAR from 0 to 2500 µmol m−2 s−1, which was provided by a CI 301 LA light module.

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Relative humidity in the leaf chamber was 50%, and the air temperature was

103

controlled at 40 ± 0.1 °C. The incoming air CO2 level in the leaf chamber was set at

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360 ppm. The leaf was positioned in the leaf chamber and allowed to acclimatize to

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the conditions in the chamber. The analyses were taken after stomata and

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photosynthesis had stabilized, and the rates remained constant. Water use efficiency

107

(WUE) was determined using the following formula: WUE = the current net CO2

108

assimilation rate (Pn)/the current transpiration rate (E).

109

Chlorophyll fluorescence parameters, including initial fluorescence (Fo), maximum

110

fluorescence (Fm), variable fluorescence (Fv), and maximum quantum efficiency of

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PSII (Fv/Fm) were monitored on the 4th leaf under both well-watered and drought

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stress conditions using IRGA following the manufacturer’s instruction using CI- 510

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CF chlorophyll fluorescence module.

114

2.2. Assays for PAL, SOD, CAT and POX activities

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Frozen plant tissue (200 mg) was ground to a fine powder in a precooled mortar and

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pestle, and 2 ml of extraction buffer [0.2 M phosphate buffer (pH 7.2), 0.1 mM EDTA,

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1 mM DTT, and 2 U protease inhibitor cocktail] was added. The macerated suspension

118

was centrifuged at 10,000 rpm for 5 min at 4 °C. The supernatant was collected and

119

used as the source of enzyme. PAL activity was assayed by measuring the l-

120

phenylalanine formation at 290 nm using a UV-1800 UV–vis spectrophotometer

121

(Genesys 5, Thermo Spectronic, Rochester, NY, USA), and calculated using a

122

standard l-phenylalanine curve. The enzyme reaction mixture contained 100 mM

123

Tris−HCl, 40 mM trans-cinnamic acid, and an aliquot of the enzyme in a total volume

124

of 1 ml. PAL activity was expressed in U g−1 FW according to (Nagarathna et

125

al.,1993). SOD activity was determined by quantifying the inhibition in photo-

126

reduction of nitro blue tetra zolium (NBT) by SOD enzyme according to

127

(Giannopolitis et al., 1977). The reaction mixture contained 50 mM sodium carbonate,

128

50 mM sodium phosphate buffer (pH 7.6), 0.1 mM EDTA, 50 µM NBT, 10 µM

129

4

riboflavin, 12 mM L-methionine and 100 µl of crude extract in a final volume of 3.0

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ml. The reaction mixture exposed to white light for 15 min at room temperature and

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the absorbance was recorded at 560 nm using a spectrophotometer. A control reaction

132

was performed without crude extract. One unit (U) of SOD activity was defined as the

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amount of enzyme causing 50% inhibition of photochemical reduction of NBT. POX

134

activity was estimated using a UV/Vis spectrophotometer (Genesys 5, Thermo

135

Spectronic, Rochester, NY, USA), as described previously (Kim and Yoo, 1996). The

136

reaction mixture, which consisted of 0.8 ml of 0.2 M phosphate buffer (pH 7.2), 1 ml

137

of 15 mM guaiacol, 1 ml of 3 mM hydrogen peroxide, and 0.2 ml of crude enzyme

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extract, was incubated at room temperature for 3 min. The absorbance of the colored

139

product was monitored at 470 nm. POX activity expressed as∆470 g−1 fresh weight

140

(FW) min−1 was calculated using the following formula :U/ml = [Change in

141

absorbance min−1× Reaction mixture volume (ml) × Dilution factor]/ [ε470× Enzyme

142

extract volume (ml)]. CAT activity was determined spectrophotometrically at 240 nm

143

as described previously (Aebi, 1984). CAT activity expressed as ∆240 g−1FW min−1

144

was calculated using the following formula, modified with hydrogen peroxide

145

coefficient ε240: U/ml = [Change in absorbance min−1× Reaction mixture volume (ml)

146

× Dilution factor]/ [ε240× Enzyme extract volume (ml)].

147

2.3. Determination of total saponins

148

The dry materials were extracted according to the method described by Mostafa et al.

149

(2013). Total saponin content was determined spectrophotometricallyat 473 nm

150

(Ebrahimzadeh and Niknam, 1998). Saponin contents were calculated based on the

151

average value of absorbance at each concentration of the diosgenin standard.

152

2.4. Determination of total carbohydrates

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The water-soluble carbohydrates and insoluble carbohydrates were quantified by an

154

anthrone-sulfuric acid method which carried out according to Fales (1951) and

155

(Trevelyan et al., 1952).The developed blue-green color was read at the wavelength of

156

620 nm.

157

2.5. Determination of total flavonoids

158

The total flavonoid content of the plant extract was determined by the aluminum

159

chloride colorimetric method using absorbance wavelength at 510 nm (Chang et al.,

160

2002). The total flavonoid content was calculated from a calibration curve, and the

161

result was expressed as mg quercetin equivalent per g dry weight.

162

2.6. Determination of total proteins

163 5

Total soluble and insoluble proteins were determined according to the method adopted

164

by (Lowry et al., 1951).

165

2.7. Determination of total phenolics

166

Total phenolics compounds were determined spectrophotometrically according to the

167

Folin-Ciocateu method (Ough et al., 1988).

168

2.8. Determination of ascorbic acid

169

Ascorbic acid content was assayed as described by (Omaye et al.,1979).

170

2.9. Determination of proline

171

Proline content of leaves was determined according to a modification of method of

172

(Bates et al., 1973).

173

2.10. Determination of chlorophyll content

174

We measure the chlorophyll content spectrophotometrically according to (Ni et al.,

175

2009).

176

2.11. Statistical analysis

177

Data obtained were subjected to a one-way analysis of variance (ANOVA). Significant

178

differences between the control and treatments (P ≤0.05) obtained by student t-test

179

using Minitab 12-21(Minitab Inc., 1998. Users' Guide 2: Data Analysis and Quality

180

Tools, Release 12:12, Minitab Inc.). Values shown in the figures are the means ±

181

standard errors (SEs) of three independent replicates.

182

3. Results 3.1.

Photosynthesis response against PAR

183 184

Photosynthesis (pn) of R. minima was higher than that of L. purpureus at 2500 mmol s-

185

1

m-2pn (6.29, 5.22) µmol s-1m-2 at 2 and 12% soil moisture content (Fig.1). As drought

186

stress increased pn of L. purpureus revealed that there were sharper decrement in

187

comparison to R. minima at high level of light intensity 1250 mmol s-1m-2 (0.82, 2.53

188

µmol s-1m-2), respectively. L. purpureus reached its maxima at 750 mmol s-1m-2 with

189

-1

-2

pn of 3.5 µmol s m . The pn of R. minima was significantly higher than those of L.

190

purpureus under drought stress and under high light intensity (>800 µmol m-2s-1)

191

(Fig.1).

192

3.2.

Transpiration

193

Transpiration rate (E) of L. purpureus exhibited highest values with maximum of 5.32

194

mmol m-2s-1at PAR 2500 µmol m-2s-1. These values decreased sharply as soil water

195

6

content decrease reaching 1.0 mmol m-2s-1 at the same light intensity. R. minima

196

showed lower semi-constant values than those of L. purpureus at well-watered and

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starved levels with 2.45 mmol m m-2s-1at PAR 2500 µmol m-2s-1 (Fig.1). E at 2% soil

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water level showed stability ranged from 1.31 to 1.47 mmol m-2s-1at zero to 2500 µmol

199

m-2s-1PAR compared to L. purpureus at the same water regime. From two-way

200

analysis of variance, L. purpureus photosynthesis showed differences attributed to

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PAR and soil moisture content (SMC) where F= 63.95, P<0.0001 and F= 5.04,

202

P<0.001 respectively, while transpiration rate indicated differences attributed to SMC

203

where F= 20.70, P<0.0001. In R. minima the photosynthesis showed differences

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attributed to SMC where F= 16.40, P<0.001, while transpiration rate indicated

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differences attributed to SMC and PAR where F= 16.9, P<0.0001 and F= 6.06,

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P<0.0001, respectively.

207

3.3.

Water-use efficiency

208

Transpiration (E) and photosynthesis (pn) of L. purpureus and R. minima are strongly

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linked. The relationship between Pn and E can be studied in greater details by

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examining the ratio Pn/E, an index of short-term water-use efficiency (WUE). Under

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well-watered conditions, are generally functions of net radiation, in R .minima at 12%

212

-2 -1

-2 -1

water regime a maximum WUE (2.45µmolm S /mol m s ) reached at highly PAR

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2500 µmol m-2s-1while at 2% a maximum value of WUE (1.93µmolm-2S-1/mol m-2s-1)

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at PAR 1250 µmol m-2s-1. In L. purpureus at 12% WUE showed a high value

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(1.10µmolm-2S-1/mol m-2s-1 at PAR 2500 while WUE at 2% showing maximum value

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(3.63 µmolm-2S-1/mol m-2s-1 at 750µmol m-2s-1. (Fig.1)

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3.4. Changes in R. minima and L. purpureus metabolite contents and antioxidant

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activities in response to drought stress

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R. minima showed a higher stress tolerance than L. purpureus with highly activity of

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antioxidant enzymes (superoxide dismutase, catalase, peroxidase and phenyl ammonia

221

lyase) to avoid the oxidative damage of reactive oxygen species (Fig.2). The obtained

222

results showed that SOD, CAT, POD and PAL were signficantly higher (58.7, 64.91,

223

-1

49.34, 84.26 U g FW, respectively) in stressed R. minima, compared with their well-

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watered controls (16.99, 13.68, 28.54, and 29.22 U g-1 FW, respectively), In stressed

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L. purpureus, these enzymes showed slight increase (17.39, 22.77, 31.49, 45.00 U g-1

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FW, respectively) compared to their unstressed well-watered plants (13, 16.53, 17.44

227

7

and 27.7 U g-1 FW, respectively). Generally, the results of SOD, CAT, POD and PAL

228

activities were higher in R. minima than L. purpureus under drought stress condition.

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Stressed plants showed a different change in metabolite content in which stressed L.

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purpureus had a higher content of ascorbic acid, saponins, insoluble proteins, soluble

231

carbohydrates (131.4, 107.33 and 150 and 106.99 mg g-1 DW, respectively) in

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corresponding to unstressed plants. Under drought stress, L. purpureus showed

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decrease in insoluble carbohydrates, proline and phenolics (100.3,4.0 and 4.5 mg g-1

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DW, respectively).

Stressed R. minima revealed significant increase in soluble,

235

insoluble proteins and flavonoids (74.9, 219.5 and 70.8 mg g-1 DW, respectively)

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while insoluble carbohydrates, ascorbic acid and phenolics content decreased with

237

drought stress severity (42.7, 22, 4.5 and 5.8 mg g-1 DW, respectively). R. minima

238

showed no significant change (P≥ 0.05) in ascorbic acid, saponins and proline (Fig3).

239

3.5. Chlorophyll and chlorophyll fluorescence

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In stressed plants chl a was similar in L. purpureus and R. minima of about 1.01 mg /g

241

FW. Chl b in R. minima showed values of 1.40 mg /g F.W while in L. purpureus chl b

242

was 0.5mg /g FW. Under well-watered conditions, the correlations among initial

243

fluorescence (Fo), maximal fluorescence (Fm), variable fluorescence (Fv) and Fv/Fm

244

were highly significant (P<0.01), The Fv/Fm was decreased with the decrease in soil

245

water potential (Fig.4), but Fv/Fm of L. purpureus decreased sharply than those

246

corresponding to R. minima. A significantly positive correlation between Fv/Fm ratio

247

and SMC (r=0.743 and p= 0.006) was found, In chlorophyll a content there was no

248

significant differences (P > 0.05) but there was a significant difference in chlorophyll

249

b (p < 0.05) between these two plant species (Fig. 5).

250

4.

251

Discussion

Water deficit is an important limiting factor that affects all physiological processes

252

including growth and developments of plants (Centritto et al., 2009). It can inhibit

253

activity of enzymes related to Calvin cycle and inhibits activity of PSII, which is the

254

primary cause of the photosynthetic rate decrease (Taiz et al., 2017). Our results

255

showed that especially Pn decreased dramatically under drought stress and increased

256

under high photosynthetically active radiation (PAR) in L. purpureus, while in R.

257

minima the photosynthesis rate remained the same during reducing the water

258

availability under high PAR. High leaf WUE is a water-saving strategy allowing plants

259

to maintain strong drought tolerance. It is generally believed that reduced transpiration

260

8

and increased photosynthesis jointly lead to improvement in leaf WUE (Base et al.

261

2016). In our study, R. minima showed increasing in WUE at high PAR where in L.

262

purpureus the WUE showed lower value at the same PAR under severe drought stress.

263

These results showed agreement with Santos et al. (2017) study on Ricinus communis.

264

R. minima was more tolerant to drought stress than L. purpureus explaining how desert

265

plants have the ability to increase their photosynthetic rate in response to increasing

266

PAR under high water regime and decreasing transpiration rate to guarantee a higher

267

WUE. By different mechanisms such as closing stomata and condense root system,

268

these plants can prevent water content loss, and thereby reduce levels of tissue damage

269

(Li. Y et al., 2017).

270

Another strategy is a system including important protective antioxidant enzymes in

271

which SOD, PAL, POD and CAT played an important role in scavenging harmful

272

oxygen species (Li-Pet al., 2006). The amount of antioxidant enzymes activity in L.

273

purpureus were lower in compared to R. minima which may reflect the low ROS

274

scavenging capacity and increased damage in L. purpureus.

275

The comparison between the four enzymes indicated that activity of PAL was highest

276

and CAT, SOD and POX came next. This result indicates that PAL was the main

277

protective enzyme against the drought stress. Some previous studies reported that

278

SOD was more sensitive to the drought stress than other enzymes (Li et al., 2015), also

279

(Iturbe-o et al., 1998) demonstrated that pea plants that exposed to mild drought stress

280

showed increase in SOD activity and severe decrease in CAT activity .

281

Plants produce new metabolites and can also alter composition of existing chemicals

282

to survive in different environmental stresses (Qasim et al., 2017) such as

283

carbohydrates which is considered sensitive osmotic markers for drought stress and

284

presence of flavonoids, phenolics and saponins in plant responsible for antimicrobial

285

activity and antioxidant effect. Results from this study showed that L. purpureus is a

286

good source for proteins and carbohydrates while R. minima was rich in flavonoid and

287

phenolic compounds. Ascorbic acid is an antioxidant compound accumulated in plant

288

reducing the damage caused by ROS (Reddy et al., 2004). Our experiment revealed

289

that L. purpureus and R. minima contained considerable amount of proline has been

290

reported to act as an osmo-protectant, a protein stabilizer, a metal chelator and an

291

inhibitor of lipid peroxidation (Kokila et al., 2014). Chlorophyll fluorescence emitted

292

9

from plant leaves enables to monitor and quantify the changes induced in the

293

photosynthetic apparatus rapidly during drought stress. Decreases in Fv/Fm was

294

dependent on stress severity (Yang et al., 2014).Fv/Fm decreased dramatically with

295

soil water potentials declining in both R. minima and L. purpureus. The R. minima

296

maintained the higher Fv/Fm than L. purpureus. A study on sugar beet showed

297

decreasing in Fo values and increasing in Fv/Fm during the later stage of drought

298

stress. Our result also showed decrease in Fo which could reflect damage to PSII and it

299

is in agreement with (Guo et al., 2008) and (Li et al., 2015) finding in their research.

300

Rhynchosia minima is an ideal desert plant acts as water saver under extreme arid

301

environment and maybe promising potential feed and food crop.

302

5. Conclusion

303 304

Drought stress affects plant development processes, reduces transpiration and

305

photosynthetic rates, and leads to poor productivity. The two legume plants Lablab

306

purpureus and Rhynchosia minima have differential responses and various signaling

307

pathways to minimize the deleterious effects of water stress. This study showed that R.

308

minima maintained higher photosynthetic and transpiration rate than that of L.

309

purpureus under low water regime (2%). R. minima performed better than L.

310

purpureus under severe drought stress and that was attributed to its strong antioxidant

311

enzymes system and the higher accumulation of compatible solutes and proteins.

312 313

Conflict of interest: The authors declare that they have no conflict of interest.

314 315

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Fig.1. photosynthesis rate (Pn), Transpiration rate (E) and water use efficiency (WUE) for L. purpureus and R. minima under different soil moisture contents (12 and 2 % by weight) and at different photosynthetic active radiation (PAR).

Fig. 2. Differences in antioxidant enzyme activity between well watered (12%) L. purpureus, stressed (2%) L. purpureus, well watered (12%) R. minima and stressed (2%) R. minima. Catalase, CAT; Peroxidase, POX; Superoxide dismutase, SOD and Phenylalanine ammonia lyase, PAL. Values are means ± standard errors (SEs) of three independent replicates (n =3). Asterisks indicate significant difference as determined by a Student’s ttest (*P < 0.05; **P < 0.01;***P < 0.001).

Fig. 3. Differences in soluble and insoluble carbohydrate contents, soluble and insoluble protein contents, phenolics, saponins, flavonoids, ascorbic acid and proline (mg g−1 DW) between well watered (12%) L. purpureus, stressed (2%) L. purpureus, well watered (12%) R. minima and stressed (2%) R. minima. Values are means ± standard errors (SEs) of three independent replicates (n = 3). Asterisks indicate significant difference in L. purpureus and R. minima, as determined by a Student’s t-test (*P < 0.05; **P < 0.01; ***P < 0.001).

Fig.4. The effects of the drought stress on the maximum photochemical quantum yield of PS II (Fv/Fm) in compared to well-watered plant.

Fig.5. Chlorophyll content of well watered (12%) L. purpureus leaves, stressed (2%) L. purpureus, well watered (12%) R. minima and stressed (2%) R. minima under two level of water regime 12% and 2%. Values are means ± standard errors (SEs) of three independent replicates (n = 3). Asterisks indicate significant difference in L. purpureus and R. minima, as determined by a Student’s t-test (*P < 0.05; **P < 0.01; ***P < 0.001).

Highlights • • • • •

Changes in physiological behavior between desert and riverain legume plants was compared. The rate of transpiration in desert plant Rhynchosia minima was lower than Lablab purpureus under high water regime. The photosynthesis rate decreased by increasing drought stress in all plants. Drought stress induced significant accumulation of total sugars, flavonoids, saponins ,protiens and phenolics. Rhynchosia minima is an ideal desert plant acting as water saver under extreme arid environment.