Journal of Plant Physiology & Pathology ISSN: 2329-955X

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Research Article, J Plant Physiol Pathol Vol: 4 Issue: 3

Physiological and Agromorphological Responses of Tossa Jute (Corchorus olitorius L.) to Drought Stress

Amira Racha Ben Yakoub1*, Mohamed Ali Benabderrahim1 and Ali Ferchichi2
1Arid and Oases Cropping Laboratory, Institute of Arid Lands (IRA), Medenine, 4119, Tunisia
2National Institute of Agronomy, 43, Avenue Charles Nicole, 1082, Mahrajène City Tunis, Tunisia
Corresponding author : Amira Racha Ben Yakoub
Arid and Oases Cropping Laboratory, Institute of Arid Lands (IRA), Medenine, 4119, Tunisia
Tel: 00216 75227325
Fax: 00216 75 227835
E-mail: [email protected]
Received: November 02, 2016 Accepted: June 20, 2016 Published: June 25, 2016
Citation: Yakoub ARB, Benabderrahim MA, Ferchichi A (2016) Physiological and Agro-morphological Responses of Tossa Jute (Corchorus olitorius L.) to Drought Stress. J Plant Physiol Pathol 4:3. doi:10.4172/2329-955X.1000152

Abstract

The effect of water deficit on physiological and agro-morphological parameters related to water deficit tolerance was studied in Tossa Jute (Corchorus olitorius L.), from Tunisian oasis. The experiments were carried at the Arid and Oases Cropping Laboratory, Institute of Arid Lands (IRA), Tunisia. Seeds were allowed to germinate in pots filled with sand and peat at a 2:1 ratio, respectively. After 1 month, the plants were subjected to 3 water treatments: control irrigation (R1: 100% of field capacity, FC), moderate water deficit (R2: 70% FC), and severe water deficit (R3: 40% FC). At 4 weeks of stress, the plants were harvested and subjected to some agrophysiological and biochemical analyses related to tolerance. The effect of different treatments on all studied traits was significantly important. Whole growth and leaves traits and reproductive traits were more significantly affected by 40% FC than the 70% FC and control. In addition, the water limitation for 40% (R1) and 70% (R2) of field capacities caused severe reduction of dry weight of aerial part by 50.6 and 79.4 % respectively and relative water content (RWC) of 20.99 and 53.35% respectively compared to controls plants. The net photosynthetic, the transpiration rates and the contents of chlorophyll significantly decreased in plants subjected to water deficit. Plants submitted to 40% FC accumulated higher concentrations of proline (2.07 mg/g DW) and soluble sugars (12.68 μg/g FW) than the controls ones. Tossa jute seedlings make different strategies to tolerate the water deficit by increasing the osmo-regulators contents, developing roots and reducing leaves size.

Keywords: Corchorus olitorius; Water deficit; Field capacities; RCW; Proline

Keywords

Corchorus olitorius; Water deficit; Field capacities; RCW; Proline

Introduction

Tossa jute (corchorus olitorius) is an important green leafy vegetable in many tropical area including Egypt, Sudan, Bangladesh, in tropical Asia such as Philippine and Malaysia, as well as in tropical Africa, Japan, the Caribbean and Cyprus. It belongs to the family Tiliaceae [1]. Tossa jute was cultivated to provide bark for fibers production (Jute) and mucilaginous leaves utilized in food [2]. It is an edible leafy vegetable of considerable importance in the diet by supplying nutrient and rending food more palatable.
These leaves known as ‘mloukiya’ in Arabic countries where it is consumed either fresh or dried are a source of proteins, lipids, fiber and vitamin C. Their mineral composition revealed high concentration of magnesium, calcium, zinc, phosphorus, sodium, iron and folate which were useful for the prevention of anemia [2,3]. In the arid and semi-arid areas of the world, drought is one of the main limiting factors affecting plant productivity worldwide and influences almost all aspects of plant biology [4]. However, it is major ecological factors limiting crop production and food quality globally. It is well documented that accessibility of water for plant growth is a key aspect determining plant distribution in natural ecosystems and is the single most important limiting parameter in agricultural ecosystems. An understanding of the genetic and physiological basis of drought tolerance would facilitate the development of improved crop management and breeding techniques and lead to better yield on unfavorable environments [5]. Globally, reductions in yield in all arable regions are periodically noted due to the ffects of drought and the tendency for climate changes may increase this phenomenon [4]. Despite its nutritional quality and medicinal value of Tossa crop, its production is limited to the rainy season due to scarcity of water supply during the off period. This green leafy vegetable is susceptible to moisture stress owing to its shallow rooting depth which can be prevented by using irrigation. Distribution of this plant in arid-region is thought to be attributed to its tolerance to soil moisture stress [6]. Furthermore, the water deficit, permanent or temporary, limited growth and the performance of plants more than other environmental factors. Their tolerance to water limited conditions is a complex phenomenon that involves specific morphological and developmental mechanisms with physiological change. Understanding plant responses to drought is of great importance and also a fundamental part for making the crops stress tolerant and select or create new varieties of crops to obtain a better productivity under water stress conditions [7]. However the characteristics of drought tolerance of C. olitorius are not well known. Therefore, this study aimed to identify physiological, agromorphological traits affected by the water-stress in C. olitorius for assessing its tolerance level.

Materials and Methods

Plant material and experimental trial
The plant materials used were composed of C. olitorius seeds collected from Gabes oasis in the south of Tunisia (33.50N, 10.06E, 16m a.s.1) in September 2010. The trial was carried out, in Mai 2011, in the laboratory, in the Laboratory of Arid Areas Institute (Médénine, Tunisia) located in the southeast of Tunisia and characterized by a loamy sandy soil. Tossa seeds were sterilized with 50% Clorox for 5 min, and then repeatedly washed with distilled water. The sterilized seeds were placed on paper in Petri dishes where soaked in water at 100°C with sulphuric acid for 5 min. This pretreatment improve seed germination and seedling emergence [8]. Seeds were germinated at 25° C, in the peat and watered every three days. Transplanting was effected when the seedling reached the stage of three leaves (one plant per pot) in pots of 12 cm diameter filled with a uniform soilpeat mixture in 2/3:1/3. After that, plants were irrigated two times at week with tap water and grown in glasshouse (temperature of 25°C and natural lighting photoperiod of 10 hours). Individual plants presenting homogenous development and size were selected for experiment. The experiment was arranged in three lines completely random design with eight replicates (an additional number of pots were used and for possible replacement on failure). Three water treatments were applied at four weeks after emergence and differed by field capacity (FC): R0: 100% of FC, R1: 70% of FC (moderate) and R2: 40% of FC (stress condition).
Agronomic and yield parameters
Four weeks after applying water deficit, destructive analysis was done, by harvesting the plants according to treatment, and collected samples were properly labeled and taken to the laboratory for data collection. Agronomic attributes scored were; plant height (cm), stem diameter (mm), number of leaves, flowers and pods per plant (counted), leaf elongation (cm). At the end of the experiment, eight mature leaves per treatment were gathered to determine leaf area. The leaves were obtained by using the software mesurium. Tossa jute yield was determined by the fresh and dry weights of aerial and roots parts. Samples were dried in an oven at 80°C for 48h and weighted by using electronic balance.
Plant water status
The relative water content (RWC) of plants for each treatment was determined by cutting the leaf balance into leaf blade into small squares, weighed to determine fresh mass (FW). Then, samples were taken out and placed into a Petri dish at 5°C with filter paper. After 24 hours, leafpieces were removed and immediately weighted to obtain their fully turgid mass (TW). Subsequently, they are placed in an oven at 80°C for 24 h and weighted again to determine the dry mass (DW). The relative water content (RWC) was calculated as:
RWC= (FW-DW) / (TW −DW) × 100 [9].
Eight replicates per treatment were obtained from the youngest fully expanded leaves after 30 days of treatments.
Gas exchange measurements
Photosynthetic traits were measured in situ at mature stage before harvesting. During the late morning (10:00-11:00 h), the plants fully sun-exposed leaves of Tossa jute of eight different seedling per treatment (one leaf per plant) were scanned with a portable system for measuring of photosynthesis Lci in order to determine light –saturated net photosynthetic rate (A), stomatal conductance (Gs) and transpiration (E). Chlorophyll contents at the last day of the experiment, leaf discs were taken from fully expanded leaves ofcomparable physiological age. Then the chlorophyll a (chla), chlorophyll b (chl b) and the total chlorophylls (chl a+b), concentrations were determined spectro-photometrically using 80% acetone as a solvent [10].
Soluble sugars and proline
In order to determine compatibles solutes, eight replicate per treatment were obtained from the youngest fully expanded leaves of different individuals at the midday after 30 days of treatments. The determination of soluble sugars phenols method of Dubois et al., [11] was applied. The method used for the determination of the accumulation of proline is that of Bates et al., [12].
Statistical analyses
Statistical analyses were performed using XLSTAT software ( http://www.xlstat.com). Data were subjected to one-way analysis of variance (ANOVA) to determine significant differences among the treatments. Duncan test was applied to ascertain any significant differences between the treatments. The results were considered at P ≤ 0.05.

Results

Vegetative and yield variation
Whole growth: Plant high and steam diameter were used to estimate the whole growth of Tossa jute under the different treatments. Figure 1 represents the variation of these growth traits of C. olitorius for the three different treatments. They reached their highest values at control treatment (100% FC) than at the drought treatments; R1 and R2 (Figure 1). After 6 weeks for treatments, they decreased significantly when the intensity of water deficit increased. Statistical analysis showed a significant difference between water treatments after two weeks of the application of drought for both parameters. At the end of the deficit period, plant height was significantly inhibited by the moderate deficit water R1 (70% FC) by 37.78%. This depressive effect was more important in plants irrigated with the second treatment R2 (40% FC) which showed a reduction of 52.33% compared to the control (Figure 1a; P<0.05). In other hand, Figure 1b shows that steam diameter was affected by the drought (R1 to R2). However, two weeks after the application of water deficit, the diameter enlargement was reduced compared to the control. This decline is more pronounced for the treatment R2 but there were no significant effects between the two water deficit treatments. At the end of the drought period, when compared with the control treatment R0, the basal diameter was reduced by 37.29 and 41.39% under R1 and R2 treatments, respectively.
Figure 1: Effect of water stress on plant height (a) and stem diameter (b) of C. olitorius when 1 month old plants were subjected for four weeks to 100% (R0), 70% (R1) or 40% (R2) field capacity (FC). a, b and c; Different letters above bars are significantly different at the P = 0.05 level for the given watering treatment (mean ± 95% confidence limits)
Dry weight: The mean values of dry weight of aerial parts and roots in the three treatments are shown in Figure 2. One of the major consequences of these morphological changes of the application of deficit water was the decrease in the fresh and consequently the dry mass of aerial part. A significant reduction was observed in stressed plants compared to control plant (Figure 2; P<0.05). However, after four weeks of water deficit, ADW (dry weight of aerial part) variation was inversely proportional to the drought stress increasing from R0 to R2. The treatments R1 and R2 caused an important reduction of ADW by 50.6 and 79.4% respectively. The root system was developed under at moderate (0.43 g/plant) and severe water (0.73 g/plant) treatments compared to control (0.29 g/plant). The increase in dry weight is manifest as an increase in root growth (Figure 2; P<0.05). Under the application of R2 treatment C. olitorius developed the heist root system compared to the treatment R0.
Figure 2: Effect of three water treatments on dry mass production of C. olitorius .ADW: dry weight of aerial part; RDW: dry weight of root. *Superscript letters with different letters in the same parmeter, indicate significant difference (P <0.05) analyzed by Duncan’s multiple range test.
Leaf growth: Table 1 illustrates the large variation for leafsgrowth traits (number of green leaves per pant, Leaf elongation and leaf area) among control and drought treatments. The number of green leaves per plant was significantly and linearly decreased under water deficit (Table 1; P<0.05). Plants at the control treatment (R0) had the highest number of leaves (38 per plant). However, the leaf number decrease when the field capacity decrease. This depressive effect was more pronounced with treatment time. The highest number of the senescent leaves was observed under the R2 treatment showing a reduction of 54.26% compared with the control. In other part, the leaf elongation follows a linear evolution during the first month (seedling stage). Two weeks after the application of water deficit (6 weeks after sowing), it reached 7.59 cm for irrigated plant with control treatment. After 8 weeks after sowing and one month of the water application treatments (full vegetative state), the leaf length reached 9.75 cm for the irrigated plants against 6.55 and 5.43 cm respectively for plants received a moderate and severe (Table 1; P<0.05).
Table 1: Leaf growth traits of C. olitorius under three different treatments: 100%, 70% or 40% field capacity (FC) in period of 8 weeks. The application of each treatment started on 4th week after sowing. Values followed by a common letter within each period (a, b, c) are not significantly different at 5% level.
Stress treatments, with a significant reduction of 32.28 and 44.3% respectively. The leaf area of C. olitorius was decreased as the water deficit was amplified. After four weeks of the application of the treatment R1, the reduction was 48.7% compared to the controls plants. When the treatment R2 was applied, this decline attaints 67.5% (Table 1; P<0.05).
Reproductive traits
In treatments period, reproductive traits (flowering and fructification) varied according the water treatments (Figure 3). Means of these traits for both dates of measures were significantly different among control and drought treatments. The number of flowers and pods were negatively affected by the drought conditions. Two weeks after the application of water deficit, the number of flowers for treatments R1 and R2 was reduced compared to the control. This decrease is more pronounced for the treatment R2 but there were no significant effects between these two water deficit treatments (Figure 3a). At the end of the experimental period, all flowers were transformed on pods. The maximum of fruits produced was obtained at control treatment (seven pods per plant). Nevertheless, it reached its lowest value on treatment R2. Analysis ANOVA confirms that significant differences were found between the moderate (R1) and severe stress (R2) (Figure 3b; P<0.05).
Figure 3: Effect of water stress on number of flowers (a) and pods (b) in C. olitorius when 1 month old plants were subjected for four weeks to 100% (R0), 70% (R1) or 40% (R2) field capacity (FC). a, b and c; Different letters above bars are significantly different at the P = 0.05 level for the given watering treatment (mean ± 95% confidence limits).
Physiological traits
Relative water content (RWC) and chlorophyll a and b contents: The relative water content (RWC), as indicated by the extent dehydration was used to assess cellular damage. It was significantly changed along with increase of water stress (Table 2; P<0.05). The highest RWC was observed under the first water treatment (R0) compared to the water deficit conditions (R1 and R2). It was about 61.93% under fully watered conditions. Nevertheless, the application of treatments R1 and R2 caused a reduction of 20.99 and 53.35% respectively compared to controls plants. In other hand, the contents of chlorophyll in leaves of C. olitorius seedling decreased in plant subjected to water deficit (Table 2). Under well- watered condition, the values of chl a, chl b and chl a+b were significantly higher than those observed in the values of chl a, chl b and chl a+b were significantly higher than those observed in the water deficit treatments. After 1 month of treatments, chlorophylls contents were reduced at both moderate and severe water deficit compared to controls grown plants. At the treatment R1 the reductions were about 25.84% of chl a, 55.66% of chl b and 40.36% of total chlorophyll contents. At the treatment R2 they were in order of 45.63% of chl a, 72.4% of chl b and 58.67% of total chl.
Table 2: Effect of water stress on chlorophyll content and relative water content (RWC) of C. olitorius when 1 month old plants were subjected for four weeks to 100%, 70% or 40% field capacity (FC)
Photosynthetic and transpiration rates: As shown in Figure 4, four weeks after applying water deficit, values of three physiological traits A, gs and E decreased under the different irrigation treatments from R0 to R3. The differences founded among treatments were significant (P ≤ 0.05) for these characters. The net leaves photosynthetic rates of plants fully sun-exposed leaves of Tossa jute grown under a water stress condition were significantly lowers than that of the control (Figure 4a). At the end of the experiment (30 days of withholding irrigation), plants irrigated at 70% FC reveled less reduction in A (27.06%) than plants receiving the treatments R2 (56.28%). Similar results were found for the stomata conductance (gs). There was a significant difference in this last trait difference in this last trait (P ≤ 0.05) among the tree water treatments. The maximum value was observed in the control treatment. However, it was strongly reduced with the increase of water deficit (Figure 4b). Under water limitation, transpiration rate (E) was significantly decreased when the water stress was applied (Figure 4C; P ≤ 0.05). Plants received the treatment R2 were the most affected and they was recorded the highest drop in transpiration with the increase in water stress (55.9% compared to controls plants).
Figure 4: Effect of water treatments on photosynthetic gaseous exchange of C. olitorius. Amax: light-saturated net photosynthetic Rate (a) gs: stomatal conductance (b). E: transpiration rate (c). Different letters above bars are significantly different at the P = 0.05 level for the given watering treatment (mean± 95% confidence limits).
Osmotic adjustment: As shown in Table 3, the amount of proline and sugars accumulation in leaves was dependent on the water availability, where water deficit increased these two compounds contents in the leaves. Plants submitted to treatment R1 accumulated 0.76 mg/g DM of proline and 8. μg/g MF of soluble sugars; these means are higher than the controls values. When the treatment R2 was applied, the proline and soluble sugars accumulation increase to reach respectively 2.07 mg/g and 12.68μg/g by dry matter. Statistical analysis of these two parameters showed a significant difference between water treatments (P ≤ 0.05).
Table 3: The effect of different water treatments on accumulation of proline and soluble sugars in of C. olitorius leaves. Column sharing the same letters indicates no significant differences at P<0.05.

Discussion

Tolerance to abiotic stresses is very complex, due to the intricate of interactions between stress factors and various molecular, biochemical and physiological phenomena affecting plant growth and development [13]. The reactions of plants to water stress differ significantly at various organizational levels depending upon intensity and duration of stress as well as plant species and its stage of growth [14]. C. olitorius is annual plants native to the semi-arid tropics, temperate regions and lowlands areas of Africa and Asia and serves as an important source of nutrients for indigenous populations. In these regions the water stress is the main factor limiting plant development. The knowledge of Tossa jute adaptation in arid and semi-arid areas is less documented. The present study allowed important details on responses of C. olitorius under water deficit. In this experiment, the effects of three water supply treatments during 30 days (100% of the field water capacity (FC), 70% of FC and 40% of FC) were addressed at the agronomic and physiological parameters in C. olitorius. Significant differences were found at 0.05 in all studied traits among the watering treatments on agro-morphological, reproductive and physiological levels. When the water deficit increased, some parameters decreased (growth, leafs dimension, chlorophyll contents, relative water content, etc) and other ones increased such as root development, proline and sugars oluble concentration in leaves. These various reactions to water deficit used by Tossa jute are as strategies to conserve water and to maintain normal physiological functions.
Agro- morphological traits
The differential provision of water to plants influences not only their morphology but also their dry matter partitioning between roots and shoots [15]. In our study, all agro- morphologic parameter measured (plant height, stem diameter, number of green leaves, leaf elongation, leaf area and dry weights) except root development were decreased under soil moisture stress condition (Figure 1; Figure 2; Table 1). Plots under the control irrigation R0 exhibited higher values of dry yield and of growth traits when compared with other treatments. Under water deficit (R1 and R2), significant declines were found in all vegetative traits. This reduction in plant growth was more pronounced in 40% FC than in 70%. When the 40% FC was applied, the reduction rates were more than 50% for some traits like leaf size, leaf production and plant height. So the water state of 40% FC can be considered a water stress condition for tossa. This result agrees with some investigations in which it was shown that water deficit mostly reduced leaf growth and in turn the lead areas in C. olitorius [16] and in Sesamum indicum [17]. Shiwachi et al. [19] reported that plant growth in acute stress (AMS) as 40-30% is generally difficult for most of leaf development. The reduction in plant height was associated with a decline in the cell enlargement and more leaf senescence under water stress [18]. In Tossa jute, Ayodele and Fawusi [19] reported that we can find sensitive and tolerant cultivars to water stress. They found that at the mid-vegetative stage, stress did not significantly reduce leaf size and leaf production in the cultivar “Oniyaya” comparably to “Angbadu” indicating its better tolerance to water stress. In plants growing in drying soil, the development of the root system is usually less inhibited than shoot growth, and may even be promoted. This redistribution of dry matter in favor of roots at the expense of shoots is probably due to the necessity of plants to maintain root surface area under drought conditions to preserve an adequate plant water supply and reduce the evaporation surface area [17]. This tendency indicated greater the ability of C. olitorius to adapt to mild and severe moisture stress. Roots/shoot ratio was significantly higher in plants subjected to water deficit than in controls. This change of plant dry mass allocation patterns among its components are often reflected by lower leaf area ratios and higher root biomass ratios. Indeed root dry weight accounted for 19-49% of the whole plant biomass under water limitation, against only 7% in controls. This result was in discordance with those of Rejeb [20] which shown that water stress increased dry matter allocation to the aerial part in Ceratonia siliqua.
As a result, the Tossa jute plants submitted to water stress allow a morphological strategy to conserve the water by decreasing the leaf size and by increasing the root system.
Reproductive traits
The similar inhibitory effect of water deficit was observed on reproductive traits such as flowering and fructification of Tossa jute (Figure 3). The highest values were observed under the control (100% FC) and the lowest ones were detected under the 40% FC. Pod production starts from the fifth week after planting, one week after the application of water deficit. Appling the moderate deficit water (70%FC) before the fructification reduced pod formation by 41.66%. This depressive effect was more marked in plants watered with the treatment R2 and shows a diminution of 58.33% compared to the control. Thus, the water deficit applied at vegetative stage induces a reduction and delay flowering at the reproductive stage. Our findings were similar to results reported by Ayodele and Fawusi showing that the water stress influences negatively the flowers number in the majority of species [21].
Photosynthesis and transpiration
Our results show that water decreasing treatment caused a significant decline in these both photosynthetic and transpiration traits in Tossa jute (Figures 4a and 4b). As the transpiration is controlled by the closing and opening of the stomata, the decline in theses physiological characters reflects a stomata adjustment to avoid excessive water loss under water stress constituting an adaptation developed by this specie. Consequently, this adjustment limits the CO2 diffusion through the stomata causing a decline in the photosynthetic rates. Similar results were reported by Sucre and Suárez [22] explaining that the water deficit induced an important reduction of photosynthetic gaseous exchange. In addition the stomata conductance was significantly changed when the water deficit was applied on Tossa jute plants which showed a tolerance reaction to the drought (Figure 4c; P≤0.05). The more inhibition of stomata conductance was observed with the treatment 40% FC. Stomata can be regarded as hydraulically and chemically driven valves in the leaf surface, which open to allow CO2 and close to prevent excessive loss of water [23]. Movement of these valves is regulated by environmental cues, mainly light, CO2 and atmospheric humidity. The increased stomatal resistance may have led to reduce water transport in the leaves further causing a decrease in stomatal conductance, transpiration and limit photosynthesis. Severe water stress may result in the arrest of photosynthesis, disturbance and finally the death of plant. Therefore, the dry matter yields depend on leaves areas and stomata adjustment which determine the photosynthetic rate [24]. It seems that the inhibitor effect of water deficit on agronomic traits (dry matter, leaf dimension and steam diameter) of Tossa jute is indirectly and throught the deterioration of physiological aspects (transpiration and photosynthesis) which determine the water statue and Carbone dioxide content in plant. By the way the chlorophyll content change has been used to account for the stress effects on plants, and earlier study proved that chlorophyll contents usually decreased under drought stress due to their slow synthesis or fast breakdown. Masoumi et al. [25] reported that this diminution at decreasing leaf water potentials can be attributed to the sensibility of this pigment to environmental stresses, especially drought. Maybe this limitation causes an increase in chlorophyllase activity resulting in a decrease in the amount of chlorophyll with intensifying water deficit [26]. These founding are confirmed in Tossa Jute by ours results that the contents of chl a, chl b and (chl a+chl b) in leaves of C. olitorius decreased in plants subjected to this water deficit (Table 2).
Relative water content (RWC) is the appropriate measure of plant water status in terms of physiological consequence of cellular water deficit and it is usual used to assess the tolerance to drought So the reduction of RWC indicates organ dehydration. This parameter, in our results, decreased significantly as water stress intensified (Table 2). This founding is similar to these reported by Gindaba et al. [27] indicating that RWC in tolerant plant is higher than in sensitive ones. The decline of RWC under drought condition leads to stomatal closure, further resulting in decreased CO2 assimilation. So this decrease in under the possible effect of both leaf water potential and osmotic adjustment. Osmotic adjustment in terms of accumulating compatible solutes has been considered as an important physiological adaptation for plant to resist drought [7], which facilitate extracting water from dry soil and maintaining cell turgor, gas exchange and growth in very dry environments [28]. Soluble sugars and proline are two kinds of the most important compatible solutes in plants [29]. The organic molecules accumulated such as proline and Glycine Betaine are termed compatible solutes [30], because they can be accumulated in high concentrations without perturbing the normal physiological functions [31,32]. Our results shown that C. olitorius had high capacity of adjustment in terms of accumulating proline and soluble sugars especially when the treatment R2 (40% FC) was applied (Table 3). Ended, the proline and soluble sugars increased to reach respectively 2.07 mg/g (8 times higher than control) and 12.68 μg/g, by dry matter (4 times higher than the control). This augmentation of osmo-regulators maintains the water retention under droughts conditions. This data confirmed that proline is an important amino acid with sugars soluble for osmotic adjustment in Tossa jute subjected to water deficit. These results were in agreement with founding reported by Berka et al indicating the ability of this species to use these compatible solutes for osmotic adjustment and to grow under heavy soil moisture stress condition [29].

Conclusion

The application of 40% water filed in Tossa jute (C. olitorius) affects negatively the majority of agro-morphological, physiological and reproductive traits but some tolerance strategies were observed. The forage yield, plant growth, traits, photosynthetic and transpiration rate, stomatal conductance, relative water content (RWC) and chlorophyll a and b contents were inhibited by the water deficit. At morphological level, Tossa jute plants submitted to water stress decrease leaf size and increase root system to conserve water in case of deficit. At physiological level, to avoid excessive water loss under water stress they exploit a stomata adjustment. The deterioration of physiological aspects (Transpiration and photosynthesis) which determine the water statue and Carbone dioxide content in plant induce the inhibition of agronomic traits (dry matter, leaf dimension and stem diameter) of Tossa jute is indirectly and through. The decreasing of RWC is under the possible effect of both leaf water potential and osmotic adjustment. Osmotic adjustment in terms of accumulating proline and soluble sugars is considered as an important physiological adaptation for Tossa Jute plant to resist drought.

Acknowledgments

We thank Mrs Kamel Nagaz (Head of laboratory of Arid and Oases Cropping Laboratory, Institute of Arid Lands (IRA), Medenine, 4119, University of Gabes, Tunisia) and her Staff for their technical assistance during the all experiments. We appreciate the help of Belgacem Lichehib during the laboratory analysis.

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