Effect of Trinexapac-Ethyl Growth Inhibitor and Drought Stress on Some Morpho-Physiological Traits of Wheatgrass (Agropyron cristatum L.)

Research On Crop Ecophysiology

مقاله 1، دوره 13، شماره 2، شهریور 2018، صفحه 53-63   

شناسه دیجیتال (DOI): 10.30486/roce.2018.669083

نویسندگان

Hengameh Vakili Ramezan¹؛ Hossein Ali Asadi-Gharneh²؛ Nematollah Etemadi³

¹Department of Horticulture, Faculty of Agriculture, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran

²Department of Horticulture, Faculty of Agriculture, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran.

³Department of Horticulture, College of Agriculture, Isfahan University of Technology, Isfahan, Iran

چکیده

Abstract
The wheatgrass (Agropyron cristatum L.), is a plant with potential source of turf in arid and semi-arid regions. It can be also cultivated in order to prevent the soil erosion by coverage of earth's surface. Drought stress is one of the most important factors that influence growth and productivity of plants in arid and semi-arid condition. In order to evaluate the effect of trinexapac ethyl concentrations (0, 0.25 and 0.5 kg/h) and drought stress (25, 50 and 75% of field capacity) treatments on some wheatgrass morphological traits, a pot experiment was conducted as factorial in completely randomized block designs with four replications in research greenhouses of Islamic Azad University, Isfahan (Khorasgan) Branch during 2015. The results showed that the maximum plant height and the lowest amount of proline obtained in 75% drought stress treatment. The lowest fresh weight of the aerial parts and the relative water content (RWC) were observed in 25% drought stress treatment. The highest dry weight of the shoots was measured in control, 0.25 kg/h trinexapac-ethyl and 75% drought stress treatments. The highest proline content and the lowest height of the plants were observed in 25% drought treatment with 0.5 kg/h oftrinexapac-ethyl. In general, the research results indicated that under drought stress condition, application of trinexapac-ethyl by increasing the amount of proline and relative water content reduced stress damage and increased resistance to drought stress in the wheatgrass.
 
Keywords: Agropyron cristatum L, Proline, Relative water content, Plant growth regulator.

کلیدواژه‌ها

Keywords: Agropyron cristatum L؛ Proline؛ Relative water content؛ Plant growth regulator

اصل مقاله

Original Research

                 Research on Crop Ecophysiology                                   Vol.13/2, Issue 2 (2018), Pages: 53 -  63

 

 

 

 

 

 

 

Effect of Trinexapac-Ethyl Growth Inhibitor and Drought Stress on Some Morpho-Physiological Traits of Wheatgrass (Agropyron cristatum L.)

 

Hengameh Vakili Ramezan¹, Hossein Ali Asadi-Gharneh^2*, Nematollah Etemadi³

 

1- Department of Horticulture, Faculty of Agriculture, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran.

2- Department of Horticulture, Faculty of Agriculture, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran.

3- Department of Horticulture, College of Agriculture, Isfahan University of Technology, Isfahan, Iran

                                                                     

^*Corresponding author email: [e-mail]

Received: 20 May 2018                                              Accepted: 10 June 2018                                       

 

 

Abstract

The wheatgrass (Agropyron cristatum L.), is a plant with potential source of turf in arid and semi-arid regions. It can be also cultivated in order to prevent the soil erosion by coverage of earth's surface. Drought stress is one of the most important factors that influence growth and productivity of plants in arid and semi-arid condition. In order to evaluate the effect of trinexapac ethyl concentrations (0, 0.25 and 0.5 kg/h) and drought stress (25, 50 and 75% of field capacity) treatments on some wheatgrass morphological traits, a pot experiment was conducted as factorial in completely randomized block designs with four replications in research greenhouses of Islamic Azad University, Isfahan (Khorasgan) Branch during 2015. The results showed that the maximum plant height and the lowest amount of proline obtained in 75% drought stress treatment. The lowest fresh weight of the aerial parts and the relative water content (RWC) were observed in 25% drought stress treatment. The highest dry weight of the shoots was measured in control, 0.25 kg/h trinexapac-ethyl and 75% drought stress treatments. The highest proline content and the lowest height of the plants were observed in 25% drought treatment with 0.5 kg/h oftrinexapac-ethyl. In general, the research results indicated that under drought stress condition, application of trinexapac-ethyl by increasing the amount of proline and relative water content reduced stress damage and increased resistance to drought stress in the wheatgrass.

 

Keywords: Agropyron cristatum L, Proline, Relative water content, Plant growth regulator.

 

Introduction

 

The wheatgrass (Agropyron cristatum L.), comprises over 150 species, which 19 species are found in Iran. This type of lawn is compatible with different soil types and its establishment in the soil is easy. Wheatgrass is very resistant to drought stress, adapts to different environmental conditions (Sheikh-Mohammadi et al., 2015; Turgeon, 1999) and introduced as a plant with potential source of turf for arid and semi-arid regions (Bayat et al., 2016). Various species of wheatgrass are found in most rangelands of Iran and are considered as rangeland plants. Some species of wheatgrass are cultivated in order to prevent the soil erosion by coverage of earth's surface with roots (Sadeghi et al., 2014).

Drought is one of the most important factors limiting the production of successful agricultural products around the world (Mahajan and Tuteja, 2005). Water scarcity and rapid decline in water resources are increasingly becoming the most important issue in many parts of the world, specifically in dry and semi-arid regions of the world. Actually, drought stress is a condition in which the cells and tissues are in a position in which no complete inflammation is observed (Rashidi and Yadegari, 2014). The range of effects of drought stress varies from a slight decrease in water potential to permanent withering and dryness of the plant. When the moisture content in the root zone is significantly reduced, the plant does not have water absorption ability, the plant is under drought stress condition. In drought condition, osmotic stress and disordering the ionic balance, can lead to disruption of the plant's activities, and finally, growth decline (Chai et al., 2010; Bian and Jiang, 2009). Environmental stresses such as drought affect germination, growth and performance of plants (Altahawa et al., 2013; Abedi and Pakniyat, 2010). Specific traits such as roots system features, the relative water content of the leaves and the osmoregulation ability affect the plant's function directly or indirectly during the drought stress conditions (Abbasi et al., 2014).

Today, plant growth regulators can play an important role in the management of the grass, among which we can refer to trinexapac-ethyl as the growth inhibitors. Trinexapac-ethyl, with the formula C₁₁H₁₂O₅, is one of the growth regulators in the management of lawns. Trinexapac-ethyl has great help in management of sports fields such as golf and football (Etemadi et al., 2015). Under salinity stress, trinexapac-ethyl increases the resistance of the Poa pratensis lawn and increases the antioxidant capacity (Stir, 2006; Beasley & Baranham, 2005). Application of trinexapac-ethyl significantly reduced shoot growth in creeping bentgrass (Agrostis stolonifera L.) and hybrid bermudagrass [Cynodon dactylon (L.) Pers. Cynodon transvaalensis Burtt-Davy] (Wherley and Sinclain, 2009).  This growth regulator reduces cellular elongation in green tissue by preventing gibberellin biosynthesis. Trinexapac-ethyl is a cyclohexanedione that prevents the conversion of GA_2O to GA₁ by 3- beta hydroxylase and such as paclobutrazol inhibits the oxidation of ent-kauran to ent-kauronic acid, which is the primary step in the synthesis of Gibberellin (Heckman et al., 2001; Lickfeldt et al., 2001).

Under drought stress, trinexapac-ethyl increased content of soluble sugar content and proline considerably and improved drought tolerance in wheatgrass (Etamadi et al., 2015) and reduces the height of aerial parts in 4 to 6 weeks after treatment (Pessarakli, 2008).

The main objective of the present study was to evaluate the effects of trinexapac-ethyl growth inhibitor on some morphological characteristics of wheatgrass under drought stress conditions.

 

 Materials and methods

 

The present study was carried out in four replications at the Greenhouse condition of Islamic Azad University, Isfahan, Iran, in 2015. Greenhouse day temperatures was 21 to
26 ^°C, with night temperatures somewhat lower (16 to 21^°C). Relative humidity was set at 70 percent under natural light with average of 800 µmol m^-2 s^-1. Study was done as a factorial experiment based on completely randomized design. The first factor was drought stress in three levels (25, 50 and 75% of field capacity) and the second factor was trinexapac-ethyl consist of three levels (0, 0.25 and 0.5 Kg/ha). Seeds of wheatgrass were purchased from local market in Isfahan, Iran. Culture medium consists of mixture of equal ratios of garden soil, cow manure (with the average total N content of 3%) and sand. The pH, Ec and field capacity of the studied soil were 7.5, 5.2 and 48%, respectively.

In each pot (with 18.5 cm diameter and 21 cm length with volume of
3.5
liter), 30 g/m² of seed were planted and covered with 1 cm of cow manure. Then, the pots were irrigated immediately and irrigation was carried out repeatedly 2-3 times a day until the seeds germinated. After sufficient growth (height of 4 cm) of grass, a tensiometer (model 2725, Soil moisture, USA) was used to apply drought treatments (25, 50 and 75% of field capacity). In current study, growth period was taken 2 month and trinexapac-ethyl was sprayed twice (once per month) by a hand sprayer during late afternoon. The volume of the spraying was maintains just to cover completely the plant foliage until drip.

 

Evaluated characteristics

 

In order to measure the fresh weight of the aerial parts (stem, node, internode, axillary bud, petiole, leaf and apical bud), the wheatgrass was collected after topping from 4 cm above ground by a scissor. Then removing the plants from the rinsing the mud with the water pressure and removed of the excess moisture and then immediately weighed by a digital scale with a precision of 0.0001. To measure the fresh and dry weight of the plant samples, the plants at first were weighted to determine fresh weight and then were placed in an oven at a temperature of 65^°C for 48 hours and then weighed by the balance (Wherley and Sinclain, 2009).

The proline content of fresh weight was measured by spectrophotometer (Spectronic Instruments, Rochester, NY) by absorbing light at a wavelength of 520 nm (Bates et al., 1973).

The relative water content (RWC) of the leaf was calculated as percentages. For this purpose fresh leaves samples were collected from all pots, weighted [fresh weight (FW)], and placed in a petri dish filled with distillated deionized water for 24 hours. After removing surface water on the leaves by tissue paper, the leaves were weighted [turgor weight (TW)] and then were dried at 80 ^°C for 48 hours and weighted [dry weight (DW)]. Leaf RWC was calculated according to the following formula (Barrs and Weatherley, 1962).

12RWC= FW-DWTW-DWأ—100">

Statistical Analysis

 

This research project was conducted in a factorial experiment based on completely randomized design with four replications. The obtained data were analyzed by SAS software (Ver. 9.2) and means were compared using Duncan's Multivariate Range Test at P£ 0.05.

 

Results and discussion

 

Height of the plant

 

The analysis of variance in this study showed that the effect of drought and trinexapac-ethyl growth inhibitor on plant height was significant at the 1% level and the interaction between drought and trinexapac-ethyl on plant height was significant at the level 5% (Table
1). In current study, the highest plant height (34.55 cm) was observed in the treatment with 75% of the field capacity without the use of trinexapac-ethyl. Meanwhile, the lowest plant height (4 cm) was observed in the treatment of 25% field capacity with 0.5 kg/ha trinexapac-ethyl (Figure 1).

 

Table 1. Analysis of variance of drought and Trinexapac-ethyl on plant characteristics of wheatgrass

		Mean squares
Source of Variation	Degree of Freedom	Plant High	Fresh Weight (aerial part)	Dry Weight  (aerial part)	Relative Water Content	Proline
Replication	3	ns 2.00	*1.69	ns 0.05	*51.35	ns 50314
drought	2	**34.55	**6.52	**4.20	**1122.50	**8361624
Trinexapac-ethyl	2	**13.06	ns 0.71	*0.39	*58.62	**1372600
drought × Trinexapac-ethyl	4	*4.58	ns 0.11	ns 0.17	ns 5.07	**185879
Error	24	1.29	0.52	0.10	15.38	42704
Cv (%)	-	13.39	19.34	17.78	14.80	9.50

*, *: Significant at 1% and 5%, respectively; ns: not significant^.

Figure1. The mean comparison of drought and trinexapac-ethyl effect on the plant height

 

A reason for the reduction of plant height under the influence of the trinexapac-ethyl regulator is that it is generally used to reduce height and frequency of topping (Lickfeldt et al., 2001). Since trinexapac-ethyl involved in the synthesis of gibberellic acid and prevents the conversion of GA_2O to GA₁, it also inhibits the activity of the enzyme 3 beta-hydroxylase, thereby reducing height of the plant (King et al., 1997). It also increases photochemical activity and has no negative effect on the fresh and dry weight of roots (Fagerness and Yelverton, 2001; Zhang and Sehmidt, 2000). On the other hand, trinexapac-ethyl, that being absorbed in leaves and crowns, prevents cell elongation through reduction of the production of gibberellic acid, and continuously decreases the number of toppings, increases the visual quality, improves the growth characteristics and, as a result, resistance to environmental stress (Rohallahi and Kafi, 2011).

 

Fresh and dry weight of the aerial part

 

The results of analysis of variance showed that the effect of drought treatment at 1% level on fresh and dry weight of aerial part was significant (Table 1). Trinexapac-ethyl had significant effect (5%) on dry weight of aerial part. The results of mean comparison of drought treatment revealed that the highest fresh weight of aerial part in treatments with 75 and 50% of the field capacity was observed with 4.42 g and 3.83 g respectively, which did not show any significant difference. The lowest fresh weight of aerial part was obtained in the treatment of 25% of the field capacity with 2.96 g (Table 2).

The results of mean comparison under effect of drought condition indicated that the highest dry weight of the aerial part (2.34 g) was obtained in 75% of the field capacity. Meanwhile, in the treatment of 25% of the field capacity, it was observed with a minimum of 1.16 g (Table 2). Also, the dry weight of the aerial part did not show any significant difference in control and 0.25 kg/ha of trinexapac-ethyl (1.96 g and 1.76 g, respectively). The lowest dry weight of the aerial part (1.60 g) observed in 0.5 kg/ha treatment (Table 2).

Trinexapac-ethyl inhibits aerial lengthening by Gibberellin synthesis, so it reduces dry and wet weights (Rademacher, 2000). Johnson (1997) investigated the effect of trinexapac-ethyl on the Tifway bermuda grass and observed that the fresh and dry weight of the topped portion was reduced by 28 to 75% by using trinexapac-ethyl. In addition, Huang and Gao (2000) also reported that the fresh and dry weight of the aerial part decreased under drought stress conditions.

 

Relative water content

 

The results of variance analysis indicated that the effect of drought at 1% level and the effect of trinexapac-ethyl at the level of 5 kg/ha had significant effect on the relative water content the relative water content in wheatgrass (Table 1). Also, the means comparison of drought effect showed that the highest relative water content (37%) was observed in 75% of the field capacity. In treatment with 25% of field capacity the relative water content was less than other treatments (Table 2). Also, the results of the comparison of the means effect of trinexapac-ethyl on the relative water content indicated that the highest effect (29%) was obtained with 0.5 kg/ha of trinexapac-ethyl and no significant difference was observed between control treatments and 0.25 kg/ha of trinexapac-ethyl (Table 2).

The relative water content of the plant is one of the most important factors in determination of the balance between the water supply to the leaf and the speed of transpiration. So, it is considered as an important indicator in choosing the drought tolerant plants (Blum and Ebercon, 1981). Water stresses in protoplasts that sensitive to dehydration cause damage to membrane systems. So, the continuity of the membranes of the plastids, mitochondria, nuclei, dictyosomes and cell membranes is reduced. Permeability of membranes to salts soluble in the low-potential water confirms the theory of membrane degradation during water stress (Oliver, 1991).

 In this study, by increasing the concentration of trinexapac-ethyl, the relative water content of the leaf increased. Trinexapac-ethyl increased the relative water content of the Kentucky bluegrass, which is consistent with resulted of present study (Xu and Huang, 2011). Also, by increasing the concentration of trinexapac-ethyl in Festuca arundinacea cultivar Rebel increasing the leaf relative water content observed (Sheikh-Mohammadi et al., 2015). Trinexapac-ethyl inhibits aerial lengthening by Gibberellin synthesis, so it reduces dry and wet weights (Rademacher, 2000). Johnson (1997) investigated the effect of trinexapac-ethyl on the Tifway bermuda grass and observed that the fresh and dry weight of the topped portion was reduced by 28 to 75% by using trinexapac-ethyl. In addition, Huang and Gao (2000) also reported that the fresh and dry weight of the aerial part decreased under drought stress conditions.

 

 

Table 2. Effect of drought stress and Trinexapac-ethyl on some traits of wheatgrass

treatments	levels	Fresh weight of the aerial part (g)	Dry weight of the aerial part (g)	Relative water content (%)
Trinexapac-ethyl	Control	3.97a†	1.96a	25.50b
	0.25	3.77a	1.76ab	24.96b
	0.5	3.49a	1.60b	29.03a
Drought stress	25	2.96b	1.16c	17.50c
	50	3.83a	1.82b	25.26b
	75	4.42a	2.34a	36.72a

^†Values followed by the same letter whiten columns were not significantly different at 5% level (DMRT).

 

Proline content

 

The results of variance analysis indicated that the effect of drought treatment, trinexapac-ethyl and the interaction effects of drought and trinexapac-ethyl on plant proline content were significant at 1% level (Table 1). According to the results, the highest amount of proline (3726 µg/kg FW) was observed in 25% of field capacity and 0.5 kg/ha of trinexapac-ethyl which showed a significant difference with other treatments. Also, the lowest amount of proline (1336 µg/kg FW), was observed in 75% of the field capacity without using the trinexapac-ethyl, which did not show significant difference with the treatments of 75% field capacity with 0.5 and 0.25kg/ ha of trinexapac-ethyl (Figure 2).

.

Figure 2. The various levels of drought and trinexapac-ethyl effect on the amount of proline

In current study, the effect of proline was also analyzed. Increasing resistance of plants to drought stress conditions under the influence of trinexapac-ethyl could be an increase in compatible solutions, including proline. In fact, the proline accumulation and chlorophyll fluorescence prevention are among the drought tolerance markers that make the plant adaptable to water scarcity conditions (Keyvan, 2010; Zhu and Gong, 2005). By sweeping hydroxyl radicals under oxidative stress conditions, proline prevents cell membrane deterioration and preserves the structure of proteins and enzymes as an osmolite (Blum, 2011; Talebi et al., 2013). Changing the proline content in relation with drought stress helps maintain the water level in plant (Simova-Stoilova et al., 2008). Increasing the concentration of this amino acid that helps with osmotic regulation can result from prevention of proline decomposition, reduction of protein synthesis or increase of protein breakdown. It can be assumed that growth inhibitors, including trinexapac-ethyl, are effective preventers of proline decomposition, reducers of proline content and adjusters of its biosynthesis under drought stress.

By metabolite accumulation such as proline, soluble carbohydrates and some ions, most plants adjust the osmotic balance and deal with environmental stresses such as drought in order to maintain their water level (Hosseinian-Khoshroo et al., 2013). Also, trinexapac-ethyl improved the water relationships in the plant and increased relative water content of the leaves. The relationship between the relative water content of the leaves and the water potential of the tissues may be due to the increase of compatible soluble ingredients, glucose and the increase of proline (Amiri-Nasab et al., 2013).

Furthermore, the amount of proline in the plant was increased to maintain osmotic balance, protect the membranes and macromolecules (Nayyar, 2003; Mahajan and Tuteja, 2005). The synthesis and accumulation of osmolites are different between plant species and different varieties of a species (Pinhero et al., 2001). It can be argued that osmolites accumulate in cytosol can adjustment osmotic pressure. Also, this increasing trend of soluble sugars is consistent with proline (Jiquan et al., 2000). The accumulation of proline in the plant under stress conditions can help maintain plant balance. The proline accumulation in the cells is accompanied by the prohibition of protein denaturation. Maintenance of the structure and activity of enzymes and also the membrane from ROS damage under the water scarcity conditions and also catabolism of proline by the dehydrogenase enzyme is stopped in this situation (Teulat et al., 2006; Chaves et al., 2002).

 

Conclusion

 

In general, trinexapac-ethyl growth regulators with increasing proline and relative water content of plants under drought stress conditions reduced stress damages and increased the drought stress resistance in wheatgrass. In addition, according to the current results, drought stress reduced the weight of plant tissue and the relative water content of the plant, which reduced the stem growth and fresh and dry weight of the plant organs. That is why we count it as one of the most important plant traits in response to drought stress. Therefore, this growth inhibitor can be used to increase the resistance of wheatgrass to drought stress and improve the growth characteristics of this plant.

 

References

Abbasi AR, Sarvestani R, Mohammadi B, Baghery A. (2014). Drought stress-induced changes at physiological and biochemical levels in some common Vetch (Vicia sativa L.) genotypes. Journal of Agricultural Science and Technology, 16: 505-516.

Abedi T, Pakniyat H. (2010). Antioxidant enzyme changes in response to drought stress in ten cultivars of oilseed rape (Brassica napus L.). Czech Journal of Genetics and Plant Breeding, 46: 27-34. https://doi.org/10.17221/67/2009-CJGPB.

Al-Tawaha A, Al-Karaki G, Massadeh A. (2013). Comparative response of essential oil composition, antioxidant activity and phenolic contents spearmint (Mentha spicata L.) under protected soilless open field conditions. Advances in Environmental Biology, 7: 902-910.

Amiri-Nasab K, Qhasemnejad M, Zakizadeh H, Biglooi M. (2013). The effect of drought pretreatment on enzyme antioxidant activity and reducing the drought stress of two species of grass, Agrostis stolonifera cv. Palustris and Festuca arundinacea cv. Greystone. Iranian Horticultural Science, 4, 440-429.

Barrs HD, Weatherley P.E. (1962). A re-examination of the relative turgidity techniques for estimating water deficits in leaves. Australian Journal Biological Science, 15, 413–428. https://doi.org/ 10.1071/BI9620413.

Bates LS, Waldren RP, Tevre I.V. (1973). Rapid determination of free proline for water- stress studies. Plant Soil, 39, 205- 207. https://doi.org/10.1007/BF00018060.

Bayat H, Nemati H, Tehranifar A, Gazanchian A. (2016). Screening Different Crested Wheatgrass (Agropyron cristatum (L.) Gaertner.) Accessions for Drought Stress Tolerance, Archives of Agronomy and Soil Science, 62(6), 769-780. https://doi.org/1080/03650340.2015.1094182.

Beasley JS, Branham BE. (2005). Trinexapac-ethyl affects Kentucky bluegrass root architecture. Hortscience, 40, 1539-1542.

Bian S, Jiang Y. (2009). Reactive oxygen species, antioxidant enzyme activities and gene expression patterns in leaves and roots of Kentucky bluegrass in response to drought stress and recovery. Scientia Horticulturae, 120, 264-270 https://doi.org/10.1016/j.scienta.2008.10.014.

Blum, A. (2011). Plant Water Relations, Plant Stress and Plant Production. Pp. 11-52. In: Plant Breeding for Water-Limited Environments, Springer-Verlag, London. https://doi.org/10.1007/978-1-4419-7491-4.

Blum A, Ebercon A. (1981). Cell membrane stability as a measure of ought and heat tolerance in wheat, Crop Science, 21, 43-47.

Chai Q Jin F, Merewitz E, Huang B. (2010). Growth and physiological traits associated with drought survival and post-drought recovery in perennial turfgrass species. Journal of the American Society for Horticultural Science, 135, 125-133.  https://doi.org/10.21273/JASHS.135.2.125.

Chaves MM, Pereira JS, Maroco J, Rodrigues ML, Ricardo CPP, Osorio ML, Carvalho I, Faria T, Pinheiro C. (2002). How plants cope with water stress in the field, Photosynthesis and growth. Annual Botany, 89, 907–16. https://doi.org/ 10.1093/aob/mcf105.

Etemadi N, Sheikh-Mohammadi MH, Nikbakht A, Sabzalian M.R, Pessarakli M. (2015). Influence of trinexapac-ethyl in improving drought resistance of wheatgrass and tall fescue. Acta Physiologiae Plantarum, 37, 53-60. https://doi.org/10.1007/s11738-015-1799-6.

Fagerness MJ, Yelverton FH. (2001). Plant growth regulator and mowing height effects on seasonal root growth of penncross creeping bentgrass. Crop Science, 41, 1901–1905. https://doi.org/10.2135/cropsci2001.1901.

Heckma NL, Horst GL, Gaussion RE. (2001). Influence of Trinexapac-ethyl on specific leaf weight and chlorophyll content of Poa pratensis. International Turfgrass Society, 9, 287- 290.

Hosseinian-Khoshro H, Taleei A, Bihamta MR, Shahbazi M, Abbasi A.R. (2013). Expression Analysis of the genes involved in osmotic adjustment in bread wheat (Triticum aestivum L.) cultivars under terminal drought stress conditions. Journal of Crop Science and Biotechnology, 16, 173-181. https://doi.org/10.1007/s12892-013-0040-7.

HuangB, Gao H. (2000). Root physiological characteristics associated with drought resistance in tall fescue cultivars. Crop Science, 40, 196-203. https://doi.org/10.2135/cropsci2000.401196x.

Jiquan L, Gougu G, Ying Bai S, Shenys LJG. (2000). Changes of volatiles from drought stressed ash leaf maple (Acer negundo) in July and August. Forestry Studies in China, 2, 27-33.

Johnson B J. (1997). Growth of `Tifway' bermudagrass following application of nitrogen and iron with trinexapacethyl. HortScience, 32, 241-242. https://doi.org/10.21273/HORTSCI.32.2.241.

Keyvan S. (2010). The effects of drought stress on yield, relative water content, proline, soluble carbohydrates and chlorophyll of bread wheat cultivars. Journal of Animal and Plant Sciences,8, 1051- 1060.

King RW, Gocal GFW, Heide OM. (1997). Regulation of leaf growth and flowering of cool season turf grasses. Turfgrass Society Research Journal, 8, 565–573.

Lickfeldt DW, Gardner DS, Branham BE, Voigt TB. (2001). Implications of repeated Trinexapac-ethyl applications on Kentucky bluegrass. Argonomy Journal, 93, 1164-1168. https://doi.org/10.2134/agronj2001.9351164x.

Mahajan S, Tuteja N. (2005). Cold, salinity and drought stress: an overview. Journal Biochemistry Biophysiology, 444, 139-158. https://doi.org/10.1016/j.abb.2005.10.018.

Nayyar H. (2003). Accumulation of osmolytes and osmotic adjustment in water-stressed wheat (Triticum aestivum). Current Plant Biology, 5, 388-395. https://doi.org/10.1016/S0098-8472(03)00038-8.

Oliver MJ. (1991). Influence of protoplasmic water loss on the control of protein synthesis in the desiccation-tolerant moss Tortula ruralis: ramification for a repair-based mechanism of desiccation tolerance. Plant Physiology, 97, 1501-1511. https://doi.org/10.1104/pp.97.4.1501.

Pessarakli M. (2008). Turfgrass Management and Physiology. CRC Press, Taylor and Francis Group, New York.  https://doi.org/10.1201/9781420006483.

Pinhero RG, Rao MV, Palyath G, Murr DP, Fletcher R.A. (2001). Changes in the activities of antioxidant enzymes and their relationship to genetic and Paclobutrazol-induced chilling tolerance of maize seedling. Plant Physiology, 114, 695-704. https://doi.org/10.1104/pp.114.2.695.

Rademacher W. (2000). Effects on gibberellin biosynthesis and other metabolic pathways. Plant Biology, 51, 501-531. https://doi.org/10.1146/annurev.arplant.51.1.501.

Rashidi M, Yadegari M. (2014). The effect of salinity and drought stress on seed germination, seedling growth and biochemical changes in marigold. Advances in Environmental Biology, 8, 510-515.

Rohallahi A, Kafi M. (2011). Evaluation of two methods of measuring the undergrowth of rootstock of Poa pratensis, CV. Barimpala under the influence of growth regulators and irrigation treatments. Journal of Horticulture Sciences (Food Science and Technology), 24, 36-25.

Sadeqhi A, Etemadi N, Nikbakht A, Sabz Aliyan M. (2014). Investigating tolerance to different levels of shade in cold season grass of Agropyron desertorum and Festuca arundinaceae Schreb. Forager, Plant Process and Function, 9, 33- 43.

Sheikh Mohamadi MH, Etemadi N, Nikbakht A. (2015). The effect of trinexapac-ethyl and traffic stress on physiological and morphological characteristics of Festuca arundinacea cultivar Rebel. Iranian Horticultural Science, 3, 465-455.

Simova-Stoilova L, Demirevska K, Petrova T, Tsenov N, Feller U. 2008. Antioxidative protection in wheat varieties under severe recoverable drought at seedling stage. Plant Soil Environment, 54, 529–536. https://doi.org/10.7892/boris.30419.

Stier J. (2006). A brief review of turfgrass growth regulators. The Grass Roots, 35: 4-9.

Talebi R, Ensafi MH, Baghbani N, Karami E, Mohammadi KH. (2013). Physiological responses of chickpea (Cicerarietinum) genotypes to drought stress. Environmenatal and Experimental Biology, 11, 915-921.

Teulat B, Rekika D, Nachit  M, Monneveux  P. (2006). Comparative osmotic adjustments in barley and tetraploid wheats. Plant Breeding,116, 519-525. https://doi.org/ 10.1111/j.1439-0523.1997.tb02183.x.

Turgeon A. (1999). Turfgrass  Management. 5^th, New Jersey: Prentice-Hall Publishing Company, 99p. ISBN-13: 978-0137074358

Wherley B, Sinclair TR. (2009). Growth and Evapotranspiration Response of Two Turfgrass Species to Nitrogen and Trinexapac-ethyl. Hortscience, 44(7), 2053–2057.

Xu C, Huang B. (2011). Proteins and Metabolites Regulated by Trinexapac-ethyl in Relation to Drought Tolerance in Kentucky bluegrass. Plant Growth Regulator, 31, 25-37. https://doi.org/ 10.1007/s00344-011-9216-x.

Zhang X, Schmidt RE. (2000). Application of trinexapac-ethyl and propiconazole enhances superoxide dismutase and photochemical activity in creeping bentgrass. HortScience, 125, 47–51. https://doi.org/ 10.21273/JASHS.125.1.47.

Zhu X, Gong HG. (2005). Different soluble levels in two spring wheat cultivars induced by progressive field water stress at different development stages. Journal of Arid Environments, 62, 1-14. https://doi.org/ 10.1016/j.jaridenv.2004.10.010.