Taifi rose extract improves the growth and physiology of cowpea seedling stage under drought stress

1 Introduction

Cowpea (Vigna unguiculata L. Walp) is a very famous legume crop which is formed initially in Africa and furtherly extended to global world for using as one of the diets by humans. It takes up a limited area for cultivation and has a much lower yield than cereals. The prediction for cowpea production assumed a global coverage of around 14 million hectares by 2025. It belongs to Fabaceae family and it is well-known for warm season, as a vascular annual pulse crop (Carvoalho et al 2019; Alexandre et al 2016). Cowpeas are essential in the nourishment of the impoverished since they are a reasonably cheap source of substantial protein (Carvoalho et al 2019). Thus, it is a critical issue for research in Saudi Arabia due to its financial and dietary value.

Environmental variables known as abiotic stressors may have negative effects on agricultural yields (Jahan et al., 2021a). Agricultural plants alter their morphology, cellular structure, physiological function, biochemical and molecular level responses in response to abiotic stressors (Jahan et al., 2021b). Among abiotic stressors, drought is a significant constraint on vegetable crops, impairing its efficiency and threatening its yield. Oxidative stress, characterized by the excessive production of activated atmospheric oxygen (O₂), also known as reactive oxygen species (ROS), can be brought on by both climate change and the resulting drought stress (Choudhury et al., 2017; Alabdallah et al., 2021; Hasan et al., 2021a; Hasan et al., 2021b). Possible side effects of ROS generation include oxidative stress and lipid peroxidation, both of which can cause cell death (Alabdallah and Hasan, 2021; Jumrani and Bhatia, 2019). Antioxidants play an important part in keeping ROS production and removal in cells at a steady equilibrium (Hasan et al., 2021c; Hasan et al., 2023). In plants, the removal of excess ROS via a variety of antioxidant defense after systems plays a crucial role in the evolution of drought tolerance, and it also aids in maintaining the cell's full metabolic function during drought (Rahman et al., 2022). Increase in proline and sugar levels during the adaptation process is possible because these compounds contribute significantly in the osmoregulation, the redox balance, and the scavenging of ROS under stressful conditions (Krasensky and Jonak, 2012). It has been demonstrated that drought stress causes changes in the morpho-physiological features of plants as well as the composition of their chlorophyll content (Jaleel et al., 2009). As a result, it appears that drought stress is implicated in the loss in photosynthetic efficiency in crops (Ashraf and Harris, 2013).

Several studies have demonstrated that extracts from leaves and flowers can help plants recover from stressful situations by resetting their physiological systems to normal (Basra et al., 2011; Khan et al., 2020). In light of rose's usefulness as a natural chemical and effective growth stimulant, it has been the subject of numerous studies recently (Nadeak et al., 2021; Tatke et al., 2015). The use of RW has the potential to improve plant tolerance to drought stress by lowering oxidative stress. The impacts of phytohormones and other plant extracts on plants have been extensively researched; However, pretreatment RW's impacts on plants under drought stress have not been adequately explored. The objective of this study was to examine the impact of RW on antioxidant enzymes and biochemical responses in cowpea plants exposed to various levels of drought stress. By understanding how RW affects antioxidant enzymes and biochemical responses in cowpea plants subjected to varying degrees of drought stress, we could develop an innovative agricultural practices and sustainable farming methods to boost cowpea yields and mitigate the impacts of drought stress on food production, thereby securing adequate food supplies for an ever-growing global population. Therefore, in our research, we investigated the following: cowpea's physiological reactions to drought, including its relative water content (RWC), proline content, total soluble carbohydrate, and antioxidant enzymes, and its morphological responses to RW treatment.

2 Materials and procedures

2.1

2.1 Extract by the traditional technology and phytochemical analysis of waste rose water

Roses from the Al Qurashi Rose Industry in Al Hada, Taif, Saudi Arabia (Rosa damascina var. trigintipetala) were gathered. The traditional technology as depicted in Fig. 1, includes a copper distillation system with a volume of 70–100 L. Cooling process is achieved by a single inclined pipe moving inside a separated water bath and then reaching outside connected with 20–25 L glass bottles. The copper system consumes 8–10 Kg of rose flowers (24000 – 30,000 flowers), which are first pressed by hands and then rose water added to them. The system is tightly closed by sticky tape. The mix is heated by a gas source (propane and butane) for 12–16 h at the boiling stage. The first period of heating is about 40 min for 100 °C after that the temperature gradually decreases to become 50–70 °C. Limited rose oil factories in the region utilize firewood as a source for heating the distillation system. The arising water vapor passes through the pipe and then condenses forming the distillate. Finally, the resultant products gather in the glass bottle, in which the oil floats at the top. Samples from rose water residue in the copper container have been collected and cooled in a refrigerator for the study. Phytochemical analysis of obtained samples of Taif rose water waste presented in Table 1.

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Fig. 1

Schematic view of Taif rose traditional distillation technology.

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Table 1 Phytochemical analysis of taif rose water.

Chemicals	Concentration
Phenol	0.58 ppm
Styrene	0.36 ppm
Toluene	0. 12 ppm
Mesitylene	0.15 ppm
Volatile Organic Compounds	0.23 ppm

3 Result

We investigated the favorable effects of pretreatment of RW on cowpea seedlings across a range of morphological and physiological parameters. According to the current study, increasing RW dose not only benefited plants subjected to drought stress, but also increased the growth and physiology of control plants. Drought stress significantly reduced shoot and root length, shoot fresh and dry weight, root fresh and dry weight, and leaf area in cowpea plants (Table 2). These growth metrics, however, were significantly enhanced in cowpea plants that had been pretreated with RW after experiencing drought stress (Table 2). Significant reductions in RWC of 4% and 4% were observed in cowpea seedlings subjected to drought treatments (65% FC and 35% FC, respectively) compared to control seedlings. However, relative to the RWC in the drought-stressed cowpea plants alone, RWC was raised by 4%, 8%, and 13% after being pretreated with RW (15%, 25%, and 35% RW), and by 4%, 12%, and 15% after being pretreated with RW (35% FC) (Fig. 2). Both the net photosynthetic rate (Pn) and transpiration rate (E) were significantly reduced by the drought treatments (65% and 35% FC), with Pn being reduced by 37% and E by 63%, respectively. Nevertheless, cowpea seedlings exposed to 35% FC after being pretreated with RW (15%, 25%, or 35% RW) saw increases in Pn of 7%, 41%, and 67% and E of 23%, 45%, and 69% (Fig. 2).

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Fig. 2

Pretreatment of cowpea seedling leaves with rose water (RW) affects relative water content (A), leaf photosynthetic rate (B), and transpiration rate (C) A p < 0.05 indicates a significant difference between RW with letters that aren't the same as each other in the data, which are the mean from three independent experiments.

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The proline content was 24% and 46% higher under drought stress, respectively, compared to the controls. Total soluble protein (TSP) and total soluble carbohydrate (TSC) concentrations were also raised in drought-stressed (65% and 35% FC) cowpea plants by 25%, 45%, and 41%, 53%, respectively, compared to those in untreated plants. A reduction in proline, total soluble protein, and total soluble carbohydrate was seen in RW pretreated cowpea plants compared to drought-stressed (65% and 35% FC) seedlings (Fig. 3).

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Fig. 3

For drought stress, pretreatment with rose water (RW) had an effect on the levels of proline and total soluble protein in the leaves of cowpea seedlings, as well as the levels of total soluble carbohydrate. A p < 0.05 indicates a significant difference between RW with letters that aren't the same as each other in the data, which are the mean from three independent experiments.

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Drought treatments of 65% FC and 35% FC significantly enhanced the malondialdehyde (MDA) concentration in cowpea seedlings that had been subjected to salt stress without first being pretreated with RW. Nonetheless, pretreatment of RW (15%, 25%, and 35% RW) decreased the MDA content by 14%,32% and 50% at 65% FC and 24%,35%,48%, respectively, at 35% FC. Cow pea plants subjected to drought conditions of 65% and 35% FC showed significant increases in antioxidant enzymes, including superoxide dismutase (SOD) and catalase (CAT), as compared to control. Moreover, RW pretreated drought stressed seedlings showed increased SOD and CAT activity (Fig. 4) (See Fig. 5.)

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Fig. 4

MDA concentration, SOD activity, and CAT activity in the leaves of drought-stressed cowpea seedlings were all affected by RW pretreatment (Fig. 3). P < 0.05 indicates a significant difference between RW with letters that aren't the same as each other in the data, which are the averages (±SE) from three independent experiments.

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Fig. 5

A schematic depicts how rose water improves the growth and physiology of cowpea seedlings under drought stress.

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4 Discussion

We evaluated morphological and physiological characteristics of cowpea to see how drought stress affects growth. Cowpea growth was considerably reduced by drought stress (Table 1). Past studies reported that cowpea showed similar findings when subjected to abiotic stressors (Matsui and Singh, 2003).

Due to drought conditions, the relative water content of cowpea leaves reduced significantly. Earlier studies have also documented that drought leads to a reduction in relative water content (RWC) in cowpea plants (Zegaoui et al., 2017). Cowpea plants pretreated with RW had higher water content after being subjected to drought, suggesting that this may have boosted the plants' ability to absorb water. The rate of carbon dioxide assimilation is affected by drought stress and other environmental conditions, which has a negative effect on biomass accumulation (Hasan et al., 2020). Photosynthetic and transpiration rates of cowpea were shown to be decreased in our study as a result of drought stress. These decreases in gas exchange characteristics might be a result of a decreased rate of water and nutrient intake. Pretreatment with RW enhanced photosynthesis and transpiration rates, indicating that RW helped mitigate the adverse impacts of drought on gas exchange-related parameters, most likely by decreasing hydrogen peroxide formation (H₂O₂) (Kumari et al., 2018).

Proline is just one of several organic molecules that plants either create or store (Hasan et al., 2018; Hasan et al., 2020). Protecting plant cells from osmotic and other environmental stresses, proline is an osmoprotectant. Cowpea seedlings have a higher concentration of the amino acid proline after being subjected to drought stress, as discovered by our research. Under drought stress, RW pretreatment decreased proline content, most likely because of a decrease in osmotic stress. RW may be able to maintain the proline concentration that protects plant cells under drought. The impact of drought stress on plants' soluble proteins has been investigated in a number of different ways. Some research has shown that drought stress reduces the amount of soluble protein in plants (Zahoor et al., 2017), whereas other research has shown that a lack of water actually causes an increase in the amount of soluble protein in plants (Aziz et al., 2018; Zhang et al., 2019). Cowpea seedlings' soluble protein content increased during the drought, which is consistent with previous studies. Similar to other osomo-protectants like proline, RW lowers the amount of soluble protein in cowpea seedlings under drought stress, which may be due to a reduction in protein biosynthesis. Plants use carbohydrates as their main source of energy for their metabolic processes. During environmental stresses, carbohydrates accumulate in large amounts, and photosynthesis is inhibited, leading to a decrease in plant growth (Rook et al., 2010; Richter et al., 2015). Based on our findings, cowpea leaves accumulate more soluble carbohydrates when subjected to drought stress. Nevertheless, RW reduces the buildup of total soluble carbohydrates in cowpea leaves in response to drought stress, suggesting that it improves soluble sugar transport across cell membranes. Such carbohydrate contents may aid in the osmoregulation of plants and help in their water intake during times of stress (Farhangiabriz and Torabian, 2017; Abdellaoui et al., 2018).

Most research has focused on malondialdehyde (MDA), an aldehydic lipid peroxidation product. Similar to our findings, Hasan et al. (2018) reported that Moringa species experiencing drought stress had a higher total MDA content. The MDA concentration in cowpea was reduced, however, after being treated with RW, most likely because of the antioxidants' ability to scavenge free radicals (Hasan et al., 2018). Despite the fact that environmental influences have a major effect on the activity of antioxidant enzymes, these enzymes are crucial for maintaining health (Abdulmajeed et al., 2021, Alharbi et al., 2021). Our research showed that the effectiveness of RW varies with the amount administered. Antioxidant enzyme activity was boosted when RW-pretreated seed was used. Our results demonstrated that pretreatment of cowpea seed with RW at varying doses increased SOD and CAT activity when the seeds were subjected to drought stress.

5 Conclusion

Our findings offer novel insights into the physiological response to drought stress and the role of RW regulation in this process. These results lead us to propose that pretreating cowpea plants with RW is a highly effective approach for enhancing their drought tolerance. When cowpea plants were treated with different concentrations of RW (15%, 25%, 35%), their biomass, relative water content, gas exchange parameters, and antioxidant levels all increased. The highest RW concentration of 35% exhibited the most significant enhancement in cowpea plants' ability to withstand drought stress.