Effect of gibberellin, nano-nutrition with titanium, zinc and iron on yield and some physiological and qualitative traits of white beans

Plant nutrition has a vital role in crop production. This study was performed to investigate the effects of different application methods of some nutrients (nano Fe, Zn, and Ti), and gibberellin on yield, some morphophysiological and grain protein of white beans in 2018 as a factorial experiment in a randomized complete block design with four replications. Experimental factors included seed priming (hydropriming, gibberellin priming, titanium nano dioxide, and nano-Zn priming) and micronutrient foliar spraying (zinc, iron, and zinc + iron). The results illustrated that seed priming and foliar application significantly affected yield, yield components and chlorophyll content. Plant height increased in seed priming treatment with gibberellin and foliar application of zinc + iron by 13% compared to the control. Furthermore, this treatment enhanced the number of sub-branches per plant by 32% compared to the control. Grain yield components such as the number of pods per plant and 100-grain weight were also affected by seed priming with nano-Zn, and the simultaneous spraying of iron and zinc that grain yield by 18%, so that grain yield by 2649 kg ha –1 in hydropriming treatment reached to 3211 kg ha –1 in nano-Zn priming with simultaneous application of zinc and iron. Nano-Zn priming with iron foliar application caused the highest biological yield (9011 kg ha –1 ), which increased by 19% compared to control. Nano-Zn priming increased grain protein percentage by 21%. This treatment along with the foliar application of zinc + iron, significantly enhanced leaf chlorophyll content compared to other treatments. Therefore, to increase the yield of white beans, priming treatment with nano-Zn as well as foliar application of zinc + iron can be used .


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Priming is one of the ways to improve seed efficiency. Primed seeds germinate faster and more uniformly over a wider temperature range. During priming, some water is provided to the seed that induces pregermination metabolic activities, but root emergence is prevented (Hasanuzzaman and Fotopoulos, 2019). Various priming methods such as priming with water, nutrients, microorganisms, plant hormones, salt solutions as well as nanomaterials were suggested for seed priming. Seed hydropriming was proved to increase the germination rate, drought resistance, increase pod number as well as cowpea seed dry weight (Singh et al., 2014).
Crop production is threatened by various environmental stresses and the reduction of resources. A novel revolution in crop production is needed to increase the productions and guarantee the quality and safety of food, in a sustainable way. Nanotechnology can play an important role in this revolution. Seed nano-priming can change seed metabolism and signaling pathways, affecting not only germination and seedling establishment but also the entire plant lifecycle. Studies have shown various benefits of using seed nano-priming, such as improved plant growth and development, increased productivity, and a better nutritional quality of food. Nano-priming modulates biochemical pathways and the balance between reactive oxygen species (ROS) and phytohormones, resulting in the promotion of stress and diseases resistance resulting in the reduction of pesticides and fertilizers (do Espirito Santo Pereira et al., 2021). Seed priming using nanomaterials should be carefully conducted, otherwise not only does not increase the germination rate but can also impair its performance (Xiang et al., 2015).
Understanding the mechanism of reaction at the molecular level between nanoparticles and biological systems is somewhat unknown (Alpana et al., 2019). Nevertheless, there are reports of the positive effects of these compounds on cropping systems. Therefore, the discussion of the biological effects of nanoparticles requires valuable scientific findings. Numerous reports indicate the improvement of germination behavior and related indicators, including germination rate, seed vigor, root length, shoot length, and early establishment of seedling (Lee and Kim, 2000). The accelerated germination in primed seeds can be attributed to increased activity of degrading enzymes such as alpha-amylase, increased bioenergy level in the form of increased ATP, increased RNA and DNA synthesis, simultaneously increased number, and improved yield of mitochondria (Bewley et al., 2013;Hasanuzzaman and Fotopoulos, 2019). Seed priming KCl2 in pinto beans improves growth (Hajikhani et al., 2011). It has also been stated that seed priming with nano-Zn has improved the physiological characteristics and thus the yield of peanut plants (Prasad et al., 2012).
The application of titanium nanoparticles affects the biochemical and physiological properties of plants (Mishra et al., 2014). In addition to nano-Zn, the application of titanium at the nano level has also positively affected bean seed germination. Alpana et al. (2019) stated that priming bean seeds with nano-titanium caused a significant increase in seed germination percentage and other traits associated with seed germination. They reported that bean seed germination enhanced more by increasing nano-titanium concentration. Furthermore, it was found that the titanium nanoparticle's application increased the final grain yield in wheat (Jaberzadeh et al., 2013).
Providing the essential nutrients for the plant is one of the important aspects of crop management to achieve maximum quantitative and qualitative yield. Applying trace elements in the form of seed priming and foliar spraying can be useful in the cropping system. Micronutrients, especially zinc, are essential for higher plants growth, involving various biochemical activities. Zinc plays a key role in the synthesis of proteins, RNA, and DNA (Marschner, 2011;Taiz et al., 2014). Although plants need little zinc, if the plant face zinc deficiency, physiological stresses will reduce plant growth and yield due to the inefficiency of multiple enzyme systems and other metabolic functions related to zinc (Baybordi, 2006).
Iron is also one of the essential elements for plant growth. Wheat and barley, among crop species, are resistant to iron deficiency, while some cultivars of soybean, peanut, and bean are sensitive to it (Tehrani and Malakouti, 2000). Iron deficiency reduces the number of seeds per pod and the number of pods in plants of the Fabaaceae family, this phenomenon can be explained by the vital role of this element in nitrogen fixation and reduction (Brear et al., 2013). It is important to maintain sufficient zinc in the soil during seed germination 3 and early seedling development (Sytar et al., 2019). Foliar spraying and nutri-priming are effective methods to meet the nutritional needs of plants for trace elements.
This study firstly aimed at the application of gibberellin to accelerate germination and use the benefits of this rapid and uniform germination. Secondly, to investigate the possibility of addressing the zinc and iron deficiency through priming and foliar application of these elements; and thirdly, the evaluation of titanium nanoxide priming effect on quantitative and qualitative yield and some physiological traits of Pak white beans cultivar.

Materials and Methods
Experimental site, design and materials The factorial experiment was conducted in a randomized complete block design with four replications on white beans of Pak cultivar in a research farm located in Dorud city, Lorestan province (33° 40' N, 48° 70' E) with an elevation of 1650 meters above sea level in 2018. Before planting, samples were taken from 0-30 cm soil depth and mixed. The properties of soil are listed in Table 1.
Each plot consisted of 6 m six rows, with plant spacing between and per rows 50 and 5 cm, respectively. The distance between the plots was 1m, and the spacing of the blocks was 2 m. The seeds of Pak bean cultivar were inoculated with bacteria (Rhizobium phaseoli) then were sowed. Experimental factors included priming treatments (hydropriming, gibberellin 250 ppm, nano titanium dioxide 30 ppm, and nano-zin 5 ppm), all of them were performed for 12 hours at 25 °C. Aquarium pump was used for aeration. Foliar spraying treatments included (5 ppm zinc in the form of zinc sulfate, 5 ppm iron in the form of iron sulfate, and 5 ppm zinc and iron combination) were applied in two stages before flowering and pod formation at 8 to 10 am. Plastic protection was used to prevent the spread of spraying to adjacent plots.

Measurement of chlorophylls b, a, and a+b
Measurement of leaf chlorophyll based on Arnon (1949) was determined using a spectrophotometer at 663 and 645 nm. Half of a gram of fresh leaves in the early stages of flowering was grounded using liquid nitrogen in a pestle and mortar; then, transferred into 15 ml test tubes. Next, 10 ml of acetone was added to it and kept in the dark for 2 hours; centrifuged for 15 min at 8000 rpm at 15 °C and the supernatant was used. Then, the adsorption rate was measured to determine the concentration of chlorophyll a, b, and a + b at the associated wavelengths using the following equations (1), (2), and (3) (Arnon, 1949) Where, ABS is the absorption rate at the desired wavelengths (nm), V is the volume of acetone consumed, and W is the weight of fresh leaf .
Field plant sampling for nodules, yield, yield components and harvest index Plant height and number of sub-branches per plant were measured using an average of ten plants after physiological maturity in each plot. The number of nitrogen-fixing nodules per plant was measured at the start of the podding stage. To count the nitrogen-fixing nodules, the roots were removed from the soil to a depth of 50 cm, and after washing, the active nitrogen-fixing nodules (those with pink color after cutting) were counted. Furthermore, after harvest, the number of pods per plant, the number of seeds per pod, and 100-seed weight were determined by random selection of ten plants from each plot. Finally, after removing the marginal effects, grain yield and biological yield were measured based on each plot's 2 m 2 harvesting area. Using the following formula, harvest indices were also calculated: Harvest index (HI) = (Grain yield/Biological yield) ×100 Grain protein analysis A NIR instrument (DA 7250, Perten, Sweden) was used for determination the grain protein percent.

Statistical analysis
Data were analyzed using SAS software version 9.1, and the means were compared using Duncan's multiple range test. Graphs were drawn with Excel software.

A brief result from ANOVA about all traits
The results of analysis of variance showed that the effect of priming treatment on plant height, number of sub-branches per plant, number of nodules per plant, 100-seed weight, grain yield, biological yield, and harvest index were significant, but there was no significant effect on other traits. Besides, the foliar application significantly affected plant height, number of sub-branches per plant, 100-seed weight, grain yield, biological yield, and harvest index but it had no significant effect on other traits. The interaction effect of priming and foliar application on plant height, number of sub-branches per plant, 100-seed weight, grain yield, biological yield, and harvest index were significant ( Table 2). The results showed that seed priming significantly affected grain protein, Chl a and Chl b, and total chlorophyll contents. The effect of fertilizer foliar application and the interaction between seed priming and fertilizer foliar treatment on Chl. a, Chl. b and total Chl was significant (Table 3). Table 2. ANOVA (mean of squares) for yield and yield components of white bean affected by priming treatments and foliar application of Fe and Zn ns,*, and **; represent non-significant, significant at 5% and 1%, respectively.  ns,*, and **; represent non-significant, significant at 5% and 1%, respectively.

Plant height
Mean comparison showed that the highest plant height (51 cm) was obtained in the priming treatment with gibberellin and foliar application of zinc + iron, while the lowest height (44.8 cm) was associated with hydropriming + zinc foliar application (Table 4). The plant height increased in co-treatment of gibberellin priming and simultaneous foliar application of zinc and iron, with a 13% increase compared to the lowest height. This phenomenon can be explained by the hormonal effect of gibberellin on growth. Although priming with gibberellin at the level of simultaneous foliar co-application of zinc + iron and iron only increased the plant height more than other experimental treatments, but it was observed that priming with zinc nanoparticles was placed following this treatment, especially foliar application with iron and zinc + iron caused higher plant height than others by 49 and 49.3 cm, respectively.

The number of sub-branches per plant
The highest number of sub-branches per plant (21.3) was obtained from nano-Zn priming + zinc and iron spraying, while the lowest one was observed in hydro-priming and separate iron and zinc spraying ( Table  4). The priming treatment with nano-Zn and simultaneous foliar spraying of zinc and iron increased plant height and enhanced the number of sub-branches per plant by nearly 32% compared to the control.

Nodule per plant
The results showed that the number of nodules per plant in titanium dioxide and gibberellin priming treatment (13 and 12 nodules per plant, respectively) was higher than other priming treatments. It was also found that the hydropriming treatment had the lowest number of nodules per plant (11 nodules per plant) ( Figure 1A). The results showed that simultaneous foliar application of zinc and iron had a more positive effect on the number of nodules, and using this treatment, the number of nodules per plant was higher than others (13 nodules per plant). Although the difference between foliar co-application of zinc and iron did not significantly affect nodules per plant, but findings illustrated that iron foliar application had the lowest number of nodules (11 nodules per plant) ( Figure 1B).

Pods per plant
The main effect of seed priming and foliar application treatments significantly affected the number of pods per plant, while their interaction was not significant. The results illustrated that nano-Zn priming had the highest number of pods per plant (17 pods). Besides, there was no significant difference between gibberellin and titanium dioxide primers, and plant pods in hydropriming were significantly less than others (Figure 2A). Co-application of zinc + iron produced the highest number of pods per plant (16 pods) ( Figure 2B). The number of pods per plant with simultaneous application of zinc and iron along with nano-Zn priming was higher than others, and it was found that nano-Zn priming increased the number of pods by nearly 40% compared to hydropriming.

Pod length
The pod length was only affected by seed priming treatment. Pod length under nano-Zn and nanotitanium priming were longer than gibberellin and hydropriming treatments. There was no significant difference between gibberellin priming and hydropriming in terms of pod length (Figure 3).

100-grains weight
Nano-Zn priming + foliar application of zinc + iron spraying resulted in a 100-grain weight increase that the highest one was 29.4 g. The lowest 100-grain weight was associated with the priming with titanium dioxide + zinc foliar application (Table 4). Simultaneous application of zinc and iron along with nano-Zn priming increased the 100-grains weight by 25%. Foliar spraying treatments accompanied with gibberellin priming resulted in an increase in 100-grain weight of bean compared to hydropriming (Table 4).

Grain yield
The grain yield was strongly affected by the simultaneous foliar application and seed priming. So that, priming with nano-Zn along with the simultaneous application of zinc and iron increased grain yield (3211 kg ha -1 ). The lowest grain yield was achieved by hydro priming and foliar application of zinc (Table 4). Priming with nano zinc and foliar application of zinc and iron increased grain yield by 18% compared to the control. Gibberellin priming showed a superior effect on grain yield rather than hydropriming (Table 4).

Biological yield
Biological yield was affected by priming and foliar application treatments. Priming treatment with nano-Zn, foliar application of iron resulted in the highest biological yield by 9647 kg ha -1 (Table 4). Nano-Zn priming increased the biological yield by about 19% compared to hydropriming. Nano-Zn priming and foliar application with iron were the superior treatment, which led to a 19% increase in biological yield compared to hydro-priming. In addition to the simultaneous foliar spraying of zinc and iron, nano-Zn priming further increased the biological yield. Biological yield in priming treatment with gibberellin was higher than hydropriming at all different foliar treatments.

Harvest index
The highest harvest index (36.7%) was achieved in gibberellin priming + foliar application of iron and zinc, also titanium dioxide priming + zinc foliar application. The lowest one was found in nano-Zn priming + iron foliar application (Table 4).

Grain protein
Considering the significant effect of seed priming treatment on the percentage of grain protein, it was found that priming with nano-Zn had a more positive effect on this trait (24%), while the lowest one was observed in hydropriming treatment (Figure 4).

Chlorophyll a
Mean comparison demonstrated that the highest content of Chl a was obtained in the priming with nano-Zn and foliar application of zinc + iron (Table 5).

Chlorophyll b
Priming with nano-titanium and foliar application of iron had the highest chlorophyll b content. The lowest content of chlorophyll b was related to hydropriming and foliar application of iron (Table 5).

Chlorophyll a+b
The maximum Chl a+b was observed in priming with nano-Zn accompanied with nano-Fe + nano-Zn foliar application. The lowest one was in the hydropriming treatment with foliar application of zinc (Table 5). Summarized results including all treatments and major traits is presented as a graphical abstract in Figure  5. Increasing the plant height by gibberellin can be explained by the hormonal effect of gibberellin on growth. Pouryousef Miandoab and Esmaeilzadeh (2017) stated that gibberellin priming caused an enhancement in plant height. By gibberellin, the height of dwarf plants such as corn, peas, and beans return to the normal situation (Itoh et al., 1999). Since zinc is an essential trace element, it regulates plant growth by interfering with the formation of indole acetic acid and activating many enzymes, as well as it increases plant height by synthesizing chlorophyll and producing carbohydrates, and transporting them to growth points (Shafiee et al., 2015). However, zinc deficiency reduces plant growth (Tehrani and Malakouti, 2000). Seed priming with zinc nanoparticles leads to improved seed germination and better plant establishment, which leads to a final increase in plant height by increasing plant growth (Laware and Raskar, 2014). On the other hand, our findings showed that foliar spraying of iron performed better than zinc and increased plant height. Further increase in plant height under iron foliar application can be due to the vital role of iron in chlorophyll synthesis; thus, the availability of photosynthetic iron and the final growth of the plant will be affected (Jin et al., 2008) .

The number of sub-branches per plant
The nano-Zn priming and foliar spraying of zinc and iron increased enhanced the number of subbranches per plant. The production of indole acetic acid regulates plant growth by activating many enzymes; ultimately, the number of sub-branches per plant increases (Shafiee et al., 2015). A decrease in plant growth occurred due to zinc deficiency; subsequently, the number of sub-branches per plant reduced (Tehrani and Malakouti, 2000). Foliar application of zinc and iron has resulted in the availability of micronutrients during vegetative and reproductive growth, and also this process combined with nano-Zn priming has led to a further increase in the number of sub-branches in the plant. The increased number of sub-branches can be attributed to further plant growth as well as enhanced photosynthetic activities of the plant along with increased leaf area. It has also been suggested that the application of nano-Zn elements leads to further induction of photosynthesis and the availability of photo-assimilates to increase plant growth (Gorczyca et al., 2015).
Nodule per plant Although co-application of zinc and iron caused more nodules along with more vegetative growth, titanium dioxide priming had a more positive effect on the number of bacterial nodules per plant rather than other priming levels. Increased growth by zinc availability has led to the expansion of roots in the plant rhizosphere, and titanium dioxide priming had more effect on increasing the growth of plant roots; therefore, more expansion of roots in the plant rhizosphere increased the number of nodules per plant. The use of zinc in the co-application of zinc and iron increased vegetative growth in the plant (Hajikhani et al., 2011); and subsequently, the number of nodules per plant increased. However, it should be noted that the increased number of nodules per plant in priming treatments with gibberellin and titanium dioxide might be due to vegetative growth increase, and expanded root growth in the rhizosphere leads to more production of bacterial nodules per plant. The effectiveness of titanium in an increased number of nitrogen-fixing nodules per plant can be explained by the more facilitated passage of nano-sized elements from cell walls and their influence on specific target genes when plants were primed with these elements (Tymoszuk and Wojnarowicz, 2020).

Pods per plant
The zinc application can cause pollination improvement in plants that led to better fertility; thus, it increases the number of reproductive organs in the plant; which ultimately, positively affects the number of pods per plant. In a study on soybeans, Bank (1982) found that zinc foliar treatment increased the number of pods per plant and the number of seeds per pod, which confirms the results of this study. The number of pods per plant was affected by seed priming treatment (Hajikhani et al., 2011), which accords with the findings of this study. The zinc nanoparticles increased the number of pods per plant (Makarian et al., 2017). Furthermore, zinc significantly affected chlorophyll synthesis and also increases energy production, the metabolism of lipids, carbohydrates, proteins, and phosphorus in the plant; and thus, has a positive effect on plant reproductive activities (Eisvand et al., 2018). It is also illustrated that the zinc nanoparticles increase reproductive organs; and thus, enhance production. The production increase in plants using nano forms of zinc is more than the forms of zinc sulfate and zinc chelate (Prasad et al., 2012).

Pod length
The increase in pod length can be explained by the increase in plant vegetative growth resulting from seed priming treatments. Other researchers reported increased vegetative growth due to seed priming (Hajikhani et al., 2011). Application of nano-Zn and nano-titanium increased pod length compared to gibberellin and hydropriming. This increase can be due to the nano-titanium effects on the metabolic activities before seed germination; thus, it will affect the germination process and plant establishment that ultimately leads to improved plant growth characteristics (Shah et al., 2021).

100-grains weight
The higher efficiency of zinc nanoparticles may be due to the structure of nanoparticles and their very small dimensions, so they have a high specific surface area, which leads to higher reactivity and mobility in the plant. It seems that all of the mentioned reasons can improve the yield components and protects the plant against serious damage, especially under abiotic stress (Nair et al., 2010). A study indicated that the developmental stage from pod formation to full seed set significantly affects 1000-grain weight. The supply of nutrients at this stage can increase the number of grains per plant. At different levels of priming, co-application of zinc and iron increases the 100-grains weight largely. A possible explanation for this increase can be the key role of zinc and iron in photosynthetic processes and carbohydrate accumulation (Bahre and Dehnavi, 2012) . An increase in 1000-grain seed caused by gibberellin and auxin can be attributed to the increase in sink strength.
Using gibberellin, the cell division speed and the number of storage cells in seeds may have increased (Taiz et al., 2014) .

Grain yield
The zinc increases grain yield by affecting leaf chlorophyll content, indole acetic acid concentration, and increasing photosynthesis (Ravi et al., 2008). Since nano fertilizers release nutrients gradually, so they are superior to conventional fertilizers to provide the required elements of plant in both methods (leaf or root absorption) (Würth, 2007). A study suggested that nano-Zn has led to increased grain yield in mung beans (Dhoke et al., 2013). It has also been stated that seed priming with nano-Zn has improved the physiological and functional characteristics of the peanut (Prasad et al., 2012).
Zinc involves the formation of pollen tube which leads to increased pollination and fruit and seed formation (Makarian et al., 2017), which increases yield by the number of seeds per plant. The zinc oxide nanoparticles are more available to the plants and play a key role in seed formation in the pod, that is because of their stability and durability; thus, increase the final grain yield. In this study, although zinc nanoxide priming increased the grain yield, it was observed that this increase in the co-application of zinc and iron is more than the foliar application of each of these elements solely. High grain yield in titanium nano oxide priming can be due to titanium oxide's positive effect on increasing plant fertility, and the more reproductive organs, the more final grain yield (Jaberzadeh et al., 2013). Another reason for increasing grain yield in nanotitanium priming treatment is that bean seed priming with nano-titanium improves seed germination characteristics (Alpana et al., 2019) and increases seedling establishment speed, thus yielding. Seeds also increased as plant growth improved. Mahmoodzadeh et al. (2013) studied rapeseed and found that nanotitanium improves root and shoot growth in germinated seeds, and ultimately, the final grain yield increases by improving plant growth.

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It seems that the improvement of growth rate by gibberellins may be due to the effective leaf area increase, stimulation of photosynthesis, activation of some enzymes, and changes in the distribution of the photosynthetic material. By stimulating the activity of some protease enzymes, they convert proteins into amino acids, including tryptophan, which is an auxin precursor (Pouryousef Miandoab and Esmaeilzadeh, 2017).

Biological yield
As zinc plays a key role in enzymatic activities and the participation of iron in chlorophyll production, plant's biological performance has increased by improving photosynthesis and production of the essential nutrients (Tehrani and Malakouti, 2000). Because nano-Zn has a very fine particle size with a higher specific surface area. Therefore, this specific feature can improve the physiological functions of plant through enzymatic activities which ultimately leads to increased grain and biological yields (Bhattacharjee and Mukherjee, 2002). Using zinc significantly increased biological yield (Rengel, 2001). Gibberellin priming increases biological yield due to increase leaf area and enhance photosynthetic performance. It also increases CO2 fixing by opening stomata, increasing Rubisco and sucrose phosphate synthetase activities (Ashraf and Foolad, 2005).

Harvest index
Treatments that increase the ratio of grain yield to biological yield will increase the harvest index. Titanium dioxide increases the number of grains per plant by enhancing the fertility process and has a higher yield, following that increases the harvest index (Jaberzadeh et al., 2013). It seems that the increase in harvest index at different levels of foliar application of micronutrients and titanium dioxide treatment was more than other ones. Hence, iron and zinc foliar treatment illustrated a higher increase than others did.

Grain protein
The increase in seed protein content with nano-Zn priming is probably attributed to the role of zinc in enzymatic processes; ultimately, it leads to increased protein production. Madadi et al. (2016) found that the nano-priming treatment resulted in a significant increase in the protein percentage in black seed.

Chlorophylls
Iron is the main element involved in the production of chlorophyll. One of the main reasons for the increase in chlorophyll content can be the synthesis of new chlorophyll and prevent its degradation via the inhibition of chlorophyllase. By iron and zinc foliar application as well as nano-Zn priming, the activity of some antioxidant enzymes such as catalase increased; this enzyme can prevent chlorophyll degradation via inhibition of chlorophyllase, and accelerate DNA synthesis (Farhoudi and Sharifzadeh, 2006). According to Rengel (2001), zinc is required for chlorophyll production in plants, and its application significantly increase the chlorophyll content, which was consistent with the results of this study. Simultaneous application of iron and zinc, especially with nano-Zn priming, further increased the content of chlorophyll a, b, and Chl a+b. The reason for this phenomenon can be the limitation in the amount of delta-aminolevulinic due to iron deficiency (Kiani, 2012), so the simultaneous foliar application of iron and zinc provides iron availability, and therefore, the chlorophyll content increased. Ru et al. (2018) also stated that the simultaneous application of iron and zinc increased the chlorophyll content of wheat. In current study, it was found that the use of iron solely compared to the separate zinc application led to a further increase in chlorophyll a, b, and a+b content. This can be explained by the main role of iron in increasing chlorophyll synthesis (Jin et al., 2008). Some other studies indicate an increase in leaf chlorophyll content due to foliar application of iron, which is consistent with the findings of this study (Mohamed Amanullah et al., 2012;Sharifi et al., 2016).
Increasing the content of Chl a, b and a+b by the titanium nanoparticles treatment can be attributed to the titanium nanoparticles' roles in stabilizing chloroplast membrane and protecting the chloroplast from aging. They also can improve the chlorophyll structure and pigments' light absorption (Morteza et al., 2013).
13 Sartip and Sirousmehr (2017) reported that titanium nanoparticles increase chlorophyll synthesis by the improvement of nitrogen uptake and metabolism.

Conclusions
The improvement of grain yield, biological yield chlorophyll content, grain protein, and some other physiological and morphological traits of white bean by nutri-priming and hormonal priming along with foliar application of important micronutrients such as zinc and iron as well as titanium ( Figure 5) indicate that we can use such nutritional treatments to improve yield quantity and quality of this crop. Using nutrients at nano size will be efficient and economic because in such way, a low amount of nutrients is required.

Authors' Contributions
Conceptualization: HRE and SMA; Investigation: NA and AM; Methodology: HRE, AM, and NA; Formal analysis: AI; Writing-original draft: SMA; and Writing-review and editing: HRE and SMA. All authors read and approved the final manuscript.