Relationship between the levels of zeatin, zeatin nucleoside and indoleacetic acid and wheat grain development
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https://www.eduzhai.net/ International Journal of A griculture and Forestry 2013, 3(7): 322-326 DOI: 10.5923/j.ijaf.20130307.10 Zeatin, Zeatinriboside and Indolyl-3-acetic Acid Levels in Relation to Grain Development of Wheat Mohsen Salami1, Mansoureh Gholami2,* 1Department of Agronomy and Plant Breeding, Islamic Azad University, SavehBranch, Saveh, Ir an 2Department of Natural resources, Sanandaj Branch, Islamic Azad University, Sanandaj, Iran Abstract Indolyl-3-acet ic acid (IAA), Grain growth rate (GGR) andcytokinin levels were studied with different types of grain and positions in developing wheat grains (Triticu maestivum L. var. Bahar). Main spikes were divided into three grain positions which include pro ximal, middle and distal reg ions, and further into two grain types: Basal and apical grains. Grain dry weight, cytokin ins which include zeatin (Z) and zeatinriboside (ZR), and IAA levels were determined in ten label spikes sampled seven times, with four days interval. Th is started fro m the third day after a thesis (DAA) up to the 23rd DAA; and seven days interval from 23rd DAA up to maturity. Cytokinins and IAA contents increased unit the 11th and 19th DAA, respectively. The maximu m level of grain growth rate (GGR) was observed at the 15th DAA. Furthermore, the difference in both cytokinins and IAA, contents among spikelets in d ifferent reg ions of the spike and also among grains within a spikelet was positively correlated with the differences in dry matter accu mu lation. The results suggest that cytokinins and IAA levels play an important role in regulating grain filling pattern. Keywords Indoly l-3-acetic Acid (IAA), Spike, Spikelet, Triticu maestivum L 1. Introduction Cytokinins play a considerab le role in regu lating p lant growth and development. In addition to regulating the rate of cell div ision and cell elongation, cytokinins influence the intensity and direction of assimilate flo w. In cereals, peas, and beans, h igh levels o f cyto kin ins are generally found in the endosperm of developing seeds, which may be required fo r active cell div ision during the early phase of grain setting[5, 16]. Morris et al. reported that Zeatin (Z) and Zeatin riboside (ZR) in develop ing rice wheat g rains showed large t rans ient Increases fo llo wing po llinat ion, wh ich co in cid ed with th e period o f seed sett ing and maximu m endosperm cell division"1It is generally believed that cytokinins in higher plants are synthesized main ly in the root system and transported via the transpiration system to the abov eground parts where they regu late g ro wth and development. So me studies indicate that cytokinins may also be synthes ized in developing grains . It was suggested by Michael and Seiler-Kelb itsch that transient grain cytokin in content is correlated with final grain y ield. Increased grain set and g rain yield by the applicat ion of exogenous cytokinins has been reported in wheat, barley, and maize. Wheat (triticu maestivu m L.) is the most * Corresponding author: firstname.lastname@example.org (Mansoureh Gholami) Published online at https://www.eduzhai.net Copyright © 2013 Scientific & Academic Publishing. All Rights Reserved important cereal crop in the food culture of both developed and developing countries in the world. World wheat production increases by approximately 1.5% annually to meet the growing demand for food that results from population growth and economic develop ment. A Substantial increase in g rain y ield potential, together with good use of water and fertilizer is required to ensure food security in the future. For imp rovements in photosynthetic capacity to result in additional wheat yield, ext ra assimilates must be partitioned to develop grains and/or potential grain weight be increased to accommodate the extra assimilates[8, 11, 12]. The position of grain within a spike to some extent determines its final g rain weight wh ich can range fro m 20 to 60 mg. the grains fro m spikelet’s in the middle region of the spike and fro m the basal reg ion within each spikelet are mo re towards the upper level of this rand[7, 13] Wheat (Triticu maestivum L.) is the most important cereal crop in the food culture of both developed and developing countries in the world. World wheat production increases by approximately 1.5% annually to meet the growing demand for food that results fro m population growth and economic development. A substantial increase in grain yield potential together with good use of water and fertilizer is required to ensure food security in the future. For improvements in photosynthetic capacity to result in additional wheat yield extra assimilates must be partitioned to develop grains and/or potential grain we ight be increased to accommodate the extra assimilates. The position of grain within a spike to some e xtent determines its final gra in International Journal of A griculture and Forestry 2013, 3(7): 322-326 323 weight which can range fro m 20 to 60 mg . The grains from The secondary tillers were removed as they appeared. Ten spikelets in the middle reg ion of the Spike and from the basal region within each spikelet are more towards the upper level of this range. Various factors such as assimilate availability and/or transport capacity or the possible role labeled spikes were sampled seven times; every four days started from th ird day after synthesis (DAA) up to the 23rd DAA, and every s even days from 23rd DAA up to maturity at 37th DAA. Sp ikes were div ided into three grain positions, of plant growth regulators[15, 25] are offered to explain including pro ximal (spikelet number 1 to 5), middle (spikelet these differences. Cytokinins play important role in number 6 to 15), and distal (spikelet nu mber 16 to 20) regulating plant growth and development such as intensity regions, and further into two gra in types: basal (bold) (gra in and direction of assimilate flo w, cell elongation, and cell No. 1 and 2) and apical (s mall) (grain No. 3 upward ). division rate. In cereals, h igh levels of cytokin ins are All samples were d ivided into two parts; one was dried in generally found in the endosperm o f developing seeds, an oven at 70°C for 72 h, then weighted for dry matter which may be required for act ive cell d ivision during the accumulat ion; and another was fro zen in liquid N2 fo r one early phase of grain setting. min and kept in a freezer at 70°C for Zeaten (Z), Michael and Seiler-Kelbitsch reported that transient Zeatinriboside (ZR), and IAA (indolyl-3-acetic acid) grain cytokinin content is correlated with final grain y ield of analysis. Grain growth rate (GGR) was calculated using the barely. The findings of Alizadeh et al. showed an increase following equation: in grain y ield o f wheat cult ivars by the application of exogenous cytokinins. IAA is the major au xin involved in GGR (mg d-1) = W2−W1 T2 −T1 regulation grain develop ment[2, 9]. A wanand Alizai observed that the application of IAA significantly reduced spikelet sterility in rice. Wang et al. suggested that the poor grain filling of rice was associated with low grain doses Where, W1 is the total dry matter of gra in at time t1; W2 is the total dry matter of gra in at time t2; T1 is the time of first observation and T2 is the time of second observation. Cytokin ins and IAA contents were exp ressed on dry of both IAA and ABA (abscisic acid). weight (DW). Linear regression was used to evaluate the In evaluating the relat ion of dry matter accu mulation, relationships between traits. cytokinins and IAA leve ls at diffe rent grain type and position could be important fo r identifying the role of p lant growth regulator on differences in dry matter accu mulation of grains in a spike, which could be the key in developing wheat with higher grain y ield potential. Hence, the objective of this study was to evaluate the cytokinins and IAA levels along with dry matter accu mulat ion at different grain type and position within a spike of wheat. Cytokinins and IAA analysis The methods for e xtractions and purification of Z, ZR and IAA were mod ified fro m those described by Bollmarket al. and Yang et al.. Samp les consisting of approximately 50 frozen grains were ground in an ice-cold mortar in 10ml 80% (v/v) methanol extraction mediu m containing 1 mmol L-1butylatedhydroxytoluence (BHT) as an antioxidant. The methanolic ext ract was incubated at 4ºC for 4 h and 2. Materialsand Methods Single plants of the wheat (Triticu maestivum L. var. Bahar) were g rown in plastic pots with a diameter of 4.5 cm and depth of 20 cm. the pots were filled with a pasteurized soil which is classified as a clay loam with 28.1% sand, 25.7% clay and 46.2% silt, an electrical conductivity (ECe) of 1.2 dS m-1, a pH of 7.1 (saturated paste), and organic C of 0.62%. The plants were grown in a screen covered hall under otherwise natural conditions. The pots were watered as described by Holakoyedet al. (2008), and fert ilized once a week with half strength Peter's solution (NPK=10:10:10). centrifuged at 4000 rp m for 15 min at the same temperature (4ºC). The supernatants were passed through Chromosep C18 colu mns (C18 Sep-Park Cartridge, Waters Corp, Millfo rd, MA, USA), prewashed with 10 ml 100% (v/v) and 5 ml of the purified fract ion including cytokininsand IAA was collected and dried under N2 and then dissolved in 2 ml phosphate buffer saline (PBS) containing 0.1% (v/v) Tween 20 and 0.1% (w/v) gelatin (pH 7.5) for the determination by an enzy me-lin ked immunosorbent assay (ELISA). The method for quantification of Z, ZR and IAA was added to 1 g of fresh grains before purification. Recovery percentages of Z, ZR and IAA we re 77.1 ± 7.0, 78.5 ± 4.1, respectively. Table 1. Cytokinin content (ng grain-1) at different grain type and position within developing grains of wheat Grain Posi tion Dist al Grain Type Ba Ab 3rd 7.0±0.9c 4.7±0.7 7th 10.3±1.0 7.0±0.9 11th 18.8±1.9 12.4±1.0 (Day afte r anthesis) DAA 15th 19th 28.7±3.7 38.0±4.2 20.4±2.0 27.7±4.9 23rd 45.0±3.9 42.8±4.7 30th 47.5±4.9 44.7±4.4 Ma tu rity 49.0±4.0 47.1±4.8 Middle B A 7.5±0.9 4.2±0.7 11.7±1.2 7.5±1.0 20.7±2.4 15.4±2.0 41.0±4.5 24.4±2.9 40.7±5.0 42.7±4.1 47.7±4.7 48.7±4.9 50.0±5.2 41.0±4.8 51.1±5.2 42.7±4.8 Proximal B A 7.2±0.9 4.0±0.8 10.8±1.2 7.7±0.9 19.5±2.2 14.9±1.9 Ba, Basal grains; Ab, apical grains; c±, standard deviation of five samples. 29.7±4.4 22.5±4.0 49.0±4.2 40.5±4.0 47.1±4.9 47.4±4.8 48.7±5.2 48.8±4.8 50.0±4.9 40.2±4.9 324 M ohsen Salami et al.: Zeatin, Zeatinriboside and Indolyl-3-acetic Acid Levels in Relation to Grain Development of Wheat 3. Results Figure 1 demonstrate the grain dry matter accumu lation at different grain types and positions within the developing grains of wheat. The grain dry weight was positively correlated with the age of the plant fro m the 3rd to 37th DAA (r2 = 0.8999). Grain dry weight was diversely affected due to different grain positions. Grain dry weight of middle region of spike as compared to pro ximal and distal regions and grain dry weight of pro ximal reg ions as compared to distal region improved at all sampled DAA. Furthermore, grain dry weight was positively influenced by grain types. Hence, the maximu m levels of grain dry weight were obtained in basal grains as seen in Table 1 which indicate the cytokin ins content of different grain types and positions at various DAA. The cytokinins level increased fro m 3rd DAA to 11th DAA, and then decreased fro m 11th DAA to 37th DAA. Therefore, the maximu m levels of grain cytokinins fo r all d ifferent grain types and positions were observed at 11th DAA. The increase in cytokin ins concentration is closely correlated to dry matter accumulat ion (r2 = 0.9544). Based on grain type and position, the maximu m cytokinins levels of grain were obtained in middle region of spike and in basal grains at all sampled DAA. Fu rthermore, the differences in cytokin ins concentration of grains positively correlated to GGR (r2 = Figure 1. Grain growth rate (GGR) at different grain type and position within developing grains of wheat. B and A are basal and apical grains, resp ect ively Table 2 presents the IAA content at different grain type 0.7349). These correlations hold true both for co mparisons between spikelets in various regions of the spike, and also between florets within spikelets. and position with in developing grains of wheat. The IAA level increased fro m the 3rd DAA to 19th DAA, and then decreased from the 23rd DAA to 37thDAA. Hence, the All sampled DAA Generally, grain growth rate (GGR) was high during 11th to 23rd DAA. GGR improved fro m the 7th to 15th DAA and then decreased from 15th to 37th DAA. The lowest amount of GGR was observed during 30th to 37th DAA. Furthermore, the differences in GGR levels were proportionally dependent on both grain type and position of dry weights. The only exceptions were at the 30th to 37th DAA, middle position/ basal grains, where the GGR was lower as compared to middle position/ apical grains, and distal and proximal regions/ basal and apical gra ins (Figure 1). highest levels of grain IAA for all d ifferent grain types and positions were observed at 19thDAA. The IAA level of gra in in the middle region of spike as compared to both proximal and distal reg ions improved grain IAA content in all sampled DAA. The IAA level of g rain was positively affected by grain types. Therefore, the maximu m levels of grain IAA were obtained in basal g rains for all determined growth stages. The increase in IAA concentration was nearly paralleled to dry matter accu mulat ion (r2 = 0.9520). Furthermore, the differences in IAA concentration of grains positively correlated to GGR (r2 = 0.8795). These correlations also hold true for both comparisons between different grain types and positions. Table 2. IAAcontent (ng grain-1) at different grain type and position within developing grains of wheat Grain Posi tion Dist al Grain Type Ba Ab 3rd 3.3±0.1c 3.1±0.1 7th 11.9±3.8 10.5±1.5 11th 33.3±4.1 30.7±3.3 (Day afte r anthesis) DAA 15th 19th 31.9±3.4 37.1±3.3 39.3±4.3 35.8±4.3 23rd 14.3±3.4 13.7±1.4 30th 7.1±1.1 7.1±1.0 Ma tu rity 3.0±0.9 1.3±0.7 B 3.7±0.3 13.7±3.5 37.3±4.7 39.8±7.5 44.7±5.7 17.8±3.0 8.5±1.3 3.9±0.7 Middle A 3.0±0.3 10.8±3.0 34.4±4.1 35.7±4.4 39.3±3.9 13.7±3.0 7.8±1.7 3.1±0.5 B Proximal A 3.3±0.3 1.9±0.3 10.5±3.4 9.7±3.8 35.7±4.3 31.3±3.8 Ba, Basal grains; Ab, apical grains; c±, standard deviation of five samples. 31.1±5.3 33.3±4.3 37.1±3.4 35.9±3.4 15.9±3.7 13.7±3.1 7.4±1.0 3.9±1.1 1.8±1.0 0.9±0.7 International Journal of A griculture and Forestry 2013, 3(7): 322-326 325 4. Discussion Grain filling period is an influential stage of crop life cycle which strongly affects grain yields Plant growth regulators play an important role in regulat ing plant growth and development. The d ifferences in dry weight per grain are highly flexible. M iddle region of spike as compared to proximal and distal regions produces the maximu m level of grain dry weight. We have investigated the relation between cytokinins and IAA levels, along with dry matter accumulat ion and related GGR at d ifferent grain type and position within developing grains of wheat. Both cytokin ins and IAA levels increased remarkably in the early phase of grain setting while the GGR was mixed. Fu rthermore, the differences in both cytokinins and IAA levels among spikelets in different reg ions of the spike and also among grains within a spikelet were positively correlated with the differences in dry matter accu mulat ion. Yang et al. suggested that differences in sink strength due to cytokinins and IAA are responsible for variat ions in grain filling between superior and inferior spikelets of rice. Mounlaand Bangerth observed a maximu m au xin content of barely grains between the 22nd and 29th DAA. Higher IAA and cytokinins content in grain at its early filling stage may promote the division of endosperm cells[22, 25].  Bangerth F, Aufhammer W, Baum O (1985). IAA level and dry matter accumulation at different positions within a wheat ear. Physiol. Plant. 73: 121-125.  Banowetz GM , Ammar K, Chen DD (1999). Temperature effects on cytokinin accumulation and kernel mass in a dwarf wheat. Ann. Bot. 83: 303-307.  Bhardwaj SN, Verma V (1985). Hormonal regulation of assimilate translocation during grain growth in wheat. Indian J. Exp. Biol. 23: 719-721.  Bollmark M , Kubat B. Eliasson L (1988). Variations in endogenous cytokinin content during adventitious root formation in pea cuttings. J. 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