Seed Priming with Selenium: Consequences for Emergence, Seedling Growth, and Biochemical Attributes of Rice Abdul Khaliq, Farhena Aslam, Amar Matloob, Saddam Hussain, Mingjian Geng, Abdul Wahid & Hafeez ur Rehman Biological Trace Element Research ISSN 0163-4984 Biol Trace Elem Res DOI 10.1007/s12011-015-0260-4
1 23
Your article is protected by copyright and all rights are held exclusively by Springer Science +Business Media New York. This e-offprint is for personal use only and shall not be selfarchived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com”.
1 23
Author's personal copy Biol Trace Elem Res DOI 10.1007/s12011-015-0260-4
Seed Priming with Selenium: Consequences for Emergence, Seedling Growth, and Biochemical Attributes of Rice Abdul Khaliq & Farhena Aslam & Amar Matloob & Saddam Hussain & Mingjian Geng & Abdul Wahid & Hafeez ur Rehman
Received: 4 October 2014 / Accepted: 28 January 2015 # Springer Science+Business Media New York 2015
Abstract The present study was undertaken to appraise the role of selenium priming for improving emergence and seedling growth of basmati rice. Seeds of two fine rice cultivars (Super and Shaheen Basmati) were primed with concentrations of 15, 30, 45, 60, 75, 90, and 105 μmol L −1 selenium. Untreated dry- and hydroprimed seeds were maintained as the control and positive control, respectively. Selenium priming resulted in early commencement of emergence, triggered seedling growth irrespective of rice cultivar over untreated control, and was more effective than hydro-priming except at higher concentrations. Lower electrical conductivity of seed leachates, reduced lipid peroxidation, greater α-amylase activity, higher soluble sugars, and enhanced A. Khaliq : F. Aslam : A. Matloob : S. Hussain (*) Department of Agronomy, University of Agriculture, Faisalabad, Pakistan e-mail:
[email protected] A. Matloob Department of Agronomy, Muhammad Nawaz Shareef University of Agriculture, Multan, Pakistan S. Hussain College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, Hubei, China S. Hussain : M. Geng College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China A. Wahid Department of Botany, University of Agriculture, Faisalabad, Pakistan H. ur Rehman Department of Crop Physiology, University of Agriculture, Faisalabad, Pakistan
activities of enzymatic antioxidants (superoxide dismutase (SOD), peroxidase (POX), catalase (CAT), and glutathione peroxidase (GPX)) were observed in seeds primed with selenium. Rice seedlings derived from selenium-primed seeds exhibited more chlorophyll contents, while total phenolics were comparable with those of the control seedlings. The improved starch metabolism, greater membrane stability, and increased activity of antioxidants were considered as possible mechanisms responsible for such improvements in emergence and seedling vigor of rice mediated by selenium priming. Priming with selenium (15–60 μmol L−1) favored rice emergence and seedling growth. Nevertheless, soaking seeds in relatively concentrated (90 and 105 μmol L−1) selenium solution had overall detrimental effects.
Keywords α-Amylase . Antioxidants . Basmati rice . Selenium priming . Soluble sugars
Abbreviations CAT Catalase E50 Time taken to 50 % emergence EI Emergence index FEP Final emergence percentage GPX Glutathione peroxidase GR Glutathione reductase MDA Malondialdehyde MET Mean emergence time POX Peroxidase ROS Reactive oxygen species Se Selenium SOD Superoxide dismutase TSE Time to start emergence
Author's personal copy Khaliq et al.
Introduction Looming water scarcity has compelled rice growers to shift to direct seeding as an alternative to the current practice of transplanting in flooded soils. Nevertheless, erratic germination and poor stand establishment in direct-seeded rice is a major deterrent for achieving an optimal crop growth and better productivity especially under unfavorable conditions during emergence. Seed priming is an effective and pragmatic approach for increasing seed vigor and synchronization of germination, as well as the seedling growth of many crops [1]. It is a pre-sowing technique in which seeds are partially hydrated to a point where germination-related metabolic processes begin but radicle emergence does not occur [2]. Many of the recent studies emphasize on standardization of seed priming techniques to improve germination and curtail emergence time in quest of a uniform crop stand [3, 4]. Such positive effects of seed priming might originate from de novo synthesis of certain germination-promoting substances, early DNA replication, greater ATP availability, osmotic adjustments and membrane re-organization through restoring their original structures, and reducing leakage of metabolites [5, 6]. Seed priming techniques can also induce/enhance the level and activity of enzymes of antioxidant defense [7], thereby preventing lipid peroxidation during germination [8]. A number of compounds ranging from salts, polyamines, hormones, compatible solutes, and aqueous plant extracts have been employed and found beneficial as priming agents [4]. Efforts are still underway to discover and optimize new priming agents. Use of trace or micro-elements as priming agent has got a little attention and so far has been restricted to boron [9, 10] and zinc [11, 12]. Selenium (Se) is an essential trace element for both animals and humans [13]. Nonetheless, its essentiality for plants remains in doubt [14] as vascular plants lack seleno-protein like glutathione peroxidase enzyme (GSH-Px; EC 1.11.1.9) [15]. Although higher plants do not essentially require Se and show a low level of tolerance, there is growing consensus that it might contribute positively towards plant metabolic functions at lower concentrations [16, 17]. Soaking seeds in Se solution is one way of delivering Se to have growth regulatory effects in plants [14]. Besides increasing the nutritional value of produce, it may also help improve crop productivity. Positive effects of Se on plants have been extensively reported in literature and include protection against UV-induced oxidative damage [18, 19], enhanced germination under sub-optimal temperatures [2], delayed senescence [20], increased starch synthesis [21], remediation of heavy metals [22], increased phosphorylation and ATP content [23], and regulation of plant water status during drought [24]. Despite associated improvements in germination and seedling growth, nutri-priming also involves several hazards, which are particularly related to the concentration of that
specific nutrient [4]. Hence, pre-optimization seems indispensable if Se is to be used as a seed priming agent. Despite the availability of volumetric information on rice seed invigoration techniques [4], Se has rarely been tried as a priming agent in rice. It is hypothesized that Se priming may improve rice emergence and early seedling growth by modulating associated biochemical changes and activities of the antioxidant system. The present study intends to unravel the role of Se priming in regulating rice emergence and early seedling growth. Priming-induced changes in biochemical attributes of rice seeds and seedlings are also investigated and discussed.
Materials and Methods Seed Priming Treatments Seeds of two Indica inbred rice cultivars, viz., Super Basmati and Shaheen Basmati, were obtained from the Rice Research Institute, Kala Shah Kaku, Sheikhupura, and Salinity Research Institute, Pindibhattian, Hafizabad, Pakistan, respectively. The initial moisture content of seeds of both cultivars was 8.54 % (Super Basmati) and 8.92 % (Shaheen Basmati) on a dry weight basis. The seeds were primed at 27 °C±3 for 24 h in an aerated solution of sodium selenite (Na2O3Se, Applichem GmbH, Darmstadt, Germany) at 15, 30, 45, 60, 75, 90, and 105 μmol L−1 concentrations. Selenite was used as a preferred source of Se over selenate due to a greater capacity of the former to promote antioxidant systems [25]. For hydropriming (HP), seeds were soaked in aerated distilled water for 24 h at the same temperature. The ratio of seed weight to solution volume in both cases was 1:5 g ml−1 [26]. Untreated dry seeds of both rice cultivars were used as control. A 70 % increase in seed moisture content was noticed following seed treatments. After each seed treatment, seeds were washed thrice with distilled water and then re-dried with forced air to their original moisture content. The moisture content of treated and non-treated seeds was equilibrated for 2 days at room temperature. Seeds were then sealed in aluminum foil bags covered with polyethylene, and stored in a refrigerator at 5 °C until subsequent use. Seed Bioassay Thermocol trays (18×12 cm) were filled with dried and well-mixed field soil (1000 g) collected from the Agronomic Research Area, University of Agriculture, Faisalabad, Pakistan. The pH of saturated soil paste and electrical conductivity of the saturation extract (ECe) were 7.6 and 0.79 dS m−1, respectively. The soil was sandy clay loam with sand, silt, and clay in proportion of 48.20, 23.47, and 28.33 %, respectively. Fifteen rice seeds were uniformly sown in each tray at field capacity (−0.03 MPa). The trays were placed in a screen
Author's personal copy
1.907 0.537 1.046 0.373
HP hydro-priming, TSE time to start emergence, E50 time taken to 50 % emergence, MET mean emergence time, EI emergence index, FEP final emergence percentage
8.096
84.44 93.33 95.55 100.00 100.00 97.78 97.78 91.11 77.78 93.08 82.22 95.55 97.78 100.00 100.00 97.78 100.00 84.44 75.55 92.59 6.43 BC 5.91 C 8.02 AB 8.44 A 8.50 A 7.53 ABC 7.43 ABC 6.80 ABC 6.26 BC 6.04 5.68 7.92 7.51 9.09 7.69 6.92 6.83 6.68 7.15 6.82 6.14 8.12 9.36 7.91 7.38 7.94 6.78 5.85 7.37 6.46 A 5.94 AB 5.78 BC 5.31 CDE 5.05 E 5.24 DE 5.49 B–E 5.75 BCD 5.79 BC 6.42 5.87 5.72 5.25 5.09 5.48 5.30 5.79 5.69 5.62 6.50 6.00 5.85 5.37 5.00 5.00 5.69 5.72 5.89 5.67 5.29 A 5.19 A 4.66 ABC 3.97 BC 3.80 C 4.37 ABC 4.86 AB 4.49 ABC 4.46 ABC 5.79 5.36 4.40 4.21 3.65 4.50 4.69 4.64 4.32 4.62 4.79 5.03 4.91 3.72 3.95 4.24 5.02 4.35 4.61 4.51 4.00 A 3.17 B 3.00 BC 3.00 BC 3.00 BC 3.00 BC 3.00 BC 3.00 BC 2.67 C
Means not sharing a letter in common differ significantly at 5 % probability level by HSD Tukey’s test. Subscript numbers after Se denote the selenium concentration (μmol L−1 ) used for seed priming
Shaheen Basmati
4.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.11 4.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 2.00 3.00
Shaheen Basmati Super Basmati Super Basmati
Mean
E50 (days) TSE (days)
Rice Seeds Immediately after employing seed priming treatments, treated and non-treated rice seeds (5 g) were washed thrice with deionized water to remove any salt imposition and then soaked in 50 mL of deionized water at 25 °C. The electrical conductivity (EC) of seed leachates was then measured at 0, 1.5, 3, 6, 9, 12, 18, and 24 h after soaking with a digital conductivity meter (HI-9811, Hannah Instruments, USA). Lipid peroxidation of treated and non-treated rice seeds was determined as malondialdehyde (MDA) content using the thiobarbituric acid method [31]. The activity of α-amylase of ground rice seeds (1 g) was measured as per procedure of Lee and Kim [32]. The rate at which maltose is liberated from
Treatments
Biochemical Analyses
Table 1
Root and shoot lengths of five randomly selected seedlings were measured 18 days after sowing (DAS) from each experimental unit. Roots and shoots of five randomly selected seedlings were cut separately and oven dried at 70 °C for 48 h to get the dry biomass of each component, and both the components were summed up to record the total seedling biomass.
Influence of selenium seed priming on the emergence attributes of rice
No: of emerged seeds No: of emerged seeds þ……⋯ þ Days o f f irst count Days of f inal count
Mean
MET (days)
where n is the number of seeds, which were emerged on day D, and D is the number of days counted from the beginning of emergence. The emergence index (EI) was calculated as described by AOSA [30]:
Control HP Se15 Se30 Se45 Se60 Se75 Se90 Se105 Mean HSD p≤0.05
Shaheen Basmati Mean Shaheen Basmati Mean
Dn MET ¼ X n
Super Basmati
X
EI¼
Super Basmati
FEP EI
where N is the final number of emerged seeds, and ni and nj are the cumulative number of seeds emerged by adjacent counts at times ti and tj where ni
