ФИЗИОЛОГИЯ РАСТЕНИЙ, 2014, том 61, № 4, с. 493-499
ЭКСПЕРИМЕНТАЛЬНЫЕ СТАТЬИ
УДК 581.1
EFFECTS OF SILICON ON Zea mays PLANTS EXPOSED TO WATER
AND OXYGEN DEFICIENCY1
© 2014 S. A. Sayed, M. A. A. Gadallah
Botany Department, Faculty of Science, Assiut University, Assiut, Egypt Received July 11, 2013
Effects of shoot and root supplementation with silicon on the response of Zea mays L. plants to matric water potential (¥m) and oxygen deficiency (waterlogging) stresses were studied. The soil water limitation (¥m) and oxygen deprivation significantly reduced shoot dry weight, chlorophyll (Chl) content, ascorbic acid content, as well as leaf relative water content. Both soil drying and waterlogging caused a significant increase in the leaf membrane injury by heat (51 °C) and dehydration (40% PEG) stresses. The levels of lipid peroxidation (POL) and hydrogen peroxide (H2O2) content were increased by excess soil drying and oxygen deficiency. Supplementary silicon at 1.0 mM significantly increased Chl content and improved water status. Concentrations of H2O2, MDA, and proline and leaf membrane injury were significantly reduced by Si application. The reverse helds true for ascorbic acid. The results of this study indicate that application of silicon might improve growth attributes, effectively mitigate the adverse effect of drought and waterlogging, and increase tolerance of maize plants. The silicon-induced improvement of drought and anoxia tolerance was associated with the increase in oxidative defense abilities.
Keywords: Zea mays - anoxia - antioxidant - drought - flooding - matric potential - soluble sugars
DOI: 10.7868/S0015330314040162
INTRODUCTION
Drought is an important environmental stress that adversely affects growth and causes a reduction in the growth rate, stem elongation, and leaf expansion [13]. Drought stress usually causes a decrease in crop production. It inhibits the photosynthesis, causes changes in the chlorophyll (Chl) content, and damages the photosynthetic apparatus [4]. Gong et al. [5] reported that drought induced changes in the oxidative damage to wheat photosynthetic pigments, proteins, and lipids.
In many areas, plants face soil oxygen deficiency, another environmental constraint. In flooded soil, diffusion of gases through soil pores is strongly inhibited by excessive water content. For most crops, excess water is a major constraint to productivity in many regions and situations [6]. Milroy et al. [7] reported that waterlogging treatment reduced the concentration of the major nutrients and a number of micronutrients in cotton plants.
1 This text was submitted by the authors in English.
Abbreviations'. AscA - ascorbic acid; Chl - chlorophyll; POL -peroxidation of lipids; - matric potential; RWC - relative water content; SS - soluble sugars; WL - waterlogging. Corresponding author. Suzan A. Sayed. Botany Department, Faculty of Science, Assiut University, Assiut, Egypt. Fax. 0020-88234278; e-mail. drsuzan1@hotmail.com
The role of silicon in plant metabolism has received increasing attention [1]. It has a number of beneficial effects on growth under biotic and abiotic stresses [1, 8].
With respect to the role of silicon to waterlogging stress, relevant works are limited. In the present work, it seems interesting to focus on the physiological behavior underlying maize plant responses to exogenous silicon application during water stress or anoxia. Accordingly, we have investigated the effects of shoot and root silicon supplementation on growth and some metabolic aspects in maize plants exposed to soil water limitation and oxygen deprivation.
MATERIALS AND METHODS
Plant material and experimental conditions. Maize (Zea mays L., cv. Fard 4) plants were grown in plastic pots containing 4 kg of air dry soil (sand/clay, 1 . 2) in the Experimental outdoor greenhouse at of the Faculty of Science, Assiut University (Egypt), under natural field conditions of temperature, humidity, light, and day/night regime. The plants (4 per pot) were watered with full nutrient solution prepared according to Down and Hellmers [9]. Plants were grown for 15 days in the soil, the water content of which was maintained at field capacity. One set of the plants was then subjected to decreased soil moisture content. Soil matric water potential (¥m) levels were chosen at -0.03 (un-
Table 1. Dehydration (40% PEG) and heat (51°C) injury of leaf discs excised from unstressed = -0.03 MPa), water stressed (¥m = -0.5 and -1.0 MPa), and waterlogged (WL) Zea mays plants in the presence or absence of Si
Membrane injury, %
Parameter Si, 1.0 mM Si, 1.0 mM
control PEG, 40% control 51 °C
* m> PEG, 40% root shoot 51°C root shoot
MPa application application application application
-0.03 16.57 ± 1.42c 16.03 ± 1.54a 13.55 ± 2.01b 39.04 ± 2.03c 38.55 ± 2.11c 30.92 ± 2.11b
-0.50 17.25 ± 0.98c 7.73 ± 1.02c 14.30 ± 1.02b 43.99 ± 1.98b 25.62 ± 1.98d 32.10 ± 2.98ab
-1.00 22.63 ± 1.35b 8.16 ± 0.89c 3.44 ± 0.11c 62.24 ± 2.43a 46.38 ± 2.40b 29.57 ± 1.98c
WL 32.43 ± 2.11a 12.53 ± 0.97b 19.44 ± 1.56a 62.17 ± 2.56a 56.88 ± 3.11a 35.09 ± 3.01a
LSD
1% 3.82 4.63 4.67 5.32 5.98 4.48
5% 2.78 3.37 3.40 3.87 4.35 3.56
Data are means of five replicates ± SD. Different letters in columns show significant difference between treatments based on Duncan's multiple range test.
stressed control), -0.5, and -1.0 MPa. The moisture content of the soil in each pot was adjusted gravimet-rically to the desired level. Another set of plants was subjected to waterlogging. In waterlogging treatment the plants were flooded by maintaining the water 1 to 2 cm above the soil surface [10] by periodically adding of water.
The plants were kept under these conditions for two weeks before starting treatment with silicon. Silicon (1.0 mM, as sodium silicate) was applied by two different ways: (a) spraying the shoots (three times at 3-day intervals) of plants grown in drained or flooded soil; or (b) root application by irrigation or flooding with the Si solution. Five pots were assigned at random to each treatment combination at each stress level. A week after last silicon applications, the plants were harvested and analyzed.
Membrane stability. The stability of leaf membranes was assessed by determining the electrolyte leakage from leaf discs exposed to dehydration (40% PEG) and heat (51°C) stresses, according to the method used by Blum and Ebercon [11] on wheat.
The degree of membrane injury (based on electrical conductance measurements) was calculated according to the following formula:
% injury = 1 - [(1 - T1/T2)/(1 - C1/C2)] x 100,
where T1 and T2 represent the first and second measurements of the treatment samples and C1 and C2 the first and second measurements of the control.
Chlorophyll determination. The pigment fractions (chlorophylls a and b) were estimated following the spectrophotometry method (Unico UV-21 00 spectrophotometer) recommended by Lichtenthaler [12].
Leaf relative water content. The leaf relative water content (RWC) was calculated as described by Silveira et al. [13].
Proline determination. Proline was determined according to the method described by Bates et al. [14].
Determination of MDA. The level oflipid peroxida-tion in plant tissues was measured by determination of MDA content as described by Madhava Rao and Sres-ty [15].
Determination of H2O2. The H2O2 content in leaf samples was measured colorimetrically as described by Mukherjee and Choudhuri [16].
Determination of ascorbic acid. Ascorbic acid was estimated by the method of Jagota and Dani [17].
Dry weight determination. At the end of the experiment, three randomly chosen shoots were cut just above soil surface, washed in the detergent solution to remove dust from leaf surfaces, and then dried at 70°C for 48 h to constant weight.
Soluble sugars (SS). The content of SS was determined using the method of Buysse and Merckx [18].
Statistical analysis. Statistical analysis necessary to evaluate the effects of drought, waterlogging, and silicon on the parameters tested included the analysis of variance (ANOVA) using Ostle [19] method. Mean comparisons were accomplished by Duncan's multiple range test at P< 0.01 or P< 0.05.
RESULTS
Membrane stability
The solution of 40% PEG applied to leaf discs isolated from the leaves ofunstressed plants (Tm = -0.03 MPa) caused 16.57% injury (table 1). Discs of water-stressed plants at = -1.0 MPa were more injured (22.63%
Table 2. Effects of root and shoot application of Si on growth (dry weight), leaf relative water content (RWC), and proline concentration in Zea mays plants grown under decreased soil matric potential (¥m) and soil oxygen deficiency (waterlogging, WL)
Treatment Control Si, 1.0 mM
Parameter ¥m, MPa root application shoot application
Dry weight, g -0.03 9.23 ± 0.32a 9.97 ± 0.45a 10.91 ± 0.51a
-0.50 5.70 ± 0.35b 6.48 ± 0.32b 6.98 ± 0.44b
-1.0 3.78 ± 0.19c 4.66 ± 0.28c 5.29 ± 0.40b
WL 1.93 ± 0.12b 2.95 ± 0.39d 6.43 ± 0.31b
LSD 1% 1.95 2.05 2.63
5% 1.42 1.49 1.92
RWC, % -0.03 86.34 ± 2.34a 86.16 ± 1.33a 86.86 ± 1.33a
-0.50 79.71 ± 1.90b 82.74 ± 2.86b 85.56 ± 2.25a
-1.0 73.59 ± 2.11c 83.62 ± 1.81ab 84.53 ± 1.67a
WL 70.81 ± 2.56d 82.79 ± 2.02b 85.44 ± 2.01a
LSD 1% 3.43 3.99 4.03
5% 2.49 2.90 2.93
Proline, ^mol/g fr wt -0.03 17.95 ± 1.22c 14.03 ± 1.02a 11.30 ± 0.98b
-0.50 27.05 ± 2.11ab 13.82 ± 0.93b 10.05 ± 1.34bc
-1.0 29.15 ± 2.61a 11.52 ± 0.84b 21.16 ± 2.11a
WL 24.71 ± 1.93b 9.22 ± 1.01b 5.88 ± 0.50c
LSD 1% 5.21 3.41 2.56
5% 3.79 2.48 1.86
Data are means of five replicates ± SD. Different letters in columns show significant difference between treatments based on Duncan's multiple range test.
injury) than those of the unstressed plants. Soil oxygen deficiency also enhanced membrane injury (32.43% injury).
Silicon application decreased cell membrane injury. Under aerobic and anaerobic conditions, discs derived from plants stressed at = -0.5 and -1.0 MPa or flooded pl
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