Seed protein, oil, fatty acids, and minerals concentration as affected by foliar K-glyphosate applications in soybean cultivars

doi:10.4236/as.2012.36103

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Vol.3, No.6, 848-853 (2012) Agricultural Sciences

http://dx.doi.org/10.4236/as.2012.36103

Seed protein, oil, fatty acids, and minerals

concentration as affected by foliar K-glyphosate

applications in soybean cultivars*

Manju Pande1#, Mudlagiri B. Goli1, Tyneiseca Epps1, Nacer Bellaloui2

1Department of Natural Sciences and Environmental Health, Mississippi Valley State University, Itta Bena, USA;

#Corresponding Author: [email protected]

2Crop Genetics Research Unit, USDA-ARS, Stoneville, USA

Received 4 July 2012; revised 22 August 2012; accepted 10 September 2012

ABSTRACT

Previous studies showed that glyphosate (Gly)

may chelate cation nutrients, including potas-

sium (K), which might affect the nutritional

status of soybean seed. The objective of this

study was to evaluate seed composition (protein,

oil, fatty acids, and minerals) as influenced by

foliar applications of K + Gly. A greenhouse ex-

periment was conducted at Mississippi Valley

State University, using two glyphosate-resistant

soybean cultivars DK 4968 and Pioneer 95Y70

grown in a randomized complete block design.

The treatments were foliar applications of K

alone, Gly alone, K + Gly combined, and non-

treated control (C). A single application of po-

tassium (1.75% as K2SO4) was applied, and Gly

was applied at a rate of 0.75 ae/ha at V5 stage.

Leaf samples were harvested one week after

treatment (1WAT) and 3WAT. Mature seeds were

collected at harvest maturity (R8). The results

showed that K, nitrogen (N), and phosphorus (P)

concentrations increased in leaves in K alone

and K + Gly treatme nts at 1WAT, but significantly

increased at 3WAT in all treatments. The con-

centration of iron (Fe) and zinc (Zn) showed a

decre ase in l eaf con cen tra tion in Gly and K + Gly

treatments compared to C. Boron (B) concentra-

tion increased in Gly treatment. Seed protein

percentage was higher in all treatments in cul-

tivar DK 4968, and the increase was about 4.0%

in K treatment, 6.9% in Gly treatment, and 3.5%

in K + Gly treatment compared to C. The oppo-

site trend was observed in oil concentration,

especially in Gly treatment where the percen t age

decrease was 11.2% compared to C. Stearic fatty

acid was significantly higher in K + Gly treat-

ment compared to K treatment for DK 4968. A

higher percentage increase in linolenic acid was

observed in DK 4968 in K treatment (an increase

of 24.5%) and in K + Gly treatment (an increase

of 29.5%) compared to C. In Pioneer 95Y70, the

decrease in oil was 2.7% in K treatme nt and 2.3%

in K + Gly treatment compared to C. Stearic acid

in Pioneer 95Y70 was significantly higher in Gly

treatment, an increase of 8.3%, compared to C.

Our research demonstrated that foliar applica-

tion of K and Gly altered mineral concentration

in leaves and shifted seed composition towards

protein and stearic concentration. Further re-

search under field conditions is needed before

final conclusions are made.

Keywords: Fatty Acids; Glyphosate; Nu trition; Oil;

Potassium; Protein; Seed Composition; Soybean

1. INTRODUCTION

Soybean is a source of protein, desirable amino acids,

and fatty acids. Recent research showed that soy protein

contains balanced amino acids and phytoestrogen such as

isoflavones, which have positive health benefits [1]. Soy

products have also been used to prevent and treat bone

resorption, inhibiting ovarian and colon cancer and other

chronic diseases [2-6]. Compared with casein, dietary

soy has been found to slow the progression of chronic

renal injury in animals [7]).

Potassium (K) is one of the three major essential nu-

trients required by plants. Plants need large quantities of

potassium, and K is removed by most crops more than

any other nutrients, indicating the need to apply an ade-

quate amount of K fertilizer [8]. Since K is involved in

enzyme activation, sugar transport, chlorophyll produc-

*Mention of trade names or commercial products in this publication is

solely for the purpose of providing specific information and does not

imply recommendation or endorsement by the US Department of Ag-

riculture.

M. Pande et al. / Agricultural Sciences 3 (2012) 848-853 849

tion, and in regulating water balance, K deficiency can

severely impair protein synthesis resulting in accumula-

tion of free amino acid concentration in soybean plant

tissue [9], affecting plant growth, yield, and increased

susceptibility to pests. Potassium is transferred from

vegetative parts to seed during pod- and seed-fill. The

mature soybean seed contains nearly 60% of the total K

in a plant [10-12], any deficiency of K during rapid

vegetative growth until seed fill stages will affect soy-

bean yield and seed quality. Earlier studies have reported

that K deficiency in soybean resulted in reduction in

yield, seed oil, and K concentrations in seed [13]. Recent

research confirms the importance of maintaining high

concentration of K in plant tissue and seed, and higher

seed K is positively associated with yield and quality

[1,14]. Glyphosate (Gly) herbicide application has been

efficient for weed control, but its possible binding to

cation nutrients such K is still a concern. Since previous

results showed that there were no conclusive effects of

glyphosate on K concentration in leaves and seeds in

glyphosate-resistant soybean, the objective of this re-

search was to examine the effect of foliar application of

combined K and Gly on mineral concentrations in leaves

and seed protein, oil, and fatty acids in two soybean cul-

tivars.

2. MATERIALS AND METHODS

2.1. Treatment and Experiment Design

A greenhouse experiment was conducted at Missis-

sippi Valley State University (Itta Bena, MS). Gly-

phosate-resistant soybean cultivars DK 4968 and Pioneer

95Y70 were planted in 96 pots, arranged in a randomized

complete block design. Four replicates were used. Soil

moisture was monitored using soil water potential sen-

sors (densitometers), and plants were grown under natu-

ral light during the normal growing season (from April to

September) for the Early Soybean Production System in

the misdoubt USA. Temperature during the soybean

growing season ranged from 21˚C to 40˚C. The plants

were watered as needed. Treatments were applied six

weeks after planting (V4-V5 stage). The treatments were:

control (non-treated), foliar potassium treatment alone (K)

(1.75% as K2SO4), glyphosate (Gly) application alone at

a rate of 0.75 ae/ha, and K + Gly combined (1.75% as

K2SO4 + Gly at rate of 0.75 ae/ha).

2.2. Harvesting

Soybean leaves, stems, and root were collected from

each treatment one week after the treatment (1WAT) and

3WAT. At 12WAT (harvest maturity, R8), mature seeds

were collected for seed protein, oil, and fatty acid

analysis.

2.3. Leaf and Seed Analysis

Leaf and seed samples were collected from each

treatment. Five grams of dry, ground leaf samples were

analyzed by Soil, Plant, and Water laboratory, Athens,

GA. Twenty five grams of whole seed samples were

analyzed for protein, oil, and fatty acids using Near Infra

Red (NIR) reflectance [15] at USDA-ARS Delta States

Research Center in Stoneville, MS. Statistical analyses

were performed using ANOVA in SAS. Level of sig-

nificance was at P ≤ 0.05.

3. RESULTS

3.1. Leaf Mineral Concentration

Foliar application of K and K + Gly at both 1WAT

and 3WAT resulted in higher leaf K concentration in

cultivar DK 4968 (Tables 1 and 2). Nitrogen concentra-

tion increased in Gly treatment at 1WAT, whereas N

concentration increased in all treatments at 3WAT (Ta-

bles 1 and 2). Phosphorus increased in Gly and K + Gly

treatments at 1WAT and increased in all treatments at

3WAT. Sulfur increased in K and Gly at 1WAT and

3WAT (Tables 1 and 2). The concentration of Fe de-

creased in all treatments at 1WAT and decreased in Gly

and K + Gly at 3WAT. Zinc concentration increased

Table 1. Mean values of leaf mineral concentration after 1 week after treatment (1WAT) in DK 4968 and Pioneer 95Y70 as affected

by K, glyphosate (Gly), and K + Gly applications.

DK 4968 Pioneer 95Y70

Treatment K (%) N (%) P (%) S (%) B

(mg/kg)

(mg/kg) TreatmentK (%)N (%)P (%)S (%) B

(mg/kg)

C 2.7b 4.1cb 0.47c 0.45b 58.6b 235a64.2bC 2.9b4.2c0.49c0.44c 63.4bc 140a72.8a

K 3.0a 4.3b 0.47c 0.53a 58.9b 101b61.3bK 2.9b4.6b0.55b0.54b 62.2c 106c69.3ab

Gly 2.8b 5.0a 0.58a 0.57a 65.6a 100b62.6bGly 2.9b4.8ab0.60ab0.54b 68.5a 123b66.6b

K + Gly 2.9a 3.8c 0.59a 0.35c 65.7a 116b72.0aK + Gly3.1a4.8a0.63a0.60a 64.2b 123b69.0ab

Note: Means within a column between treatments, followed by the same letter are not significantly different at P ≤ 5%.

M. Pande et al. / Agricultural Sciences 3 (2012) 848-853

850

Table 2. Mean values of leaf mineral concentration after 3 weeks after treatment (3WAT) in DK 4968 and Pioneer 95Y70 as affected

by K, glyphosate (Gly), and K + Gly applications.

DK 4968 Pioneer 95Y70

Treatment K (%) N (%) P (%) S (%) B

(mg/kg)

(mg/kg) TreatmentK (%)N (%)P (%)S (%) B

(mg/kg)

C 2.3c 2.7c 0.35c 0.23c 56.4c 77.6a135bC 2.6c 2.9c 0.31c0.23a 62.8b 177a73.8a

K 2.7b 3.5ab 0.40b 0.28b 67.9a 74.0ab160aK 2.7b3.3a 0.38b0.23a 65.0ab 155b74.8a

Gly 2.9a 3.7a 0.45a 0.36a 63.2b 57.9c151abGly 3.0a 3.1b0.42a0.24a 66.0a 139c56.1c

K + Gly 2.87a 3.5b 0.45a 0.23c 63.3b 66.3bc152abK + Gly2.8b3.3a 0.43a0.26a 62.3b 140c66.0b

Note: Means within a column between treatments, followed by the same letter are not significantly different at P ≤ 5%.

in K + Gly at 1WAT, while increased in K at 3WAT

(Tables 1 and 2). Concentration of B increased in Gly

and K + Gly treatment at 1WAT and in all treatments at

3WAT (Tables 1 and 2).

In cultivar Pioneer 95Y70, foliar application of K +

Gly treatment at 1WAT and 3WAT resulted in higher

leaf K concentration in all three treatments. Concentra-

tions of N and P increased in all treatments at 1WAT and

3WAT. Sulfur concentration increased in all treatments

at 1WAT, while no changes were found at 3WAT. Iron

concentration decreased in all treatments at 1WAT and

3WAT. Zinc concentration decreased in Gly treatment at

1WAT and decreased in Gly and K + Gly treatments at

3WAT, contrasting to what was recorded in DK 4968.

Significant increase in B concentration was observed in

Gly treatment at 1WAT and 3WAT.

3.2. Seed Mineral Concentration

The mineral concentration in seed of DK 4968 fol-

lowed similar trend as those in leaf minerals (Table 3).

Concentrations of P increased in Gly and K + Gly treat-

ments, K increased in K + Gly treatment. However, no

significant changes were observed in seed N concentra-

tion. Seed S concentration decreased in all treatments

unlike leaf concentrations. The concentration of Fe de-

creased in seeds following similar pattern as in the leaves.

Zinc concentration in seeds also decreased, whereas B

concentration increased only in K treatment. In Pioneer

95Y70, K and P concentrations increased in Gly and K +

Gly treatments, whereas N decreased in all treatments in

seeds. Sulfur concentration decreased in seed in Gly and

K + Gly combined treatment. Iron concentration de-

creased in K and Gly, whereas Zn and B increased in all

treatments.

3.3. Seed Protein, Oil, and Fatty Acid

In DK 4968, protein percentage was higher in all

treatments compared to the control (Table 4). The per-

centage increase was 3.9% in K treatment, 6.9% in Gly

treatment, and 3.5% in K + Gly combined treatments. Oil

percentage decreased in Gly and K + Gly treatments, and

the lowest percentage decrease of 11.2% was recorded in

Gly treatment, and the highest protein percentage in-

crease was also observed in the same treatment. Palmitic

and stearic acid percentages decreased in K treatment,

while no significant changes were found in Gly or K +

Gly (Tabl e 4). A percentage increase of 6.5% in unsatu-

rated fatty acids oleic and 2.1% in linolenic was ob-

served in Gly treatment, The K treatment resulted in a

decrease of oleic acid by 8.8% and linolenic acid by

24.5%, while in K + Gly combined treatment no signifi-

cant change was observed in oleic acid. However, the

combined treatment resulted in an increase in linolenic

acid by 29.5%, while decreasing linoleic acid by 0.9% in

Gly and 2.34% decrease in K + Gly respectively (Table

4).

In Pioneer 95Y70, however, protein percentage de-

creased by 4.7% with Gly treatment, whereas, no sig-

nificant changes were observed in K or K + Gly treat-

ments (Table 5 ). The decrease in oil was 2.7% in K and

2.3% in K + Gly treatments compared to control.

Palmitic acid increased by 14.2% in K and by 9.8% in K

+ Gly treatments. Stearic acid increased by 6.9% in K

and by 8.3% in Gly treatments, while oleic acid de-

creased by 12.5% in K treatment and 12.7% in K + Gly

treatment. Linoleic and linolenic acids were relatively

stable in all treatments, except in Gly treatment where

linolenic acid decreased by 11.2% compared to control.

4. DISCUSSION

4.1. Leaf and Seed Minerals

The higher concentrations of K, N, P, and B in leaves

and seeds as a result of K and Gly applications indicated

that K and glyphosate enhanced the accumulation of

these nutrients in leaves and seeds. The mechanisms of

how Gly affects nutrients uptake is not fully understood.

Previous research showed that K application enhanced

uptake of macro- and micronutrients in soybean under

M. Pande et al. / Agricultural Sciences 3 (2012) 848-853 851

Table 3. Mean values of seed mineral concentrations in DK 4968 and Pioneer 95Y70 as affected by K, glyphosate (Gly), and K +

Gly applications.

DK 4968

Treatment K (%) N (%) P (%) S (%) B (mg/kg) Fe (mg/kg) Zn (mg/kg)

C 1.84b 5.90a 0.48b 0.33b 26.44b 71.2a 50.8a

K 1.84b 5.85a 0.49b 0.26c 30.62a 62.6b 41.3b

Gly 1.80c 5.88a 0.52a 0.35a 27.68b 68.2ab 43.6b

K + Gly 1.89a 5.85a 0.52a 0.242c 27.40b 65.0b 40.6b

Pioneer 95Y70

Treatment K (%) N (%) P (%) S (%) B (mg/kg) Fe (mg/kg) Zn (mg/kg)

C 1.81b 5.94a 0.48b 0.31a 32.8c 114a 48.7b

K 1.87b 5.79b 0.5b 0.29a 35.5b 84b 53.33a

Gly 1.90a 5.77b 0.56a 0.25b 35.7b 84b 53.2a

K + Gly 189a 5.72b 0.56a 0.25b 37.8a 99ab 55.5a

Note: Means within column in the treatments, followed by the same letter are not significantly different at P ≤ 5%.

Table 4. Mean values of protein, oil, and fatty acid percentages (%) in soybean seeds in cultivar DK 4968 as affected by K, gly-

phosate (Gly), and K + Gly applications.

Treatment Protein Oil Palmitic Stearic Oleic Linoleic Linolenic

C 37.97c 22.63a 10.8a 4.03a 20.83b 59.13a 6.47c

39.48b 21.9ab 9.98b 3.68b 19c 59.43a 8.05ab

(+3.9) (−3.2) (−7.6) (−8.8) (−8.8) (+0.5) (−24.5)

40.6a 20.1c 10.9a 4a 22.2a 58.6b 6.6b

Gly

(+6.9) (−11.2) (−0.1) (−0.83) (+6.5) (−0.9) (+2.1)

39.3b 21.7bc 11a 4.08a 20.3b 57.75b 8.38a

K + Gly

(+3.5) (−4.1) (+1.8) (+1.03) (−2.56) (−2.34) (+29.5)

Notes: Values within a column between treatments, followed by the same letter are not significantly different at P ≤ 5%. Values in parenthesis indicate percent-

age increase (+) and decrease (−) compared to control.

Table 5. Mean values of protein, oil, and fatty acid percentages (%) in soybean seeds in cultivar Pioneer 95Y70 as affected by K,

glyphosate (Gly), and K + Gly applications.

Treatment Protein Oil Palmitic Stearic Oleic Linoleic Linolenic

C 39.25ab 22.82a 10.2c 3.6b 20.17a 59.95ab 7.35a

39.5a 22.2b 11.65a 3.85a 17.65b 60.5a 7.05ab

(+0.64) (−2.7) (+14.2) (+6.9) (−12.5) (+0.9) (−4.0)

37.37c 22.95a 10.67bc 3.9a 19.75a 59.3b 6.52b

Gly

(−4.7) (+0.57) (+4.6) (+8.3) (−2.08) (−1.08) (−11.2)

38.47b 22.3b 11.2ab 3.67b 17.6b 59.72b 7.4a

K + Gly

(−1.9) (−2.3) (+9.8) (+2.3) (−12.7) (−0.38) (+0.68)

Notes: Values within a column between treatments, followed by the same letter are not significantly different at P ≤ 5%. Values in parenthesis indicate percent-

ge increase (+)/decrease (−) compared to control. a

M. Pande et al. / Agricultural Sciences 3 (2012) 848-853

852

soybean-wheat-maize rotation conditions [12]. The in-

crease of N in leaves and seed could be due to the close

relationship between K and nitrogen assimilation, espe-

cially nitrate reductase activity, the limiting step in ni-

trogen assimilation. Potassium application resulted in

increased chlorophyll content, nitrate reductase activity

in soybean, whereas the application of Gly at 0.84, 1.68,

2.52 + 2.52, and 0.84 + 0.84 kg ae/ha reduced foliar ni-

trogen by 26% - 42% [16]. Reports on N acquisition and

mobilization from vegetative tissue to seed, which de-

termine seed protein, are still conflicting [17], although

the role of K, B and Zn in protein synthesis have been

well established [18]. For example, it was found that K

application at anthesis to K-deprived plants enhanced the

photosynthetic capacity, leading to alteration in seed

protein and oil [13]. Our study showed consistent higher

concentrations of K, N, P, and B in Gly and K + Gly

treatments.

Application of Gly and K + Gly decreased micronu-

trients Fe and Zn concentrations in leaf and seeds of DK

4968, which is supported by previous research [12,19,

20]. However, Zn increased in cultivar Pioneer 57Y90,

suggesting complex genotype × environment interaction.

It was confirmed that Gly application significantly de-

creased Fe in plant tissues of glyphosate-resistant soy-

bean. Earlier studies on glyphosate-sensitive sunflower

showed that the application of Gly influenced uptake and

translocation of micronutrients, including Fe, Mn, and

Zn. It was explained that the reduction of Fe uptake may

be due to Fe-Gly complexes. Working on target and non-

target plants and sunflower, other researchers [21] showed

that Gly in the rhizosphere can inhibit acquisition of

micronutrients that are associated with plant disease re-

sistant mechanism. Iron deficiency has been increasingly

observed in crops with frequent Gly applications, and

Gly application negatively influenced plant growth and

micronutrient levels in plants, even in glyphosate-re-

sistant soybeans [20].

4.2. Seed Protein, Oil, and Fatty Acids

Foliar application of K and Gly treatments resulted in

higher protein percentages in all treatments in DK 4968,

while oil percentage decreased. However, in Pioneer

95Y70, protein decreased with Gly treatment. The dif-

ferent response of cultivars to K and Gly treatments

could be due to genotype differences. The different pro-

tein /oil ratio in the two cultivars may be due to genotype

x environment interactions which are reported to be sig-

nificant for seed yield, protein, and oil [22]. The inverse

relationship between protein and oil (r = −0.87) was pre-

viously reported [23,24].

The higher protein might be due to increased N, K, P,

and B concentrations in leaf and seeds. The role of K, B,

and Zn in protein synthesis and nitrogen metabolism was

reported in other species [18]. Conflicting reports exists

on whether or not N acquisition by plants and N and C

mobilization from vegetative tissue to seed determine

seed protein [17], although a close association exists

between soil nutrient levels and protein, oil, and unsatu-

rated fatty acids [24]. The increase of protein by Gly

treatments, as previously suggested [25], could be due to

altered patterns of nitrogen repartitioning at seed fill in

these treatments. Since increased N, P, K, and B concen-

trations were observed in both leaves and seed, higher

uptake and translocation of these minerals from leaves to

seed may have occurred, influencing seed protein levels.

Higher percentage of palmitic with K and K + Gly and

higher percentage of stearic acid in K and Gly treatment

in Pioneer 95Y70 was observed, while oleic acid per-

centage decreased. This observation was in contrast with

previous reports [24,25], where an increased percentage

of oleic acid and decreased percentage of linoleic acid

were observed. These researchers further reported that

saturated fatty acids, palmitic, and stearic percentages

were relatively constant. The higher stearic acid and

lower oleic acid reported in our study could be due to

possible effect of these chemicals (K and Gly treatments)

on the activity of fatty acid desaturases. The relative sta-

bility of saturated fatty acids by K treatment was re-

ported by others [24,25]. The increase in linolenic acid in

DK 4968 by combined treatment (K + Gly) is inconsis-

tent with previous research, indicating that saturated and

unsaturated fatty acids response to K and Gly could be

due to genotype differences and genotypes × environ-

ment interactions. The inconsistency in the results in the

literature emphasizes the need for further research in the

area of glyphosate application and mineral nutrition.

5. ACKNOWLEDGEMENTS

We would like to thank Ms. Sandra Mosley for technical assistance

and lab analysis. This research was funded by USDA/Faculty Student

Research grant at MVSU. The US Department of Agriculture (USDA)

prohibits discrimination in all its programs and activities on the basis of

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USDA is an equal opportunity provider and employer.5

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