Accumulation and relationship of essential micro-nutrients with aluminum uptake
in winter canola (Brassica napus) cultivars
ABSTRACT
Ernst Cebert*, Rhona Lee Miller-Cebert, Nahid Sistani and Martha Verghese
Department of Natural Resources and Environmental Sciences Alabama A&M University,
Normal, AL 35762 ernst.cebert@aamu.edu
Al
Fe
Mn
Zn
Cu
29.5
Micro nutrients content
(mg/100g Freeze-wt Dry weight)
Species in the Brassica genus representing canola (B. napus and B. rapa) have been
classified as phyto-accumulator for their characteristics to accumulate some elements
at levels which are toxic to other plant species. Since many Brassica species are
consumed as green vegetables or as forage, accumulation of some elements beyond a
certain threshold may be toxic to the consumers. Canola (B. napus) cultivars were
grown at pH 5.3 in a Decatur silty-loam soil at the Alabama A&M University
Agricultural Research Station, and were analyzed for copper (Cu), iron (Fe),
manganese (Mn), zinc (Zn) and aluminum (Al) content in their leaves at the rosette,
budding/bolting and blooming growth stages. Results for the essential micronutrients,
Fe, Cu, and Zn indicated no significant difference among the five canola cultivars. The
range content of these minerals in leaf tissues were: 23.7 – 25.3 mg/100g dry wt. for
Fe; 0.27 – 0.31 mg/100g dry wt. for Cu; and 2.9 – 3.1 mg/100g dry wt. for Zn.
However, result for Mn indicated significant difference among cultivars, with Jetton at
18.3 mg/100g dry wt. having significantly greater manganese content than Abilene and
Wichita with 15.1 and 15.4 mg/100g dry wt. respectively. Concentration of the nonessential element Aluminum ranged between 16.7 – 24.3 mg/100g dry wt. in leaf
tissues, with no significant difference among cultivars. Regression analysis also
showed significant linear relationship (r2 = 0.89) between Al and Fe accumulation in
leaf tissues. Fe and Al decrease, while Cu, Zn and Mn increase in the leaf tissues as
plants transitioned from rosette, to budding, and blooming growth stages.
Rosette = , Bolting = , Flowering = .
19.5
Coeff Var
9.5
4.5
-0.5
Rosette
Bolting
Flowering
Harvest stages
of plant growth indicate Al and Fe are highest at the rosette
Figure3 - (a, b). Accumulation of Al in relation to Fe showed rapid uptake during the rosette growth
stage, which represents the early establishment period of the crop (120 days after planting.) Previous
report by Shen and Ma (2001) reported that early accumulation of Al in leaf tissues is not mobile.
Therefore, lower level of the element in subsequent samplings indicates a depletion of its availability
within the root zone. Fig 3b shows significant positive relationship between Al and Fe.
Rosette = , Bolting = , and Flowering = .
to obtain optimal levels of desired nutrients. Fe and Al which
were significantly higher (P<0.001) at the rosette stage decreased
in subsequent samplings at bolting and reaching the lowest levels
at the blooming stage. Shen and Ma, (2001) reported that The
mobility of Al in acid soils can be taken up rapidly by plants and
it creates a problem of chemical stress in plants.
Figure 4 - (a, b). In the process of high aluminum accumulation, these results show that Cu accumulates
at a lower rate when compared to Fe in the presence of Al. An increase in Zn accumulation was
observed as Al decreased during the bolting stage. Both elements were significantly lower during the
last sampling period at flowering. Fig 3b does not indicate statistical significance in the relationship
between AL and Zn based on the regression across the three harvesting periods; rosette, bolting and
flowering.
Rosette = , Bolting = , an Flowering = .
Cultivars grouped by Harvest
Rosette
Bolting
Flowering
y = -0.4429x + 17.036
R² = 0.1446
leaves of winter canola grown on soil pH 5.3, compared to locally
purchased kale, collard and cabbage. Therefore, establishment of
winter canola (Brassica napus) as a multi-purpose crop in Alabama
requires further investigation of cultivars’ reaction to prevailing soil
conditions such as elevated aluminum content in acid soils.
The Objective of this presentation was to determine the relationship
of Al accumulation with essential micronutrients iron (Fe), copper
(Cu), manganese (Mn) and zinc (Zn) in leaves of winter canola at three
growth stages of the plant.
APPROACH: Five canola cultivars (Abilene, Kronos, Jetton,
Wichita and Virginia) were grown at the Alabama A&M
University (AAMU) Winfred Thomas Agricultural Research
Station (WTARS), located in Hazel Green, Alabama
Soil pH = 5.3
Samples were harvested at: Rosette, Budding/Bolting, and
Blooming/100% Flowering
Microwave digested samples were analyzed using a Varian Vista
MPX inductively coupled plasma optic emission spectrometer
(ICP-OES)
Statistical Analysis includes the use of
SAS (2006) Proc GLM to
determine significance among treatments, Tukey’s mean
separation (a=0.05), was used to analyze the data; Proc Reg and
Graph-and-Go for regression analysis and graphical illustrations.
Winter Canola Cultivars
Figure 2. Although significant differences exist for Al accumulation
between growth stages, among winter canola cultivars no
statistically significant variation was observed within growth stages.
The lowest level of 2.7 mg 100g-1 dry weight was obtained during
Figure 5 - (a, b). Similar to Cu, manganese (Mn) accumulation is lowest when Al is high during
early establishment of the crop at the rosette stage and reached its highest at the bolting and
flowering stages when Al is low. Variations for Mn among winter canola cultivars was apparent at
all growth stages, indicating sensitivity of its accumulation based on genotypic characteristics of the
cultivars. Further evaluation to identify cultivars which can accumulate high levels of all microelements is being evaluated.
rosette = , bolting = , and Flowering = .
flowering for cultivar Abilene, while the highest level of 21.5 mg
y = -3.4488x + 24
R² = 0.4124
100g-1 was for Jetton at the rosette growth stage.
The results, however, indicated that only Mn consistently showed
significant statistical differences among cultivars for all stages of
growth. In all stages, cultivar Jetton registered the highest level of
Mn, while Wichita and Abilene had the least. Other significant
differences in accumulation of micronutrients among cultivars were
observed for Zn at the flowering and for Cu during the rosette
stages of growth. Winter canola cultivar Jetton was consistent in
having higher accumulation of other micro-elements along with Al.
Figure 6- (a, b). Zinc (Zn) accumulation is similar to Cu and Mn. Its uptake is low
when Al is high during early establishment of the crop and reached its highest at
the bolting. However, its accumulation during flowering stage decreased
significantly from the bolting, where significant variation was observed among the
cultivars. Regression analysis for each growth stage would provide more specific
relationship between individual micro-nutrients with Al.
E. Cebert
0.7060
18.65500 Adj R-Sq
0.6276
Variable
DF
Parameter
Estimate
Standard
Error
Intercept
1
-11.87518
7.56274
-1.57 0.1372
Cu (mg/100g)
1
-2.55944
8.45504
-0.30 0.7663
Fe (mg/100g)
1
2.11015
0.44906
4.70 0.0003
Mn (mg/100g)
1
0.22721
0.26707
0.85 0.4083
Zn (mg/100g)
1
-1.18365
2.19651
-0.54 0.5979
t Value
Pr > |t|
Table 2. Regression analysis for model: Al= Cu Fe Mn Zn, for
foliage samples harvested at bolting stage of growth
Root MSE
1.63365 R-Square
0.5861
Dependent
Mean
6.04650 Adj R-Sq
0.4757
Coeff Var
27.01808
Parameter Estimates
Variable
used to determine specific stages of growth for harvest in order
AL (mg/100g dry wt.
et al., (2009) reported significantly higher level of Al in
y = -17.295x + 17.363
R² = 0.1186
2.56799 R-Square
13.76569
Parameter Estimates
14.5
Raymer et al., (1990); Lema et al., (2004); Salt and Kramer, (2000).
Miller-Cebert
Root MSE
Dependent
Mean
Alabama A&M University (AAMU) has shown that winter canola
could be an alternative to winter wheat and feasible for double- stage, while Zn and Cu show very little change from rosette to
cropping with traditional summer crops, and become an addition to flowering. These variations during the growth cycle of canola, as
current cropping system in the southeast United States (Hopkinson et al.,
previously observed by Mendham and Salisbury (1995), may be
2002; Kumar et al., 2007; Bishnoi et al., 2007).
Canola has been given the QHC label or qualified health claim based
on evidence that consumption of about 19 grams of canola oil daily
may reduce the risk of coronary heart disease, (http://www.uscanola.com).
The crop has also been labeled as a phytoremediator for its ability to
accumulate high content of selenium and other elements found at toxic
levels in polluted soils (Salt and Kramer, 2000; Palmer et al., 2000). The use
of canola as a potential leafy green vegetable was investigated by,
Bhardwaj et al., (2003) and Miller-Cebert et al., 2009a, 2009b and 2009c who
reported that the crop can provide nutritional benefits similar to those
of other traditional leafy greens. Canola is also being used as a forage
crop for winter grazing; it is being promoted as a feedstock for
biofuels; and its meal is an important source of protein for animal feed
y = 2.0502x - 13.326
R² = 0.888
24.5
Figure 1. Micro minerals in canola leaves at three different stages
INTRODUCTION
Table 1. Regression analysis for model: Al= Cu Fe Mn Zn, for
foliage samples harvested at rosette stage of growth
DF Parameter
Estimate
Standard
Error
t Value
Pr > |t|
Intercept
1
0.16620
3.78748
0.04
0.9656
Cu (mg/100g)
1
-9.01044
7.44177
-1.21
0.2447
Fe (mg/100g)
1
0.96158
0.22081
4.35
0.0006
Mn (mg/100g)
1
0.13964
0.07093
1.97
0.0677
Zn (mg/100g)
1
-0.17304
0.33382
-0.52
0.6118
Table 3. Regression analysis for model: Al= Cu Fe Mn Zn, for
foliage samples harvested at flowering stage of growth
Root MSE
0.50585 R-Square
0.8742
Dependent
Mean
3.29650 Adj R-Sq
0.8406
Coeff Var
15.34510
Parameter Estimates
Variable
D
F
Parameter
Estimate
Standard t Value
Error
Pr > |t|
Intercept
1
-6.00327
1.06684
-5.63
<.0001
Cu (mg/100g)
1
3.42829
1.24177
2.76
0.0146
Fe (mg/100g)
1
1.17882
0.14051
8.39
<.0001
Mn (mg/100g)
1
0.01552
0.01955
0.79
0.4396
Zn (mg/100g)
1
-0.36718
0.29059
-1.26
0.2257
Tables 1,2 and 3 show regression analysis
indicating the interaction of Al with essential
micro-nutrients Cu, Fe, Mn and Zn is effective
at the flowering (R2 = 0.87). However, at this
stage negative attributes from reduced uptake
would have already caused their harmful
effects. Low accumulation of Cu, Mn and Zn at
the rosette stage, while Al accumulates to its
highest level compromises the nutritional value
of canola if grown in soils with low pH.
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