**5.1 Materials and methods**

Commercialized artificial soil (pH, 5.2; EC, 1240 mS m–1; NO3––N, 280 mg Kg–1; available P2O5, 1020 mg Kg–1) was used for this experiment. Plant culture and MAA treatment were the same with that of pot experiment of radish with high NO3 – soil. The sampling and analysis of plant and soil also were according to procedures adopted for radish with high NO3– soil.

Effect of Mixed Amino Acids on Crop Growth 141

A0 A1 A2 A3

Treatments

– soil. Values are means ± SD (n=4).

– (Wang et al., 2000). The activities of NR and NiR

–

– soil. The different

Fig. 15. Effect of mixed amino acids on glutamine synthetase activity of radish leaves 28 day

With respect to enzyme activity of GS (Fig. 15), the application of MAA led to significant decrease in the activity in leaves of radish in this experiment, the lowest activity being recorded in treatment A1, with a decrease of 27% in relation to the highest activity, found in the reference treatment A0 (*P* > 0.01). Treatment A2 and A3 also showed decreases of 22%

Like some of the N transporters, NR is induced by its own substrate, NO3–, and this induction is fast, occurring within several minutes, and requires very low concentrations (< 10 μM) (Craw ford, 1995; Sueyoshi et al., 1995). NO3– is the primary factor, although other factors also influence the regulation of NO3– reduction and assimilation, including the end– products of assimilation such as amino acids. NiR and NR are similarly transcriptionally regulated for the reason of that NiR is strongly induced by the same factor, NO3–, probably

were much lower than that of radish which was planted in high NO3– soil due to the poor

In the present experiment, the activities of three enzymes decreased when treated with MAA. These results are in agreement with other researches which indicated that downstream N assimilation products such as amino acids can feed back to regulate NO3

uptake and reduction (Deng et al., 1991; Sivasanker et al., 1997; Vincentz et al., 1993). However, the effects of MAA on activities of enzymes are opposite to other experiments of ours, which indicated that treatment of MAA and amino acid fertilizer could enhance activity of NR in radish when supplied with high rate of NO3–. The contradictory results are

The data in Table 13 showed that N contents of the plants were not affected significantly by using MAA. The highest concentrations of all N forms were observed in treatment A2 (*P* >

0.05). These results differed from radish which was planted in high NO3

b b b

0

5

GSA (mol C

after sowing in pot experiment with low NO3

to prevent the accumulation of toxic NO2

due to the different NO3– levels of the soils.

**5.2.2 Effect of MAA on N contents** 

NO3– in the soil used in the present experiment (Table 15).

and 26%, respectively.

H5 10

N

O2

4 g-1 (FW) h-1

)

10

15

20

a

#### **5.2 Results and discussion**

#### **5.2.1 Effect of MAA on enzyme activities**

Significant differences were found in the NR activity among the treatments (*P* < 0.01) (Fig. 13). The NR activity was inhibited by foliar application of MAA in this experiment, contrary to that of radish in which was planted in high nitrate soil. The lowest activity was attained with A2, showing a decrease of 28% compared with the activity attained in treatment A0. Treatment A1 and A3 were less effective in decreasing the activity of NR than A2, with decreases of 8% and 17%, respectively.

Fig. 13. Effect of mixed amino acids on nitrate reductase activity of radish leaves 28 day after sowing in pot experiment with low NO3– soil. Values are means ± SD (n=4).

The response of activity of NiR to the MAA application resembled that of NR (Fig. 14). The lowest activity of NiR was found in treatment A2, showing 40% decrease compared with the control treatment (*P* < 0.001). Treatment A1 and A3 also showed 23% and 32% decrease in relation to A0, respectively.

Fig. 14. Effect of mixed amino acids on nitrite reductase activity of radish leaves 28 day after sowing in pot experiment with low NO3 – soil. Values are means ± SD (n=4).

Significant differences were found in the NR activity among the treatments (*P* < 0.01) (Fig. 13). The NR activity was inhibited by foliar application of MAA in this experiment, contrary to that of radish in which was planted in high nitrate soil. The lowest activity was attained with A2, showing a decrease of 28% compared with the activity attained in treatment A0. Treatment A1 and A3 were less effective in decreasing the activity of NR than A2, with

a

A0 A1 A2 A3

Treatments

Fig. 13. Effect of mixed amino acids on nitrate reductase activity of radish leaves 28 day after

The response of activity of NiR to the MAA application resembled that of NR (Fig. 14). The lowest activity of NiR was found in treatment A2, showing 40% decrease compared with the control treatment (*P* < 0.001). Treatment A1 and A3 also showed 23% and 32% decrease in

b

A0 A1 A2 A3

Treatments

Fig. 14. Effect of mixed amino acids on nitrite reductase activity of radish leaves 28 day after

c

– soil. Values are means ± SD (n=4).

sowing in pot experiment with low NO3– soil. Values are means ± SD (n=4).

b

ab

bc

**5.2 Results and discussion** 

relation to A0, respectively.

**5.2.1 Effect of MAA on enzyme activities** 

decreases of 8% and 17%, respectively.

0.0

0

1

NiRA (mol NO2

sowing in pot experiment with low NO3


g


)

2

3

4

a

0.2

NRA (mol NO2


g


)

0.4

0.6

0.8

a

Fig. 15. Effect of mixed amino acids on glutamine synthetase activity of radish leaves 28 day after sowing in pot experiment with low NO3 – soil. Values are means ± SD (n=4).

With respect to enzyme activity of GS (Fig. 15), the application of MAA led to significant decrease in the activity in leaves of radish in this experiment, the lowest activity being recorded in treatment A1, with a decrease of 27% in relation to the highest activity, found in the reference treatment A0 (*P* > 0.01). Treatment A2 and A3 also showed decreases of 22% and 26%, respectively.

Like some of the N transporters, NR is induced by its own substrate, NO3 –, and this induction is fast, occurring within several minutes, and requires very low concentrations (< 10 μM) (Craw ford, 1995; Sueyoshi et al., 1995). NO3 – is the primary factor, although other factors also influence the regulation of NO3– reduction and assimilation, including the end– products of assimilation such as amino acids. NiR and NR are similarly transcriptionally regulated for the reason of that NiR is strongly induced by the same factor, NO3–, probably to prevent the accumulation of toxic NO2– (Wang et al., 2000). The activities of NR and NiR were much lower than that of radish which was planted in high NO3 – soil due to the poor NO3– in the soil used in the present experiment (Table 15).

In the present experiment, the activities of three enzymes decreased when treated with MAA. These results are in agreement with other researches which indicated that downstream N assimilation products such as amino acids can feed back to regulate NO3 – uptake and reduction (Deng et al., 1991; Sivasanker et al., 1997; Vincentz et al., 1993). However, the effects of MAA on activities of enzymes are opposite to other experiments of ours, which indicated that treatment of MAA and amino acid fertilizer could enhance activity of NR in radish when supplied with high rate of NO3 –. The contradictory results are due to the different NO3– levels of the soils.

#### **5.2.2 Effect of MAA on N contents**

The data in Table 13 showed that N contents of the plants were not affected significantly by using MAA. The highest concentrations of all N forms were observed in treatment A2 (*P* > 0.05). These results differed from radish which was planted in high NO3– soil. The different

Effect of Mixed Amino Acids on Crop Growth 143

The commercialized artificial soil used in this experiment was with lower soil density (about 0.4 g cm–3) and higher water–holding capacity. Although the NO3– contents of 62.2~70.3 mg

this experiment. This might be the probable reason, that effects of MAA on N assimilation in the present experiment were different from that of radish which was planted in high NO3

soil. Whether in our experiments or in other researches, different effects of amino acids on

In conclusion, the results of the present experiment suggest that application of MAA can decrease activities of three enzymes of N assimilation (NR, NiR and GS). However, except N utilization, the application of MAA did not have significant effects on growth, and concentrations of proteins, amino acids, total N and NO3– content in plant shoots. The difference in the results were found in both the present experiment and pot experiment

soil solution. The hypothesis that effect of amino acids on NO3– uptake, reduction and

The study was conducted in summer of 2005 at the experimental farm of the Chungnam National University, Daejeon, Korea. The average chemical properties of the soil of the field are described in Table 16. The fertilizer mixture was uniformly broadcasted onto the soil surface and incorporated before ridging. The seeds of radish were sown at the end of May 2005 and arranged in a completely randomized block design, with three replications. The

At 15 and 22 days after sowing, AAF was applied 2 times to plots by spraying to leaves after diluting 500, 1000 and 2000 times by water, respectively. The main chemical contents of the

**matter** 

 **(1:5) (mS m–1) (g Kg–1) (mg Kg–1) (g Kg–1) (mg Kg–1)**  Before fertilization 6.0 122 15.6 170 0.81 80.2 After fertilization 6.0 191 15.8 279 0.87 191.2

Table 16. Chemical properties of soils used in field experiment of radish

**Available P2O5**

**Total** 

**<sup>N</sup>NO3––N** 

Kg–1 are not low in ordinary soil, available NO3

which radish was planted in high NO3

**6. Field experiment of radish** 

plots were 5 m × 2 m consisting of 2 rows.

AAF and application quantities are shown in Table 17.

**Soils pH EC Organic** 

**6.1 Materials and methods** 

NO3– reduction and assimilation were observed (Aslam et al., 2001).

assimilation depends on concentration of NO3– was justified.

**(1:5) (mS m–1) (mg Kg–1)** 

**––N** 

– soil

–

– for plants is very poor in soil solution in

– soil may be due to different levels of NO3– content in

**Treatments pH EC Available P2O5 NO3**

NP 5.4 1485 878 214.7 A0 5.7 482 384 68.2 A1 5.7 515 303 62.2 A2 5.7 349 264 70.3 A3 5.7 503 277 68.6 Table 15. Chemical properties of soil at the end of pot experiment for radish with low NO3


effects of MAA on N contents of radish in high NO3– soil and low NO3 – soil are in agreement with the supposition that amino acids have different effect on NO3– uptake and assimilation.

Data are means ± SD (n=4). Analysis of variance (ANOVA) was employed followed by Duncan's new multi range test. Values with similar superscripts are not significantly different (P>0.05).

Table 13. Effect of mixed amino acids on nitrogen contents of radish leaves 30 day after sowing in pot experiment with low NO3– soil

#### **5.2.3 Effect of MAA on radish yield and N utilization**

The plant production in fresh weight was found to be higher (*P* < 0.01) in treatment of A2, with an increase of 9% compared with the control treatment (Table 14). The response of production in dry weight to MAA treatments was not as sensitive as that in fresh weight (Table 14), only with slight influences. The results of N utilization (Table 14) were similar to dry yield, registering the highest value in A1, with an increase of 15% compared with A0 (*P* < 0.01).


Data are means ± SD (n=4). Analysis of variance (ANOVA) was employed followed by Duncan's new multi range test. Values with similar superscripts are not significantly different (P>0.05).

Table 14. Effect of mixed amino acids on radish yield and nitrogen utilization 30 day after sowing in pot experiment with low NO3– soil

#### **5.2.4 Effect of MAA on chemical properties of soil**

The chemical properties of soil at the end of experiment were showed in Table 15. The planting of radish affected these chemical properties of soil clearly. However, there were no differences in pH of soil among treatments planted with radish. On the other hand, either planting treatment or MAA treatment showed effect on soil nitrate reduction. Compared with the non planting treatment, the treatments of planting showed decrease of 86~88% for nitrate and decrease of 56~70% for available P at 30 days after sowing, respectively. The different rates of decrease were due to the different growth rates resulted from by MAA treatment. And the EC decreased accordingly.

effects of MAA on N contents of radish in high NO3– soil and low NO3– soil are in agreement with the supposition that amino acids have different effect on NO3– uptake and assimilation.

A0 1.89 ± 0.07 a 7.35 ± 0.40 a 1.30 ± 0.06 a 20.5 ± 1.5 a A1 1.87 ± 0.11 a 7.60 ± 0.37 a 1.32 ± 0.16 a 20.3 ± 2.4 a A2 1.77 ± 0.12 a 7.92 ± 0.46 a 1.35 ± 0.08 a 21.0 ± 0.7 a A3 1.97 ± 0.12 a 7.06 ± 0.50 a 1.34 ± 0.08 a 20.0 ± 0.8 a Data are means ± SD (n=4). Analysis of variance (ANOVA) was employed followed by Duncan's new

multi range test. Values with similar superscripts are not significantly different (P>0.05).

A0 8.38 ± 0.40 b 0.84 ± 0.05 a 17.06 ± 0.85 b A1 8.57 ± 0.34 b 0.88 ± 0.09 a 19.71 ± 0.58 a A2 9.83 ± 0.32 a 0.89 ± 0.05 a 18.52 ± 0.51 ab A3 8.44 ± 0.26 b 0.85 ± 0.03 a 18.88 ± 0.42 a

multi range test. Values with similar superscripts are not significantly different (P>0.05).

sowing in pot experiment with low NO3– soil

sowing in pot experiment with low NO3– soil

treatment. And the EC decreased accordingly.

**5.2.4 Effect of MAA on chemical properties of soil** 

**5.2.3 Effect of MAA on radish yield and N utilization** 

Table 13. Effect of mixed amino acids on nitrogen contents of radish leaves 30 day after

The plant production in fresh weight was found to be higher (*P* < 0.01) in treatment of A2, with an increase of 9% compared with the control treatment (Table 14). The response of production in dry weight to MAA treatments was not as sensitive as that in fresh weight (Table 14), only with slight influences. The results of N utilization (Table 14) were similar to dry yield, registering the highest value in A1, with an increase of 15% compared with A0 (*P* < 0.01).

> **Fresh weight Dry weight N utilization (g/plant) (mg/plant)**

Data are means ± SD (n=4). Analysis of variance (ANOVA) was employed followed by Duncan's new

Table 14. Effect of mixed amino acids on radish yield and nitrogen utilization 30 day after

The chemical properties of soil at the end of experiment were showed in Table 15. The planting of radish affected these chemical properties of soil clearly. However, there were no differences in pH of soil among treatments planted with radish. On the other hand, either planting treatment or MAA treatment showed effect on soil nitrate reduction. Compared with the non planting treatment, the treatments of planting showed decrease of 86~88% for nitrate and decrease of 56~70% for available P at 30 days after sowing, respectively. The different rates of decrease were due to the different growth rates resulted from by MAA

**Amino acids Proteins NO3– Total N (mg g–1 FW) (mg g–1 DW)** 

**Treatments** 

**Treatments** 


Table 15. Chemical properties of soil at the end of pot experiment for radish with low NO3 – soil

The commercialized artificial soil used in this experiment was with lower soil density (about 0.4 g cm–3) and higher water–holding capacity. Although the NO3– contents of 62.2~70.3 mg Kg–1 are not low in ordinary soil, available NO3– for plants is very poor in soil solution in this experiment. This might be the probable reason, that effects of MAA on N assimilation in the present experiment were different from that of radish which was planted in high NO3 – soil. Whether in our experiments or in other researches, different effects of amino acids on NO3– reduction and assimilation were observed (Aslam et al., 2001).

In conclusion, the results of the present experiment suggest that application of MAA can decrease activities of three enzymes of N assimilation (NR, NiR and GS). However, except N utilization, the application of MAA did not have significant effects on growth, and concentrations of proteins, amino acids, total N and NO3– content in plant shoots. The difference in the results were found in both the present experiment and pot experiment which radish was planted in high NO3– soil may be due to different levels of NO3– content in soil solution. The hypothesis that effect of amino acids on NO3– uptake, reduction and assimilation depends on concentration of NO3– was justified.
