2. Tryptophane, auxin, and niacin interrelations in the corn kernel.

 

Corn is an unusually rich source of the plant growth hormone, indoleacetic acid (IAA), and at the same time deficient in tryptophane and niacin. It seemed possible that one of the reasons for tryptophane deficiency in corn was not because corn grains fail to form the amino acid, but rather that the amino acid is formed and then enzymatically converted to IAA. A study of the free auxin1, auxin complex2, tryptophane, and niacin relationships has been completed on two strains (CC5/L317 and suKYS) of corn differing widely in the amount of auxin found in the kernels.

 

1  Free auxin is considered to be that auxin extracted with dither at 0íC.

 

2  Auxin complex has been used in this work as that auxin released from the corn kernel under alkaline conditions, and may not represent the absolute total auxin. Work is now in progress to identify this substance. At present it appears to be a small molecule with a molecular weight around 500 units.

 

a. The auxin complex, free auxin, and niacin were shown to reach a peak content during the milk stage, and that individual values for free auxin, niacin, nitrogen, and tryptophane contents were nearly the same when compared at the corresponding stages between the two strains. In the case of suKYS, as much as forty per cent of the tryptophane may have been directed into IAA production.

 

b. A tryptophane converting enzyme was demonstrated in the kernel, and was found to reach a peak of activity correlated to the production of free auxin and auxin complex.

 

c. The tryptophane converting enzyme had three times as much activity in the high auxin strain which seems to be reflected in the fact that this strain also contains three times as much auxin as the low one.


Comparison of the CC5/L317 and suKYS strains of corn for tryptophane, free auxin, auxin complex, niacin, nitrogen, and tryptophane converting enzyme activity. All values are expressed in micrograms per kernel or in the case of enzyme conversion are expressed in activity units per kernel.

 

Days after pollination

Free auxin

Auxin complex

Niacin

Total tryptophane

Total nitrogen

Activity of tryptophane converting enzyme

CC5/L317

suKYS

CC5/L317

suKYS

CC5/L317

suKYS

CC5/L317

suKYS

CC5/L317

suKYS

CC5/L317

suKYS

 

 

 

 

 

 

 

 

 

 

 

 

 

0

0

0

.005

.007

.06

.04

2.1

1.9

30

27

0.3

0.6

4

0

0

.002

.003

.15

.15

4.6

5.1

87

94

1.2

2.7

8

0

0

.02

.05

.34

.23

808

11.0

170

168

9.7

19.2

12

.02

.003

.31

.89

1.19

.66

181.0

8.4

407

273

65.0

47.0

16

.22

.013

3.41

4.95

2.52

1.64

30.0

25.3

700

443

95.5

93.7

20

.51

.07

8.15

17.0

3.54

2.87

47.0

40.5

964

763

355.0

700.0

24

.15

.48

9.62

26.8

3.95

5.17

58.0

66.7

1160

1170

330.0

1050.0

28

.14

.55

6.90

34.8

3.86

5.80

72.0

78.6

1740

1480

139.0

348.0

32

.11

.48

2.96

32.2

6.34

4.84

81.0

80.1

2180

1820

89.0

52.0

36

.07

--

1.80

--

5.10

--

--

--

2160

--

--

--

39

.04

--

.69

--

4.55

--

--

--

2530

--

--

--

 


d.    It has been hypothesized, on the basis of the insole balance between the two strains, that high IAA content is a reflection of the potential for the plant to manufacture tryptophane and its precursors, rather than of the tryptophane content at any stage. This balance was determined by summation of tryptophane, auxin complex, and niacin values at the respective stages.

 

e.    This balance of the indole nucleus further shows that the discrepancies in the later stages were mainly due to the higher production of auxin complex in suKYS.

 

f.    Apparently the auxin complex does not give rise to the free auxin, but rather that the reverse may be the actual situation. Thus, the auxin complex may be a "postcursor" rather than a "precursor" of indoleacetic acid. It would appear, therefore, that tryptophane is converted to free auxin by an enzyme system, and this free auxin is in turn transformed into the auxin complex.

 

M. L. Stehsel and S. G. Wildman