COLUMBIA, SOUTH CAROLINA

University of South Carolina
 
 

Variants with altered kernel oil composition --Robin F. Keith1 and Anthony H.C. Huang2

Present addresses: 1Dept. Agronomy, Univ. Minnesota, St. Paul; 2Dept. Bot. Plant Sci., Univ. California, Riverside

Maize kernel oils are triacylglycerols which contain linoleic acid (ca. 50%) and oleic acid (30%) as the major fatty acid constituents. We attempted to identify genetic variants which possess altered acylglycerol and fatty acid components. Kernels of M2 generation were kindly provided by M. G. Neuffer of the University of Missouri. Mutation was induced by treatment of pollen with ethylmethane sulfonate in paraffin oil, and the average induction frequency of recessive mutations per locus was estimated to be about 10-3 (M. G. Neuffer and W. F. Sheridan, Genetics 95:929, 1980).

The M2 kernels were screened by analyzing scutellar slices of eight kernels from each of 1000 different M2 generation lines. Biometric calculation shows that the analyses will provide a 90% chance of detecting a homozygous recessive mutant in the M2 generation (E. H. Coe, in Maize for Biological Research, W. F. Sheridan, ed., 1982). Scutellar slices of 1-3mg were carefully dissected from the kernels such that the embryonic axes remained intact, and the lipids were extracted with boiling hexane. Half of the lipid extract was applied to thin layer chromatography plates to determine lipid composition. The other half of the extract was transesterified with methanol and boron trifluoride to produce fatty acid methyl esters, which were identified by gas liquid chromatography.

Of the M2 lines tested, 2.6% have kernels showing dramatic decreases in triacylglycerols with concomitant increases in free fatty acids (Table 1). In these variants, accompanying increases in mono- and diacylglycerol content were slight or non-observable. Other variant lines, 3.6% of the M2 lines surveyed, have kernels showing dramatic decreases in linoleic acid with a concomitant increase in oleic acid (Table 1). In this second group of variants, the amount of stearic acid and palmitic acid did not appear to be affected.

Table 1. Changes in acylglycerol and fatty acid composition of kernel oils in several representative M2 maize lines.
 
Seed Identity Ratio of linoleic/oleic Ratio of free fatty acid/triacylglycerol
Mo17 (control) 5.67 0.02
M 387-3a 1.38 --
M 495-1b 0.82 --
M 496-1a 0.67 --
M 660-1b 0.69  --
M 4-4a -- 4.0
M 625-1a -- 2.0
M 855-1c -- 3.3
M 966-2a -- 4.0
--Denotes values not appreciably different from the control.

Attempts by both our laboratory and Pioneer HiBred International have failed to produce germination from any of the detected variant kernels. Presumably, the age of the kernels (more than 6 years old), the damage to the scutella, and the genetic alterations contribute to the non-viability. From the variant lines which have kernels with altered lipid composition, we successfully germinated some unanalyzed (scutella undamaged) kernels. The seedlings have been grown to maturity, and the plants were self fertilized. The resulting M3 kernels will be analyzed in an attempt to determine if the variations are heritable.

We thank M. G. Neuffer for his generous supply of the M2 lines and his valuable suggestions, and Rongda Qu for scientific advice.


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