Development of Cotton Fruit. III. Amino Acid Accumulation in Protein and Nonprotein Nitrogen Fractions of Cottonseed¹

Abstract

This study was conducted to determine the metabolic events occurring during cottonseed development as revealed by N and amino acid compositions of both the whole seed and the free amino acid pool. Flowers on field grown cotton (Gossypium hirsutum L.) plants were tagged the day of anthesis, and bolls were sampled at intervals between 10 days after bloom and maturity. Developing seed were analyzed for both total N and nonprotein N (NPN). While total N was accumulated by the seed throughout development, NPN increased until 21 days after anthesis and then declined. At boll opening, only about 1% of the total N was in the NPN fraction.Amino acid compositions of the seed and the NPN fraction were also determined. In juvenile seed tissue, over 50% of the NPN was accounted for by asparagine. Other amino acids prominent in this free amino acid pool of young cottonseed were, in descending order, glutamine, aspartic acid, glutamic acid, and arginine. At maturity, asparagine and glutamic acid each accounted for about 15% of the NPN. Gamma‐amino butyric acid and ethanolamine were also observed in the NPN fraction. Significant shifts in total amino acid distribution were seen to occur during the fourth week of seed development. The amino acid profile of cottonseed after the fifth week of development closely approximated that of mature seed.

Nature and Patterns of Proteins during Cotton Seed Development

“…Not until midway in seed development does the amino acid composition of the cotton seed begin to resemble the mature seed profile (6). Studies of seed protein development have commonly measured crude protein accumulation and/or dynamic aspects of amino acid composition (6,14,20) (1 1, 12). Differential solubility of proteins can also be employed to separate seed proteins into classes, the development of which can be further investigated with other techniques (3).…”

“…During the first few weeks of cotton seed development, nearly half of the seed nitrogen is found in the nonprotein pool (6). Although the amino acids in this nonprotein nitrogen pool show little similarity to the amino acid profile of mature cotton seeds, they probably reflect the composition of the amino acids supplied to the developing seeds.…”

“…The quantity of water-soluble nitrogen increased through the first 21 days of development, then declined until 42 days, when it again began to increase; it reached its highest level at maturity. There was evidence of a high peptide content 7 weeks postanthesis.Although seed development in cotton (Gossypium hirsutum L.) has been described in several reports (5,6,16,18), studies of the pattern of protein accumulation during cotton seed development are lacking. Analyses of dry matter and mineral accumulation and distribution within the developing cotton fruit indicated that the carpel walls contribute a significant proportion of their nitrogen to developing seed (16, 18).…”

“…Although the amino acids in this nonprotein nitrogen pool show little similarity to the amino acid profile of mature cotton seeds, they probably reflect the composition of the amino acids supplied to the developing seeds. Not until midway in seed development does the amino acid composition of the cotton seed begin to resemble the mature seed profile (6). Studies of seed protein development have commonly measured crude protein accumulation and/or dynamic aspects of amino acid composition (6,14,20) while others have investigated structural aspects of seed protein development (4,7) or the nuclear regulation of protein synthesis (5).…”

“…Not until midway in seed development does the amino acid composition of the cotton seed begin to resemble the mature seed profile (6). Studies of seed protein development have commonly measured crude protein accumulation and/or dynamic aspects of amino acid composition (6,14,20) while others have investigated structural aspects of seed protein development (4,7) or the nuclear regulation of protein synthesis (5). Several investigators, however, have examined the development of protein fractions through the developmental changes revealed by electrophoresis or gradient centrifugation of seed proteins.…”