Major differences in isoform composition of starch synthase between leaves and embryos of pea ( Pisum sativum L.)

Abstract

Isoforms of starch synthase (EC 2.4.1.21) in pea (Pisum sativum L.) leaves have been identi®ed and compared with those in developing pea embryos. Puri®cation and immunoprecipitation experiments show that most of the soluble starch synthase activity of the leaf is contributed by a novel isoform (SSIII) that is antigenically related to the major soluble isoform of the potato tuber. The major soluble isoform of the embryo (SSII) is also present in the leaf, but contributes only 15% of the soluble activity. Study of the leaf starch of lam mutant peas, which lack the abundant granule-bound isoform responsible for amylose synthesis in the embryo (GBSSI), indicates that GBSSI is not responsible for the synthesis of amylose-like material in the leaf. Leaves appear to contain a novel granule-bound isoform, antigenically related to GBSSI. The implications of the results for understanding of the role of isoforms of starch synthase are discussed.

Characterization of a Granule-Bound Starch Synthase Isoform Found in the Pericarp of Wheat

“…For example, low-amylose (lam) mutants of pea (Denyer et al, 1995) had a major SGP in starch from leaf (Tomlinson et al, 1998) and pod (Denyer et al, 1997) Figure 6. SDS-PAGE of starch granule-bound proteins (A) and SDS-PAGE immunoblots using anti-maize waxy protein antibody (B) and anti-potato GBSSI antibody (C).…”

“…This protein was reported to be a GBSSI isoform (Denyer et al, 1997;Tomlinson et al, 1998), suggesting that pea also has more than one gene encoding GBSS. In contrast, a single GBSS may be responsible for the synthesis of amylose in potato.…”

Causal Relations Among Starch Biosynthesis, Structure, and Properties

“…These enzyme classes appear to have different relative activities, depending on plant species and tissues, even though all appear to be ubiquitous in starch-synthesizing cells [157]. For instance, the activity of SSI is higher than that of SSIII in developing rice endosperms [51], whereas SSII and SSIII have higher activities in potato tubers [118] and pea embryos [178] than does SSI.…”

The Function of Rice Starch Synthase I Expressed in Escherichia coli

“…SSI probably plays important role(s) in starch biosynthesis in plants because it has no multiple isoforms, unlike all other SS types having multiple isoforms in rice (SSII, SSIII, SSIV, and GBSS), 8) maize (SSII), 9) kidney beans (SSII and GBSS), 10,11) and wheat (GBSS). 12,13) SSI and SSIII are major SS isozymes in the developing endosperm of the monocots such as rice, 1) maize 14) and wheat, 15) whereas the SSII and SSIII account for the major SS activities in the storage tissues of the dicots such as peas 16) and potatoes. …”

“…SSI probably plays important role(s) in starch biosynthesis in plants because it has no multiple isoforms, unlike all other SS types having multiple isoforms in rice (SSII, SSIII, SSIV, and GBSS), 8) maize (SSII), 9) kidney beans (SSII and GBSS), 10,11) and wheat (GBSS). 12,13) SSI and SSIII are major SS isozymes in the developing endosperm of the monocots such as rice, 1) maize 14) and wheat, 15) whereas the SSII and SSIII account for the major SS activities in the storage tissues of the dicots such as peas 16) and potatoes. 17,18) To understand the function of SSI, Guan and Keeling 19) analyzed the chain length distribution of glucan synthesized by different combinations of recombinant maize SS and maize BE isoforms expressed in Escherichia coli and found that SSI preferentially synthesizes short chains (DP 6 15).…”