Zeins, the seed storage proteins of maize, are a group of alcoholsoluble polypeptides of different molecular masses that share a similar amino acid composition but vary i n their sulfur amino acid composition. They are synthesized on the rough endoplasmic reticulum (ER) in the endosperm and are stored in ER-derived protein bodies. Our goal i s to balance the amino acid composition of the methionine-deficient forage legumes by expressing the sulfur amino acid-rich 15-kD zeins in their leaves. However, it is crucial to know whelher this protein would be stable i n nonseed tissues of transgenic plants. The major focus of this paper is to compare the accumulation pattern of the 15-kD zein protein with a vacuolar targeted seed protein, p-phaseolin, in nonseed tissues and to determine the basis for i t s stability/instability. We have introduced the 15-kD zein and bean p-phaseolin-coding sequences behind the 35s cauliflower mosaic virus promoter into tobacco (Nicofiana fabacum) and analyzed the protein's accumulation pattern in different tissues. Our results demonstrate that the 15-kD seed protein i s stable not only i n seeds but in all nonseed tissues tested, whereas the P-phaseolin protein accumulated only i n mid-and postmaturation seeds. Interestingly, zein accumulates in novel protein bodies both in the seeds and in nonseed tissues. We attribute the instability of the p-phaseolin protein i n nonseed tissues to the fact that it is targeted to protease-rich vacuoles. The stability of the 15-kD zein could be attributed to its retention i n the ER or to the proteaseresistant nature of the protein.Seed storage proteins constitute a potentially useful class of proteins for the improvement of forage crops if they can be made to accumulate in leaves. It is a fairly simple genetic engineering feat to introduce a seed protein-coding sequence behind a strong constitutive promoter into transgenic plants and ensure high rates of synthesis of the corresponding protein. However, stability of the protein in an alien environment is still not clearly defined and has to be treated on a case by case basis.Seed proteins are synthesized during seed development and accumulate in protein bodies. These proteins are then utilized by the emerging seedling during germination. The major seed protein in dicotyledonous plants are the saltsoluble globulins, which are stored in vacuole-derived protein bodies. Most monocot seed storage proteins are '
Zeins, the major seed storage proteins of maize, are of four distinct types: alpha, beta, delta, and gamma. They are synthesized on the rough endoplasmic reticulum (ER) in a sequential manner and deposited in ER-derived protein bodies. We investigated the potential for producing sulfur-rich beta-zein and delta-zein proteins in leaf and seed tissues by expressing the corresponding genes in a constitutive manner in transgenic tobacco. The delta-zein and beta-zein, when synthesized individually, were stable in the vegetative tissues and were deposited in unique, zein-specific ER-derived protein bodies. Coexpression of delta-zein and beta-zein genes, however, showed that delta-zein was colocalized in beta-zein-containing protein bodies and that the level of delta-zein was fivefold higher in delta-/beta-zein plants than in delta-zein plants. We conclude that delta-zein interacts with beta-zein and that the interaction has a stabilizing effect on delta-zein.
Zeins, the major seed storage proteins of maize, are of four distinct types: (Y, p, S, and y. They are synthesized on the rough endoplasmic reticulum (ER) in a sequential manner and deposited in ER-derived protein bodies. We investigated the potential for producing sulfur-rich p-zein and 6-zein proteins in leaf and seed tissues by expressing the corresponding genes in a constitutive manner in transgenic tobacco. The 6-zein and @-zein, when synthesized individually, were stable in the vegetative tissues and were deposited in unique, zein-specific ER-derived protein bodies. Coexpression of 6-zein and p-zein genes, however, showed that 6-zein was colocalized in p-zein-containing protein bodies and that the leve1 of 6-zein was fivefold higher in 6-/@-zein plants than in S-zein plants. We conclude that 6-zein interacts with p-rein and that the interaction has a stabilizing effect on 6-zein.
Diamines and polyamines are ubiquitous components of living cells, and apparently are involved in numerous cellular and physiological processes. Certain "uncommon" polyamines have limited distribution in nature and have been associated primarily with organisms adapted to extreme environments, although the precise function of these polyamines in such organisms is unknown. This article summarizes current knowledge regarding the occurrence in higher plants of the uncommon polyamines related to and including norspermidine and norspermine. A putative biosynthetic pathway to account for the occurrences of these uncommon polyamines in higher plants is presented, with a summary of the supporting evidence indicating the existence of the requisite enzymatic activities in alfalfa, Medicago sativa L.The term "polyamines" is used here as a collective term for the naturally occurring diamines
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