Independent Regulatory Aspects and Posttranslational Modifications of Two β-Amylases of Rye

Daussant, J.; Sadowski, Jan; Rorat, Tadeusz; Mayer, Christiane; Laurière, Christiane

doi:10.1104/pp.96.1.84

Cited by 21 publications

(13 citation statements)

References 15 publications

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“…Little work has been done to determine whether the decreased ␤-amylase activity levels in these plant lines affect later, vegetative, stages of development. In fact, at least one of these plant lines, despite having greatly decreased levels of ␤-amylase activity in seeds, exhibits wild-type ␤-amylase levels in leaves and shoots (Daussant et al, 1991).…”

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The ram1 Mutant of Arabidopsis Exhibits Severely Decreased β-Amylase Activity

2001

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Despite extensive biochemical analyses, the biological function(s) of plant ␤-amylases remains unclear. The fact that ␤-amylases degrade starch in vitro suggests that they may play a role in starch metabolism in vivo. ␤-Amylases have also been suggested to prevent the accumulation of highly polymerized polysaccharides that might otherwise impede flux through phloem sieve pores. The identification and characterization of a mutant of Arabidopsis var. Columbia with greatly reduced levels of ␤-amylase activity is reported here. The reduced ␤-amylase 1 (ram1) mutation lies in the gene encoding the major form of ␤-amylase in Arabidopsis. Although the Arabidopsis genome contains nine known or putative ␤-amylase genes, the fact that the ram1 mutation results in almost complete loss of ␤-amylase activity in rosette leaves and inflorescences (stems) indicates that the gene affected by the ram1 mutation is responsible for most of the ␤-amylase activity present in these tissues. The leaves of ram1 plants accumulate wild-type levels of starch, soluble sugars, anthocyanin, and chlorophyll. Plants carrying the ram1 mutation also exhibit wild-type rates of phloem exudation and of overall growth. These results suggest that little to no ␤-amylase activity is required to maintain normal starch levels, rates of phloem exudation, and overall plant growth.␤-Amylases are found in vegetative tissues as well as in storage and reproductive organs, such as tubers and seeds. ␤-Amylases hydrolyze ␣-1,4-glucosidic linkages from the reducing ends of polysaccharide chains to form maltose (Beck and Ziegler, 1989). The genomes of many plant species contain several genes that encode ␤-amylases. For example, according to the database maintained by The Institute for Genomic Research (TIGR), the Arabidopsis genome includes nine genes that are identified as ␤-amylase or putative ␤-amylase genes (http://www.tigr.org/ tdb/edb2/ath1/htmls/GeneNameSearch.html). Despite the fact that they have been well characterized in vitro, the in vivo biological function(s) of ␤-amylases remains under debate (Ziegler, 1999).Several functions have been proposed for ␤-amylases in vivo. The fact that ␤-amylases hydrolyze starch in vitro (Beck and Ziegler, 1989) suggests a role for ␤-amylases in starch degradation. In addition, immunolocalization studies have shown an apparent association between ␤-amylases and starch granules (Okamoto and Akazawa, 1979;Hagenimana et al., 1992). However, these studies were conducted using polyclonal antibodies that may cross-react with starch phosphorylase. Consequently, the results of these studies should be interpreted with caution (Wang et al., 1995). In addition, starch is localized to plastids, whereas most ␤-amylases lack chloroplast transit peptides (Kreis et al., 1987;Monroe et al., 1991;Yoshida and Nakamura, 1991). Although chloroplast-localized ␤-amylases have been identified (Lao et al., 1999), the majority of ␤-amylase activity is extrachloroplastic (Beck and Ziegler, 1989;Nakamura et al., 1991). For example, 80% of the amylas...

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The ram1 Mutant of Arabidopsis Exhibits Severely Decreased β-Amylase Activity

2001

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“…This allows a comparison with the fl-amylase system well documented for the Triticeae (members of the Festucoideae, the other subfamily of the Gramineae). The maize ,B-amylase greatly differs from the major endosperm fl-amylases of barley, wheat, and rye, and resembles the minor ubiquitous fl-amylase described for wheat and rye (3,6) subjected to posttranslational modifications during germination. Moreover, the molecular specific activity of the enzyme (activity/amount of antigen) remained constant at all physiological stages investigated (Fig.…”

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confidence: 93%

“…Assay of the Rate of Secretion Scutella and aleurone layers were isolated from mature caryopses after 6 …”

Section: Plant Material Dissection and Extractionmentioning

confidence: 99%

“…The enzyme undergoes posttranslational modifications during germination (1,2,11,13,14,22), during which it is not further synthesized to a detectable extent (2,8 tified in the endosperms as well as in other caryopsis and vegetative plant parts of barley (Hordeum vulgare), wheat (Triticum aestivum), and rye (Secale cereale). This 'ubiquitous' enzyme is regulated in a different manner than is the main endosperm 1-amylase (3,6,20).Only fragmentary data are available concerning f-amylases of other tribes. They suggest, however, that the f3-amylase developmental scheme reported for the Triticeae might not apply to all cereals.…”

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“…In addition to this main endosperm 13- tified in the endosperms as well as in other caryopsis and vegetative plant parts of barley (Hordeum vulgare), wheat (Triticum aestivum), and rye (Secale cereale). This 'ubiquitous' enzyme is regulated in a different manner than is the main endosperm 1-amylase (3,6,20).…”

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β-Amylases in Cereals

Laurière¹,

Doyen²,

Thévenot³

et al. 1992

Plant Physiol.

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ABSTRACT,B-Amylase of maize (Zea mays L.) caryopses was studied during development and germination by means of enzymic, electrophoretic, and immunochemical techniques. ,B-Amylase activity increased during caryopsis development to a maximum value at the beginning of the water content plateau (at this stage the enzyme was located primarily within the pericarp) and then decreased. Almost no ,-amylase (activity or antigen) was found in either free or bound forms in the mature maize caryopsis. The activity increased again during seedling growth and reached much higher values. Both the aleurone layer (to a major extent) and the scutellum produced and secreted 6-amylase during germination, the secretion being stimulated by Ca2". No posttranslational modification of the enzyme was detected during germination. The molecular specific activity of the enzyme remained unchanged during the observed periods, indicating that the regulation of the activity is based essentially on protein turnover. The enzyme from developing and germinating caryopses was found to be identical in terms of antigenicity, isoelectric point, and molecular mass to the 8-amylases extracted from the roots and the leaves of the maize seedling. The maize ,B-amylase resembles in all respects the ubiquitous ,-amylase described for rye and wheat, whereas the major jl-amylase of those cereals appears to be lacking in the maize caryopsis.A considerable body of information has accumulated with respect to cereal K3-amylases. Although the data encompass the biochemistry, physiology, and genetics of the enzyme, they are largely restricted to the members of one tribe of the Festucoideae subfamily, the Triticeae. The developmental pattem of the enzyme is quite similar in the caryopses of the members of this tribe throughout the life history of the caryopsis. Briefly, the enzyme accumulates in the endosperm in both free and bound forms, which can be extracted with saline solution and reducing agents, respectively (for review see ref. 9). The enzyme undergoes posttranslational modifications during germination (1,2,11,13,14,22), during which it is not further synthesized to a detectable extent (2,8 tified in the endosperms as well as in other caryopsis and vegetative plant parts of barley (Hordeum vulgare), wheat (Triticum aestivum), and rye (Secale cereale). This 'ubiquitous' enzyme is regulated in a different manner than is the main endosperm 1-amylase (3,6,20).Only fragmentary data are available concerning f-amylases of other tribes. They suggest, however, that the f3-amylase developmental scheme reported for the Triticeae might not apply to all cereals. For instance, rice caryopsis ,Bamylase is synthesized during germination (16). To obtain a comprehensive insight into the developmental pattern of cereal f3-amylases, further investigations should be oriented toward members of other tribes of the Gramineae. The present study was concerned with the ,3-amylase of one member of the Panicoideae subfamily: maize (Zea mays L.), a cereal of major economic importance in whic...

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