Identification and Characterization of a Phloem-Specific [beta]-Amylase

Wang, Qi; Monroe, Jonathan D.; Sjölund, Richard D.

doi:10.1104/pp.109.3.743

Cited by 89 publications

(86 citation statements)

References 29 publications

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“…The major form of ␤-amylase in Arabidopsis has been shown to be localized to phloem sieve elements (Wang et al, 1995) and to be inducible by sugars (Caspar et al, 1989;Mita et al, 1995). Based on these findings, the major form of Arabidopsis ␤-amylase has been postulated to facilitate phloem transport by preventing accumulation of polysaccharides in sieve elements.…”

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confidence: 99%

“…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).…”

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confidence: 99%

“…Vacuolar ␤-amylases could play a role in polysaccharide metabolism in vacuoles. However, the identity(s) of vacuolar substrates for ␤-amylases remains to be determined, making difficult any assessment of a possible role for ␤-amylases in vacuoles.The major form of ␤-amylase in Arabidopsis has been shown to be localized to phloem sieve elements (Wang et al, 1995) Article, publication date, and citation information can be found at www.plantphysiol.org/cgi …”

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confidence: 99%

“…The major form of ␤-amylase in Arabidopsis has been shown to be localized to phloem sieve elements (Wang et al, 1995) Article, publication date, and citation information can be found at www.plantphysiol.org/cgi…”

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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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confidence: 99%

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

2001

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“…The detection of other proteolytic systems active during sieve element differentiation has not been reported. A Streptanthus tortuosus tissue culture system developed for the characterization of proteins present in differentiated sieve elements (Wang et al, 1995) has led to the identification of b-amylase as a sieve element marker and may prove useful for identifying additional biochemical and molecular markers for this unique selective autolysis. Sexton and Roberts (1982) noted that abscission is sometimes erroneously referred to as a process requiring cell senescence or degeneration.…”

Section: Selective Autolysis Of Sieve Elementsmentioning

confidence: 99%

Programmed cell death during plant growth and development

Beers

1997

Cell Death Differ

147

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This review describes programmed cell death as it signifies the terminal differentiation of cells in anthers, xylem, the suspensor and senescing leaves and petals. Also described are cell suicide programs initiated by stress (e.g., hypoxiainduced aerenchyma formation) and those that depend on communication between neighboring cells, as observed for incompatible pollen tubes, the suspensor and synergids in some species. Although certain elements of apoptosis are detectable during some plant programmed cell death processes, the participation of autolytic and perhaps autophagic mechanisms of cell killing during aerenchyma formation, tracheary element differentiation, suspensor degeneration and senescence support the conclusion that nonapoptotic programmed cell death pathways are essential to normal plant growth and development. Heterophagic elimination of dead cells, a prominent feature of animal apoptosis, is not evident in plants. Rather autolysis and autophagy appear to govern the elimination of cells during plant cell suicide.

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Involvement of five catalytically active Arabidopsis β‐amylases in leaf starch metabolism and plant growth

Monroe

2020

Plant Direct

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Starch degradation in chloroplasts requires β‐amylase (BAM) activity, but in Arabidopsis, there are nine BAM proteins, five of which are thought to be catalytic. Although single‐gene knockouts revealed the necessity of BAM3 for starch degradation, contributions of other BAMs are poorly understood. Moreover, it is not possible to detect the contribution of individual BAMs in plants containing multiple active BAMs. Therefore, we constructed a set of five quadruple mutants each expressing only one catalytically active BAM, and a quintuple mutant missing all of these BAMs (B‐Null). Using these mutants, we assessed the influence of each individual BAM on plant growth and on leaf starch degradation. Both BAM1 and BAM3 alone support wild‐type (WT) levels of growth. BAM3 alone is sufficient to degrade leaf starch completely whereas BAM1 alone can only partially degrade leaf starch. In contrast, BAM2, BAM5, and BAM6 have no detectable effect on starch degradation or plant growth, being comparable with the B‐Null plants. B‐Null plant extracts contained no measurable amylase activity, whereas BAM3 and BAM1 contributed about 70% and 14% of the WT activity, respectively. BAM2 activity was low but detectable and BAM6 contributed no measurable activity. Interestingly, activity of BAM1 and BAM3 in the mutants varied little developmentally or diurnally, and did not increase appreciably in response to osmotic or cold stress. With these genetic lines, we now have new opportunities to investigate members of this diverse gene family.

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Identification and Characterization of a Phloem-Specific [beta]-Amylase

Cited by 89 publications

References 29 publications

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

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

Programmed cell death during plant growth and development

Involvement of five catalytically active Arabidopsis β‐amylases in leaf starch metabolism and plant growth

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