The Role of Phosphorylase in the Synthesis of Starch in Maize Leaf Bundle Sheath Cells

Fekete, M. A. R. de; Vieweg, G. H.; Thomas, W. Walsh

doi:10.1016/b978-0-12-474150-8.50015-x

Cited by 1 publication

(2 citation statements)

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“…a-Amylase and starch phosphorylase cleave only a-(1-*4) glucosidic linkages (9,12,16,23). This means that during the first 40 h of seed imbibition a-( l-4), glucan oligosaccharides having a-(1-*6) glucose branches may accumulate in embryo and megagametophyte cells.…”

Section: Resultsmentioning

confidence: 99%

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Starch Degradation Metabolism towards Sucrose Synthesis in Germinating Araucaria araucana Seeds

Cardemil

Varner²

1984

Plant Physiol.

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As starch is the main seed reserve material in both species ofAraucaria of South America, A. araucana and A. angustifolia, it is important to understand starch breakdown in both embryo and megagametophyte tissues of Araucaria seeds. Sugar analysis by thin layer chromatography indicates that sucrose is the main sugar produced in both tissues. Enzyme reactions coupled to benzidine oxidation indicate that sucrose is the main sugar moved from the megagametophyte to the growing regions of the embryo via the cotyledons.Phosphorylase was detected in both embryo and megagmetophyte tissues by the formation of I2Pjglucose-I-P and by formation of 114q amylopectin from ['4Cjglucose-I-P. The enzyme activity increases 5-fold in both embryo and gametophyte to a peak 18 hours after the start of imbibition. Debranching enzyme, a-glucosidase, and hexokinase are also present in both embryonic and megapmetophytic tissues.Branched glucan oligosaccharides accumulate during this time, reaching a maximum 40 hours after imbibition starts, and decline after germination occurs.The pattern of activity of the enzymes studied in this work suggests that starch degradation is initiated by a-amylase and phosphorylase in the embryo and by phosphorylase mainly in the megagametophyte. Sucrose-P synthase seems to be the enzyme responsible for sucrose synthesis in both tissues.of special interest to Chile, Brazil, and Argentina (6), it is convenient that the Araucaria seed are so very large. Thus, a complete range of analyses, with several replicates, can be done on embryo and megagametophyte tissues from a single seed. It is also fortunate that the megagametophyte cells are large. Being coenocytes they are about 180 gm in diameter (5) and can be observed under the stereomicroscope in thick sections of in vivo tissue. This allows in situ cytochemical identification of molecules that are being secreted by the megagametophytic cells into the intercellular spaces and transported from there to the cavity where the embryo is lying.The question which arises is: how is starch degraded by Araucaria seeds in the first 90 h after the start ofimbibition? Therefore, the purposes of this work were to investigate whether there are other enzymes beside a-amylase which may initiate starch degradation in the embryo and in the megagametophyte and to identify the enzymes that might be involved in the degradation ofstarch and formation ofsoluble sugars. Ultimately, the increase in the amount of soluble sugars and soluble metabolites in the embryo will increase osmotic pressure and the seed will germinate (17).This research then indirectly addresses the question of how the osmotic 'push' required for germination is developed. This is an important question because it is closely related to the problems of understanding dormancy, triggers for germination,

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Section: Resultsmentioning

confidence: 99%

“…Starch phosphorylase coexists with a-amylase in plant tissues (8,9,11,13,22,23) and both are responsible for initiation of starch degradation in plants. Therefore, both enzymes must initiate starch degradation in the embryo.…”

Section: Resultsmentioning

confidence: 99%

Starch Degradation Metabolism towards Sucrose Synthesis in Germinating Araucaria araucana Seeds

Cardemil

Varner²

1984

Plant Physiol.

View full text Add to dashboard Cite

show abstract

The Role of Phosphorylase in the Synthesis of Starch in Maize Leaf Bundle Sheath Cells

Cited by 1 publication

References 11 publications

Starch Degradation Metabolism towards Sucrose Synthesis in Germinating Araucaria araucana Seeds

Starch Degradation Metabolism towards Sucrose Synthesis in Germinating Araucaria araucana Seeds

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