Enzymes of carbohydrate metabolism in the developing endosperm of maize.
TL;DR: The pattern of invertase activity in comparison with that of Sucrose-uridine diphosphate glucosyltransferase supports previous suggestions, that the latter plays a key role in the conversion of sucrose to starch.
Abstract: A number of enzymes presumably implicated in starch synthesis were assayed at various stages of endosperm development ranging from 8 days to 28 days after pollination. Activity for invertase, hexokinase, the glucose phosphate isomerases, the phosphoglucomutases, phosphorylase I, uridine diphosphate glucose pyrophosphorylase, and the starch granule-bound nucleoside diphosphate glucose-starch glucosyltransferase was present at the earliest stage of development (8 days) studied. Activity was detectable for phosphorylase III, the soluble adenosine diphosphate glucose-starch glucosyltransferase, adenosine diphosphate glucose pyrophosphorylase, and sucrose-uridine diphosphate glucosyltransferase at 12 days. For phosphorylase II and cytidine diphosphate glucose pyrophosphorylase, activity was first detectable at the 14- and 16-day stages, respectively. Rapid increases in starch content are observed prior to detectable activity for adenosine diphosphate glucose pyrophosphorylase, the soluble adenosine diphosphate glucose-starch glucosyltransferase and phosphorylases II and III. For all enzymes, except invertase, activity per endosperm rises to a peak at 22 or 28 days. Greatest activity for invertase is found at 12 days with a steady decline thereafter. The pattern of invertase activity in comparison with that of sucrose-uridine diphosphate glucosyltransferase supports previous suggestions, that the latter plays a key role in the conversion of sucrose to starch. In addition to phosphorylases I, II, and III, multiple forms of glucosephosphate isomerase and phosphoglucomutase were detected.
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TL;DR: Advances have been made in elucidating possible oxygen-sensing systems and regulatory components that are involved in these responses, which lead to the induction of a plant-specific and energy-conserving pathway of sucrose degradation, which decreases oxygen consumption and improves plant performance.
522 citations
01 Jan 1984
TL;DR: Starch granules range in size from sub-micron elongated granules of chloroplasts to the relatively huge oval granule of potato and canna as discussed by the authors, and these differences in size and shape make it possible to recognize most of the ordinary food and commercial starches.
Abstract: Publisher Summary
Starch granules range in size from sub-micron elongated granules of chloroplasts to the relatively huge oval granules of potato and canna. Semi-compound granules originate as two or more distinct granules, which then fuse together. Pseudo-compound granules, such as pea starch granules, start out as individual granules, which then develop several large cracks while remaining a single entity. These differences in size and shape make it possible to recognize most of the ordinary food and commercial starches. Starch granules contain small amounts of non-carbohydrate components—lipids, proteins, phosphate, and ash—that affect the behavior of starch in various applications. The tiny starch granules of chloroplasts are important as a temporary carbohydrate reserve and show diurnal synthesis and degradation. Native starch granules show growth rings when observed by optical microscopy, scanning electron microscopy of eroded granules, and transmission electron microscopy of thin sections, especially after chemical treatment. Starches that show prominent growth rings, such as potato starch, require high or saturating water levels for ring visibility.
517 citations
TL;DR: In this review, some of the research that has been done on endosperm is summarized, making note of comprehensive reviews and pointing out important questions that remain open to scientific inquiry.
Abstract: Endosperm has been studied from a variety of vantage points: evolution, role in seed development and germination, genetics, physiology, and biochemistry. This tissue represents a renewable, biodegradable source of materials; much effort has been directed to improve its use in feed and food making as well as its refinement to secondary products such as oils and plastics. Although there is a vast literature dealing with each of these topics, we still have a remarkably superficial understanding of most of them. There has been revitalized interest in understanding the endosperm in relation to seed-specific developmental processes. lnformation from these studies could provide a basis for developing more efficient approaches for plant improvement and use. Recent advances in molecular biology have created the possibility for detailed study of many of the genetic and molecular mechanisms involved in endosperm development. This research could conceivably lead to answers to many basic questions in developmental biology as well as to new tools that enhance practical uses of endosperm. In this review, it is not our intention to present a comprehensive overview of what is known about endosperm. Rather, we have chosen to summarize some of the research that has been done, making note of comprehensive reviews and pointing out important questions that remain open to scientific inquiry.
411 citations
01 Jan 1984
TL;DR: This chapter reviews nonmutant starch granule composition and development, and focuses on genetic mutants and how they have been useful in understanding the complexity of polysaccharide biosynthesis and development.
Abstract: Publisher Summary This chapter reviews nonmutant starch granule composition and development, and focuses on genetic mutants and how they have been useful in understanding the complexity of polysaccharide biosynthesis and development. Plant species, which are important sources of commercial starch production are focused on, especially maize, because of the many known endosperm mutants of maize, which affect polysaccharide biosynthesis. The information gained applies to other species, and these effects are illustrated in the chapter. General trends in the genetics and physiology of starch development have been illustrated with examples. Starch is a common constituent of higher plants and a source of carbohydrates. Starch in chloroplasts is transitory and accumulates during the light period and is utilized during the dark. Storage starch accumulates in reserve organs during one phase of the plant's lifecycle and is utilized at another time. Starches from reserve organs of many plants are important in commerce. Although considerable effort has been directed at characterizing the enzymes involved in starch synthesis, the role of these enzymes and other factors in determining subtle variations in starch granule structure and starch fine structure remain largely unknown. Variations in granule structure can be associated with plant species, cultivars of a species, the environment in which a cultivar is grown, and genetic mutations.
328 citations