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12: Starch Biosynthesis in Maize Endosperm

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12 

Starch Biosynthesis in Maize Endosperm

L. Curtis Hannah* and Susan Boehlein

Program in Plant Molecular and Cellular Biology and Horticultural Sciences,

University of Florida, Gainesville, Florida, USA

12.1 Introduction

12.2  Maize Endosperm Starch

Starch constitutes approximately 70% of the maize kernel and provides energy for the germinating seed, allowing embryo growth and development until the seedling is photosynthetically active. Starch provides approximately 50% of calories for humans and other animals and is used to manufacture many products, including biofuels. With incipient climate change and adverse environmental conditions, plant scientists are challenged to find ways to enhance starch synthesis in order to meet the needs of a growing human population.

Because of the importance of starch and the availability of seminal mutants affecting its biosynthesis, our knowledge of this process is robust. Here we describe our current understanding of this process in maize endosperm, the primary storage site for starch in the kernel. Our understanding of this process is incomplete, and questions are identified that serve as a guide for those interested in investigating starch synthesis.

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1: Kernel Evolution: From Teosinte to Maize

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1  Kernel Evolution: From Teosinte to Maize

Sherry A. Flint-Garcia*

U.S. Department of Agriculture, Agricultural Research Service, Columbia, Missouri, USA

1.1 Introduction

1.2 Domestication

Maize is the most productive and highest value commodity crop in the U.S. and around the world: over 1 billion tons were produced each year in 2013 and 2014 (FAO,

2016). Together, maize, rice, and wheat comprise over 60% of the world’s caloric intake (http://www.fao.org). The importance of maize in terms of production and caloric intake is not a recent development.

In fact, Native Americans have relied on maize and its ancestor for more than 9000 years. The “Columbian exchange” allowed maize to spread around the world, to adapt to new environments and become a major crop that feeds large portions of the human population. Maize, and the kernel in particular, has undergone dramatic changes over the past 9000 years. The biology of maize seed size and its starch, protein, oil content, and food characteristics, are described in other chapters of this book. Here

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15: Determinants of Kernel Sink Strength

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15 

Determinants of Kernel Sink Strength

Karen E. Koch* and Fangfang Ma

Department of Horticultural Science, University of Florida, Gainesville, Florida, USA

15.1 Introduction

As a large, C4-photosynthetic plant, maize provides an abundant amount of photosynthate for sinks, compared to the more

“source-limited” small-grain species (rice, wheat, barley) with C3 photosynthesis. In a general sense, “sink strength” refers to factors responsible for transport of metabolites from one plant part to another. This is typically phloem-borne sucrose from leaves, but other nutrients, plant organs, and non-phloem paths can be involved, e.g. endosperm-to-embryo transfer. Sinks acquire a spectrum of assimilates containing C, N, S, as well as other vital resources. By the time the maize kernel reaches maturity, its cumulative sink strength accounts for its composition. Consequently, yield is highly dependent on sink strength.

Some determinants of sink strength in maize kernels are common among other plant species, but differences exist. While we have learned much about how sink strength is generated, many aspects of this process are poorly understood. Our overall understanding is as follows: (i) Sucrose moves down a turgor gradient through phloem tissue toward the kernel, which has diverse mechanisms, hence

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7: Embryo Development

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7 

Embryo Development

William F. Sheridan* and Janice K. Clark

Department of Biology, University of North Dakota, North Dakota, USA

7.1 Introduction

The maize embryo develops over a 40–50-day period from a single-celled zygote into a miniature plant consisting of five or six leaf primordia and a single primary root. The first detailed description of the development of the maize embryo and caryopsis, wherein it is formed, was by Randolph (1936). This was followed by an extensive report on the structure and reproduction of corn by Kiesselbach (1949). In both publications the authors utilized ink drawings and photographic images to illustrate embryo morphogenesis throughout its development. Genetic analysis of this process began early in the 20th century with the reports of Jones (1920), Demerec (1923), Mangelsdorf (1923, 1926), and Wentz (1930). Following the iconic publications of Randolph (1936) and Kiesselbach

(1949), a third descriptive paper was published by Abbe and Stein (1954). These authors introduced the terminology currently used to describe the stages of embryo development. In this chapter we describe the process of maize embryo morphogenesis and mutations that have been shown to disrupt this process.

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2: Gametophyte Interactions Establishing Maize Kernel Development

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2 

Gametophyte Interactions Establishing

Maize Kernel Development

Erik Vollbrecht1 and Matthew M.S. Evans2,*

Department of Genetics, Development and Cell Biology, Iowa State University, USA;

2

Department of Plant Biology, Carnegie Institution for Science, Stanford, California, USA

1

2.1 Introduction

This chapter focuses on tissue- and cell-level interactions required to set in motion foundational processes that lead to and promote maize kernel development. After pollination, key cell biological, genetic, and epigenetic interactions occur, including those between the male gametophyte and the pistil, between the male and female gametophytes, and between the female gametophyte and the other seed tissues, ultimately leading to successful fertilization and initiation of kernel development (Fig. 2.1). The unicellular pollen tube germinates and grows through the transmitting tract of the silk until it reaches the ovule. It is guided by chemical cues to the ovule’s micropyle and the female gametophyte’s synergid cell. Upon interaction with the synergid, the pollen tube penetrates it and ruptures, releasing two sperm cells.

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