chapter
A short overview of the very large and diverse group of plasma membrane transport systems is presented here. Emphasized are the transporters with important physiological functions in higher plants, which are localized to the plasma membrane. Members of gene families or transporters that do not localize to the PM are generally not discussed in this overview. In most cases, structural features of transporters...
chapter
The plasma membrane separates the cellular contents from the surrounding environment. Nutrients must enter through the plasma membrane in order to reach the cell interior, and toxic metabolites and several ions leave the cell by traveling across the same barrier. Biological pumps in the plasma membrane include ABC transporters, vacuolar (V-type) H+ pumps, and P-type pumps. These pumps all utilize...
chapter
Aquaporins are a class of intrinsic membrane proteins that are primarily associated with water movement across membranes. In plants, biophysical studies indicated that water fluxes could not be explained by simple diffusive movement. The discovery of aquaporins that facilitate water movement across membranes in other organisms rapidly led to the identification of this class of proteins in plants....
chapter
Efficient nitrogen acquisition and allocation are important to enable plants to successfully compete for limited and fluctuating nitrogen sources in the soil and sustain vigorous growth. Over the past two decades, several types of nitrogen transporters, such as nitrate transporters, ammonium transporters, and amino acid transporters (Frommer et al. Proc Natl Acad Sci USA 90:5944–5948, 1993; Tsay et...
chapter
Phosphorus is a major plant macronutrient, but it is also one of the less accessible mineral elements for these organisms due to the very low solubility of phosphate and phosphorus incorporation in organic matter in soils. Plants have developed multiple strategies to enhance phosphorus acquisition, and much of that activity takes place at the plasma membrane. Phosphorus remobilization from membrane...
chapter
Potassium channels are found in all living organism from bacteria to men, and even in viruses. They were among the first transport proteins to be discovered on the molecular level. Pioneering work on potassium channel structure and function has led to the most comprehensive understanding about the physiology and regulation of potassium transport on cellular and organism levels. Since their discovery...
chapter
Calcium is an essential plant nutrient, thus the influx of Ca2+ into plant cells is a critical process. In addition, the efflux of Ca2+ out of a cell is important to prevent toxicity resulting from Ca2+ excess, and to modulate levels of cytosolic Ca2+ required for signaling functions. Biochemical and genetic analysis of plants has begun to identify the complement of Ca2+-permeable channels and Ca2+...
chapter
The SulP gene family in plants consists of approximately 14 genes, depending on species, of which around 10 are thought to encode plasma membrane sulfate transporters. On the basis of sequence, five clades or Groups are distinguishable, of which three contain probable plasma membrane sulfate transporters. Isoforms with both high (Group 1) and low affinities (Group 2) for sulfate catalyse cellular...
chapter
One-third of all proteins require metal cofactors for function, yet metals can be toxic and need to be tightly controlled. Metal homeostasis is basically the equilibrium between metal uptake and metal efflux, making metal transporters key players in controlling cellular metal content. Here, we review the major families of metal transporters that participate in transport of divalent metal cations,...
chapter
During growth and storage phases, plant cells import large amounts of carbon (C) and nitrogen (N) assimilates to drive their metabolism and to facilitate synthesis of storage products. Following assimilation, organic C and N metabolites are transported via the phloem (C) or via the xylem followed by phloem (N) to sink tissues. These translocation processes involve participation of metabolite transporters...
chapter
The plasma membrane (PM) constitutes the outer boundary of the plant cell. As such, it functions in communication with the neighboring cells and with the environment. Moreover, the PM serves as the principal barrier for the small molecules that enter or exit the cell. To function in this regulatory capacity, the PM harbors a large number of transporters, channels, and carriers that provide selectivity...
chapter
Hormone transport in plants is a fundamental process governing all aspects of plant development. Identification and functional analysis of plasma membrane proteins, which regulate the import and export of plant hormones, is a requirement if we are to develop a systems biology level understanding of these processes. For several plant hormones, the characterization of the transporters has produced remarkable...
