H. Logan et al., PLASMA-MEMBRANE TRANSPORT-SYSTEMS IN HIGHER-PLANTS - FROM BLACK-BOXESTO MOLECULAR PHYSIOLOGY, Physiologia Plantarum, 100(1), 1997, pp. 1-15
Considerable progress in identifying transport systems of the plant pl
asma membrane has been made recently. The putative systems cloned to d
ate comprise H+-ATPases, potassium, chloride and water channels, and c
arriers involved in the transport of glucose, sucrose, amino acids, pe
ptides, potassium, nitrate, ammonium, phosphate, sulfate, iron and cop
per. Most of these systems were identified first in Arabidopsis thalia
na. Successful cloning strategies have involved the following variety
of techniques: complementation of yeast mutants, screening of Arabidop
sis mutants, immunoscreening of a cDNA expression library expressed in
mammalian cells, screening of genomic and cDNA libraries with probes
(or degenerate oligonucleotides) derived from yeast and/or animal gene
s, or database screening for sequence similarity to eukaryotic counter
parts. Many related transport systems have subsequently been identifie
d either by screening Libraries directly, or by systematic cDNA sequen
cing programs. Surprisingly large gene families have been revealed. He
terologous expression systems, such as yeast, Xenopus oocytes or insec
t cells, provide tools for studying the transport activities, biochemi
cal properties and structure-function relationships of these systems.
Their expression and functions in planta are investigated using northe
rn blot analysis, in situ hybridization, and transgenic approaches. In
dividual systems encoded by the same gene family can differ in their t
ransport properties and have distinct tissue expression patterns. Such
diversity might be central to the integration of solute transport at
the whole plant level, allowing the differential expression of sets of
transport systems specifically tailored to the requirements of each t
issue.