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H + AND Ca 2+ IN PHLOEM AND SYMPLAST: RELATION OF RELATIVE IMMOBILITY OF THE IONS TO THE CYTOPLASMIC NATURE OF THE TRANSPORT PATHS
Author(s) -
RAVEN J. A.
Publication year - 1977
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.1977.tb02229.x
Subject(s) - symplast , phloem , xylem , cytoplasm , biophysics , ion transporter , membrane transport , chemistry , biochemistry , biology , apoplast , botany , cell wall , membrane
SUMMARY The capacity of the symplast and the phloem to transport Ca 2+ and H * (OH − ) is discussed in relation to the concentrations of free and bound Ca 2+ and H * in these transport systems, and the general restrictions on the concentrations of free Ca 2+ and H * in cytoplasm. It is concluded that the low Ca 2+ and H + transport capacity of symplast and phloem are consequences of the cytoplasmic nature of these transport systems. The significance of the low transport capacity for these two ions relative to the rate at which the plant produces or consumes H + or can take up Ca 2+ and transport it in the xylem is discussed. Other transport characteristics of the phloem can also be related to the cytoplasmic nature of the transport conduit: the nature of the transported organic C and N compounds is partly dependent on the requirement that high concentrations of these solutes can be tolerated by cytoplasmic enzymes, i.e. sucrose, mannitol and amino‐acids are ‘compatible solutes'. The properties of the intracellular transport systems (symplast and phloem) are contrasted with those of extracellular transport systems such as plant xylem and animal blood.