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This Week’s Citation Classic________
[‘Stewart G R & Lee I A. The role of proline accumulation in halophytes.
Plania 120:279-89, 1974.
[Department of Botany, University of Manchester, Englandi
Many halophytic angiosperms were shown
phytes merged in collaborative studies
to accumulate large amounts of proline
with John Lee. We spent many pleasurwhen growing in the presence of NaCl. The
able days collecting material and carrycapacity to accumulateproline was correlat- ing out various field assays on the salt
ed with salt tolerance. Praline was suggested
marshes of North Wales and refreshing
to function as a cytoplasmic solute in intra- ourselves at the Gwydyr Arms in Betwscellular osmotic adjustment. [The Sd® indi- y-Coed. One of these trips coincided
cates that this paper has been cited in over
with the acquisition of an amino acid
165 publications since 1974.]
analyser and I decided to collect samples to examine the soluble nitrogenous components in some halophytes.
It was somewhat fortuitous that the
first sample analysed was a leaf extract
G.R. Stewart
of
Triglochin maritima. The 440 nm
Department of Botany
channel registered an enormous offBirkbeck College
scale peak at an elution time correUniversity of London
sponding to that of proline. The proline
London WC1 E 7HX
content was over ten percent of the dry
England
weight and when subsequent analyses
showed many other species to have
December 16, 1982 similar high proline contents, it was
impossible not to ask the question,
“My interest in salt marsh plants
‘Why so much proline?’ These initial
began back in the early-1960s when I
observations provided the impetus for
the work described in this paper, but
was taken on a field excursion to the
marshes described so vividly by Charles
there was much frustration in waiting
Dickens in Great Expectations. It was
and growing up plants for the exduring my PhD study that I began phys- perimental work.
iological studies on these plants to ex“Among the reasons for the frequent
amine the influence of high ion levels
citation of this paper is probably that
on plant enzymes. The basic hypoth- the paper spans the physiological and
esis was that halophytic plants have en- ecological areas and in both of these
zymes capable of functioning in an en- there is much interest in proline accuvironment of high ion concentration.
mulation and its possible role. The very
This was advanced on the basis of stud- large amounts of proline accumulated
ies with halophilic bacteria which had
by some halophytes are suggestive of
shown 1them to have ‘salt requiring’ en- an adaptive function. 2 3
zymes. There turned out to be little ev“More recent studies . have impliidence for such adaptation at the mac- cated compounds other than proline in
romolecular level in plants, and after
the osmotic relations of angiosperm
obtaining my PhD I turned to another
halophytes and other work is suggesinterest, plant nitrogen metabolism.
tive of a more generalised protective
“After some three to four years at
role for these compatible solutes in the
the University of Manchester, I found
adaptation4of plants to extreme envithat my interests in nitrogen and haloronments.”
1. Laaea H. Biochemical aspects of extreme halophilism. Adpan. Microb. Physiol. 1:97-132, 1967.
2. Wya hues B G, Stony B, Leigh B A, Abmed N B & Paused A. A hypothesis on cytoplasmic osmoregulation.
(MarrE H & Cifern 0, eds.) Regulation of cell membrane activities inplants.
Amsterdam: North-Holland. 1977. p. 121-36.
3. Stewart G B, Lasher F, Abond I C Lee J A. Nitrogen metabolism and salt tolerance in higher plant halopbytes.
(Jefiries R L & Davy A 3. ads.) &ological processes in coastal environments.
Oxford: Blackwell Scientific, 19’79. p. flI-7.
4. Nash D, Pakg L G C Whitish 3 T. Effect of proline, betaine and anme other solutes on the heat stability of
mitochondrial enzymes. Aus:. I. Plant Physiol. 9:47-57, 1982.
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