Plant Molecular Biology 39: 1257–1265, 1999.
© 1999 Kluwer Academic Publishers. Printed in the Netherlands.
Enzymatic activity and gene expression under water stress of
phospholipase D in two cultivars of Vigna unguiculata L.Walp. differing in
Hayat El Maarouf
, Yasmine Zuily-Fodil
, Monique Gareil
Laboratoire de Physiologie Cellulaire et Mol´eculaire du Stress chez les Plantes, Equipe BPAV, Universit´eParis
7 Denis Diderot, case 7019, 2 Place Jussieu, 75251 Paris cedex 05, France (
author for correspondence);
7632 CNRS (Physiologie Cellulaire et Mol´eculaire des Plantes)
Received 2 June 1998; accepted in revised form 14 December 1998
Key words: cowpea (Vigna unguiculata L.), drought, gene expression, lipid degradation, phospholipase D
Phospholipase D, a major lipid-degrading enzyme in plants, was studied in two cultivars of Vigna unguiculata
L.Walp, differing in their tolerance to drought (cv. EPACE-1, drought-tolerant, and cv. 1183, drought-susceptible).
Enzymatic activities, measured with
C-PC as substrate, increased when plants were submitted to water stress, the
increase being much higher in the drought-sensitive cultivar. A 2911 bp cDNA encoding a putative phospholipase
D (VuPLD1) was isolated from a cDNA library prepared from V. unguiculata leaves. The deduced amino acid
sequence (809 residues) shows 85.5% identity and 91.3% similarity to that of PLD from Ricinus communis.The
expression of the VuPLD1 gene in the leaves is differently modulated by water deﬁcit, depending on the intensity
of stress and the tolerance or sensitivity of the plants. In the drought-susceptible V. unguiculata cv. 1183, it readily
increased under water stress, reaching maximum values at mild water deﬁcit (−1.5 MPa). In the drought-tolerant
cv. EPACE-1, VuPLD1 mRNA remained low throughout the whole drought treatment. Dehydration of leaves
led to a dramatic increase in transcript level in both cultivars. Changes in protein amounts semi-quantiﬁed by
immunoblotting correlated well with variations in transcript steady-state level. Taken together, these results showed
that phospholipase D in cowpea plants is essentially regulated at the transcriptional level, and that gene expression
is strongly stimulated even by moderate water deﬁcit in the drought-sensitive plant. On the contrary, the drought-
tolerant plant presents a remarkable stability of PLD gene expression in conditions of water stress.
Abbreviations: PA, phosphatidic acid; PC, phosphatidylcholine; PLD, phospholipase D; PM, phosphatidyl-
, phosphatidylinositol 4,5-bisphosphate.
Among the various strategies developed by higher
plants to cope with drought, tolerance to dehydration
at the cell level is one of the most important , es-
pecially in conditions of prolonged water stress. Cell
membranes are main targets of damage induced by
The nucleotide sequence data reported will appear in the
EMBL and GenBank Nucleotide Sequence Databases under the
accession number U92656 (VuPLD1).
environmental stresses [15, 21], and it has been shown
that plants tolerant to drought at the cell level also pos-
sess more resistant membranes [47, 48]. Lipids are im-
portant membrane components and under water stress,
signiﬁcant modiﬁcations of the lipid membranes occur
[19, 23, 26, 29, 34].
In cowpea leaves, we have shown that severe
drought led to a massive breakdown of membrane
lipids, the degradation being more severe in the sen-
sitive plants than in the tolerant ones . Phos-