Plant Molecular Biology 27: 887-899, 1995. © 1995 Kluwer Academic" Publishers. Printed in Belgium. 887 Repression of the pea lipoxygenase gene loxg is associated with carpel development Manuel Rodrlguez-Concepci6n and Jos6 Pio BeltrAn* Instituto de Biologia Molecular y Celular de Plantas, Universidad PolitOcnica de Valencia-CSIC, Camino Vera s/n, 46022 Valencia, Spain (* author for correspondence) Received 13 September 1994; accepted in revised form 12 January 1995 Key words: carpel development, fruit-set, gibberellins, lipoxygenase, pea Abstract A cDNA clone (loxg) corresponding to a gene repressed during carpel development has been isolated from a cDNA library of unpollinated carpels induced to grow by treatment with gibberellic acid (GAJ. The sequences of loxg cDNA and the deduced polypeptide have a high similarity with legume type 2 lipoxygenases, especially with Phaseolus loxl (78.5 ~o similarity at the protein level) and pea and soybean lox3 (83.6 ~o and 85.4 ~o, respectively), loxg expression is constant in unstimulated carpels but it decreases in carpels induced to keep growing by fertilization or hormone treatment. A similar pattern of repres- sion was observed in lipoxygenase activity of pea and tomato carpels. In situ hybridization studies showed that loxg mRNAs are present in the endocarp and the mesocarp of pea pods; no loxg expres- sion was detectable either in the pod exocarp or in the ovules. Loxg is also expressed in other young growing tissues, especially in flower organs. Nevertheless, the natural pattern of flower and fruit devel- opment is associated with loxg repression. Introduction Pea (Pisum sativum L.) carpels are naturally in- duced to develop by pollination and fertilization. Self-pollination occurs one day before anthesis (day - 1) and by the time of full blossom (day 0), fertilization has taken place. The growth of the pod precedes that of its enclosed seeds, reaching more than half its final weight before the seeds enter their exponential phase of growth [5, 26]. Since all ovules in the pod are usually fertilized, normal development of the pod seems to be es- sential to avoid embryo failure. Fruit-set and de- velopment in the pea plant is under the control of gibberellins [18, 20, 34]. Removing the anthers two days before anthesis (day -2) leads to an unpollinated pea carpel which keeps growing until two days after anthesis (day + 2) when both pod growth and assimilate import by the carpel cease [28]. Before this, development of unpollinated carpels can be induced by application of plant hormones such as gibberellins (GAs), auxins and The nucleotide sequence data reported will appear in the EMBL, GenBank and DDBJ Nucleotide Sequence Databases under the accession number X76124 (loxg mRNA).