GROWTH-RELATED GENE-EXPRESSION IN NICOTIANA-TABACUM MESOPHYLL PROTOPLASTS

Eight cDNAs whose genes are more strongly expressed in suspension cell s in growth phase than in stationary phase and at a low level in matur e leaves have been isolated. The corresponding mRNAs are abundantly ac cumulated in young plant organs and in germinating seeds but are almos t undetectable in mature plant tissues and dry seeds. Six of these cDN As were characterized by comparison of nucleotide and protein sequence s to the EMBL and SWISSPROT databanks. These eight growth-related gene s are expressed in protoplasts isolated from Nicotiana tabacum mesophy ll cells shortly after preparation (4 h). Two of them are expressed in freshly isolated protoplasts (early genes), while the other six are d etected after 4 h of culture (late genes). Seven are more abundantly e xpressed in protoplasts than in growing plant organs while one growth- related gene is weakly expressed in protoplasts, as is the histone H4 gene. They seem to be induced in protoplasts by a synergistic effect o f wounding and maceration. Sustained expression of the early genes is dependent on the presence of sucrose in the culture medium.