DIFFERENTIAL EXPRESSION OF A CHLOROPHYLL A B BINDING-PROTEIN GENE ANDA PROLINE-RICH PROTEIN GENE IN JUVENILE AND MATURE PHASE ENGLISH IVY (HEDERA-HELIX)/

Two cDNA clones representing mRNAs which are differentially expressed during in vitro culture of juvenile and mature leaf petioles of Englis h ivy (Hedera-helix L.) were isolated by differential screening. The m RNA represented by clone HW101 is expressed at a higher level in untre ated juvenile than in untreated mature in-vitro-cultured petioles. Tre atment of petioles with cr-naphthaleneacetic acid (NAA) at the initiat ion of culture decreases HW101 mRNA levels in juvenile but not mature, petioles. In intact plants, HW101 mRNA is expressed at a higher level in juvenile laminae, petioles and stems than in identical tissues of mature plants. DNA sequence analysis indicates that HW101 cDNA is sign ificantly similar to a light harvesting chlorophyll a/b, binding prote in gene (Lhcb) of pea. The gene represented by the second clone, HW103 , is expressed al a higher level in mature than in juvenile in-vitro-c ultured petioles. Treatment of petioles with NAA at the initiation of culture decreases HW103 mRNA levels in chronologically young mature bu t not older mature and juvenile petioles. However, expression of the H W103 gene is not delectable in petioles, or in any other vegetative or gan tested, immediately after excision. It is, however, expressed in d eveloping seeds. In otherwise intact plants, the HW103 gene is express ed in wounded petioles of mature plants 5 days after wounding but not in wounded petioles of juvenile plants. It is also expressed at a high er level in wounded stems of mature plants than in those of juvenile p lants. However, it is not expressed in wounded lamina of either juveni le or mature plants. DNA sequence analysis indicates that HW103 cDNA i s similar to a cell wall proline rich protein (PRP) gene of soybean. T his is the first report of differential expression of a PRP gene in ti ssues from juvenile and mature plants. Southern blot analysis of nucle ar DNA of H. helix shows that both HW101 and HW103 are members of smal l gene families.