Gene Expression in Suspension Culture Cells of The Halophyte Distichlis spicata during Adaptation to High Salt1

Abstract

Responses of cultured cells from Distichlis spicata (salt grass) to salt stress were studied with emphasis on changes in gene expression during the first 24 h. Total RNA was isolated from cell suspension cultures grown without salt or grown in the presence of 260 mM NaCl. Poly-(A+)RNA was used for in vitro translations, for the construction of cDNA libraries, for the synthesis of cDNA probes, and for northern blot analyses. Protein gel electrophoresis of in vitro translation products indicated that salt stress affected mRNA complexity in subtle ways. Some mRNA either increased or decreased within 24 h of stress. However, most changes in the amounts of in vitro translated polypeptides were transient. A cDNA library in lambda gtlO was searched for salt stress-related transcripts by differential screening. Eighteeen clones were found in the initial analysis, fifteen of which represented up-regulated mRNAs while three represented transcripts whose steady-state level declined during salt stress. Northern hybridizations revealed different kinetics of mRNA accumulation during stress for two up-regulated transcripts. The amount of mRNA of one clone (pDZ2.8) increased rapidly within 4 h to 8 h, then decreased below control level within 24 h. In contrast, transcripts of another clone (pDZ6.2) increased continuously over 24 h by a factor of a least 10. Our results suggest a controlled response to salt stress in this euhalophyte which includes fluctuations in relative mRNA amounts.