Transformed hairy roots of <i>Mesembryantemum crystallinum</i>: gene expression patterns upon salt stress

Abstract

In Mesembryanthemum crystallinum L. (common ice plant), salinity initiates a series of events that contribute to increases in osmotically active metabolites and the establishment of water conserving Crassulacean Acid Metabolism. To better understand the role of isolated root‐specific responses during salt stress, a vigorously growing root culture was needed. Thus, we took advantage of the ability of Agrobacterium rhizogenes to transform and generate growing hairy roots. Treatment of the morphologically similar hairy and nontransformed roots of whole plants with 400 m M NaCl caused an 8‐fold increase in proline levels in these tissues. A heat shock protein 70 cognate, isolated from a root specific cDNA library, was also present at simlar levels in unstressed and stressed samples of both types of roots. However, the steady state abundance of 6 other root cDNAs differed dramatically between transformed hairy and normal roots in response to salt stress. These observations suggest that several responses to salt stress are conserved between roots of whole plants and hairy roots. Additionally, a portion of transcripts reacting to salt stress may be modulated by other factors exclusive to A. rhizogenes transformed hairy root growth. The complex and hierarchical environmental stress response of this halophyte relies on several tissue‐specific interactions, and these responses are most accurately characterized in whole plant tissues.