The pathway from glucose 6-phosphate (G 6-P) to myoinositol 1-phosphate (Ins 1-P) and myo-inositol (Ins) is essential for the synthesis of various metabolites. In the halophyte Mesembryanthemum crystallinum (common ice plant), two enzymes, myo-inositol O-methyltransferase (IMT1) and ononitol epimerase (OEP1), extend this pathway and lead to the accumulation of methylated inositols, D-ononitol and D-pinitol, which serve as osmoprotectants. This paper describes transcripts for the enzyme, Inps1, encoding myo-inositol 1-phosphate synthase (INPS1), from the ice plant. Two Inps-like sequences are present in the genome. The deduced amino acid sequences of the cloned transcript are 49.5% and 87-90%, respectively, identical to those of yeast and other higher plant sequences. Inps1 RNA amounts are upregulated at least fivefold and amounts of free Ins accumulate approximately 10-fold during salinity stress. Inps1 induction is by transcription, similar to the induction of Imt1. In contrast, Arabidopsis thaliana does not show upregulation of Inps1 or increased amounts of Ins when salt-stressed. The lack of Inps1 induction in Arabidopsis exemplifies differences in glycophytic and halophytic regulation of gene expression at the point of entry into a pathway that leads to osmoprotection. The stress-induced coordinate upregulation of this pathway and its extension by novel enzymes in the ice plant also highlights biochemical differences.
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 mM 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.
C. 1994. Transformed hairy roots of Mesembryanthemum crystalUnum: gene expression patterns upon salt stress In Mesembryanthemum cry.'itallinunt L. (common ice plant), salinity initiates a series of events that contribute to increases in osmoticaliy 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 Agrohaclerium rhizogenes to transform and generate growing hairy roots. Treatment of the morphologically similar hairy and nontransformed roots of whole plants with 400 mM NaCl caused an 8-fold increase in proiine 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.
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