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PLANT PHYSIOLOGY , Vol 101, Issue 3 847-856, Copyright © 1993 by American Society of Plant Biologists

MOLECULAR BIOLOGY AND GENE REGULATION

Stress Responses in Alfalfa (Medicago sativa L.) (XIV. Changes in the Levels of Phenylpropanoid Pathway Intermediates in Relation to Regulation of L-Phenylalanine Ammonia-Lyase in Elicitor-Treated Cell-Suspension Cultures)

J. D. Orr, R. Edwards and R. A. Dixon
Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, Oklahoma 73402

We have used high-resolution gas chromatography to determine the levels of trans-cinnamic acid (CA) and trans-4-coumaric acid (4CA) in alfalfa (Medicago sativa L.) cell-suspension cultures to address the role of these phenylpropanoid pathway intermediates as potential negative regulators of phenylalanine ammonia-lyase (PAL) in vivo. Exogenous addition of CA to elicitor-treated cultures resulted in rapid increases in endogenous CA, 4CA, and CA-conjugate levels associated with inhibition of the appearance of PAL transcripts. Treatment of elicited cultures with [alpha]-aminooxy-[beta]-phenylpropionic acid (AOPP), a potent and specific inhibitor of PAL activity in vivo, resulted in reductions of CA and 4CA, with concomitant increases in PAL transcripts and extractable enzyme activity. In contrast, treatment with tetcyclacis, an inhibitor of CA 4-hydroxylase, resulted in increased CA and CA-conjugate levels, decreased 4CA levels, and decreased PAL transcript levels and enzyme activity. In tetcyclasis-treated cells, the inhibition of PAL transcript appearance preceded the increase in the levels of free CA and its conjugates. In elicited cells in which the phenylpropanoid pathway was not perturbed by metabolic inhibitors, PAL transcripts accumulated rapidly and transiently, beginning to decline by 2 h postelicitation. Changes in levels of total free or conjugated CA or 4CA did not consistently correlate with these changes in transcript levels. We propose that regulation of PAL transcript levels by endogenous phenylpropanoid pathway intermediates could involve compartmentalized pools that may exist because of the microsomal localization of cinnamic acid 4-hydroxylase.


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J. W. Blount, K. L. Korth, S. A. Masoud, S. Rasmussen, C. Lamb, and R. A. Dixon
Altering Expression of Cinnamic Acid 4-Hydroxylase in Transgenic Plants Provides Evidence for a Feedback Loop at the Entry Point into the Phenylpropanoid Pathway
Plant Physiology, January 1, 2000; 122(1): 107 - 116.
[Abstract] [Full Text] [PDF]


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Copyright © 1993 by the American Society of Plant Biologists