ADH can be induced in seedling roots by a variety of methods including anaerobic stress and treatment with 2,4-D. We present here evidence that addition of exogenous amino acids can induce ADH1 and ADH2 under aerobic conditions, as well as enhance the induction of ADH during anaerobic stress.
Typically anaerobic induction of ADH is accomplished by totally immersing seedlings in .005 M phosphate buffer. When this buffer is made .3 mg/ml with respect to casein amino acids a 15-40% enhancement of ADH induction is observed. If just the tips of seedling roots (1 cm) are immersed in a 5 mg/ml solution of casein amino acids (or any number of single amino acid combinations) these roots show a 200-300% increase in ADH activity over control seedlings whose root tips were immersed in the buffer without amino acids.
Single amino acids also cause induction. When seedlings were grown anaerobically on blotting paper saturated with various amino acid solutions, all of the 15 amino acids tested gave induction of ADH. The ADH levels in seedlings grown on .005 M amino acids varied from 3-19% above control seedlings grown on buffer saturated paper, depending upon the particular amino acid used. Amino acid concentrations as low as .0005 M showed induction of ADH. On starch gels, bands for both ADH1 and ADH2 were observed in extracts from amino acid induced roots.
These results explain an interesting problem we've experienced in studies of the process of ADH induction. In vitro translation fails to detect any trace of ADH mRNA in aerobically grown roots, yet in vivo pulse labelling with labelled amino acids consistently detected small amounts of ADH protein synthesis which seemed to indicate presence of the mRNA.
Craig Echt and Rob Ferl
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