Background: (Need help with problem in photo) Methanol is produced by fruit duri

Question

Background:

(Need help with problem in photo)

Methanol is produced by fruit during the ripening process. The major source of this methanol is likely to be from the enzyme pectin methylesterase (PME) which acts upon pectin methyl esters to de-esterify them and produce methanol and other pectic substances. One might assume that the production of methanol is correlated with PME activity, but this has not been firmly established. In this case, the investigators at the Plant Science Department at Rutgers University developed a transgenic tomato which was deficient in PME activity. By comparing the behavior of the transgenic tomato with the wild type tomato, the production of methanol in the ripening tomato fruit may be better understood.

5. In order to understand the mechanism for ethanol production, the investigators measured the activity of the alcohol dehydrogenase (ADH) enzyme in both the wild type and transgenic tomatoes at each stage of the fruit-ripening process. The results are shown in Figure 12.4. What factor or factors might influence ADH activity in the ripening tomato? 0.5 0.4 0.3 0.2 Developmental Stage Figure 12.4: Alcohol dehydrogenase activity in ripening wild-type and transgenic tomato fruit (based on Frenkel, et al., 1998).

Explanation / Answer

Answer:

Here, methanol may regulate ethanol metabolism in ripening fruits. The decline in methanol may have caused metabolic conditions for accumulation of ethanol in the PME antisense tissue. An increase in ADH activity during tomato fruit ripening suggests that the capacity of fruit tissue for alcoholic fermentation is not a limitation to the production of ethanol.

ADH-catalyzed reduction of acetaldehyde to ethanol is the only known pathway for ethanol biosynthesis and thus may be a putative target for methanol regulated ethanol production. The figure supports the hypothesis that methanol is an inhibitor in vivo since the transgenic fruit had an overall higher ADH activity than did the wild-type fruit indicating that methanol does possibly regulate ADH.

Also, there are indications that the ADH activity in the PME antisense pericarp was overall higher than in the fruit tissue of wild-type fruit suggesting that ADH activity in the mutant was not a limitation to the enzyme catalyzed conversion of acetaldehyde to ethanol.

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