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beta-Galactosidases in Ripening Tomatoes
1Richard B. Russell Agricultural Research Center, Agricultural Research Service, United States Department of Agriculture, Athens, Georgia 30613.
Plant Physiology
|January 1, 1983
Summary
Tomato ripening involves changes in beta-galactosidase enzyme activity. While total activity remains stable, individual enzyme levels shift, with beta-galactosidase II increasing significantly, potentially aiding tomato softening.
Area of Science:
- Biochemistry
- Plant Science
- Enzymology
Background:
- Tomatoes (Lycopersicon esculentum L.) exhibit significant beta-galactosidase activity.
- This activity is attributed to multiple enzyme isoforms.
- Understanding these enzymes is crucial for comprehending fruit ripening processes.
Purpose of the Study:
- To investigate the changes in beta-galactosidase activity during tomato ripening.
- To characterize the different forms of beta-galactosidase present in tomatoes.
- To explore the potential role of these enzymes in fruit softening.
Main Methods:
- Separation of beta-galactosidase isoforms using DEAE-Sephadex A-50 and Sephadex G-100 chromatography.
- Enzyme activity assays at varying pH.
- Characterization of enzyme kinetics, molecular weight, and stability.
- Analysis of polysaccharide hydrolysis by isolated enzymes.
Main Results:
- Three distinct beta-galactosidase forms were identified.
- Total beta-galactosidase activity remained constant during ripening, but individual isoform levels varied.
- Beta-galactosidase II levels increased over 3-fold during ripening, while I and III decreased.
- Beta-galactosidase II uniquely hydrolyzed a tomato-derived beta-1,4-linked galactose polysaccharide.
Conclusions:
- Beta-galactosidase II plays a significant role during tomato ripening due to its increased activity.
- The specific ability of beta-galactosidase II to degrade galactan suggests its involvement in tomato softening.
- Isoform-specific changes in enzyme activity are key to understanding fruit ripening.
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