Superoxide dismutase in ripening fruits

Area of Science:

• Biochemistry
• Plant Physiology
• Enzymology

Background:

• Superoxide dismutase (SOD) is a crucial antioxidant enzyme involved in cellular defense against reactive oxygen species.
• Understanding SOD activity during fruit ripening and senescence is important for plant physiology and food science.

Purpose of the Study:

• To investigate quantitative changes in SOD activity during fruit ripening and senescence.
• To purify and characterize SOD from tomato fruit.

Main Methods:

• Enzyme activity assays were performed on preclimacteric and postclimacteric fruits.
• Tomato SOD was localized to soluble, mitochondrial, and plastid fractions.
• Purification involved ammonium sulfate fractionation, column chromatography, and isoelectric focusing.
• Molecular weight and protein components were analyzed using gel filtration and polyacrylamide gel electrophoresis.

Main Results:

• SOD activity showed no significant quantitative changes in apple, banana, avocado, and tomato fruits during ripening or senescence.
• Tomato SOD was primarily found in the soluble fraction.
• Purified tomato SOD had an apparent molecular weight of 31,500 Da and consisted of two components.
• The enzyme was inhibited by KCN, suggesting it is a copper/zinc-containing SOD.

Conclusions:

• Fruit ripening and senescence do not involve major quantitative shifts in SOD levels.
• Tomato SOD is a multi-compartmental enzyme, with a predominant soluble form.
• The characterization provides insights into the properties of tomato SOD, relevant for understanding fruit antioxidant systems.