|MadSci Network: Botany|
That is an interesting story but totally untrue. Watermelon fruit contains oxygen before it is cut open because all plant cells conduct cellular respiration, which requires oxygen. The red pigment in watermelon is lycopene, the same carotenoid found in red tomatoes, guava and red grapefruit. Lycopene is an antioxidant, so is very popular as a diet supplement. Possibly this antioxidant function led to the misconception. Plants with symbiotic nitrogen fixation, such as beans, peas and soybeans, contain leghemoglobin in root nodules. The leghemoglobin keeps the oxygen level in the nodule very low. The enzyme nitrogenase requires a low oxygen environment for proper functioning. Leghemoglobin also provides oxygen to the nitrogen-fixing bacteria. The nodules are red or pink when you cut them open because of the leghemoglobin. References Watermelons and Lycopene Leghemoglobin Re: What do Fabaceae do with the oxygen they bind in symbiotic nitrogen fixation?? Photo of pink root nodule
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