Hello Bana. If I recall my research from many years ago, the action is called "Pearling". I believe it's the plant's way of removing excess oxygen. This is a good thing. It means your water has a substantial amount of oxygen. When you perform a water change the incoming water mixes in oxygen. The more water you change and the more often you change it, the better for the fish because they live in a high oxygen environment. Just one of the many benefits of following an aggressive water change routine.
I'll explain a bit further, why you see this after water changes.
Photosynthesis produces oxygen as a by-product, and the plants do not need this so they get rid of it. Through the roots is usual. But after a water change you sometimes see it from the leaves. This is due to the amount of dissolved CO2 in the tap water. Provided everything is normally balanced, light and nutrients, the water change can suddenly introduce an influx of CO2. Pearling results.
It has no direct relationship to the dissolved oxygen in the water. All plants, like all fish and many species of bacteria, respirate continually 24/7, taking in oxygen and expelling CO2. But plants during photosynthesis take in CO2 (as well as the oxygen, that does not change) and as I said oxygen is a by-product of photosynthesis.