One of the reasons I’m convinced humans are not part of this worl…uh…
So like, if humans soak up too much of the sun’s natural goodness they get cancer. Yet plants stand around in the sun all day (they take a prudent rest from this activity at night as we all know–especially the damned dandelions) and not only show no ill effects, they seem to thrive!
How do they escape chromosomal damge from UV exposure?
Enzymes Give Plants UV Protection. Basically, they do suffer UV damage to their DNA, but specialized enzymes are able to repair most of the damage very efficiently.
Also the bulk of light, on trees anyway, strike the leaves. Even at the equater leaves only have a life of about a year. There just isn’t time.
Just my $.02, and probably not worth that much.
Of course animals like camels can stand out in the sun day after day for years and never get cancer from UV exposure. Why? Because they have hairs that shield there sensitive parts form the sun. Humans of the other hand have largely lost our hairs. Plants have the same kinds of solutions and problems. Many tropical desert, savanna and overstorey plants have leaves with hairs or thick way coatings to protect the leaf from UV damage. Other plants, notably forest understorey plants, have a real problem with UV damage. Many of them can never be sun hardened. Part of that is an inability to deal with the visible light input but a large part of the reason is that these plants have no UV protection. The UV doesn’t cause cancer because it doesn’t have time. Plant leaf cells are necessarily exposed directly to light to enable them to photosynthesise so if the UV levels become to high for the plant to deal with it will kill the leaf well before there is any chance of mutations occurring.
That could only possibly be true for extremely fertile and wet areas. In less fertile and drier environments leaves typicaly last 5 years or more. And of course many plants such as the cacti are completely leaftles and most of the light strikes the photocyntehtic sems, which are not shed at all.
Have you ever seen what happens when you take a plant that’s been sitting in a dim living room all winter, and put it out in full sun? Some plants will just die, others, such as jade plants, will develop a horrible sun burned crust that lasts for months.
Plants respond to increased light by increasing the level of antioxidants in their chloroplasts. One such antioxidant, ascorbic acid, reaches concentrations of 50mM or higher. The structure of photosynthetic membranes also changes in response to high light conditions. Under low light, the chlorophyll containing thylakoid membranes will stack up in order to increase light harvesting efficiency. Called grana stacks, these structures melt away as lighting gets more intense.