Plants do not have to worry much about radiation. Experiments have been conducted that show that radiation is really only a problem when a plant is in the stage of a seed. Still, large amounts of radiation can destroy any material, including plant material.
High doses of radiation can cause seeds to not sprout, grow slowly, lose fertility or develop genetic mutations that can change characteristics of the plant.
The right amounts of radiation can kill microorganisms on seeds, protecting them from dangerous diseases early on.
Dormant vs. Germinated
An experiment conducted by the San Antonio Community Hospital found that plants that have already germinated before radiation exposure are less likely to develop defects than plants that are dormant.
All molecules, from water to animal and plant material, can be damaged by radiation, as it disrupts the normal flow of electrons surrounding an atom.
Plants contain chemicals that protect them from most radiation, since they are exposed to a large amount of radiation when basking in sunlight.