Mutations in plant cells can be induced by :

The correct option is Gamma rays.

Step-by-step explanation:
1. Understanding Mutations: A mutation is a sudden, permanent, and inheritable change in the nucleotide sequence of an organism's DNA. Mutations are a key source of genetic variation in plants.
2. What are Mutagens? Agents that can artificially induce mutations in cells are called mutagens. These can be physical (such as electromagnetic radiation) or chemical (such as mustard gas or ethyl methanesulfonate).
3. Physical Mutagens and Radiation: Physical mutagens are broadly classified into ionizing and non-ionizing radiation based on their energy levels:
- Ionizing Radiation: High-energy radiation, such as gamma rays and X-rays, has strong penetrating power. It can knock electrons out of atoms, creating ions. When these rays pass through plant tissues, they break chemical bonds in the sugar-phosphate backbone of DNA, leading to mutations.
- Non-ionizing Radiation: Low-energy radiation, such as infrared rays, lacks the energy to ionize atoms or alter DNA structure. Instead, infrared rays primarily produce heat.
4. Analyzing the Options:
- Gamma rays: These are highly energetic, ionizing electromagnetic rays that can easily penetrate deep into plant tissues (like seeds, pollen, or vegetative buds) to induce stable mutations. They are widely used in agricultural biotechnology for mutation breeding.
- Infrared rays: Since they are non-ionizing and low-energy, they cannot alter DNA sequences or cause mutations.
- Kinetin and Zeatin: These are cytokinins, which are plant growth hormones (phytohormones) that regulate cell division, growth, and development. They are not mutagens.

Therefore, mutations in plant cells are induced by gamma rays.