Nitrate and magnesium ions in plant nutrition

Plants absorb mineral ions dissolved in soil water through their roots. Nitrate and magnesium ions supply different materials that plants need to grow and produce carbohydrates.

Nitrate ions and proteins

Plants use nitrate ions ($$\ce{NO3-}$$) to make amino acids. Amino acids are joined together to build proteins, which are needed to build and maintain plant cells. A plant therefore needs nitrate ions to make the proteins required for growth.

Magnesium ions and chlorophyll

Plants use magnesium ions ($$\ce{Mg^2+}$$) to make chlorophyll. Chlorophyll is the pigment that absorbs light energy, allowing the plant to use that energy in photosynthesis to produce carbohydrates.

Nitrate and magnesium ions have different roles: nitrate is needed to make amino acids and proteins, while magnesium is needed to make chlorophyll. Neither ion can replace the other.

Tobacco mosaic virus

Tobacco mosaic virus (TMV) is a widespread plant pathogen: a virus that causes disease in plants. It infects many plant species, including tomato plants.

Infected leaves develop a distinctive mosaic pattern of discolouration. The affected leaves carry out less photosynthesis, so the plant makes less glucose for growth. As a result, the plant grows less.

Rose black spot

Rose black spot is a fungal disease that infects roses. Purple or black spots develop on infected leaves. The leaves often turn yellow and fall off early.

Damaged leaves and the loss of leaves reduce photosynthesis, the process by which the plant makes glucose using light. With less glucose available for growth, the rose grows less.

The fungus can spread through the environment in water or wind. Rose black spot can be treated with fungicides and by removing and destroying affected leaves.