What is the primary function of sulfur in plant growth?

The primary function of sulfur in plant growth is its vital role in protein synthesis. Sulfur is an essential nutrient that contributes to the formation of certain amino acids, which are the building blocks of proteins. Proteins are crucial for numerous plant functions, including structural stability, enzymes for biochemical reactions, and other metabolic processes. Additionally, sulfur is involved in the synthesis of certain vitamins and coenzymes.

While there's relevance to other options, they do not capture the foundational role of sulfur in the same way protein synthesis does. For instance, although sulfur can help in chlorophyll formation, its primary attribute lies in supporting protein structure and function. Thus, in the context of plant growth, its direct relationship with protein synthesis makes it essential for overall plant health and development.