Hydrogen sulfide (H 2S) impacts biological systems in multiple ways, including the arrest of aerobic respiration rendering it a highly toxic substance. However, H 2S can paradoxically drive plant germination rates when administered in micromolar concentrations. We investigated changes in δ 34S, δ 13C, δ 15N, and masses of sulfur, carbon, and nitrogen in Zea mays L. (corn) seedling stems grown at these low concentrations of H 2S associated with growth. The δ 34S and sulfur composition in seedlings increased with concentration, but only when grown in light-exposed conditions. Light-exposed seedlings also scored lower in both compared to their dark-grown counterparts. Additionally, δ 34S signatures in seedlings with the longest stems matched values of S 0 products of the H 2S oxidation process within anoxygenic photosynthesis in Chlorobium tepidum. It appears from these findings that 34S fractionation patterns in H 2S-induced plant germination is a result of the light-dependent reactions of photosynthesis. Furthermore, this δ 34S signature could suggest the presence of anoxygenic photosynthesis via sulfur oxidation in vascular plants, challenging the current understanding of plant evolution.