Differential Effects of O-Benzyl-Serine on Sulfur Metabolism, Photosynthesis, and Growth in Two Species of Weeds

Enzymes of the sulfur assimilation pathway represent promising candidates for selective herbicide development. This study investigated the effects of O-benzyl-serine (OBS), a newly identified inhibitor of O-acetylserine(thiol)-lyase (OAS-TL), on two C3 weed species, Ipomoea grandifolia and Euphorbia heterophylla. Plants were cultivated hydroponically for 12 days in the presence of OBS (0–500 µM). OBS inhibited root growth in both species in a dose-dependent manner, with I. grandifolia being more sensitive. OAS-TL activity decreased in the roots of I. grandifolia but increased in the leaves of E. heterophylla. Nutrient profiling revealed significant alterations in sulfur, magnesium, and calcium contents, associated with chlorosis and reduced root and leaf development. While photosynthetic performance appeared unaffected at the lowest OBS concentration tested (62.5 µM), higher doses drastically reduced leaf expansion, preventing further measurements. Given this marked decline in foliar development, it is reasonable to infer that the overall photosynthetic capacity of the plants was also negatively affected under severe OBS exposure. OBS also disrupted apical dominance, promoting lateral shoot formation. These findings demonstrate that OBS differentially affects sulfur metabolism and growth in a species- and organ-specific manner, supporting its potential as a prototype molecule for herbicides targeting novel biochemical pathways.