Phytotoxic effects of Citrus aurantiifolia (Christm.) swingle essential oil on Senna occidentalis (L.) link (fabaceae) associated with alterations in carbohydrate metabolism
摘要
The present study evaluated the phytotoxic effects of Citrus aurantiifolia essential oil (EO) on Senna occidentalis (coffee weed) and its impact on carbohydrate metabolism. Seeds were treated with 0.10–1.00 mg mL−1 EO under laboratory conditions. Germination declined dose-dependently, with complete inhibition at 1.00 mg mL−1 (IC50 = 0.70 mg mL−1). Seedling growth was more sensitive than germination; at 0.75 mg mL−1, shoot and root lengths decreased by ~ 51% and ~ 71%, respectively. At this concentration, chlorophyll content and root cell viability were reduced by ~ 52% and ~ 43%, respectively. Total carbohydrates increased markedly at 0.75 mg mL−1 (~ 54% in cotyledons and ~ 81% in roots), whereas reducing sugars increased in cotyledons (~ 25%) but decreased in roots (~ 38%). Starch-mobilizing enzymes were suppressed from 0.10 mg mL−1 onward, with maximal inhibition at 0.75 mg mL−1: α-amylase decreased by ~ 45% in cotyledons and ~ 70% in roots, and β-amylase by ~ 35% and ~ 54%, respectively. Starch phosphorylase declined by ~ 55% in roots and ~ 18% in cotyledons at 0.75 mg mL−1, with no significant change in cotyledons at lower concentrations. Acid invertase decreased by ~ 27% in cotyledons and ~ 63% in roots, whereas alkaline invertase increased by ~ 17% in cotyledons but declined by ~ 64% in roots. Ultrastructural examination after 0.75 mg mL−1 EO treatment revealed distorted cotyledonary cells with chloroplast disorganization and starch accumulation. Root cells exhibited reduced cell wall thickness, enhanced vacuolization, and electron-dense cytoplasm. Together, these findings indicate that C. aurantiifolia EO suppresses S. occidentalis by disrupting carbohydrate mobilization and carbon partitioning, supporting its potential as a metabolism-targeting bioherbicide.