Rhamnolipid Effects on Water Imbibition, Germination, and Initial Root and Shoot Growth of Soybeans

Abstract

Rhamnolipid is a nontoxic and biodegradable bioproduct that offers sustainable solutions in agricultural, pharmaceutical, cosmetic, and refinery applications. Its imminent uses in agriculture warrant thorough investigations of rhamnolipid interactions with plants. In this work, the effects of rhamnolipid on soybeans during imbibition and germination under different conditions were studied. Seed coat was determined to serve as the main barrier that regulates water imbibition, and rhamnolipid at 2 g L−1 was found to increase the imbibition rate to 16.1 (% dry bean weight)/h from 12.6% h−1 at 0 g L−1 rhamnolipid in intact soybeans for 0.5–5 h, when the soybean weight increased almost linearly due to the constant permeation rate through hydrated seed coat. Rhamnolipid, however, did not transport freely into beans; only about 50% of the rhamnolipid carried in the volume of water imbibed was absorbed by beans. Two different studies showed that absorbed rhamnolipid, from up to 1.5 g L−1 solutions, did not affect the germination percentages in wet cloths and soil pots. However, an additional study with constant (7‐day) exposure of germinating beans to more concentrated rhamnolipid solutions indicated a slight decrease of germination percentage, down to ~85% at 20 g L−1 rhamnolipid. Rhamnolipid had far more pronounced effects on root development. At high concentrations (5–20 g L−1), rhamnolipid severely stunted the root growth, causing reduced root and shoot weights and visible browning and damages of roots; however, low (0.5–1 g L−1) concentrations of rhamnolipid stimulated higher lateral root development while reducing the primary root extension, causing no change in the overall root or shoot weight. The findings indicated complex rhamnolipid interactions with soybeans and warranted further study while developing agricultural applications of rhamnolipid.

The Biosurfactants Mannosylerythritol Lipids (MELs) as Stimulant on the Germination of Lactuca sativa L.

“…In observations of the germination incidence, the same incidence level in soybean seed germination (less than 80%) after treatment with rhamnolipids was observed. However, the concentrations of rhamnolipids used for seed treatment were higher than the concentrations used in this study [39]. Another study evaluated the effect of rhamnolipid on lettuce germination and growth.…”

Promoting Seed Germination of Some Plant Species by Rhamnolipid Produced by Pseudomonas aeruginosa

“…Also, rhamnolipid managed to protect wheat and barley seeds from fungal infection while reducing or delay seed germination compared with the control group. Indeed, the pre-treatment of seeds with biosurfactants can have a favorable effect on seed germination, as it increases the rate of water imbibition [ 16 ], or serve as a nutrient or facilitates the uptake of biogenic chemicals, such as phosphorus [ 12 ], as well as biosurfactants have antifungal, antibacterial, and antiviral properties [ 5 , 12 , 17 ]. Furthermore, the use of biosurfactants emerges as a safe alternative to improving agricultural soil quality by increasing nutrient bioavailability, improving the availability of hydrophobic compounds and facilitating their absorption by microbial cells, and enhancing the degradation of certain insecticides that accumulated in the agricultural soil, thus, enhancing soil fertility [ 9 , 18 ].…”