Effect of lithium and lanthanum on herbicide induced hormesis in hydroponically‐grown cotton and corn

Pretreatment of hydroponically‐grown cotton and corn with lithium (Li+) and lanthanum (La3+) chlorides, respectively, inhibited 2,4‐dichlorophenoxyacetic acid (2,4‐D) and metribuzin [4‐amino‐6‐tert‐butyl‐3‐methylthio‐1,2,4‐triazin‐5(4H)‐one (MTZ)]‐induced hormetic growth in both plant species. Lithium chloride proved to be a more effective inhibitor of hormetic growth. This may be due to the fact that the Li+ ion readily crosses cell membranes and interferes with calcium (Ca2+) metabolism. Lanthanum, on the other hand, has a relatively high affinity for specific sites in various types of Ca2+ channels and can displace Ca2+ from the cell wall, but cannot penetrate the cell membrane via the channel pore. Thus it acts as an inhibitor of Ca2+ channel activity and regulation. This work provides indirect evidence that a Ca2+ influx is involved in a hormetic (growth stimulation) response by cotton and corn plants when exposed to sublethal dosages of herbicide.