Interaction of gibberellic acid and glyphosate on growth and phenolic metabolism in soybean seedlings

Authors: Hoagland, Robert; Boyette, Clyde

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/2024
Publication Date: 3/27/2024
Citation: Hoagland, R.E., Boyette, C.D. 2024. Interaction of gibberellic acid and glyphosate on growth and phenolic metabolism in soybean seedlings. Plants. Agronomy 2024, 14(4), 684. https://doi.org/10.3390/agronomy14040684.
DOI: https://doi.org/10.3390/agronomy14040684

Interpretive Summary: Over the last several decades there has been extensive research on herbicide interactions to understand how herbicides act with other chemicals and with bioherbicides to improve weed control efficacy. Scientists at USDA-ARS, Crop Production Systems Research Unit and Biological Control of Pests Research Unit, Stoneville, MS have previously discovered that some microbial bioherbicides can interact synergistically with the herbicide glyphosate to improve efficacy when applied to either herbicide-susceptible or herbicide-resistant weeds. Now these researchers have conducted laboratory studies on the interactions of a plant growth regulator, gibberellic acid, with glyphosate on enzyme activity [phenylalanine ammonia-lyase, PAL)] and plant constituents associated with phenolic metabolism in plants. A crop plant (soybean) was used as a model for these studies since it has been used in many previous studies on biological effects of herbicides in this laboratory. Results indicated that this growth regulator, when applied with glyphosate to seedlings, could partially reverse some of the effects caused by glyphosate on seedling growth and also increase PAL activity above that caused by glyphosate alone in light-grown plants. This information will be used in further studies on certain bioherbicides that were previously found to act synergistically with glyphosate in this laboratory.

Technical Abstract: The plant growth regulator gibberellic acid (GA) and the herbicide glyphosate were examined for possible interactions on growth and phenolic metabolism in soybean [Glycine max (L.) Merr. Cv. Hill] seedlings. GA caused increases of phenylalanine ammonia-lyase activity (PAL) (per axis basis) above that of control seedling levels 48 hr after treatment in light-grown seedlings. This effect increased to 2-fold greater than control levels by 72 and 96 hr after treatment. In dark-grown plants, GA had no effect on PAL levels at 24 hr, reduced levels at 48 and 72 hr and increased PAL at 96 hr. Glyphosate, was previously shown to increase PAL levels and also reduce hydroxyphenolic compound accumulation in both light- and dark-grown soybean seedlings [Physiol. Plant. 1979, 46, 307 and 46, 357]. Treatments of GA plus glyphosate caused additive increases in PAL activity in light-grown seedlings, but GA lowered glyphosate’s increase in PAL levels at 48-96 hr after treatment in dark-grown seedlings. GA had little effect on hydroxyphenolic compound levels in either light- or dark-grown seedlings. GA treatment alone did not significantly affect root elongation, but stimulated hypocotyl and epicotyl elongation and caused marginal reversal of glyphosate inhibition of elongation in roots, hypocotyls and epicotyls in light-grown plants. These results show some differential effects of GA and glyphosate on growth and phenolic metabolism and their interactions dependent on if soybean plants are grown in light or darkness.