Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/17/2006
Publication Date: 7/1/2006
Citation: Dayan, F.E. 2006. Factors modulating the levels of the allelochemical sorgoleone in sorghum bicolor. Planta. 224:339-346. Interpretive Summary: Sorgoleone is an important compound exuded from the roots of sorghum. The molecule is phytotoxic and enables sorghum plant to repress the growth of weeds in their surroundings. This phenomenon is called allelopathy. The production of sorgoleone is linked to root growth and the development of mature root hairs. However, factors modulating root formation and the production of sorgoleone are not well known. This paper reports that the production of sorgoleone is mostly constitutive. That is, independent of plant development and most environmental conditions. Temperature had the greatest effect, with optimum root growth and sorgoleone production at 30°C. Seedling development and sorgoleone levels were greatly reduced at temperatures below 25°C and above 35°C. Other environmental factors had either no effect or reduced the overall amount of sorgoleone produced by roots.
Technical Abstract: Sorgoleone is the major component of the hydrophobic root exudate of sorghum Sorghum bicolor (L.) Moench]. The production of this allelochemical is intrinsically linked to root growth and the development of mature root hairs. However, factors modulating root formation and the biosynthesis of sorgoleone are not well known. Sorgoleone production was shown to be independent of early stages of plant development. The optimum temperature for root growth and sorgoleone production was 30°C. Seedling development and sorgoleone levels were greatly reduced at temperatures below 25°C and above 35°C. The level of sorgoleone was also sensitive to light, being reduced by nearly 50% upon exposure to blue light (470 nm) and by 23% with red light (670 nm). Applying pressure over developing seedlings stimulated root formation but did not effect the biosynthesis of this lipid benzoquinone. Sorgoleone production increased by 12% in seedlings exposed to ProAct, a plant defense elicitor and a crude extract of velvetleaf (Abutilon theophrasti Medik.) root. None of the other commercial elicitors had an effect. Exposing sorghum seedlings to a velvetleaf crude extract increased sorgoleone production but the concentrations needed exceeded those likely to occur in nature. This increase was not associated with increased osmotic stress, since increases in osmotic potential reduces sorgoleone production. Sorgoleone production does not appear to be greatly modulated by either abiotic (other than temperature) or biotic environmental factors, suggesting that the pathway is constitutively expressed in young developing plants.