A class of chemicals that produce many of the colours of petals also regulates root response in White Lupins

Phosphorus is critical to plant development. To get it, they often form partnerships with fungi to exchange carbohydrates for nutrients, but not White Lupins, Lupinus albus. Unlike most plants, white lupin cannot form mycorrhizal partnerships. Instead, they cope with phosphorus deficiency by developing cluster roots that look a bit like bottlebrushes. These release a lot of exudates into the soil to pull in phosphorus from the surroundings. A new study by Chuanyong Xiong and colleagues looks at how these roots form. Their findings could help develop crops that can make better use of phosphorus in the soil, and not require more applications of fertilizer.

Auxin is a group of plant hormones responsible for many things, including root development. Flavonoids are secondary metabolites that, among many other things, inhibit auxin transport and so can direct auxin accumulation in plant tissues. Xiong and colleagues set out to examine how flavonoids and auxin interact in white lupins to create cluster roots when the plants sense a phosphorus deficiency. They did this by growing plants using hydroponics to control the concentrations and availability of phosphorus that they were exposed to.

After growing the plants, the botanists harvested them and tested the roots. They were able to test for the concentrations of flavonoids in samples using high-performance liquid chromatography (HPLC). This is a technique that separates a chemical mixture into its components with molecules travelling a different distance on a plate, or in a column, a bit like a lateral flow test for for chemicals.

Xiong and colleagues write: “In this study, we characterized the distribution profile of flavonoids in cluster roots and found that it was affected by P status. This is evidenced by quantitative results showing precise spatial localization of flavonoid accumulation with different patterns. Disturbance of flavonoid distribution negatively regulated cluster-root formation, as evidenced by the effects of exogenous flavonoids and RNAi-attenuated flavonoid accumulation. A tissue-specific accumulation pattern of flavonoids in cluster-root primordia was further characterized, which resembled the localization of the auxin responses. Together with the inhibitory effect of naringenin on the auxin response, which is related to cluster-root formation, the present results provide evidence that flavonoids and auxin interact during cluster-root formation in white lupin under P deficiency.”

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Chuanyong Xiong, Xiaoqing Li, Xin Wang, Jingxin Wang, Hans Lambers, Carroll P Vance, Jianbo Shen, Lingyun Cheng, Flavonoids are involved in phosphorus-deficiency-induced cluster-root formation in white lupin, Annals of Botany, https://doi.org/10.1093/aob/mcab131