Xylem transport and shoot accumulation of lumichrome, a newly recognized rhizobial signal, alters root respiration, stomatal conductance, leaf transpiration and photosynthetic rates in legumes and cereals

Abstract

Summary• Root respiration, stomatal conductance, leaf transpiration and photosynthetic rates were measured in phytotron and field-grown plants following the application of 5 or 10 n M lumichrome, 10 n M ABA (abscisic acid) and 10 ml of 0.2 OD600 infective rhizobial cells.• Providing soybean and cowpea roots with their respective homologous rhizobia and/or purified lumichrome increased the concentration of this molecule in xylem sap and leaf extracts. Relative to control, rhizobial inoculation and lumichrome application significantly increased root respiration in maize, decreased it in lupin, but had no effect on the other test species.• Applying either lumichrome (10 n M ), infective rhizobial cells or ABA to roots of plants for 44 h in growth chambers altered leaf stomatal conductance and transpiration in cowpea, lupin, soybean, Bambara groundnut and maize, but not in pea or sorghum. Where stomatal conductance was increased by lumichrome application or rhizobial inoculation, it resulted in increased leaf transpiration relative to control plants. Treating roots of field plants of cowpea with this metabolite up to 63 d after planting showed decreased stomatal conductance, which affected CO 2 intake and reduction by Rubisco.• The effect of rhizobial inoculation closely mirrored that of lumichrome application to roots, indicating that rhizobial effects on these physiological activities were most likely due to lumichrome released into the rhizosphere.

Symbiotic N nutrition, bradyrhizobial biodiversity and photosynthetic functioning of six inoculated promiscuous-nodulating soybean genotypes

“…Mechanistically, this can happen through the action of rhizobial products such as abscisic acid (Phillips and Torey, 1970) or lumichrome (Phillips et al, 1999) in decreasing leaf stomatal conductance and reducing water loss via transpiration. A recent study has, in fact, shown that the application to roots of 10 nM lumichrome, 10 nM abscisic acid, or 10 mL of cultured infective cells of B. japonicum strain WB74 resulted in significantly decreased leaf stomatal conductance and reduced water loss via transpiration in soybean leaves (Matiru and Dakora, 2005). Taken together, our data suggest that bacterial presence in the rhizosphere can trigger plant response to drought, especially in arid environments where water can be a limiting factor for plant growth.…”

Legume Root Exudates: Their Role in Symbiotic Interactions

“…NGR234 (Theunis et al 2004 ); pentacyclic triterpenoid lipids, hopanoids, in bradyrhizobia and Rhizobium sp. (Kannenberg et al 1995 ); a quorum sensor-AHL and a non-AHL quorum sensor, bradyoxetin, in bradyrhizobia (Loh et al 2002 ;Mathesius et al 2003 ); and a plant growth enhancer, lumichrome, in S. meliloti Matiru and Dakora 2005 ). These compounds are required at different stages of the symbiotic development from root colonization to the formation of a functioning nodule (Cooper 2007 ).…”

Riboflavin and lumichrome in Dalmatian sage honey and other unifloral honeys determined by LC–DAD technique

“…Besides photochemical action, production of lumichrome from riboflavin by cleavage of the ribityl group can occur also by enzymatic mechanism. It is reported that several microorganisms present in the rhizosphere produce lumichrome that act as signal molecule for stimulating plant growth (Matiru & Dakora, 2005;Phillips et al, 1999). These results suggest that lumichrome is not just a waste metabolite, but can play an important role in the biological cycles.…”