Effects of root morphology, respiration and carboxylate exudation on carbon economy in two non-mycorrhizal lupines under phosphorus deficiency.

Under phosphorus (P) deficiency, Lupinus albus develops cluster roots that allow efficient P acquisition, while L. angustifolius without cluster roots also grows well. Both species are non-mycorrhizal. We quantitatively examined the carbon budgets to investigate the different strategies of these species. Biomass allocation, respiratory rates, protein amounts and carboxylate exudation rates were examined in hydroponically-grown plants treated with low (1 µM; P1) or high (100 µM; P100) P. At P1, L. albus formed cluster roots, and L. angustifolius increased biomass allocation to the roots. The respiratory rates of the roots were faster in L. albus than in L. angustifolius. The protein amounts of the non-phosphorylating alternative oxidase and uncoupling protein were greater in the cluster roots of L. albus at P1 than in the roots at P100, but similar between the P treatments in L. angustifolius roots. At P1, L. albus exuded carboxylates at a faster rate than L. angustifolius. The carbon budgets at P1 were surprisingly similar between the two species, which is attributed to the contrasting root growth and development strategies. L. albus developed cluster roots with rapid respiratory and carboxylate exudation rates, while L. angustifolius developed a larger root system with slow respiratory and exudation rates.

Copper excess promotes propagation and induces proteomic change in root cultures of Hyoscyamus albus L.

Hyoscyamus albus L. seedlings respond positively to copper (Cu) excess. In the present study, to understand how roots cope with Cu excess, propagation and proteome composition in the presence of Cu were examined using a root culture system. When H. albus roots were cultured in a medium without Cu, root growth deteriorated. However, in the presence of Cu, root growth increased in a concentration-dependent manner, and vigorous lateral root development was observed at 200 µM Cu. Cu accumulation in the roots increased with the Cu supply. Subcellular fractionation revealed that the highest amount of Cu was present in the cell wall-containing fraction, followed by the soluble fraction. However, the highest specific incorporation of Cu, in terms of fresh weight, was in the mitochondria-rich fraction. High Cu levels enhanced respiration activity. Comparative proteomic analysis revealed that proteins involved in carbohydrate metabolism, de novo protein synthesis, cell division, and ATP synthesis increased in abundance, whereas the proteasome decreased. These results indicate that Cu promotes propagation of H. albus roots through the activation of the energy supply and anabolism. Newly propagated root tissues and newly generated proteins that bind to Cu may provide space and reservoirs for deposition of additional Cu.