Root system of Medicago sativa and Medicago truncatula: drought effects on carbon metabolism

Aims Here, we assess the differential impact of drought on root carbon metabolism in the widely cultivated alfalfa (Medicago sativa, Ms) and the model legume Medicago truncatula (Mt). Understanding how carbon allocation is regulated under drought stress conditions is a central issue to improving alfalfa productivity under future climate change scenarios. Methods Alfalfa and Medicago truncatula were compared under water deficit conditions. Root carbon metabolism of the taproot and fibrous roots was analysed. M. truncatula drought tolerance variability was compared to that of alfalfa using six accessions of the Medicago Hapmap project. The prominent taproot is much less developed in M. truncatula than in alfalfa with the former exhibiting an extensive fibrous root system. Results In both examined Medicago species the taproot contained the major pools of soluble protein, sucrose and pinitol, whereas the major pools of hexoses and carbon metabolism enzymes appeared to be in the fibrous roots. Under water-deficit conditions, the response of M. sativa strongly differed from that of M. truncatula at the root level. Conclusions Water deficit conditions differentially modulate the root carbon metabolism of M. sativa and M. truncatula. Mt maintained a more active carbon metabolism in the fibRs, as sucrose, myo-inositol and pinitol accumulated to cope with the water deficit (WD). Conversely, the root system of Ms did not accumulate cyclitols and carbon metabolism was more severely affected under water deficit conditions. This differentially exerted control may determine the drought response of these two close relatives.