Root morphology and anatomy respond similarly to drought and flooding in two wheat cultivars.

BACKGROUND AND AIMS

Wheat (Triticum aestivum L.) is widely grown in regions prone to both drought and flooding conditions. Although root responses to drought and flooding have been extensively studied separately, studies comparing key anatomical root traits in wheat under both conditions side-by-side are rarely studied. We tested the hypothesis that wheat roots respond similarly to both drought and flooding, despite these being contrasting water regimes.

METHODS

Two wheat cultivars ('Jackson' and 'Frument') were grown hydroponically under control conditions, drought and flooding and the responses in plant growth, root morphology, root anatomy, development of apoplastic barriers, and their capacity to reduce radial water loss were measured.

KEY RESULTS

Xylem-to-stele ratio (XSR) decreased by 33 % under water stress compared to control conditions, whereas aerenchyma-to-cortex ratio (ACR) increased 2.1-fold during both drought and flooding compared to controls. Compared to control conditions, lateral root growth was more reduced than adventitious root growth, 86 % and 67 %, respectively, under both types of water stress. There was comparably stunted root and shoot growth under water stress and adventitious roots grew similarly slower and to one third of length compared to control conditions. Our findings did not indicate differences in soil flooding tolerances between the two cultivars.

CONCLUSIONS

We conclude that different underlying physical processes during contrasting water regimes, e.g. water limitation during drought and oxygen deficiency during flooding, result in similar root responses, e.g. increased relative aerenchyma area, lignin and suberin deposition in the endodermis and decreased lateral-to-adventitious root length. Future research should provide a more comprehensive understanding of cross-stress effects on root morphology, anatomy and physiology.