High sensitivity of roots to salt stress as revealed by novel tip bioassay in wheat seedlings

Salinity is one of major environmental constraints that adversely affect plant growth and pose a serious threat to crop productivity. One basic concern is related to tissue sensitivity differences to salt stress. It is intriguing that much more research efforts have been directed to shoots/leaves than roots, although roots are the first tissues directly encountering salt stress and acting as its sensor. We focused on the tissue sensitivity differences to salt stress in wheat seedlings by adopting a novel tip bioassay. The tip bioassay employed a set of 5-mL pipette tips filled with vermiculite placed over racks containing NaCl solution. Using this simple device, after determining the time course of growth inhibition under varying concentrations of NaCl, we compared the salt sensitivity in 19 diverse germplasms from five Triticum species after 7 and 14 days of exposure to 200 mmol/L NaCl. Markedly greater reduction in root length than shoot length was observed in all lines. Both the magnitude and relative rate of inhibition were much greater in roots than shoots and significant differences were observed in tissue, line, stress duration and their interactions. Our tip bioassay demonstrated that roots were more sensitive than shoots to the growth-suppressing effect of salt during the early seedling stage in wheat. These results point out the need of further research targeted on the role of and communication between roots and shoots in salt stress sensing and response.

Automated summary

This study revealed that roots are more sensitive to the growth-suppressing effect of salt compared to shoots in wheat seedlings. After exposure to varying concentrations of NaCl for 7 and 14 days, a significantly greater reduction in root length compared to shoot length was observed in all tested germplasms, indicating a higher sensitivity of roots to salt stress during early seedling stages.