Water relations responses of the pea (Pisum sativum L.) mutant SGECd^t to mercury

¹ All-Russia Research Institute for Agricultural Microbiology, Laboratory of Rhizosphere Microflora, 196608 Saint Petersburg, Russia
² Lancaster University, Lancaster Environment Centre, LA1 4YQ Lancaster, United Kingdom

^* Corresponding author: belimov@rambler.ru

Abstract

Mercury (Hg) is one of the most toxic heavy metals and has multiple impacts on plant growth and physiology, including disturbances of plant water status. The impact of Hg on water relations was assessed by exposing the unique Hg-sensitive pea (Pisum sativum L.) mutant SGECd^t and its wild-type (WT) line SGE in hydroponic culture. When the plants were grown in the presence of 1 or 2 µM HgCl₂ for 11 days, the SGECd^t mutant had lower whole plant transpiration rate and increased leaf temperature, indicating stomatal closure. Shoot removal of Hg-untreated plants resulted in greater root-pressure induced xylem sap flow in the SGECd^t mutant than WT plants. Treating these plants with 50 µM HgCl₂ (an inhibitor of aquaporins) for 1 h decreased xylem sap flow of both genotypes by about 5 times and eliminated differences between WT and mutant. Adding 1 mM dithiothreitol (the reducing thiol reagent used for opening aquaporins) to the nutrient solution of Hg-treated plants partially restored xylem sap flow in SGECd^t roots only, suggesting genotypic differences in aquaporin function. Thus root water uptake is important in mediating sensitivity of SGECd^t to toxic Hg.