Hypoxia-Responsive Root Hydraulic Conductivity Influences Soybean Cultivar-Specific Waterlogging Tolerance

Excess soil moisture induces hypoxic conditions and causes waterlogging injury in soybean [Glycine max (L.) Merr.]. This study investigated the mechanism underlying the development of waterlogging injury. Nine Japanese soybean cultivars with varying degrees of waterlogging tolerance were grown in a hydroponic system for 14 days under hypoxic conditions. Shoot and root biomasses and root hydraulic conductivity were measured at an early vegetative stage for plants under control and hypoxic conditions. Root morphological traits and intramembrane aquaporin proteins were also analyzed. The tolerance of each cultivar to field waterlogging was based on biomass changes induced by the hypoxia treatment. Root hydraulic conductivity responses to hypoxia were associated with changes in total dry weight, leaf dry weight, and leaf area. The effects of hypoxic conditions on root hydraulic conductivity were also represented by the changes in root morphology, such as total root length, thick-root length, and number of root tips. Additionally, a 32.3 kDa aquaporin-like protein seemed to regulate root hydraulic conductivity. Our results from a hydroponic culture suggest that the soybean cultivar-specific responses to hypoxic conditions in the rhizosphere reflect fluctuations in hydraulic conductivity related to root morphological or qualitative changes.

Responses of Japanese Soybeans to Hypoxic Condition at Rhizosphere Were Different Depending upon Cultivars and Ambient Temperatures

To investigate the soybean (Glycine max Merr.) wet endurance, and the affect of the maturity and the ambient temperature to the response, the plantlet in growth stage ranged from R1 to R2 of 8 Japanese soybean cultivars which characterized as various wet endurance in a past report were cultured under hypoxic-hydroponic condition for a month. Two experiments at different periods differed significantly in temperature of air and hydroponic solution, but the oxygenic condition were similar each experiments, as aimed for. And also, control and hypoxia treatments significantly differed in dissolved oxygenic concentration in each experiments. The hypoxic condition at higher temperature induced the reduction of survival of plantlet up to 70%. At higher temperature, the survival rate of late maturity types “Yuzuru” and “Shirotsurunoko” were decreased significantly in hypoxic condition than in control. Similarly, the shoot dry matters of them were also decreased significantly in hypoxia at higher temperature. The tendency of the decreasing in hypoxia was remarkable in the pod dry matter, and the symptoms were shown also at the lower temperature. From these results, soybean’s hypoxic tolerant may be reflected with the wet endurance, the process of hypoxic damages can be divided to sudden death symptom and biomass decreasing, and the mechanisms of hypoxic tolerance might be affected strongly by ambient temperature, and absolutely controlled with the genetic background.