Genetic variability of transpiration response of soybean [Glycine max (L.) Merr.] shoots to leaf hydraulic conductance inhibitor AgNo₃

Transpiration rate (TR) of a slow-wilting soybean [Glycine max (L.) Merr.] line, PI 416937, is constant with increasing vapor pressure deficit (VPD) at high VPD (> ~2 kPa). The basis of such a limitation on TR was recently linked to limited leaf hydraulic conductance. It was hypothesized that this genotype may lack an AgNO₃-sensi-tive protein-mediated water pathway in the leaf, possibly involving aquaporins (AQPs), causing it to have a low hydraulic conductance. The possibility of genetic variability for sensitivity of derooted plants exposed to 200 μM AgNO₃ was investigated among 12 soybean genotypes including progeny of PI 416937. Segregation among genotypes in their response to AgNO₃ was observed. Genotype PI 416937 and two of its progeny lines were insensitive to the AgNO₃ treatment indicating that they lacked a protein-mediated water pathway that is sensitive to this inhibitor. The remaining nine genotypes were sensitive to the AgNO₃ treatment, and the decrease in TR indicated that the AgNO₃ sensitivity accounted for 25 to 50% of the usual hydraulic pathway in the leaves. Among the AgNO₃-sensitive lines, the genotypes could be further segregated based on previous observations in the response of intact plants to increasing VPD. It is hypothesized that this additional segregation might be a result of a difference in hydraulic limitation in their roots.