Genetic variability of transpiration response of soybean (Glycine max [L.] Merr.) plants 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-sensitive 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 ìM 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.