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Title: Soybean leaf expansion subjected to high and low atmospheric vapor pressure deficits

item Taliercio, Earl

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2014
Publication Date: 1/24/2015
Citation: Mura, J., Taliercio, E.W., Sinclair, T. 2015. Soybean leaf expansion subjected to high and low atmospheric vapor pressure deficits. Journal of Experimental Botany. 66(7):1845–1850.

Interpretive Summary: Leaf expansion plays an import role in total leaf area and in plant productivity because leaf area and plant productivity are correlated. Deficient soil moisture is known to limit leaf expansion but it is not clear if dry air leading to vapor pressure deficit (VPD) can limit leaf expansion under well watered conditions. Two slow wilting soybeans, PI 416937 and PI 471938, and one fast wilting soybean, Hutcheson, were used to determine if leaf expansion was affected by high VPD under well watered conditions. Ten well watered replicated plantings of each genotype were split between a moist (low VPD) and dry (high VPD) plant growth chamber. Transpiration rate, leaf expansion and expression of two gene families important in leaf expansion, expansins and extensins, were measured. The transpiration rate of PI 416937 was less sensitive to high VPD than the other two genotypes but the leaf area of PI 416937 was decreased more than the other two genotypes by high VPD. Hutcheson had the greatest increase in transpiration rate in response to high VPD but leaf area was less sensitive to high VPD than the other genotypes. Overall expressions of expansins and extensins were substantially reduced in PI 416937 in response to high VPD. One expansin gene appears to be differentially regulated in the two slow-wilting PI genotypes compared to the fast-wilting Hutcheson. It appears that dry air even when soil moisture is adequate limits leaf expansion and this trait differs among slow and fast wilting soybean genotypes.

Technical Abstract: Vapor pressure deficit (VPD) is considered an important environmental factor that might affect leaf expansion and TR in plants. Two slow-wilting soybean genotypes PI 416937 and PI 471938 along with commercial cultivar Hutcheson were subjected to low (1.2 – 1.6 kPa) and high VPD (2.8 – 3 kPa) environments to study their transpiration and leaf expansion rate over five days. Among the three genotypes, PI 416937 had the lowest increase in its TR (34%) at high VPD compared to low VPD and the greatest decrease (31%) in its leaf area. In contrast, Hutcheson had the highest increase in TR (87%) under high VPD and the lowest decrease in leaf expansion rate (18%). Expansin and extension gene expressions was measured in PI 416937 to determine if changes in leaf expansion were associated with changes at the molecular level. The four studied genes were all suppressed after five days in the high VPD environment.