Melcher, Peter .
A new approach to measure hydraulic resistance in plants.
A new measurement protocol to measure hydraulic resistance in plants has been developed to remove errors associated with measuring hydraulic resistance on stem segments that result from the following: 1. working with samples that are shorter than the length of open conduits; 2. from creating artificial hydraulic paths on excised stems that have multiple years of growth that may result in perfusion solution freely flowing through pathways that do not exist in the intact plant (xylem sap in an intact stem would have to cross from older growth rings to younger growth rings at nodes); and 3. from samples that have alternative non-xylem flow paths, such as aerenchyma, thus reducing the true intact values of hydraulic resistance. This new method provides a more accurate assessment of hydraulic resistance in plants especially when measurements are made on species with long conduits (greater than the length of the sample) and with those that contain multiple (>3years) of vascular growth. A key issue that had to be resolved in order to employ this new method required that samples being measured were not wounding in response to being excised for measurement. A rapid (within seconds of excision) xylem-mediated wound response was found to be very common in most species surveyed. This wound response resulted in reduced flow by up to 80% in 5 mins in some species. Results from the use of the subtraction method in eight species will be presented. Briefly, we found that in all species studied the new subtraction method resulted in higher resistance values when compared to traditional methods, with large ranges in differences between the two methods that were species dependent. For example, Acer saccharum had resistance values that were twice as high compared to traditional methods and in other cases the differences between the two methods were only about 10%. Robinia pseudoacacia resistance values were the same for both methods. It is believed that the formation of tyloses in the older xylem of R. pseudoacacia reduces artificial flow paths from older xylem when excised for measurements. These data suggest that this new method provides a more accurate and more meaningful approach to measuring hydraulic resistance in plants. This is especially important when working with woody stems that have multiple years of growth and because it provides a measurement of hydraulic resistance that takes into account the way in which plants grow.
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1 - Ithaca College, Biology, Center for Natural Sciences, Ithaca, New York, 14850, United States
Presentation Type: Oral Paper:Papers for Topics
Date: Tuesday, July 10th, 2012
Time: 9:45 AM