Project Number: 3655-21000-049-01
Project Type: Specific Cooperative Agreement

Start Date: Aug 01, 2007
End Date: Jun 17, 2008

Objective:
The goal of this research is to determine if sugar-end is linked to changes in leaf or tuber water potential and is a response by the plant to maintain turgidity in tubers. We have two specific objectives: 1. Determine the influence of soil temperature and soil matric potential on the water potential of potato shoots and tubers at key stages of development; 2. Quantify tuber sucrose and glucose concentrations in relation to leaf and tuber water potential, and quantify invertase activity in the stem and bud end of tubers.

Approach:
Research trials will be conducted at the University of Wisconsin-Madison under tightly controlled environmental conditions in the Biotron using procedures that we have already established. Potato plants will be grown from 2 oz seed pieces in 200 different 5 gallon pots containing soil. Plants will be grown at 20' C and will be irrigated daily with half-strength Hogaland¿s solution. Potato plants will be exposed to heat stress (30'C), water stress (-25 kPa or -40 kPa soil matic potential) or a combination of heat and water stress for 10 to 14 days at early bulking (< 2.5 cm diameter), mid bulking (2.5 to 5 cm diameter), and late bulking (>5 cm diameter) stages of growth. Individual plants will receive only one stress treatment with 6 plants receiving each stress treatment at each time. Upon removal from stress conditions 3 plants will be destructively analyzed and 3 plants placed back under optimal conditions until reaching maturity. The water potential of leaves and tubers will be assessed with a pressure bomb as soon as the plants are excavated. The osmotic potential of the same tubers will be determined using an osmometer and K+ content as a measure of tuber nutrient status will be assayed with a potassium selective electrode. Total tuber weight will be measured, and representative samples of tuber tissue will be analyzed for invertase activity and sucrose and glucose concentrations. Tubers will be harvested from the remaining plants, 3 from each time and treatment, at crop maturity (natural senescence of vines). Tubers will be harvested for sugar analysis at harvest (6 from each plant) and out of 2 months cold storage (6 from each plant). Sample cores will be taken from the bud and stem and, and sugar contents assayed by HPLC. For all samples, acid invertase activity will be measured utilizing 10 g of frozen tuber tissue that will be homogenized and desalted to create a crude extract using the method of Matsuura-Endo et al (2004). Sucrose and glucose concentrations in bulked samples will be analyzed using industry standard procedures with an YSI 2700 Biochemistry Analyzer (Sowokinos, et al. 2000). Sugar concentrations in paired bud and stem end samples will be assayed by HPLC using methods that are routine in the Bethke lab.