Activated oxygen or oxygen free radical mediated damage to plants has been established or implicated in many plant stress situations. The extent of activated oxygen damage to potato (Solanum tuberosum L.) tubers during low temperature storage and long-term storage is not known. Quantitation of oxygen free radical mediated damage in plant tissues is difficult. However, it is comparatively easy to quantitate endogenous antioxidants, which detoxify potentially damaging forms of activated oxygen.Three tuber antioxidants, superoxide dismutase, catalase, and atocopherol were assayed from four potato cultivars stored at 3°C and 90C for 40 weeks. Tubers stored at 30C demonstrated increased superoxide dismutase activities (up to 72%) compared to tubers stored at 90C. Time dependent increases in the levels of superoxide dismutase, catalase, and a-tocopherol occurred during the course of the 40 week storage. The possible relationship between these increases in antioxidants and the rate of activated oxygen production in the tubers is discussed.

~l h e enzyme UDP-glucose pyrophosphorylase (UCPase) from potato (Solanum tuberosum L. cv Norchip) tubers was purified 177-fold to near homogeneity and to a specific activity of 1099 international unitslmg of protein. l h e molecular mass of the purified enzyme was 53 k D as determined by SDS-PACE and gel filtration. lmmunological and activity assays detected UGPase at similar levels in potato stems, stolons, and tubers. Leaves and roots contained lower levels of UCPase activity and protein. LineweaverBurk plots for substrates inorganic pyrophosphate and UDP-glucose were linear in the pyrophosphorolytic diredion, yielding K,,, values of 0.13 and 0.14 mM, respectively. However, LineweaverBurk plots for the substrates glucose-1-P and UTP were biphasic in nature when UCPase was assayed in the direction of UDP-glucose synthesis. At physiological substrate concentrations (Le. from 0.05-0.20 mM), K,,, values of 0.08 mM (glucose-1-P) and 0.12 mM (UTP) were obtained. When substrate concentrations increased above 0.20 mM, K,,, values increased to 0.68 mM (glucose-1-P) and 0.53

The relationships of potato (Solanum tuberosum L.) tuber membrane permeability and membrane lipid composition to sugar accumulation were examined. Tubers from four potato cultivars were stored for 40 weeks at 30C and 90C. Rates of tuber membrane electrolyte leakage, total fatty acid composition, free fatty acid composition, and sugar content were measured throughout the storage period. Storage of tubers at 30C caused dramatic increases in total fatty acid unsaturation, membrane permeability, and sugar content compared to tubers stored at 90C. Cultivars with higher levels of fatty acid unsaturation had lower rates of membrane electrolyte leakage and lower sugar contents. We propose that high initial levels or high induced levels of membrane lipid unsaturation mitigate increases in tuber membrane permeability during storage, thus positively influencing the processing quality of stored potato tubers.Sucrose, glucose, and fructose are the major sugars which accumulate in potato (Solanum tuberosum L.) tubers. High levels of reducing sugars (glucose and fructose) lower the suitability of tubers for processing. Reducing sugars react with free amino groups during frying leading to the formation of a brown pigment, which can make chips and french fries (crisps and chips in the United Kingdom) unacceptable for consumers. Excess sugars in stored tubers commonly arise from two situations. Storage of tubers longer than 7 months can lead to 'senescent sweetening,' and storage below approximately 7°C can lead to 'cold-induced sweetening' (1). However, low temperature storage of potato tubers can also have the beneficial results of lowered respiration rates, slowed physiological aging, inhibition of sprouting, reduced evaporative water loss, and minimized microbial pathogenesis (1).Sugars accumulate in tubers when there is an imbalance between starch degradation, starch synthesis, and respiration of carbohydrate. One potential source of metabolic imbalance ' From a disseration submitted to the graduate school of the

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A new method for measuring protein with Coo-massie Brilliant Blue G-250 has been adapted for use as a screening method in a potato tuber protein improvement breeding program. The method is simple, fast and inexpensive, and has successfully estimated the total protein content of a broad range of tuber genotypes having dissimilar amino acid profiles and tuber maturities. Correlation between the Coomassie method and a modified micro-Kjeldahl method, the standard method used in the potato breeding program, was 0.93. Free amino acids and other compounds which interfere with other methods for measuring protein do not interfere with the Coomassie Brilliant Blue procedure.