Control of enzymatic browning in potato (Solanum tuberosum L.) by sense and antisense RNA from tomato polyphenol oxidase.

Polyphenol oxidase (PPO) activity of Russet Burbank potato was inhibited by sense and antisense PPO RNAs expressed from a tomato PPO cDNA under the control of the 35S promoter from the cauliflower mosaic virus. Transgenic Russet Burbank potato plants from 37 different lines were grown in the field. PPO activity and the level of enzymatic browning were measured in the tubers harvested from the field. Of the tubers from 28 transgenic lines that were sampled, tubers from 5 lines exhibited reduced browning. The level of PPO activity correlated with the reduction in enzymatic browning in these lines. These results indicate that expression of tomato PPO RNA in sense or antisense orientation inhibits PPO activity and enzymatic browning in the major commercial potato cultivar. Expression of tomato PPO RNA in sense orientation led to the greatest decrease in PPO activity and enzymatic browning, possibly due to cosuppression. These results suggest that expression of closely related heterologous genes can be used to prevent enzymatic browning in a wide variety of food crops without the application of various food additives.

[Estimation of energy utilization in patients based on catabolism of endogenous proteins]. / Odhad energetické potreby nemocných podle katabolismu endogenních bílkovin.

The authors describe their own methodical procedure used for estimation of energy requirements of patients with a defined nutrition. They ascribe importance to the quantitative assessment of the degree of catabolism of endogenous proteins the value of which they transform mathematically to calculate the catabolic factor with which they multiply the basal energy output calculated according to Harris-Benedict equations. At the same time they take into account also the thermogenic action of nutrients. In 28 patients with gastroenterological diseases they confronted their own procedure with indirect calorimetry and theoretical calculations using Jabor's catabolic factor and Nejedly's formula. Differences between values of their own and other theoretical calculations, as compared with the results of indirect calorimetry, nor the results of Jabor's and Nejedly's calculation as compared with those of the authors did not reach the level of statistical significance. With regard to the assembled results the authors consider the suggested procedure for estimation of energy requirements as feasible, in particular when indirect calorimetry is not available.

Photosynthesis and Stomatal Conductance of Potato Clones (Solanum tuberosum L.) : Comparative Differences in Diurnal Patterns, Response to Light Levels, and Assimilation through Upper and Lower Leaf Surfaces.

A few potato clones, such as A6948-4, had higher rates of photosynthesis in the field than the Russet Burbank and were able to maintain higher rates not only during mid-day but also in the early morning and late evening hours. In addition, they maintained higher carbon assimilation rates over a range of photosynthetic photon flux density from 400 to 2,000 microeinsteins per square meter per second.Stomatal conductance increased linearly as irradiance increased from 500 to 2,000 microeinsteins per square meter per second with all four potato clones that were examined. Obviously, comparative measurements of stomatal conductance or diffusive resistance with potato must be taken at a known and constant photosynthetic photon flux density.The upper (adaxial) leaf surface of some potato clones provided a surprising contribution to total carbon assimilation. Neither stomatal conductance, number of stomata per unit area, total area of the stomatal apparatus, nor chlorophyll content appear to account for differences in carbon assimilation rates among clones.