Influence of Water and Temperature Stress on the Temperature Dependence of the Reappearance of Variable Fluorescence following Illumination.
The temperature dependence of the rate and magnitude of the reappearance of photosystem II (PSII) variable fluorescence following illumination has been used to determine plant temperature optima. The present study was designed to determine the effect of a plant's environmental history on the thermal dependency of the reappearance of PSII variable fluorescence. In addition, this study further evaluated the usefulness of this fluorescence technique in identifying plant temperature optima. Laboratory and greenhouse grown potato (Solanum tuberosum L. cv "Norgold M") plants had a thermal kinetic window between 15 and 25 degrees C. The minimum apparent K(m) of NADH hydroxypyruvate reductase for NADH occurred at 20 degrees C. This temperature was also the temperature providing maximal reappearance of variable fluorescence. Soybean (Glycine max [L.] Merrill cv "Wayne") plants had a thermal kinetic window between 15 and 30 degrees C with a minimum apparent K(m) at 25 degrees C. Maximal reappearance of variable fluorescence was seen between 20 and 30 degrees C. To determine if increasing environmental temperatures increased the temperature optimum provided from the fluorescence response curves, potato and soybean leaves from irrigated and dryland field grown plants were evaluated. Although the absolute levels of PSII variable fluorescence declined with increasing thermal stress, the temperature optimum of the dryland plants did not increase with increased exposure to elevated temperatures. Because of variability in the daily period of high temperature stress in the field, studies were initiated with tobacco plants grown in controlled environment chambers. The reappearance of PSII variable fluorescence in tobacco (Nicotiana tabacum L. cv "Wisconsin 38") leaves that had experienced continuous leaf temperatures of 35 degrees C for 8 days had the same 20 degrees C optima as leaves from plants grown at room temperature. The results of this study suggest that the temperature optimum for the reappearance of variable fluorescence following illumination is not altered by the plant's previous exposure to variable environmental temperatures. These findings support the usefulness of this procedure for the rapid identification of a plant's temperature optimum.
Determination of temperature and time thresholds for BIOTIC irrigation of peanut on the Southern High Plains of Texas
The timely application of irrigation water to a crop is essential for optimizing yield and production efficiency. The “Biologically Identified Optimal Temperature Interactive Console (BIOTIC)” is an irrigation protocol that provides irrigation scheduling based upon measurements of canopy temperatures and the temperature optimum of the crop species of interest. One of the goals of this paper is to document the gradual development of the method and its implementation. Two threshold values are required to implement BIOTIC irrigation of a crop in a given region, a species-specific temperature threshold and a species/environment-specific time threshold. The temperature threshold, an indication of the thermal optimum for the plant, is derived from the thermal dependence of its metabolism. The time threshold, which represents the average amount of time each day that the canopy temperature of the well-watered crop will exceed the temperature threshold, is calculated from weather data. Interest in the use of BIOTIC for irrigation scheduling for peanut ( Arachis hypogaea L.) resulted in this study in which the temperature and time thresholds for peanut were determined on the Texas Southern High Plains. A temperature threshold value of 27°C was determined from the thermal dependence of the reappearance of photosystem II variable fluorescence (PSII Fv) following illumination. A time threshold of 405 min was calculated from an analysis of weather data collected over the course of the 1999 growing season. The determination of these threshold values for peanut provides the basis for the application of the BIOTIC protocol to irrigation scheduling of peanut on the Southern High Plains of Texas.
Study of External Parasites Infesting Carcharhinus Melanopterus Fish From The Red Sea In Jeddah, Saudi Arabia
Parasitic diseases are harmful and limiting factors in breeding and rearing ornamental fish industry, such as the Monogenea ( Dactylogyrus sp and Erpocotyletiburonis ) and copepod ( Pandarus sinuatus  and Anchistrotostangi ). The copepod and the monogenean are gill parasites found on the shark; CarcharhinusMelanopterus . The primary purpose of this study was to determine the parasitic infections of sharks in red sea in Jeddah. For this purpose, 19 female C. Melanopterus and 14 male C. Melanopterus were first examined for ectoparasites using wet mount under a light microscope. All male sharks had Monogenea and/or copepod in their gill and only 3 females haven’t infections. Then, we aimed to find a combination of copepod and monogenea infection in C. Melanopterus gills. 50% of male and 42% of female were infected by copepod and monogenea. Our findings revealed that the protozoan infections are very common among sharks. Although, no gross pathology was observed among infected shark, but it is likely that in case of any changes in the environment, then parasitic infections could be harmful.