Paclobutrazol affects the resistance of black spruce to high light and thermal stress

Detached needles from 20-week-old black spruce (Picea mariana (Mill.) B.S.P.) seedlings root-drenched with 60 mg of paclobutrazol were exposed to two temperatures (22 and 50 degrees C) and two light treatments (100 and 1900 &mgr;mol m(-2) s(-1) PAR) in a factorial combination for 4 h in vitro. Mean dry weights of individual needles from paclobutrazol-treated plants were approximately 1.9 times heavier than that of needles from untreated controls at 22 degrees C, but no differences were observed following incubation at 50 degrees C. Numbers of cells per needle remained constant in all treatments. Chlorophyll and carotenoid contents per needle were higher in seedlings treated with paclobutrazol than in untreated control seedlings, and the differences were most pronounced in the high temperature plus high light treatment. In low light at 50 degrees C, quantum efficiency of photosystem II was 45% higher in needles of paclobutrazol-treated seedlings than in needles of untreated control seedlings, but quantum efficiency of needles from treated seedlings declined when needles were exposed to high light at either temperature. Peroxidase and superoxide dismutase activities were up-regulated by paclobutrazol, whereas catalase activities were depressed and no significant differences were observed between treated and control needles at 50 degrees C in either light treatment. Paclobutrazol treatment did not moderate the depressive effects of high temperature on total soluble protein or on the activity of ribulose-1,5-bisphosphate carboxylase. In contrast, high activities of phosphoenolpyruvate carboxylase were maintained in paclobutrazol-treated needles under all stress conditions, whereas large losses in activity were recorded in untreated needles at 50 degrees C. Collectively, these observations suggest that paclobutrazol treatment may convey resistance to excessive light and high temperatures by increasing the potential of conifers to limit damage caused by oxidative stress.     

A device for studying the influence of declining water table on poplar growth and survival

Riparian poplar forests are declining downstream from many dams in the western prairie regions of North America. Drought-induced seedling and sapling mortality caused by abrupt drops in water table level following river flow regulation may be contributing to this forest decline. Here we describe a device, the rhizopod, for studying the influence of a changing water table on poplar seedling survival and growth. Seeds of a natural poplar hybrid (Populus deltoides x P. balsamifera) were planted in five rhizopods and treated to water table declines of 0, 1, 2, 4, or 8 cm day(-1). Each rhizopod consisted of 15 growth tubes connected to a central water reservoir through which the water level was regulated. Seedling survival was over 90% in rhizopods in which water table declined by 0, 1 or 2 cm day(-1), but was reduced to about 40% and less than 25% in rhizopods in which the water table level declined by 4 and 8 cm day(-1), respectively. Maximum shoot height, leaf number, and leaf area were observed in the rhizopod with a constant water table and decreased progressively with increasing rates of water table decline. Maximum root mass and length were observed in plants subjected to declines in water table level of 0 and 1 cm day(-1), respectively.     

Comparison of the Level(s) of DNA Damage Using Comet Assay in Bovine Oocytes Subjected to Selected Vitrification Methods

It was suggested that the cryodamage to oocytes' DNA has been responsible for the compromised developmental competence of cryopreserved oocytes. Vitrification of bovine oocytes affected not only cellular components, but also nuclear material. A significant rate of DNA fragmentation was found in bovine frozen or vitrified oocytes analysed by Comet assay regardless of cryopreservation method. Our method of vitrification using droplet system after gentle pre-equilibration treatment is one of the most effective cryopreservation methods employed for bovine oocytes so far, making it possible to develop 30% blastocyst stage embryos. In this study, the extent of DNA damage in bovine oocytes vitrified using three vitrification methods (droplet system, Open Pulled Straw and traditional vitrification in 0.25 ml insemination straws) was compared using Comet assay. Vitrification in droplet system and Open Pull Straws vitrification did not result in detectable cryoinjuries of DNA of bovine oocytes. On the contrary, DNA fragmentation was found in four of 26 oocytes vitrified in 0.25 ml straws (15.4%, p   ≤ 0.05 in comparison with the other vitrification methods).     

Acid–Base Changes in Canine Neonates Following Normal Birth or Dystocia

There are limited data concerning blood gas parameters in neonatal dogs. Knowledge of the normal physiology may facilitate effective therapeutic intervention and potentially reduce neonatal mortality. This study examined acid–base parameters in pups born at normal parturition (n = 27) compared with those born after obstetrical assistance or caesarean operation (n = 13) and those born following oxytocin (OXY) administration for treatment of uterine inertia (n = 11). Pups were subjected to an objective scoring method of neonatal health adapted from use in humans (the Apgar score) at birth and again at 5 and 60 min after birth. Venous blood samples were collected at 5 and 60 min after birth for evaluation of blood gas parameters. At birth, all pups had low Apgar scores and a mixed acidosis. The base excess was lowest for pups delivered after OXY administration. The Apgar score improved for all pups after 5 min of birth and there was an improvement in carbon dioxide tension, base excess and venous blood pH at 1 h, although in all pups a metabolic acidosis persisted. These data provide an important insight into neonatal physiology and the variability of blood gas parameters in pups born at normal and abnormal parturition and provide the basis for clinical decision making following dystocia.