Winterkill is recurrently observed on annual bluegrass (Poa annua L.) golf greens in northern climates. Although annual bluegrass susceptibility to freezing temperatures has been pointed out as a major factor responsible for winter damages, little information exists on freezing tolerance and cold hardening of green‐type annual bluegrass. This study was conducted to assess freezing tolerance and carbohydrate changes occurring during cold acclimation of green‐type annual bluegrass ecotypes cold hardened under both environmentally controlled and simulated winter conditions in an unheated greenhouse. The 50% killing temperatures (LT50), levels of fructans, and mono and disaccharides were determined during cold acclimation in three annual bluegrass ecotypes originating from Western Pennsylvania (OK), Coastal Maryland (CO) and Central Québec (CR). The ecotypes differed significantly with regard to their freezing tolerance (LT50 ranking: OK < CO < CR) and maintained their relative ranking under both environmentally controlled and simulated‐natural winter conditions. Maximum freezing tolerance was observed after exposure to nonlethal subfreezing temperatures and annual bluegrass achieved high levels of freezing tolerance with LT50 of −31.2°C for OK, −24.6°C for CO, and −22.8°C for CR. High molecular weight fructans (DP>6) were the most abundant carbohydrates found in plants cold‐acclimated under low, nonfreezing temperature with levels up to 170 mg g−1 dry weight as compared with 60 to 70 mg g−1 dry weight in nonacclimated plants. Sucrose levels in crowns of annual bluegrass markedly increased at temperatures below freezing and maximum sucrose concentration coincided with maximum freezing tolerance of annual bluegrass. However, variations in fructan and sucrose levels were not related to differential freezing tolerance among the three annual bluegrass ecotypes tested.

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nual bluegrass culture on golf course greens in areas experiencing harsh winter conditions. Temperature fluc-Cold acclimation is associated with many metabolic changes that tuations and extreme freezing temperatures at crown lead to increase freezing tolerance. This study was conducted to assess level, occurring during winter and early spring, cause amino acid and protein changes occurring during cold acclimation of green-type annual bluegrass ecotypes cold hardened under both recurrent losses of annual bluegrass on golf greens (Dienvironmentally controlled and simulated-winter conditions in an unonne et al., 1999). Susceptibility of annual bluegrass to heated greenhouse. These biochemical changes were monitored in subfreezing temperatures has been pointed out as a three ecotypes of contrasting freezing tolerance originating from major factor responsible for winter damages on golf Western Pennsylvania (OK), Coastal Maryland (CO), and central greens. In a recent study, we determined that marked Qué bec (CR). Cold hardening induced major changes in amino acid differences in freezing tolerance exist among annual levels in overwintering crowns of the three ecotypes and the highest bluegrass ecotypes (Dionne et al., 2001). Maximum contributions to total amino acid accumulation after acclimation at freezing tolerance was observed after exposure to nonlesubfreezing temperatures came from proline, glutamine, and glutamic thal subfreezing temperatures. acid. Higher levels of amino acid and greater differences among eco-Cold acclimation of a plant is a highly active process types were observed after acclimation at subzero temperatures. Amino acid levels, including proline, were not related to the differential resulting from the expression of a number of physiologifreezing tolerance among the three annual bluegrass ecotypes tested. cal and metabolic adaptations to low temperature (Levitt, Specific soluble polypeptides and thermostable proteins showed cold 1980). Major metabolic changes have been documented responsiveness and in some cases, their peak accumulation coincided during the acquisition of cold tolerance including changes with maximum freezing tolerance of annual bluegrass. In plants hardin carbohydrates, proteins, nucleic acids, amino acids, ened to winter conditions in a unheated greenhouse, there was a growth regulators, phospholipids, and fatty acids (Li, distinct accumulation of polypeptides from fall until midwinter with 1984). Relationships between carbohydrate levels and a subsequent decrease in the spring.

We have constructed a new adenovirus (Ad) expression vector, pAdBM5, that allows for the production of unprecedented levels of recombinant protein in the human 293 cell line using the Ad expression system. The main feature of this vector is a combination of enhancer sequences that increases the activity of the ectopic major late promoter (MLP) in recombinant Ad. In 293 cells infected with helper-free Ad recombinants generated with the pAdBM5 transfer vector, both herpes simplex virus (HSV) ribonucleotide reductase R1 and R2 subunits represent the most abundant polypeptides, accounting for as much as 15-20% of total cellular proteins. Our data suggest that this level of expression is probably very close to the upper limit of the system. Furthermore, when compared to the widely utilized baculovirus (Bac)/Sf9 expression system, the improved Ad vector showed a better performance for the production and purification of active HSV-2 ribonucleotide reductase R1 and R2 subunits. The R2 subunit was about 5-fold more abundant in recombinant Ad-infected 293 cells than in Bac-infected Sf9 cells while the R1 subunit was produced at roughly similar levels with either system. However, the amount of active soluble R1 obtained from recombinant Ad-infected 293 cells was at least 5 times higher because most of the R1 produced in Sf9 cells was insoluble.

Winter protective covers are currently used in northern climates to mitigate winter damages on golf greens. Despite the critical importance of soil temperature on winter survival of golf greens, little information exists on the effects of commercially available protective covers on soil temperatures regimes during winter. This 3‐yr (1993–1996) field study was conducted to determine the influence of different winter protective covers on golf green soil temperature under two northern climate conditions (thick or thin snow cover). Six winter protection treatments were tested: permeable covers; impermeable covers; curled wood shavings mat, straw mulch, and 5 cm air space (each under an impermeable cover); and a control treatment without any protection. Daily climatological data and soil temperatures under protective covers were recorded at two experimental sites (Quebec City and St‐Lambert, Montreal, Canada). Throughout the winter seasons, soil temperatures under protective covers and control plots remained around 0°C under a thick and stable snow cover (average of 42 cm during experiment). Under .thin snow cover (average of 6 cm during experiment), minimum crown temperatures were markedly influenced by winter covers and reached a minimum over all years of −20.6, −19.5, −18.2, −11.1, −6.6,and −1.0°C for control, impermeable, permeable, curled wood mat, air space, and straw treatments, respectively. The insulating material covers (curled wood mat, air space, and straw) reduced soil temperature variation ranges, minimized the impact of freezing air temperature and thin snow cover, and consequently enhanced winter survival of golf greens under thin snow cover. Thus, depending on local conditions, and particularly on snow cover, the characteristics of specific protective covers can influence golf green soil temperatures and turfgrass survival during the overwintering period.