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Abstract

Excised Cornus stolonifera Michx. stems cultured axenically in a liquid medium were acclimated to cold when subjected to short photoperiods and low temperatures. Foliate explants acclimated effectively and defoliated ones did not when they were cultured on White's medium which contained 0.083 M sucrose. Several other concentrations of sugars (0, 0.01, 0.1, and 0.5 M glucose and 0, 0.01, 0.05, and 0.1 M sucrose) did not enhance cold acclimation of foliated explants. The exogenously supplied sugars reduced stem growth, promoted leaf abscission, and enhanced the development of typical autumnal red coloration in leaves and stems. The highest sugar concentration (0.5 M glucose) caused death of the explants.

While a minimal level of photosynthate (sugar) is almost certainly required for the active metabolic phases of cold acclimation in hardy woody species, our studies provided no evidence that sugars bear a direct causal relationship to cold acclimation.

Abstract

This study examined the leaf anatomy and water stress of Prunus insititia L. cv. Pixy grown in aseptic culture before and after transfer to the greenhouse and grown in a layerage bed in the field. The depth of palisade cells was significantly less in aseptically cultured plantlets than in greenhouse transfererred plants, and less in greenhouse transferred than in field-grown plants. Percent mesophyll air space was greater in plantlet than in plant leaves. Upper or lower leaf epidermal cell length of plantlets of field grown plants was not significantly different. Stomatal frequency for plantlet leaves was significantly less about 150 stornata per mm²) than that of plant leaves (300 stornata per mm²). Excised plantlet leaves lost greater than 50% of total leaf water content within 30 min; excised greenhouse leaves lost 50% after 90 minutes.

Abstract

A computer model was developed to predict autumn vegetative maturity, end of summer dormancy of red-osier dogwood (Cornus sericea L. syn. Cornus stolonifera Michx.). Empirical equations were developed from growth chamber data and applied to results obtained from lath house grown plants. The model required input parameters of 2-hourly temperatures and daylengths. From the data daily phototemperature values were determined. The empirical model over-estimated the time to maturity of the lath house grown plants by only 4 days, perhaps indicating the need for a more precise measure of the critical photoperiod.