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  • Author or Editor: V. Esensee x
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Woody plants can be induced to cold-acclimate by exposure to sublethal low temperatures, but only after the onset of vegetative maturity. We monitored seven woody plant taxa, at monthly intervals, to determine the date of vegetative maturity, freeze-killing temperature, cell membrane electrolyte leakage, and the quantity and diversity of endogenous oligosaccharides. The freeze-killing temperature changed from -5 to -7C before vegetative maturity to -15 to -20C after vegetative maturity. There was a 10-fold increase in raffinose and about a 3-fold increase in endogenous stachyose in samples that were cold-acclimated under controlled conditions. In field samples, endogenous raffinose increased from <0.02% in August to 2% to 11% in cortical stem tissues of all cold-acclimated taxa. The tetrasaccharide stachyose increased from <0.02% to 0.25% to 2.5% for similar comparisons. None of the other sugars or polyols showed similar, consistent patterns during the onset of cold acclimation. In response to low temperature, raffinose family oligosaccharides (RFOs) have previously been shown to increase substantially in cabbage, soybean, kidney bean, and Chlorella. RFOs also possess high water-binding characteristics and tend to enhance aqueous glass transitions. Accordingly, we hypothesize that the endogenous production of these oligosaccharides may play an important role in metabolic events associated with cryoprotection of critical cellular functions during low-temperature stress.

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Aqueous fractions in dormant buds of Amelanchier alnifolia Nutt. `Smoky', may exist either as liquid, ice or glass phases depending on the temperature history and the water content of the tissue. Phase diagrams for these states were constructed from differential scanning calorimetry (DSC) freezing and warming scans. The diagrams show that glass transition temperatures shift to warmer temperatures as cold hardening increases and as the water content is lowered by controlled desiccation. Glass transitions were detected from -60 to -20° C, during slow freezing scans in the DSC, suggesting that survival of this extremely cold hardy tissue is based upon a potential to undergo glass transitions in the dormant state. Endogenous raffinose family oligosaccharides (RFO) increase during cold hardening, and decrease as hardiness diminishes with the onset of growth.

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Nonomura and Benson (1992) reported that foliar applications of dilute solutions of methanol caused growth and yield increases and reduced water use in several crops. The request from commercial growers for explicit information regarding this report prompted our experiments using the same procedures. Growth of cantaloupe, pepper, cabbage, cauliflower and onion seedlings and mature plants were evaluated in the laboratory and greenhouse in 1993 and in the field in 1993 and 1994. Treatments of 0%, 10%, 20%, 30%, or 40% methanol (v/v water) with 0.1% surfactant generally did not cause significant growth differences. Stem diameters or lengths, shoot fresh and dry weights, or root fresh and dry weights of seedlings were unaffected as a result of methanol treatment. In the field, cabbage head weight was slightly higher after methanol application only in 1993, whereas cantaloupe fruit weight and number were significantly lower in 1993, but not in 1994.

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