Submitted to: Dynamic Biochemistry, Process Biotechnology and Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 7, 2009
Publication Date: December 15, 2009
Citation: Livingston, D.P., Tuong, T.D., Owen, S. 2009. Carbohydrate changes in winter oat crowns during recovery from freezing. Dynamic Biochemistry, Process Biotechnology and Molecular Biology. 3:16-22 Interpretive Summary: How plants use carbohydrates to improve freezing resistance is controversial. We are reporting here results of the first analysis of carbohydrate changes that occur during recovery from freezing, prior to the formation of new leaves when the plant begins to photosynthesize again. Using light microscopy, we previously identified 4 zones within the lower stems (crown) of winter cereals that differ in freeze-induced damage. Here we present results from oat, the least hardy winter cereal crop. We dissected these 4 zones of the crown and quantified fructan and the sugars, fructose, glucose and sucrose in each. Fructan was significantly more concentrated in the uppermost part of the crown called the apical meristem than it was in any of the 4 zones and during the first 7 days of recovery this fraction decreased to a greater extent than any other carbohydrate. These results suggest that fructan mobilization during recovery from freezing is an important part of overall winter hardiness and may explain discrepancies in past studies between fructan content and freezing tolerance of winter cereal cultivars and species. In addition, the biggest changes in CHO reallocation occurred in the first 3 days after freezing. This suggests that to better understand the metabolism of plants recovering from freezing a more detailed analysis should concentrate on tissue immediately after freezing.
Technical Abstract: Fructan has been recognized as an important cryoprotectant in plants for nearly half a century but its exact mode of action has been controversial. Much of the difficulty identifying mode of action is related to the lack of localization of fructan within tissues that are important for survival of the whole plant. In addition, very few if any studies have been conducted on changes in fructan concentration during recovery from freezing, prior to the formation of new leaves. During recovery after freezing, fructan could ostensibly act as an energy source as well as a source for precursor molecules involved in cell wall synthesis/repair. Using information from previous histological studies we dissected 4 zones of the crown and quantified fructan and the sugars, fructose, glucose and sucrose. Plants which had been frozen and were in recovery contained about ½ the amount of total carbohydrate of those which had not been frozen, suggesting considerable utilization by the plant in the recovery process. The zone in which freezing had the biggest effect was surprisingly the lowermost zone, subjacent to where the roots attach to the crown, called the lower crown. The percentage of DP>5 fructan in the lower crown was significantly higher in recovering plants than it was in unfrozen controls, while the percentage of DP3 fructan as well as sucrose was significantly lower in plants recovering from freezing. Percentages of glucose and fructose were in many cases double what they were in unfrozen controls. These results suggest that carbohydrate re-allocation during recovery from freezing is an important part of overall winter hardiness. In addition, the biggest changes in CHO re-allocation occur in the first 3 days after freezing. This suggests that to better understand the metabolism of plants recovering from freezing, more detailed, analyses should concentrate on the period just after freezing, prior to when new growth emerges.