Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2004
Publication Date: 2/5/2005
Citation: Livingston, D.P., Tallury, S.P., Premakumar, R., Owens, S., Olien, C.R. 2005. Changes in the histology of cold hardened oat crowns during recovery from freezing. Crop Science. 45:1545-1558. Interpretive Summary: Winter Cereal crops such as rye, wheat, barley and oat are planted in the fall and harvested in late spring to prevent exposure to hot and dry summer conditions. Provided the plant can withstand stresses encountered during winter, a fall-planted crop will yield up to twice what the spring planted crop will yield. The part of the plant that survives winter is a part of the stem that is below ground, called the "crown". Within the crown are groups of cells that produce new leaves and stems in the spring. These groups of cells are called the apical meristem. Below the apical meristem is a group of cells called the transition zone. It is called the transition zone because it helps the plant to move water and nutrients from cells in roots to leaves and stems. Using photographs of cells within crowns we have clearly shown that the apical meristem is more cold hardy than the transition zone. In addition, we developed a way to separate the apical meristem from the transition zone and showed that the two kinds of tissue differ significantly from each other in dry weight, the amount of water that freezes at -2C and the speed at which ice forms. We are continuing research to see if these differences may explain the reason the apical meristem is more cold hardy than the transition zone. This research will help breeders better understand the processes involved in freezing during the winter and will help them select more winter hardy plants.
Technical Abstract: The survival of cereal crops during winter depends primarily on the ability of tissue in the crown to withstand various stresses encountered during freezing. Freeze-induced damage to specific regions of oat crowns was evaluated by sectioning plants at various stages of recovery after they had been grown and frozen under controlled conditions. Our results confirmed those reported for barley and wheat, that the apical meristem was the tissue in the crown most tolerant of freezing. The transition zone, which is subjacent to the apical meristem, was killed at a warmer temperature than the apical meristem. Using light microscopy and digital photography we demonstrated survival and growth of the apical meristem when the overall plant was clearly dead. Closer examination revealed that the nuclei of many cells were damaged during freezing and apparently never recovered. The crown meristem (CM) complex was separated from oat crowns and fractionated into two regions: the upper portion of the CM complex, called the apical meristem, and the lower portion called the transition zone. The dry weight of both the apical meristem and transition zone increased during cold hardening but the increase in dry weight was higher in the transition zone than in the apical meristem. The dry weight of the transition zone was significantly higher than that of the apical meristem throughout the cold-hardening period. Using isothermal calorimetry we determined that in non-hardened plants, 68% of the total water in the apical meristem froze at -2C while 64% of the total water in the transition zone froze. During cold-hardening the percentage of total water freezing at -2C became lower and lower and after three weeks was 50 and 47% in the apical meristem and the transitional zone, respectively. The initial freezing rate of the apical meristem was significantly greater than that of the transition zone and reached equilibrium after freezing at -2C about two hours before the transition zone. Research is continuing to determine reasons for the differences between the two tissue regions and to explain how they are related to the differential survival of the two regions of the crown.