Additional freeze hardiness in wheat acquired by exposure to -3 degreesC is associated with extensive physiological, morphological, and molecular changes.
Cold-acclimated plants acquire an additional 3-5 degrees C increase in freezing tolerance when exposed to -3 degrees C for 12-18 h before a freezing test (LT50) is applied. The -3 degrees C treatment replicates soil freezing that can occur in the days or weeks leading to overwintering by freezing-tolerant plants. This additional freezing tolerance is called subzero acclimation (SZA) to differentiate it from cold acclimation (CA) that is acquired at above-freezing temperatures. Using wheat as a model, results have been obtained indicating that SZA is accompanied by changes in physiology, cellular structure, the transcriptome, and the proteome. Using a variety of assays, including DNA arrays, reverse transcription-polymerase chain reaction (RT-PCR), 2D gels with mass spectroscopic identification of proteins, and electron microscopy, changes were observed to occur as a consequence of SZA and the acquisition of added freezing tolerance. In contrast to CA, SZA induced the movement of intracellular water to the extracellular space. Many unknown and stress-related genes were upregulated by SZA including some with obvious roles in SZA. Many genes related to photosynthesis and plastids were downregulated. Changes resulting from SZA often appeared to be a loss of rather than an appearance of new proteins. From a cytological perspective, SZA resulted in alterations of organelle structure including the Golgi. The results indicate that the enhanced freezing tolerance of SZA is correlated with a wide diversity of changes, indicating that the additional freezing tolerance is the result of complex biological processes.
Herman
Eliot M
EM
Plant Genetics Research Unit, USDA/ARS, Donald Danforth Plant Science Center, 975 N. Warson Rd, St Louis, MO 63132, USA. eherman@danforthcenter.org
Rotter
Kelsi
K
Premakumar
Ramaswamy
R
Elwinger
G
G
Bae
Hanhong
H
Bae
Rino
R
Ehler-King
Linda
L
Chen
Sixue
S
Livingston
David P
DP
D000064:Acclimatization; D020346:Aquaporins / Q000235:genetics / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D005615:Freezing; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D006056:Golgi Apparatus / Q000648:ultrastructure; D013058:Mass Spectrometry; D020411:Oligonucleotide Array Sequence Analysis; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014908:Triticum / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure
D020346:Aquaporins; D010940:Plant Proteins; D012333:RNA, Messenger