DOI: 10.1007/s10535-016-0648-9 BIOLOGIA PLANTARUM 60 (4): 603-618, 2016 603 REVIEW Some key physiological and molecular processes of cold acclimation R. JOHN 1 , N.A. ANJUM 2 , S.K. SOPORY 3 , N.A. AKRAM 4 *, and M. ASHRAF 5 Department of Botany, University of Kashmir, Hazratbal, Srinagar, 190006, Kashmir, India 1 CESAM and Department of Chemistry, University of Aveiro, 3810-193, Aveiro, Portugal 2 Jawaharlal Nehru University, New Delhi, 110001, India 3 Department of Botany, GC University, Faisalabad, 38000, Pakistan 4 Department of Botany & Microbiology, King Saud University, Riyadh, 11451, Saudi Arabia 5 Abstract Agricultural production worldwide has been severely impacted by cold and freezing stresses. Plant capacity to acclimate to environmental conditions in their immediate vicinity largely control their survival, growth, and productivity. Molecular as well as biochemical mechanisms underpinning plant cold acclimation are very complex and interwoven. The cold-impacted plants try to modulate expression of variety genes controlling cell membrane lipid composition, mitogen-activated protein kinase cascade, total soluble proteins, polyamines, glycinebetaine, proline, reactive oxygen species (ROS) scavengers, cryoprotectants, and a large number of cold responsive factors. To this end, this paper dissects the array of transcriptional factors/genes down- or up-regulated, their identification in different plant species, recognition of cold tolerant/resistant transgenic plants, complexity of the mitogen-activated protein kinase cascade, as well as their cross talk under different stresses and molecular mechanisms. Furthermore, it also comprehensively elucidates physio-biochemical interferences in cold acclimation with a particular emphasis on endogenous content as well as exogenously supplied different types of polyamines, ROS, and osmoprotectants. Overall, low temperature stress tolerance or cold acclimation varies greatly among species depending on the stress intensity and duration and type of plant species. Additional key words: cryoprotectants, gene expression, glycinebetaine, MAPK, membrane lipids, polyamines, proline, ROS, transcription factors, transgenic plants. Introduction Low temperature is one the major environmental factors limiting growth of many plant species (Sanghera et al. 2011, Cruz et al. 2013, Jeon and Kim 2013, Chen et al. 2014). However, the responses of plants to low temperature stress vary considerably depending on the type of plant species as well as intensity and duration of the stress (Thomashow 1999, Fowler 2008, Chen et al. 2014). For example, differential tolerance in different cereal crops (barley, wheat, and rye) was reported by Fowler (2008). He was of the view that cereals monitor temperature with more precision compared with other crops. Hardy wheat cultivars have a 5.7 °C warmer activation temperature than tender genotypes when the vernalization gene is neutralized in near-isogenic lines, and a 12 °C difference in induction temperature of hardy rye relative to tender barley cultivars emphasizes the high cold adaptation potential of rye (Fowler 2008). This early response to low temperatures indicates that hardy rye has a longer time to prepare for the extremes of winter and is in a better position to cope with unexpected frosts during  Submitted 8 December 2015, last revision 3 February 2016, accepted 8 March 2016. Abbreviations: α-Gal - alpha-galactosidase; ABA - abscisic acid; ADC - arginine decerboxylase; APX - ascorbate peroxidase; BADH - betaine aldehyde dehydrogenase; bHLH - basic helix-loop-helix; CBF - C-repeat/DRE-binding factor; COR - cold- regulated; DRE - dehydration-responsive element; ERD - early-responsive to dehydration; ERF - ethylene-response factor; F v /F m - variable to maximum chlorophyll fluorescence ratio; GA - gibberellin; GB - glycinebetaine; GPX - glutathione peroxidase; ICE1- inducer of CBF expression1; MAPK - mitogen-activated protein kinase; MAPKK - MAPK kinase; MAPKKK - MAPK kinase kinase; MYB - myeloblastosis; MYC - myelocytomatosis; P5CS - pyrroline-5-carboxylate synthetase; PAs - polyamines; RCI - rare cold-inducible gene; ROS - reactive oxygen species; Spd - spermidine; Spm - spermine; TF - transcription factor. * Corresponding author; e-mail: nudrataauaf@yahoo.com