Plants Cold hardening

plant covered in snow after ice storm in 2013, ontario, canada

plants in temperate , polar regions adapt winter , sub 0 temperatures relocating nutrients leaves , shoots storage organs. freezing temperatures induce dehydrative stress on plants, water absorption in root , water transport in plant decreases. water in , between cells in plant freezes , expands, causing tissue damage. cold hardening process in plant undergoes physiological changes avoid, or mitigate cellular injuries caused sub-zero temperatures. non-acclimatized individuals can survive −5 °c, while acclimatized individual in same species can survive −30°. plants originated in tropics, tomato or maize, don t go through cold hardening , unable survive freezing temperatures. plant starts adaptation exposure cold yet still not freezing temperatures. process can divided 3 steps. first plant perceives low temperature, converts signal activate or repress expression of appropriate genes. finally, uses these genes combat stress, caused sub-zero temperatures, affecting living cells. many of genes , responses low temperature stress shared other abiotic stresses, drought or salinity.

schematic of typical plant cell

when temperature drops, membrane fluidity, rna , dna stability, , enzyme activity change. these, in turn, affect transcription, translation, intermediate metabolism, , photosynthesis, leading energy imbalance. energy imbalance thought 1 of ways plant detects low temperature. experiments on arabidopsis show plant detects change in temperature, rather absolute temperature. rate of temperature drop directly connected magnitude of calcium influx, space between cells, cell. calcium channels in cell membrane detect temperature drop, , promotes expression of low temperature responsible genes in alfalfa , arabidopsis. response change in calcium elevation depends on cell type , stress history. shoot tissue respond more root cells, , cell adapted cold stress respond more 1 has not been through cold hardening before. light doesn t control onset of cold hardening directly, shortening of daylight associated fall, , starts production of reactive oxygen species , excitation of photosystem 2, influences low-temp signal transduction mechanisms. plants compromised perception of day length have compromised cold acclimation.

cold increases cell membrane permeability , makes cell shrink, water drawn out when ice formed in extracellular matrix between cells. retain surface area of cell membrane able regain former volume when temperature rises again, plant forms more , stronger hechtian strands. these tubelike structures connect protoplast cell wall. when intracellular water freezes, cell expand, , without cold hardening cell rupture. protect cell membrane expansion induced damage, plant cell changes proportions of lipids in cell membrane, , increases amount of total soluble protein , other cryoprotecting molecules, sugar , proline.

chilling injury occurs @ 0–10 degrees celsius, result of membrane damage, metabolic changes, , toxic buildup. symptoms include wilting, water soaking, necrosis, chlorosis, ion leakage, , decreased growth. freezing injury may occur @ temperatures below 0 degrees celsius. symptoms of extracellular freezing include structural damage, dehydration, , necrosis. if intracellular freezing occurs, lead death. freezing injury result of lost permeability, plasmolysis, , post-thaw cell bursting.

when spring comes, or during mild spell in winter, plants de-harden, , if temperature warm long enough – growth resumes.