frost resistance

Upload: mudit-misra

Post on 30-May-2018

222 views

Category:

Documents


0 download

TRANSCRIPT

  • 8/9/2019 Frost resistance

    1/20

  • 8/9/2019 Frost resistance

    2/20

    ` Low temperatures are among the most importantenvironmental factors influencing plant distribution,development and survival.

    ` Many plants from temperate regions have developednatural adaptive mechanisms to tolerate low andfreezing temperatures.

    `

    Cold acclimation- plants can adjust their metabolismto cold and increase their tolerance to freezing inresponse to low-non-freezing temperatures (Levitt,1980).

  • 8/9/2019 Frost resistance

    3/20

  • 8/9/2019 Frost resistance

    4/20

    CHILLING

    ` Occurs at lowtemperatures.

    ` Results from loss offunction ofbiomembranesconnected with decreasein their fluidity and

    inactivation of themembrane-bound ionpumps

    FREEZING

    Takes place at high extent

    Ice deposition inintracellular andextracellular spaces.

  • 8/9/2019 Frost resistance

    5/20

    ` Frost hardening is a quality of a individual plant and is governed by

    its genetic potential as well as by environmental factors, thus,

    usually changes with time.

    `

    It is difficult to be achieved by classical breeding or gene transfermethods because cold resistance is not a quality conferred by the

    product of one gene, but is a syndrome.

    ` It comprises quite different traits of cell biology, such as fluidity of

    the biomembranes, synthesis and accumulation of low

    molecular weight and high molecular weight cryoprotectants,

    increase of the potential to cope with oxidative stress and

    others

  • 8/9/2019 Frost resistance

    6/20

    ` Low temperature,` Length of photoperiod.

    ` The effect of these factors have been checked for plantssuch as Picea abies, Taxus cupsidata and Cornus

    stolonifera

    FROST DEHARDENING

    ` With gradual increase in temperature, plants deharden atspecific rates.

    ` It is less dependant on photoperiod than hardening.

  • 8/9/2019 Frost resistance

    7/20

    ` Inhibited photosynthesis, slower carbohydratetranslocation,

    ` lower respiration rates and increased protein degradationrates.

    ` Impairement of integral membrane proteins involved intransport of K+ ions .

    ` Intracellular ice formation is inevitably lethal, causes efflux

    of Ca+2 ions.

    ` Ca+2 ions play important role for recovery of freezestressed cells.

  • 8/9/2019 Frost resistance

    8/20

    ` 2 types of survival strategies:

    FROSTAVOIDANCE through: Desiccation of plant tissues

    Supercooling

    FROSTTOLERANCEthrough: Tolerance of freeze-induced cellular dehydration via

    accumulation of various solutes in cell sap

    Both processes operate simultaneously in plants such asinduced in Cornus stolonifera

    But it also depends on species-specific properties andgrowth conditions.

  • 8/9/2019 Frost resistance

    9/20

    ` Exhibited by rice and wheat seeds, dried tubers

    which can sustain loss of tissue water without

    loosing viability.

    ` Remaining water is so tightly bound that it can not

    crystallize even if cooled down to -196 degree C.

  • 8/9/2019 Frost resistance

    10/20

    Mild transient` Exhibited in temp. range -0.6 to -15 0c when extracellular ice

    crystal formation takes place.` Varies with tissue moisture content.

    PersistentTemp. range -16 to -25 0cTightly packed cells and reduced intraacellular spaces allow

    supercooling in cold acclimated plants

    Deep persistentFavoured by loss of water during cold acclimation by small cells.Specifically parenchymal cells survive by tolerance to freeze-

    induced dehydration process.

  • 8/9/2019 Frost resistance

    11/20

    Thus enables plant material to persist in super cooled state even atlow subzero temp.

    Presence of solutes increase the osmotic potential of cytoplasm and inturn, decrease the freezing point.

    Solutes such as soluble sugars (sucrose, glucose, raffinose, fructose,etc.) in the vacuoles improve the water holding capacity of cells andenables avoidance of stress caused by freeze-induced dehydration.

  • 8/9/2019 Frost resistance

    12/20

    ` Adequate amount of cryoprotective solutes enable

    tolerance of freeze-induced dehydration stress.

    ` Sucrose is one o the most essential cryoprotectantand osmolyte.

    ` Others include low molecular weight sugars, sugar

    alcohols, free Amino acids, organic acids andsoluble proteins.

  • 8/9/2019 Frost resistance

    13/20

    USEOF ANTIFREEZEPROTEINS (AFPs)

    ` They have the ability to adsorb onto the surface of ice crystalsand inhibit their growth and recrystallization.

    ` It is also observed that hormone Ethylene is involved inregulating antifreeze activity in respond to cold.

    ` AFPs are homologous to pathogenesis-related proteins and alsoprovide protection against psychrophilic pathogens.

    ` It has been observed that transferring genes which encodeforAFPs, to freezing-sensitive plants will lower their freezingpoint.

  • 8/9/2019 Frost resistance

    14/20

    ` AFPs have been screened in plants Secale

    cereale, Lolium perenne, etc.

  • 8/9/2019 Frost resistance

    15/20

    ` Some cold-inducible genes have been shown to

    be involved in freezing tolerance .

    ` Although the expression of these genes seems tobe specifically regulated by low temperatures, in

    most cases it is also responsive to dehydration,

    salt stressand abscisic acid (ABA) (Thomashow,

    1999), indicating that plant responses to all thesetreatments share common features.

  • 8/9/2019 Frost resistance

    16/20

    ` Some cold-inducible genes such as

    RD29A/COR78/LTI78 and COR15A from

    Arabidopsis have been isolated and screened.

    ` Most of these genes are not uniformly regulated

    by cold, suggesting that the molecular

    mechanisms of cold acclimation are differentially

    modulated in different tissues.

  • 8/9/2019 Frost resistance

    17/20

    ` Two cold-specific-inducible genes, RCI1A (forRare ColdInducible 1 A gene) and RCI1B, encoding multifunctionalregulatory proteins were isolated (Abarca et al., 1999;Jarillo et al., 1994).

    ` In addition, RCI2A and RCI2B, two genes whoseexpression is transiently induced by cold and in responseto drought, salt stress and ABA, were also identified (Capelet al., 1997; Medina et al., 2001).

    ` The isolation and molecular characterization ofa newRare Cold Inducible gene RCI3, is lately performed.

  • 8/9/2019 Frost resistance

    18/20

    ` Isolated by screening a cDNA library prepared from cold-acclimated seedlings ofArabidopsis.

    ` Its expression is restricted to specific root cell types.

    ` Encodes an active cationic peroxidase.

    ` Overexpression ofRCI3 increases Arabidopsistolerance to frost, drought and salt stresses whilesuppression ofRCI3 expression reduces the tolerance

    ofArabidopsis to these adverse conditions.

    ` It is the only gene that has been reported to benegatively regulated by light.

  • 8/9/2019 Frost resistance

    19/20

    ` Another gene, P5CS, encodes for pyrroline-5-

    carboxylate synthetase is involved in proline

    synthesis, and the over-production ofproline

    confers drought as well as frost resistance.

  • 8/9/2019 Frost resistance

    20/20

    THANK YOU.