frost resistance
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.