Бетаин (триметилглицин)

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Conversion of solar energy into carbohydrates by a leaf.

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Shown here are the percentages of light absorbed, reflected, and transmitted,

as a function of wavelength. The transmitted and reflected green light in the wave band at 500 to 600 nm gives leaves their green color. Note that most of the light above 700 nm is not absorbed by the leaf. (From Smith 1986.)

Optical properties of a bean leaf.

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Photoprotection by dissipation of excess light energy aided by xanthophyll cycle

carotenoids

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Xanthophyll cycle

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Response of frosted orache (Atriplex sabulosa) and
Arizona honeysweet (Tidestromia oblongifolia) to

heat stress.
Photosynthesis (A) and respiration (B) were measured on attached leaves, and ion leakage (C) was measured in leaf slices
submerged in water.
(From Bjorkman et al. 1980.)

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Организация мембранных микродоменов (рафтов)

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Heat shock factor (HSF) cycle

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Heat stress Ca-mediated response

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Low temperature scanning electron microscopy of contro (A) and freezing –

stressed tobacco leaves (B-D) (Ashworth and Pearce, unpubl. res. ). Themicrographs show transverse fractures through the leaves.
Youngpottedplantsweregrowninawarmgreenhouseandweretestedatthetwo-to-fourleafstage.
Theplantsweresprayedwithwaterandcooledat28Chÿ1toÿ208Cthenfreeze-®xedinmeltingfreon12.DTAshowedtheleavesfrozebetweenÿ2.08Candÿ3.08C.DetailsofthemicroscopicalmethodsareasinPearceandAshworth(1992).A,Controlsampleshowingturgidcellsandabsenceofextracellulariceinalltissues(e,epidermis;pm,palisademesophyll;sm,spongymesophyll).Notethatorganellepro®leswerevisiblewherethefractureplanehadcutthroughthecells(starsindicatecross-fracturedcellsinthespongymesophyll;arrowheadsindicateorganellesintwoexamplecells).Theepidermalcells(e)werealsocross-fractured.BandC,Samplefrozentoÿ208Cshowingextensiveextracellularice(i).CisanenlargementoftheareaboxedinB.Inthisexampleicerami®edextensivelythroughthegasspacesbutdidnotfullyoccludethem.Thewhitearrow(B)indicatesthecollapsedepidermis.Atlowmagni®cation(B)theiceappearedsuper®ciallysimilartoturgidcells.However,whenenlarged(C)thecross-fractureofthesestructuresshowedthemtocontainnoorganellepro®lesandinsteadthefracturedsurfacehadsteps(arrowheads)typicaloffracturedice.Thecellsweremostlyhiddenbytheice.However,intheareaenlargedinCacollapsedcell(star)waseasilyidenti®edbytheorganellesitcontained:thearrowindicatestheimpressonthecellwalloforganellesinacell.D,Samplefrozentoÿ208C.Icewasremovedfromthespecimenbysublimationinthemicroscope,thusrevealingthecollapsed,dehydratedcells.Themesophyllcells(pm,palisademesophyll;sm,spongymesophyll)andepidermis(whitearrows)werecollapsed.Theoutersurfaceofcellwallsshowedanimpressoftheorganelleswithinthecells(examplesindicatedbyarrowheads).Starsindicatewherethefractureplanehascutthroughthecells,againrevealingorganelles.Allgold-coated.2kV.Bars‹10mm(AandC)or100mm(BandD).

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Low temperature scanning electron microscopy of control (A) and freezing –

stressed tobacco leaves (B-D) (Ashworth and Pearce, unpubl. res.).

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Membrane transport proteins mediating sodium, potassium, and calcium transport during salinity

stress

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Roots of maize. Scanning electron micrographs (150×). (A) Control root, supplied

with air, with intact cortical cells. (B) Oxygen-deficient root. Note the prominent gas-filled spaces (gs) in the cortex (cx), formed by degeneration of cells. The stele (all cells interior to the endodermis, En) and the epidermis (Ep) remain intact. X, xylem. (Courtesy of J. L. Basq and M. C. Drew.)

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Metabolic pathways that are active during hypoxia in plants
Narsai et al.

2011

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The transcription factors HRE1 and HRE2 were shown to play a

crucial role in inducing adaptive responses of plants to hypoxia. Overexpression of these transcription factors improved the survival rate of plants that were exposed to anoxia for 10 hours.
Licausi, 2011

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Oxygen sensing in plants is mediated by an N-end rule pathway

for protein destabilization

The transcription factor RAP2.12 is constitutively expressed under aerobic conditions. RAP2.12 protein is always present, bound to ACBP to prevent RAP2.12 from moving into the nucleus under aerobic conditions and to protect it against proteasomal degradation in air. Upon hypoxia, RAP2.12 moves into the nucleus, where it activates anaerobic-gene expression. Upon re-oxygenation, RAP2.12 is rapidly degraded via the N-end rule pathway and proteasome-mediated proteolysis to downregulate the hypoxic response.

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