Review
Effects of gamma irradiation on morphological changes and
biological responses in plants
Seung Gon Wi a ,Byung Yeoup Chung a ,*,Jae-Sung Kim a ,Jin-Hong Kim a ,
Myung-Hwa Baek a ,Ju-Woon Lee a ,Yoon Soo Kim b
a
Advanced Radiation Technology Institute (ARTI),Korea Atomic Energy Research Institute (KAERI),Jeongeup 580-185,Republic of Koera b
College of Agriculture and Life Science,Chonnam National University,Yongbong-dong 300,Gwangju 500-757,Republic of Korea
Received 1November 2006;accepted 2November 2006
Abstract
This review discusses the morphological changes and biological responses of plants irradiated with g
amma rays.Seedlings exposed to relatively low doses of gamma rays (1–5Gy)developed normally,while the growth of plants irradiated with a high dose gamma ray (50Gy)was significantly inhibited.Based on TEM observations,chloroplasts were extremely sensitive to gamma irradiation compared to other cell organelles,particularly thylakoids being heavily swollen.In addition,some portions of the mitochondria and endoplasmic reticulum were structurally altered,for example,distortion and swelling.The cerium perhydroxide deposition,as a maker for H 2O 2deposition,was typically manifest on the plasma membranes and cell walls of the tissues from both the control and irradiated plants.However,the intensities of cerium perhydroxide deposits (CPDs)were remarkably increased in the plasma membranes and cell walls of pumpkin tissues such as petiole,cotyledon,hypocotyl and especially leaf after gamma irradiation.These observations are in good agreement with the results of H 2O 2content in all tissues.The immuno-localization analysis for peroxidase (POD)on the tissues from pumpkin plant showed the same pattern between the control and irradiated plants,but the density of gold particles as indication of POD localization was significantly increased on the cell corner middle lamellae of parenchyma cells,especially in the petiole after gamma irradiation.However,accumulation and localization of H 2O 2and POD in vessels were not significantly different between both plants.The accumulation and localization of both H 2O 2and POD were differentially affected by gamma irradiation depending on the different tissue types.T
he deposition of both H 2O 2and POD in parenchyma cells appeared much higher than in vessels,suggesting that the former is more sensitive than the latter against gamma rays.#2006Published by Elsevier Ltd.
Keywords:Cerium chloride;Chloroplast;Gamma irradiation;Hydrogen peroxide;Immuno-gold labeling;Morphology;Peroxidase;Seedling growth;Transmission electron microscopy (TEM);Ultrastructure
Contents 1.Introduction .................................................................................5543.Effects of gamma irradiation on the plant growth .......................................................5544.Morphological changes after 5555.Deposition of hydrogen peroxide (H 2O 2)after gamma irradiation ............................................5596.Localization of peroxidase .......................................................................5607.
<563Acknowledgement .............................................................................563References ......................................
............................................
563
www.elsevier/locate/micron
Micron 38(2007)553–564
Abbreviations:APX,ascorbate peroxidase;CAT,catalase;CPD,scerium perhydroxide deposits;POD,peroxidase;ROS,reactive oxygen species;SOD,superoxide dismutase;TEM,transmission electron microscopy
*Corresponding author.Tel.:+82635703331;fax:+82635703339.E-mail address:kr (B.Y .Chung).0968-4328/$–see front matter #2006Published by Elsevier Ltd.doi:10.1016/j.micron.2006.11.002
1.Introduction
Gamma rays,X-rays,visible light,and UV are all of electromagnetic(EM)radiation.EM radiation differs in frequency and hence in energy.Gamma rays are the most energetic form of such electromagnetic radiation,having the energy level from around10keV to several hundred kilo-electron volts,and therefore they are more penetrating than other radiation such as alpha and beta rays(Kova´cs and Keresztes,2002).
Gamma rays belong to ionizing radiation and interact to atoms or molecules to produce free radicals in cells.These radicals can damage or modify important components of plant cells and have been reported to affect differentially the morphology,anatomy,biochemistry,and physiology of plants depending on the irradiation level.These effects include changes in the plant cellular structure and , dilation of thylakoid membranes,alteration in photosynthesis, modulation of the antioxidative system,and accumulation of phenolic compounds(Kim et al.,2004;Kova´cs and Keresztes, 2002;Wi et al.,2005).
It has generally been accepted that reactive oxygen species (ROS),such as hydrogen peroxide(H2O2),superoxide anion (O2ÁÀ),hydroxyl radicals(ÁOH)and singlet oxygen,are produced by water radiolysis(De Vita et al.,1993;Dubner et al.,1995;Kova´cs and Keresztes,2002;Luckey,1980;Miller, 1987;Quintiliani,1986).Among these ROS,H2O2is a normal meta
bolite in cells under the optimal plant growth conditions, are not particularly cytotoxic,but when its concentrations are increased by environmental stresses and ionizing radiation,it can lead to cell lethality(Halliwell,1974).Considering that water radiolysis,the predominant effect of ionizing radiation in organisms,induces ROS formation as mentioned above,it is possible to assume that plants,microorganisms,and animals should have cellular protection systems against ionizing radiation(Zaka et al.,2002).
To cope up with the damages caused by the ROS,cells possess a comprehensive and integrated endogenous enzymatic defense system.Peroxidase(POD),superoxide dismutase (SOD),and catalase(CAT)represent the endogenous enzy-matic defense of the plant cell,which become active during cell injury(Shindo et al.,1994).Actually,it has been reported that the activities of scavenging enzymes,such as POD,CAT,SOD, and ascorbate peroxidase(APX),are generally increased in various plant species by the treatment of ionizing radiation (Kim et al.,2005;Kwon et al.,2001;Lee et al.,1999;Wada et al.,1998;Zaka et al.,2002).Especially,the potential activity of POD to remove toxic H2O2contributed to the difference in response to radiation between two Nicotiana species(Wada et al.,1998).
As mentioned above,gamma irradiation would induce noticeable morphological changes in plant tiss
ues as well as a variety of biochemical responses at the cellular level.In this review,we focused the deposition and localization of H2O2and POD because H2O2is one of the most important agents in terms of cell damage and POD is one of the important antioxidant enzymes in terms of cell protection under the treatment of ionizing radiation as well as other oxidative stresses.Therefore, the TEM observations of morphological changes,H2O2 deposition,and POD localization,will make it possible to deduce how cells are damaged by and protect against gamma irradiation in the plants,and thereby provide critical keys for understanding the effects of gamma irradiation on tissues and cells of the plants.
2.Irradiation
Irradiation treatments include exposure to1–1000Gy,as generated by a gamma irradiator(60Co,ca.164,000Ci capacity;AECL,Canada).The dose rates varied with the distance between60Co column and sampling place,and were confirmed by means of a thermoluminescence dosimeter.
3.Effects of gamma irradiation on the plant growth
Physiological symptoms in a large range of plants exposed to gamma rays have been described by
many researchers(Kim et al.,2004,2005;Kova´cs and Keresztes,2002;Wi et al.,2005). The symptoms frequently observed in the low-or high-dose-irradiated plants are enhancement or inhibition of germination, seedling growth,and other biological responses(Kim et al., 2000;Wi et al.,2005).The growth of Arabidopsis seedlings exposed to low-dose gamma rays(1or2Gy)was slightly increased compared with that of the control,while the seedling growth was noticeably decreased by the high-dose irradiation of50Gy(Figs.1and2).Although no conclusive explanations for the stimulatory effects of low-dose gamma radiation
are Fig.1.The phenotypes of the control(left)and50Gy-treated Arabidopsis seedlings(right)at6days after gamma irradiation.Bar=5cm(Wi et al.,2005).
S.G.Wi et al./Micron38(2007)553–564 554
available until now,papers support a hypothesis that the low-dose irradiation will induce the growth stimulation by changing the hormonal signaling network in plant cells or by increasing the antioxidative capacity of the cells to easily overcome daily stress factors such as fluctuations of light intensity and temperature in the growth condition (Kim et al.,2004).In contrast,the growth inhibition induced by the high-dose irradiation has been attributed to the cell cycle arrest at G2/M phase during somatic cell division and/or various damages in the entire genome (Preussa and Britta,2003).
4.Morphological changes after gamma irradiation The relationship between growth of irradiated plants and dose of gamma irradiation has been manifested by investigating the morphological changes and seedling growth of the irradiated plants.No significant morphological aberrations were observed in the phenotype of the plants irradiated with relatively low doses (1–5Gy)of gamma rays (Fig.2),while a high-dose (50Gy)irradiation inhibited seedling growth remarkably (Figs.1and 2).
An approach in the ultrastrucural level,therefore,may provide insight into cellular mechanism of ionizi
ng radiation.The chloroplasts in stems from the control and low-dose (1or 5Gy)-irradiated Arabidopsis plants represent a typical struc-ture,which shows ellipsoidal shape with well-arranged thylakoid membranes of distinct grana and stroma regions (Fig.3).In contrast,the typical structure of chloroplasts in the cortical cells of stems was noticeably altered after the 50Gy irradiation and the thylakoids were considerably swollen and destructed (Fig.3).However,the size of chloroplasts between the low-and high-dose-irradiated stems was not significantly different.Ultrastructurally,mitochondria in the control and low-dose-irradiated stems possess well-organized cristae,while in the stems exposed to 50Gy,endoplasmic reticulum (ER)membranes were distended and mitochondria distorted in shape (Fig.4).The size of mitochondria was slightly enlarged after the low-dose irradiation,but not changed after the
high-dose
Fig.2.Seedling growth of 5-week-old Arabidopsis irradiated with different doses of gamma rays (mean ÆS.E.;n =10)(Wi et al.,2005
).
Fig.3.Chloroplasts in the cortical cells from stems of the control (A)and 1Gy (B),5Gy (C),and 50Gy (D)irradiated Aradiposis .Ch;chloroplast,CW;cell wall,ER;endoplasmic reticulum,IS;intercellular space,Sg;starch grain,V;vacuole.Note the numerous plastoglobuli (arrow heads)and plasmolysis (arrows).Bar =500nm (Wi et al.,2005).
S.G.Wi et al./Micron 38(2007)553–564555
Fig.4.Mitochondria in stems of the control (A)and 1Gy (B),5Gy (C),and 50Gy (D)-irradiated Aradiposis .Ch;chloroplast,CW;cell wall,ER;endoplasmic reticulum,G;golgi apparatus,M;mitochondria,IS;intercellular space,Sg;starch grain,Th;thylakoid,V;vacuole.Note the plastoglobuli (white arrows)ant the membrane of ER (arrow head)and mitochondria (black arrows).Bar =200nm (Wi et al.,2005
).
Fig.5.Nuclei in stems of the control (A)and 1Gy (B),5Gy (C),and 50Gy (D)-irradiated Aradiposis .CW;cell wall,ER;endoplasmic reticulum,Nu;nucleolus,M;mitochondria,G;golgi apparatus.Plasmolysis was detected in xylem cell (arrows).Bar =500nm (Wi et al.,2005).
S.G.Wi et al./Micron 38(2007)553–564
556
depositionirradiation (Fig.4).The cytoplasm was well preserved in the cell and the nuclei contained fairly disperse chromatin and a prominent nucleolus.In addition,envelopes of nuclei did not show any evidence of damages in all the irradiated plants as well as the control (Fig.5).However,the plasmalemma was separated from the cell wall in the 50Gy-irradiated plants (Figs.3–5).The low-dose irradiation of 1or 5Gy did not affect significantly the ultrastructures of cell organelles.
From the ultrastructural observations of the irradiated plant cells,the prominent structural changes of chloroplasts after the 50Gy irradiation revealed that chloroplasts were more sensitive to a high dose of gamma rays than other cell organelles.Similar results have been reported to be induced by other e
nvironmental stress factors such as UV,heavy metal,acidic rain,and high light (Barbara et al.,2003;Molas,2002;Quaggiotti et al.,2004;Stoyanova and Tchakalova,1997).Interestingly,the numerous plastoglobuli appeared on the chloroplasts of stems after the high-dose irradiation and the large ones were observed mainly in the stroma regions.Like the appearance of plastoglobuli,starch grains were also easily observable in the chloroplasts after the high-dose irradiation (Figs.3and 4).The accumulation of starch within the chloroplasts accompanied by damage and disorientation of grana and thylakoids would indicate the inhibition of carbohydrate transport (Bondada and Oosterhuis,2003;Carmi and Shomer,1979).However,the low-dose irradiation did not cause these changes in the ultrastructure of
chloroplasts.
Fig.6.The microphotographs of leaf (A and B),petiole (C and D),hypocotyls (E and F)and cotyledon (G and H)of the control (A,C,E,and G)and 1kGy-irradiated (B,D,F,and H)pumpkin.C,cambium region;P,phloem;X,xylem.Bar =100m m (Wi et al.,2006b ).
S.G.Wi et al./Micron 38(2007)553–564557

版权声明：本站内容均来自互联网，仅供演示用，请勿用于商业和其他非法用途。如果侵犯了您的权益请与我们联系QQ:729038198，我们将在24小时内删除。