IntroductionThe gaseous hormone eth

Introduction
The gaseous hormone ethylene (C
2
H
4
) synthesized in plant
tissues from the precursor 1-aminocyclopropane-1-carboxylic
acid (ACC) is involved in multiple physiological and devel-
opmental processes in plants, such as tissue differentiation,
lateral bud development, seedling emergence, leaf and flower
senescence, root hair development and elongation, anthocya-
nin synthesis, fruit ripening and degreening, and the produc-
tion of volatile compounds responsible for aroma in fruits
(Abeles et al.
1992
; Frankenberger and Arshad
1995
; Spaink
1997
; Bleecker and Kende
2000
). Ethylene also regulates
plant responses to biotic and abiotic stresses (Abeles et al.
1992
; Roman et al.
1995
;O
’
Donnell et al.
1996
; Penninckx
et al.
1998
). Under ambient conditions, plants produce the
required levels of ethylene, conferring beneficial effects on
plant growth and development; however, in response to biotic
and abiotic stresses the plant often significantly increases
endogenous ethylene production, which has adverse effects
on plant growth and is thought to be responsible for senes-
cence in plants (Abeles et al.
1992
; Woltering and Van Doorn
1988
;Nayanietal.
1998
; Ali et al.
2012
).
Plant growth-promoting rhizobacteria (PGPR) are a group
of free-living saprophytic bacteria that can be found in the
S. Z. Ali (
*
)
Department of Microbiology, Agri Biotech Foundation,
Behind College of veterinary Science (old), Acharya N.G Ranga
Agricultural University, Rajendranagar, Hyderabad,
Andhra Pradesh, India 500030
e-mail: [e-mail]
V. Sandhya
Department of Dryland Cereals, International Crops Research
Institute for the Semi-Arid-Tropics, Patancheru, Hyderabad,
Andhra Pradesh, India 502324
L. Venkateswar Rao
Department of Microbiology, University College of Science,
Osmania University, Hyderabad, Andhra Pradesh, India 500007
Ann Microbiol (2014) 64:493
–
502
DOI 10.1007/s13213-013-0680-3
rhizosphere in association with the root system and which
enhance the growth and development of the plant either direct-
ly or indirectly (Kloepper and Beauchamp
1992
; Liu et al.
1995
). Interestingly, these PGPR strains also possess the en-
zyme ACC deaminase (Jacobson et al.
1994
; Glick et al.
1998
;
Shah et al.
1997
) which can cleave the plant ethylene precursor
ACC to ammonia and
α
-ketobutyrate, thereby lowering the
level of ethylene under various biotic and abiotic stresses
(Glick et al.
1998
), such as salt stress (Cheng et al.
2007
,
Mayak et al.
2004a
; Zahir et al.
2009
), flooding stress (Grichko
and Glick
2001
),droughtstress(Mayaketal.
2004b
), heavy
metal stress (Belimov et al.
2005
; Stearns et al.
2005
), and
pathogen attack (Wang et al.
2000
). ACC deaminase-containing
PGPR lower the level of ACC in the stressed plants, thereby
limiting the amount of stress ethyl
ene synthesis and, consequent-
ly, damage to the plant. These bacteria are beneficial to plant
growth as plants are often subjected to stresses that induce the
production of ethylene. Soil-borne fluorescent pseudomonads
have excellent root colonizing ab
ility and catabolic versatility,
and they produce a wide range of enzymes and metabolites
which favor plant resistance to various biotic and abiotic stresses
(Ramamoorthy et al.
2001
; Mayak et al.
2004
; Vivekananthan
et al.
2004
).
Drought stress is one of the major agricultural problems
limiting crop productivity in most of the arid and semiarid
regions of the world. This form of abiotic stress affects the
plant
–
water relations at both the cellular and whole-plant
level, causing both specific and non-specific reactions and
damage. Bacteria can survive under stress conditions due to
the production of exopolysaccharide (EPS), which protects
microorganisms from water stress by enhancing water reten-
tion and regulating the diffusion of organic carbon sources
(Wilkinson
1958
; Hepper
1975
; Roberson and Firestone
1992
; Chenu
1993
; Chenu and Roberson
1996
). EPS also
helps microorganisms to irreversibly attach and colonize the
roots due to involvement of a network of fibrillar material
that permanently connects the bacteria to the root surface
(Bashan et al.
2004
). Inoculation of plants with native ben-
eficial microorganisms with drought-tolerant ACC deami-
nase may increase the drought tolerance of plants growing in
arid or semiarid areas. Therefore, we made an attempt to
isolate and characterize EPS and ACC deaminase from
drought-tolerant
Pseudomonas
strains from cropped soils
of different arid and semiarid natural habitat as a means to
provide the best benefit to drought-stressed plants.
Ma

ผลลัพธ์ (ไทย) 1:

IntroductionThe gaseous hormone ethylene (C2H4) synthesized in planttissues from the precursor 1-aminocyclopropane-1-carboxylicacid (ACC) is involved in multiple physiological and devel-opmental processes in plants, such as tissue differentiation,lateral bud development, seedling emergence, leaf and flowersenescence, root hair development and elongation, anthocya-nin synthesis, fruit ripening and degreening, and the produc-tion of volatile compounds responsible for aroma in fruits(Abeles et al.1992; Frankenberger and Arshad1995; Spaink1997; Bleecker and Kende2000). Ethylene also regulatesplant responses to biotic and abiotic stresses (Abeles et al.1992; Roman et al.1995;O’Donnell et al.1996; Penninckxet al.1998). Under ambient conditions, plants produce therequired levels of ethylene, conferring beneficial effects onplant growth and development; however, in response to bioticand abiotic stresses the plant often significantly increasesendogenous ethylene production, which has adverse effectson plant growth and is thought to be responsible for senes-cence in plants (Abeles et al.1992; Woltering and Van Doorn1988;Nayanietal.1998; Ali et al.2012).Plant growth-promoting rhizobacteria (PGPR) are a groupof free-living saprophytic bacteria that can be found in theS. Z. Ali (*)Department of Microbiology, Agri Biotech Foundation,Behind College of veterinary Science (old), Acharya N.G RangaAgricultural University, Rajendranagar, Hyderabad,Andhra Pradesh, India 500030e-mail: [e-mail]. SandhyaDepartment of Dryland Cereals, International Crops ResearchInstitute for the Semi-Arid-Tropics, Patancheru, Hyderabad,Andhra Pradesh, India 502324L. Venkateswar RaoDepartment of Microbiology, University College of Science,Osmania University, Hyderabad, Andhra Pradesh, India 500007Ann Microbiol (2014) 64:493–502DOI 10.1007/s13213-013-0680-3rhizosphere in association with the root system and whichenhance the growth and development of the plant either direct-ly or indirectly (Kloepper and Beauchamp1992; Liu et al.1995). Interestingly, these PGPR strains also possess the en-zyme ACC deaminase (Jacobson et al.1994; Glick et al.1998;Shah et al.1997) which can cleave the plant ethylene precursorACC to ammonia andα-ketobutyrate, thereby lowering thelevel of ethylene under various biotic and abiotic stresses(Glick et al.1998), such as salt stress (Cheng et al.2007,Mayak et al.2004a; Zahir et al.2009), flooding stress (Grichkoand Glick2001),droughtstress(Mayaketal.2004b), heavymetal stress (Belimov et al.2005; Stearns et al.2005), andpathogen attack (Wang et al.2000). ACC deaminase-containingPGPR lower the level of ACC in the stressed plants, therebylimiting the amount of stress ethylene synthesis and, consequent-ly, damage to the plant. These bacteria are beneficial to plantgrowth as plants are often subjected to stresses that induce theproduction of ethylene. Soil-borne fluorescent pseudomonadshave excellent root colonizing ability and catabolic versatility,and they produce a wide range of enzymes and metaboliteswhich favor plant resistance to various biotic and abiotic stresses(Ramamoorthy et al.2001; Mayak et al.2004; Vivekananthanet al.2004).Drought stress is one of the major agricultural problemslimiting crop productivity in most of the arid and semiaridregions of the world. This form of abiotic stress affects theplant–water relations at both the cellular and whole-plantlevel, causing both specific and non-specific reactions anddamage. Bacteria can survive under stress conditions due tothe production of exopolysaccharide (EPS), which protectsmicroorganisms from water stress by enhancing water reten-tion and regulating the diffusion of organic carbon sources(Wilkinson1958; Hepper1975; Roberson and Firestone1992; Chenu1993; Chenu and Roberson1996). EPS alsohelps microorganisms to irreversibly attach and colonize theroots due to involvement of a network of fibrillar materialthat permanently connects the bacteria to the root surface(Bashan et al.2004). Inoculation of plants with native ben-eficial microorganisms with drought-tolerant ACC deami-nase may increase the drought tolerance of plants growing inarid or semiarid areas. Therefore, we made an attempt toแยก และลักษณะ EPS และ ACC deaminase จากทนแล้งPseudomonasสายพันธุ์จากดินตัดความแตกต่างกันแห้งแล้ง และแล้งอาศัยอยู่ตามธรรมชาติเป็นวิธีการให้ประโยชน์เน้นภัยแล้งพืชMa