Plant-Growth-Promoting Rhizobacteria (PGPR) and Medicinal Plants

444 Pages·2015·6.84 MB·English

by  Dilfuza Egamberdieva

Soil Biology
Dilfuza Egamberdieva
Smriti Shrivastava
Ajit Varma Editors
Plant-Growth-
Promoting
Rhizobacteria
(PGPR) and
Medicinal Plants
Soil Biology
Volume 42
Series Editor
Ajit Varma,Amity Institute of Microbial Technology,
Amity University Uttar Pradesh, Noida, UP, India
More information about this series at
http://www.springer.com/series/5138
Dilfuza Egamberdieva (cid:129) Smriti Shrivastava (cid:129)
Ajit Varma
Editors
Plant-Growth-Promoting
Rhizobacteria (PGPR) and
Medicinal Plants
Editors
DilfuzaEgamberdieva SmritiShrivastava
DepartmentofBiotechnologyand AjitVarma
Microbiology,FacultyofBiology AmityInstituteofMicrobialTechnology
andSoilScience (AIMT)
NationalUniversityofUzbekistan AmityUniversityUttarPradesh
Tashkent,Uzbekistan Noida,UttarPradesh,India
ISSN1613-3382 ISSN2196-4831(electronic)
ISBN978-3-319-13400-0 ISBN978-3-319-13401-7(eBook)
DOI10.1007/978-3-319-13401-7
SpringerChamHeidelbergNewYorkDordrechtLondon
LibraryofCongressControlNumber:2015931076
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Foreword
The editors of the volume “PGPR and Medicinal Plants” asked me to write the
Forewordtothisbook.Ihavegonethroughthevolumecontentsandsomechapters,
whichpromptedmetowritetheForeword.Microorganismsareabundantlydistrib-
utedinthesoil,rangingfrombacteria,actinomycetes,fungi,algae,cyanobacteria,
and protozoa. These microbes contribute many beneficial elements, like carbon,
sulfur,phosphorus,andnitrogen,tothesoilbytakingpartinthenutrientcycle.The
zoneofcontactbetweentherootandsoilistherhizosphere.Thisregionhasintense
activity and concentration of microbes and is considered vital for plant vigor and
full development to maturity. Plant growth and development promoting
rhizobacteria (PGPR) are present in the vicinity of the root system and at times
adhering to the root. Such bacteria have been applied to a wide range of agricul-
turally important crops for the purpose of plant growth promotion, including
emergenceseedgerminationandvalueaddition.
The influence of root exudates on the proliferation of soil microorganisms
around and inside roots as well as interactions between soil microorganisms,
rhizosphere colonies, and plant hosts have been widely studied. Studies based on
moleculartechniqueshaveestimatedabout4,000microbialspeciespergramofsoil
samples. Powerful methods of estimation provide only the crudest measure of its
magnitude.Nonetheless, manysuchestimatesexist,suggestingthatasinglegram
of soil may contain over 10 billion microbial cells and more than 1,800 bacterial
species(Zhangetal.2008).
PGPRs are well established tocolonize plant roots and stimulate plantgrowth.
Theyservethepurposeofbeingusedasbiofertilizers,plantgrowthregulators,and
bioticelicitorsandpromoteplantgrowthbyseveralmechanismssuchasphospho-
russolubilization,productionofvolatileorganiccompounds,inductionofsystemic
disease resistance, nitrogen fixation, maintenance of soil fertility and nutrient
uptake, and resistance of water stress. How to classify the newly found diverse
microorganisms remains an open question. As molecular methods, such as whole
genomesequencing,aremorewidelyappliedtocharacterizebacterialdiversity,our
abilitytomaketaxonomicsenseofwhatwelearnisseverelychallenged.
v
vi Foreword
From a structural,functional, and taxonomical perspective, soil bacteria are an
impressivelydiversegroup.Itiswellknownthattheyvaryfromfree-livingbacteria
tosinglefungicapableofextendingtheirgrowthoveralargedistanceofmultiple
squarekilometers.Still,weknowlittleaboutsoilbacteriabecauseofthedifficulties
associated with their cultivation (Witzany 2011). Only a very limited number of
species have been classified because less than 1 % grow easily on nutrient agar
plates. Consequently, scientists depend on indirect analytical methodologies,
mainly biochemical markers, as well as on measures of the metabolic activity in
eitherentiresoilmicrobialcommunitiesorselectedsegmentsofsuchcommunities.
Researchhas underscored the essentialfunctionsthat microorganisms play insoil
quality.Thisisparticularlyevidentintheimportantareasofthecyclingofessential
nutrients,thedecompositionoforganicmaterials,theregulationofessentialnutri-
ents, the decomposition of organic materials, and the regulation of the productive
capacity of plant life, in the dynamics of soil microbial community considered
holistically.
Restoration-related research intothe rolesofmicrobes has branchedoff intwo
principaldirections:investigationthatdescribesconditionsandtargetlocations in
the ecosystem and research that focuses on system manipulation. This second
direction stresses the creative manipulation of system components to facilitate
more rapid arrival at desired systematic states through overcoming challenges
posedbythepaucityofmutualistsandotherpositivecomponentsorbythepresence
ofinvasiveplantsandothernegativeinfluences.
Plant–PGPRassociationsaremediatedthroughanexchangeofchemicalmetab-
olites. Root exudates provide energy-rich organic acids, sugars, and amino acids
thataremetabolizedwithinashorttimebysoilmicroorganisms,whilespecialized
microorganismsgenerateanarrayofbiologicallyactivecompoundsthatelicitplant
growthpromotion.
Fuqua et al. (1996, 2002) defined the term “quorum sensing” (QS) as the
bacterial regulatory process that couples gene expression to cell density. This
processismediatedbylow-molecular-weightsignalmoleculesthataresynthesized
by bacterial population and accumulate in the environment. The presence of
moleculesissensedbybacteria andinduces eitherthe expression orrepressionof
QS-regulated gene(s). Earlieritwasthoughtthatbacteria are unabletocommuni-
cate.InvestigationsonQShavedrasticallychangedthisviewthatbiologistshadon
bacteria. Indeed, bacteria not only communicate but they do so in multiple lan-
guagesusingQSsignals.
ConsideringthatseveralplantpathogenicbacteriaalsorelyuponQSmolecules
toregulatevirulenceorvirulence-relatedfunctions,thesameevolutionaryreading
provides potential explanation for the plant capacity to detect the presence of the
bacterialsignalmolecules.Thegeneraloccurrenceoffunctionscapableofinducing
QSsignaldegradationinfungiandbacteria,includingnoncultivableones,strongly
suggests that these functions might play a significant biological role. The QS
strategies have been developed and present a multifaceted value. They may be
developedtopreventorlimitbiofilmfunctionsonseveralstructures,ortheimpact
ofbacterialdiseasesinplants.
Foreword vii
The moot questions remain: how do microbes perceive environmental and
metabolic signals and how do they integrate this information to modulate gene
expression?Genome-widecomparisonsindicatethattheabilitytoaccuratelysense
the environment and to change gene expression accordingly is critical to the
bacteria that spend at least a part of their life cycle in the complex and uncertain
environments of soil. Quorum sensing (QS) is one of the mechanisms by which
microbeschangeglobalpatternsofgeneexpressioninresponsetoincreasesintheir
populationdensitieswithinadiffusion-limitedenvironment.
The time is ripe to commercialize the products by establishing strong linkages
betweenacademicandindustries.Thevolume“PGPRandMedicinalPlants”edited
byeminentmicrobiologistsDrs.DilfuzaEgamberdieva,SmritiSrivastava,andAjit
Varma presents innovative ideas and thoughts . I congratulate them. This volume
should be useful for active researchers, teachers, and scientists. It is published as
partoftheSoilBiologySeriesbySpringer,Heidelberg,Germany.
Secunderabad,India K.V.V.Sairam
References
Fuqua C, Greenberg EP (2002) Listening in on bacteria: acylhomoserinelactone signaling.
NatRevMolCellBiol3:685–695
Fuqua C, Wanians SC, Greenberg EP (1996) Census and consensus in bacterial ecosystems:
the LuxR-LuxI family of quorum-sensing transcriptional regulators. Annu Rev Microbiol
50:727–751
WitzanyG(2011)Biocommunicationinsoilmicroorganisms.In:AjitVarma(ed)Soilbiology
series,vol23.Springer,Berlin
Zhang H, Xie X et al (2008) Soil bacteria augment Arabidopsis photosynthesis by decreasing
glucoseandabscisicacidlevelsinplant.PlantaJ56:264–273
ThiSisaFMBlankPage
Preface
This book was conceptualized during finalizing the Soil Biology volume “Root
engineering:BasicconceptsandApplications”editedbyAsuncionMorteandAjit
Varma (2014). Soon it was realized that the basic functions of roots are heavily
regulatedbythemicroorganismsaroundthemandthusanewvolume“PGPRand
MedicinalPlants”wasdepicted.Theprimeaimandobjectiveofthisvolumeisto
highlightvarious aspects ofaction, effect, and applicationof PGPRs inmedicinal
plantstolendahandtoscientiststhroughouttheworldworkinginthisfield.
The rhizosphere concept was first introduced by Hiltner (1904) to describe the
narrow zone of soil surrounding the roots where microbial populations are stimu-
lated by root activities. The term “plantgrowth-promotingrhizobacteria (PGPR)”
wasfirstusedbyJosephW.Kloepperinthelate1970sandhasbecomecommonly
used in scientific literature. A large number of microorganisms such as bacteria,
fungi,protozoa,andalgaecoexistintherhizosphere;however,themostabundant
organism is bacteria. Plants select those bacteria contributing mostto their fitness
by releasing organic compounds through exudates creating a very selective envi-
ronmentwherediversityislow.Sincebacteriaarethemostabundantmicroorgan-
isms in the rhizosphere, it is highly probable that they influence the plants’
physiology to a greater extent, especially considering their competitiveness in
root colonization, hence, referred as plant growth-promoting rhizobacteria
(PGPR).PGPRsarethegroupofmicroorganismswhichcolonizeandhavesymbi-
otic relationship with the plant roots and promote plant growth via various plant
growth-promotingsubstancesandalsoactasbiofertilizers.
Theworldtodaycomesupwithanewailmentaftereveryshortspanoftimeand
thus our requirement of medicines and drugs continues to amplify. Natural com-
poundsaremostpreferredoversyntheticdrugsforcuringdiseasesandthesenatural
compoundsarevariedlyobtainedfrommedicinalplants.Allweneedistoenhance
qualityandquantityofplantsecondarymetabolites,whichcanbeskillfullyusedfor
drugproduction. Numerousplantgrowth-promotingrhizobacteriaarewellknown
toexhibitbeneficialeffectsonplentyofmedicinalplants.
ix