plant surface microbiology.pdf

1 The State of the Art 9
great advantage of providing detailed spatial information about root surface
colonization, quantitative and qualitative data about the structural and functional
diversity of root colonization can be obtained by a variety of complimentary
ex situ approaches.
The plant cuticle forms the solid surface environment for epiphyllic microorganisms.Detailed
analysis of a variety of microbe – cuticle interactions combining
physicochemical, ecophysiological and microbial aspects are presented
in Chapter 25.Isolated cuticles are excellent model surfaces to study the mechanisms
of such interactions. Using the in vitro system, even minor changes in
cuticular wax composition or permeability can be examined in relation to
microbial growth.Working with entire leaves such changes would probably be
masked by the physiological influence of the leaf.Therefore,this new approach
might be very helpful to reveal possible mechanisms of interactions that occur,
in reality, only in the scale of microhabitats. The impact of cuticular features
will help us to understand the observed heterogeneous colonization of the leaf
habitat and the formation of micro-colonies.Vice-versa the capacity of microbial
cells to change cuticular properties might be of crucial importance for a
successful colonization of the leaf surfaces and could contribute substantially
to microbial fitness of individual epiphyllic species.Changes in cuticular properties
in relation to microbial growth can be assessed in vitro under controlled
conditions. Pseudomonas putida GR12-2, a well-known plant growth promoting
strain, contains the enzyme 1-aminocyclopropane-1-carboxylic acid
(ACC) deaminase. This enzyme hydrolyses ACC, the immediate precursor of
ethylene in plant tissues.Ethylene is required for seed germination and the rate
of ethylene production increases during germination and seedling growth.
One model has been suggested where ACC deaminase containing growth-promoting
bacteria can lower ethylene levels and thus stimulate plant growth. A
rapid and novel procedure for the isolation of ACC deaminase-containing bacteria
has been described in Chapter 26. In order to be able to test the model, a
method for measuring ACC in plant tissues is described. Since all of the available
methods for ACC quantification had problems and limitations associated
with their use,Waters AccQ.Tag Method,designed to measure amino acids,was
successfully applied for ACC analysis. This procedure is simple and relatively
sensitive.
The protocol for understanding Rhizobium-legume root nodule symbiosis
has been taken up by various microscopy techniques including bright-field,
phase contrast, Nomarski interference contrast, polarized light, real time and
time-lapse video, dark-field, conventional and laser scanning confocal epifluorescence,
scanning electron, transmission electron, and field-emission scanning/transmission
electron microscopies combined with visual counting
techniques and manual interactive applications of image analysis. A new generation
of innovative, customized image analysis software-CMEIAS (Center
for Microbial Ecology Image Analysis System), designed specific digital
images of microbial populations and communities and extracted all the infor-