1. Rust in Beans
Hoch’s first
indications that fungal organisms navigate by a sophisticated sense of touch
came as a result of his team’s earlier work with the rust fungus Uromyces
appendiculatus. Plant pathologists and submicron engineers determined that
the fungus distinguishes minute differences in leaf surface topography in order
to decide where and when to infect its host—bean plants. The team simulated
leaf topography by micro fabricating ridges on silicon wafers using
electron-beam lithography. They then used scanning electron microscopy and
light microscopy to follow the growing rust fungus as it explored the
artificial surfaces to demonstrate that the fungus orients itself to ridges
similar to those on a real leaf surface. The fungus “crawls” across the ridges
until it senses a correct topographical feature mimicking “stomatal lips”
associated with leaf stomata, or tiny holes, on the surface of the bean leaf.
This event signals the fungus to develop the primary infection structure,
called an apressorium, precisely over the stomatal opening to invade the leaf
tissue. Hoch and his team determined that ridges 0.5 μm high were the optimum
cue that signaled for appressorium development, and that this size parameter
matched almost exactly the size of the stomatal lips of the bean leaf. “The use
of precision-made, highly reproducible surfaces allowed us to elucidate the
mechanisms involved in the fungus’s perception of signaling cues normally located
on the plant’s surface,” Hoch says. The information has provided greater
insight into the inner workings of the bean rust fungus and someday may be used
by bean breeders to develop bean plants with a smaller stomatal lip structure
that helps make the plant more rust resistant.
2. Anthracnose in Corn
In a related
project, Hoch and his associates investigated destructive events of fungi that
cause anthracnose disease on grasses. The goal was to simulate the movement of Colletotrichum
graminicola, the fungus that causes anthracnose on corn and determine what
features trigger the fungus to develop an appressorium. In this case rather
than being formed over a stomata, the appressoria develop anywhere on the leaf
surface where they exert great internal pressure needed to facilitate
penetration of the leaf cuticle. Again, they used nano techniques: lithography
to nanofabricate a pillared surface on silicon wafers. This lawn of miniature
pillars 1.4 20 μm wide and spaced various distances apart was used to examine
movement of the fungus across the surface that mimicked some of the
characteristics of the host plant. Images of the fungus crawling across the
nanofabricated surface have helped the researchers determine that the fungus
needs to make minimum contact of at least 4.5 μm before it starts to develop
appressoria. Knowing this, it is hoped that plants can be bred to possess
surfaces that are less inductive to the fungus's sensing mechanisms.
3. Pierce’s Disease in Grapes
In his
current work, Hoch and his colleagues in Geneva and at the Wadsworth Center in
Albany have moved from studying pathogenic fungi to studying pathogenic
bacteria. Their goal is to examine how Xyllela fastidiosa moves
“upstream” against the flow of sap in the plant’s vascular plumbing system, the
xylem vessels. Their upstream movement has been particularly puzzling to plant
pathologists because the bacteria do not have flagella, whiplash-like
propelling hairs, and common to many other bacterial species. The bacteria
colonize the plant’s plumbing system to the point that they block the flow of
water and cause the plant to wither and die—developing what is known as
Pierce’s disease. The bacteria cause millions of dollars worth of damage to
grape and citrus worldwide. It is of great concern to growers in the warmer
states like California, Texas, and Florida, and is of concern to grape growers
in the Eastern United States. Because the bacteria cannot be readily viewed and
studied by microscopy in living plants, Hoch and his post-doctoral associate,
Yizhi Meng ’98, MS ’01, PhD ’03, fabricated microfluidic chambers to mimic
plant xylem vessels and “infected” them with both wildtype and mutant Xylella
strains created in the lab of fellow plant pathologists Thomas Burr and
Yaxin Li. They created these artificial xylem vessels using a silicone
elastomer that was replicated from silicon wafers onto which “master” patterns
were constructed with photo-lithography. Scanning electron microscopy was used
to examine the bacteria in both artificial and bona fide grape xylem. Using
time-lapse light microscopy, they created “movies” of the bacteria as they
colonized and “clogged” the artificial xylem. With this technology, they
discovered that individual bacteria “twitched” their way upstream, against the
flow, using pili, or tiny hair-like filaments, to attach the cells to the
surface of the xylem wall. As the pili are repeatedly retracted and extended,
the cells twitch forward—a nanometer at a time. Using these movies, they
clocked bacteria moving at the microworld fast rate of 12 μm per minute against
a flow velocity of about 20,000 μm per minute. On a human scale, this feat
is comparable to a person swimming against the current of the Niagara River, a
remarkable finding. Burr and Li, and Cheryl Galvani who also works at the
Geneva experiment station, are working on transforming Xyllela so that
the bacteria can no longer “twitch.”
UK University
discovers perfect antimicrobial technology
Cheap,
safe and effective antimicrobial nanoparticles for food packaging have been
discovered just six months into a three-year-long study at the UKbased
University of Leeds' Nanomanufacturing Institute. Official results are not
expected for at least another three months, but Professors Yulan Ding and Malcolm
Povey and PhD candidate Lingling Zhang say already nanoparticles of zinc oxide and
magnesium oxide have shown to be effective in killing microorganisms. Ding says
the team is trying to find cheap, safe alternatives to nano-sized silver, which
has excellent antimicrobial properties, but is expensive and as a heavy metal,
is not suitable for human contact. 'We have already found some that work, such
as nanoparticle zinc oxide and magnesium oxide. Results so far have been very
positive,' Ding acknowledges.
Ding’s
research team is continuing to explore a larger list of cheap and inert
nanoparticles for their potential effectiveness in killing microorganisms. Ding
says they plan to incorporate effective antimicrobial nanoparticles into
packaging materials as research progresses. 'The smart nanocomposites are
assemblies of functionalized nanoparticles which are hundreds of micrometres in
size and strong enough for safe and easy handling,' Ding says. The
nanocomposites can be triggered to disintegrate in liquid into nanoparticles
that are capable of attaching to and killing or controlling microorganisms.
Conclusion:
In India, nanotechnology, which has
already made some imprints in many areas of plant pathology, is the second craze
after biotechnology for innovative research Nanotechnology now a day’s playing very important
role in daily life and in agriculture. By using nanotechnological tool we can
easily identify pathogen and easily management of pathogen which leads to
reduction in chemical use and plant damage and environment friendly option for
plant disease
management, but high toxicity of nanoparticles inadvertently released
in the environment may pose greater threat to man and other organisms. Therefore,
nanotechnological
progress is to be viewed with caution and dealt accordingly
Referencess :
Report of the OECD Workshop on the Safety of
Manufactured Nanomaterials: Building Co-operation, Co-ordination and
Communication (Organization for Economic Co-operation and Development, Paris,
2006).
Maynard, A. D. Nanotechnology: A Research Strategy for
Addressing Risk (Woodrow Wilson International Center for Scholars, Washington
DC, 2006).
Two-Year Review of Progress on Government Actions: Joint
Academies' Response to the Council for Science and Technology's Call for
Evidence (The Royal Society and The Royal Academy of Engineering, London,
2006).
Article compiled by
Mr. Amol Vijay Shitole (Ph.D. Scholar)
Dr. Panjabrao
Deshmukh Krishi Vidyapeeth, Akola (M.S.)
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