Fungus of the
Millennium – Piriformospora indica: A symbiotic player for
phosphorous acquisition
Microbial Technology Unit, School of Life Sciences, Jawaharlal Nehru
University, New Delhi, 110067. INDIA.
E-mail: vikas_jnu@mailyahoo.com
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A mycorrhizal like-fungus, has been
discovered by Varma (JNU, New Delhi) and his collaborators. It was named Piriformospora
indica based on its
characteristic pear shaped chlaymydospores.18s and 28s rDNA analysis and the
ultrastructure features, it¢s molecular taxonomic status was assigned
to Basidiomycota. P. indica tremendously improves the growth and overall biomass production of
diverse hosts, including legumes, medicinal and economically important plants.
It provides protection to the tissue culture raised plantlets by overcoming the
‘ transient transplant shock’ on transfer to the field, rendering
almost 100% survival. It forms inter-and-intracellular hyphae in the root
cortex, often differentiating into dense hyphal coils, spores and vesicle-like
structures. Like AM fungi, hyphae multiply within the host cortical tissue and
never traverse through the endodermis. Likewise, they also do not invade the
aerial portion of the plant (stem and leaves). Interestingly, the host spectrum
of P. indica is very much alike AMF. P.indica colonize the root of host plant as diverse
as Zea mays L., Nicotiana
tobacum L., Petroselium
crispym L., Populus
tremula L., Setaria
italica L., Oryza
sativa L., Sorghum
vulgare, Glycine max (L.) Merr., Cicer arietinum L., Solanum melongena L., Artemissia annua L., Pisum sativum and Bacopa monniera (L.). Also like AMF, does not colonize the
members of Brassicaceae and the myc- mutants of Glycine max and Pisum sativum. It is mass multiplied on cheap simplified
medium and shows a great potential for application in agroforestry,
florihorticulture, arboriculture and viticulture and especially for better
establishment of tissue culture raised plants much needed for the application
in plant industry. This would open up numerous opportunities for the
optimization of plant productivity in both managed and natural ecosystems,
while minimizing risks of environmental damage.
The properties of fungus, have been
patented: European Patent Office, Muenchen, Germany, Patent No.
97121440.8-2105.The culture has been deposited at Braunsweich, Germany, DMS NO.
11827, 18s rDNA fragment deposited with GenBank USA, AF 014929.
The primary effect of endomycorrhiza in
most situations is to improve the phosphate uptake by the host plant, through
transport from the soil by the fungal mycelium. Phosphatases are the enzymes of
wide specificity, which cleave phosphate ester bonds and thus play an important
role in the mineralization of organic phosphate. Acid and Alkaline phosphatases
are the two forms of the phosphatases, which are active at acid and alkaline pH
respectively. These are ubiquitous in nature, occurring in a variety of fungi,
plants, and animals. In endomycorrhizal fungi, the enzymes involved in
polyphosphate synthesis and breakdown have been shown to be active in external
and internal hyphae, respectively. The alkaline phosphate (ALP) activity was
shown to increase sharply prior to mycorrhizal stimulation of the plant growth
and declined as the mycorrhizal colonization aged and phosphate accumulated
within host tissues. The enzyme activity considerably diminished in plants
growing under high P conditions. These studies suggested the involvement of ALP
in phosphate assimilation or transport in mycorrhizal roots. Acid phosphatases
(ACP) was found to be mainly involved in uptake of P by the fungal mycelium and
ALP was linked with its assimilation. The ACP activity was found in the hyphae
growing from germinating spores only while ALP activity was shown to be
inducible as the fungus had to grow inside the host to possess alkaline
phosphatases. These extracellular enzymes are thought to leave the hyphae
through the apical region, where they reach as the cargo of the secretory
vesicles. These studies indicate the role of these extracellular enzymes in the
phosphate metabolism of filamentous fungi.
The present studies highlight
the role and scope of the involvement of phosphatases in the phosphate
metabolism of P. indica specifically those involved in the transport of
phosphate from soil to the plants. Although the mechanism of transport is not
fully known, however, observations suggested that these enzymes could serve as
a physiological marker for investigating the functional state of the symbiosis.