Page 11 - gabVol3No2

Genomics and Applied Biology, 2012, Vol.3 No.2 8-21
http://gab.sophiapublisher.com
trypsin inhibitor inhibited the spore germination of
fungal pathogen Sclerotinia sclerotiorum. However,
proteinase inhibitors induced in response to infection
differed from inhibitors present in healthy plant
(Geoffroy et al., 1990). Such induction in response to
infection by pathogenic microorganisms is not limited
to serine proteinase inhibitors, synthesis of cystatin
like inhibitor was observed in chestnut leaves
inresponse B. cinerea infection (Pernas et al., 2000).
Kim et al (2005) purified potamin-1 (PT-1), a 5.6 kDa
trypsin–chymotrypsin protease inhibitorfrom the
tubers of the potato (Solanum tuberosum). PT-1
strongly inhibited pathogenic microbial strains,
including Candida albicans, Rhizoctonia solani, and
Clavibacter michiganense subsp. Michiganinse. This
protease inhibitor, PT-1, was composed of polypeptide
chains joined by disulfide bridge(s). Reduced PT-1
almost completely lost its activity against fungi and
proteases indicating that disulfide bridge is essential
for its protease inhibitory and antifungal activity.
Wang et al (2006) purified 10 kDa proteinase inhibitor
from mung bean (Phaseolus mungo) seeds. It exerted
a potent inhibitory action toward a variety of fungal
species including Physalospora piricola,
Mycosphaerella arachidicola, Botrytis cinerea,
Pythium aphanidermatum, Sclerotium rolfsii and
Fusarium oxysporum, as well as an antibacterial
action against Staphylococcus aureus. Our own study
showed that ChTI exhibited strain specificity and
inhibited growth and development of plant fungal
pathogens. Bioassay studies on yeast strains indicated
that ΔYNK and MNN1 are more sensitive to ChTI.
The results suggest that phosphodiester linkage in cell
wall components is likely to be the key determinants
for binding of ChTI (Figure 4). It had no effect on
bacteria (Bhattacharjee et al., 2009). Shilpa and
Murugan (2010) purified a 14.3 kD proteinase
inhibitor from Coccinia grandis. PI strongly inhibited
pathogenic microbial strains, including Staphylococcus
aureus, Klebsiella pneumoniae, Proteus vulgaris ,
Eschershia coli, Bacillus subtilis and pathogenic fungus
Candida albicans, Mucor indicus, Penicillium notatum ,
Aspergillus flavus and Cryptococcus neoformans.
Examination by bright field microscopy showed
inhibition of mycelial growth and sporulation.
Morphologically, PI treated fungus showed a significant
shrinkage of hyphal tips. Reduced PI completely lost its
activity indicating that disulfide bridge is essential for its
protease inhibitory and antifungal activity.
Figure 4 Antifungal assay using fungal isolates
Note: Zone inhibition assay of ChTI against Phytopathogens;
A: Alternaria alternate; B: Aspergillus flavus; C:
Colletotrichumcapsici; D: Fusarium oxysporum; E: Fusarium
solani ( crossandra isolated); F: Fusariumsolani (chick pea
isolated); G: Rhizoctonia oryzea; H: Sclerotia sp.
4.3 Proteinase inhibitors in regulation of
programmed cell death (PCD)
The compounds that were effective in controlling
PCD in soybean- leupeptin, PMSF and AEBSF have
inhibitory activity against proteases- leupeptin is an
established inhibitor of cysteine proteases, whereas
PMSF and AEBSF are inhibitors of serine proteases
(Alonso et al., 1996). In plants, proteinase inhibitors
are subject of regulation by intercellular signaling
molecules, such as jasmonic acid (Farmer et al., 1992),
salicylic acid (Doares et al., 1995) and systemin
(Constabel et al., 1995). Salicylic acid was found to
suppress the expression of cystatin (Doares et al.,
1995). Salicylic acid also was shown to promote cell
death induced by direct oxidative stress or pathogen
attack leading to the possibility-(1) increased
generation of H2O2 and (2) repressed cystatin
expression (Shirasu et al., 1997). Controls of cellular
fate through regulated expression of specific proteases
in combination with the associated protease inhibitor
genes provide additional plasticity to responses from
outside stimuli. Plant cysteine proteases seem to play an
important role in preventing PCD triggered by
oxidative stress, wounding caused by insect chewing or
during chilling-induced oxidative stress (Prasad et al.,
1994; Solomon et al., 1999).
4.4 Proteinase inhibitors in health and disease
control-medical and industrial aspects
Proteolytic enzymes are involved in numerous
physiological processes in humans including digestion
of food, tissue remodeling, host defense, blood
coagulation and activation of proenzymes and
prohormones. Proteinase inhibitors also play an
- 15 -