**2.5. Chitinase**

plant species have been characterized [92, 93]. Barley cystatin in artificial diets hampered the life cycle of two aphid species and also in transgenic *Arabidopsis* [94]. Expression of such inhibitors in maize enhanced the resistance against phytophagous mites [95]. Inhibition of these proteases provides a promising control on insects and therefore PIs can be employed as

It is relatively less studied class, due to the rare occurrence [91]. Potato tubers possess cathepsin D, an aspartic proteinase inhibitor which showed substantial amino acid sequence similarity with the soybean trypsin inhibitor [96]. Aspartic proteases have been found in coleoptera species, such as *Callosobruchus maculatus* [97] and *H. hampei* [98], in which the acidic pH in

The metallo carboxypeptidase inhibitors (MCPIs) have been identified in solanaceaous plants tomato and potato [99]. The MCPIs are 38–39 amino acid residues long polypep‐ tide [100, 101]. Plants have evolved at least two families of metalloproteinase inhibitors, the metallo-carboxypeptidase inhibitor family in potato and tomato [102] and a cathepsin D inhibitor family in potato [103]. The inhibitor is produced in potato tubers and accumu‐ lates with potato inhibitor I and II families (serine proteinase inhibitors) during tuber development. The inhibitor also accumulates in potato leaf with inhibitor I and II in response to wounding and have the potential to inhibit all the major digestive enzymes (like trypsin, chymotrypsin, elastase, carboxypeptidase A and carboxypeptidase B) of higher

α-Amylases (α-1,4-glucan-4-glucanohydrolases) are hydrolytic enzymes, which catalyze the hydrolysis of α-1,4-glycosydic bonds in polysaccharides. They are present in microorganisms, animals and plants [105–107]. They are the most important digestive enzymes of many insects which feed exclusively on seed products. Inhibition of α-amylase impairs the digestion in an organism and causes shortage of free sugar for energy. α-Amylase inhibitors (α-AI) are found in many plants as a part of the defense system and abundant in cereals and legumes [108–111].

α-AI of *Phaseolus vulgaris* is the most studied amylase inhibitor and have shown toxic effects to several insect pests [110, 111]. Like lectins, they possess carbohydrate-binding property. There are at least four types of *Phaseolus* amylase inhibitors on the basis of α-AIs: AI-1, AI-2, AI-3 and the null type [112]. AI-1 is present in the most cultivated common bean varieties and inhibits mammalian α-amylases. It also inhibits α-amylases in insects like *C. chinensis, C. maculatus* and *B. pisorum* [106]. AI-2 is 78% homologous to AI-1 and found in few wild accessions. It inhibits the *Z. subfasciatus* larval α-amylase and pea bruchid α-amylase [106, 111, 113]. This inhibitor is a good example of co-evolution of insect digestive enzymes and plant

a potential source of defense in plants against insect pests.

344 Abiotic and Biotic Stress in Plants - Recent Advances and Future Perspectives

midgut provides a favourable condition for these proteases [58].

*2.3.3. Aspartyl protease inhibitors*

*2.3.4. Metallo-proteases inhibitors*

animals and many insects [104].

**2.4. α-Amylase inhibitors**

defense proteins.

Chitinases are being employed in plant defense in many ways. It has been used in controlling the growth of fungi and insects. Expression of poplar chitinase in tomato leads to growth inhibition in Colorado potato beetle [117]. Secretome analysis of tobacco cell suspension represents chitinase as the major defense protein [118]. A chitinase-like domain containing 56 kDa defense protein (MLX56) provides strong resistance against cabbage armyworm*, Mames‐ tra brassicae*, and Eri silkworm*, Samia ricini* [119]. Two chitinase like proteins LA-a and LA-b (latex abundant) from Mulberry (*Morus* sp.) latex are found to be toxic against *Drosophila melanogaster* [120].

Chitinases have also been isolated from insects and found to be equally promising in plant defense. Transgenic tobacco plants expressing chitinase of tobacco hornworm (*Manduca sexta*) shows resistance to tobacco budworm *Heliothis virescens* [121]. Hornworm chitinase expressing transgenic plants are also resistant against fungal infection [122]. Further, a recombinant baculovirus expressing chitinase of hard tick (*Haemaphysalias longicornis*) has been shown as bio-acaricide for tick control [123].
