Proteinase inhibitor-inducing factor

Trypsin inhibitors in cucumber were first found in a study by Walker-Simmons et /. " after wounding of leaves and treatment with proteinase inhibitor-inducing factor (PIIF). The amino acid sequence of two inhibitors isolated from Cucurhita maxima (winter squash) were determined by Wilusz et at The peptides named ITD I and ITD 111 each comprised a 29-residue sequence with six cysteine residues. The only difference between the two peptides is in position 9, which is lysine in ITD I and glutamic acid in ITD III. The reactive site is located at the peptide bond between Arg5 and Ile6. Owing to their discovery and distribution in Cucurbitaceae the inhibitor family has been named squash inhibitors. Since the initial discoveries many other members of the squash family have been found. 

Two proteinase inhibitors, Inhibitors I and II, accumulate in leaves of tomato plants when attacked by chewing Insects or mechanically wounded. The accumulation of these two antinutrient proteins is apparently a defense response and is initiated by the release of a putative wound hormone called the proteinase Inhibitor inducing factor (PIIF). The direction of flow of PIIF out of wounded leaves is primarily towards the apex and transport occurs maximally about 120 min following wounding. After a single severe wound, the vitro translatable tomato leaf mRNA specific for Inhibitors I and II Increases to a maximum within four hours and remains constant for about five hours when it decreases rapidly to about 50% of the maximum. 

Proteinase Inhibitor Inducing Factor Activity in Tomato Leaves Residues in Oligosaccharides Enzymatically Released From Cell Walls. Proceedings National Academy of Science DSA 78, 3536-... 

Bishop P D, Makus D J, Pearce G, Ryan C A 1981 Proteinase inhibitor-inducing factor activity in tomato leaves resides in oligosaccharides enzymically released from cell walls. Proc Nat Acad Sci 78 3536-3540... 

Ryan CA. The search for the proteinase inhibitor-inducing factor. Plant Mol Biol 1992 19 123-133. 

The wound-induced synthesis and accumulation of proteinase Inhibitors I and II in tomato leaves has provided a model system to study the regulation of proteinase inhibitor genes in plants. The simplicity of the phenomenon has made it possible to Isolate the wound-factor, or hormone, and to study its release, direction and rate of transport in tomato plants. Messenger RNA has been isolated from leaves of wounded plants and contains translatable mRNAs for the two proteinase inhibitors. Studies with these mRNAs have provided a basis for the initiation of a program to clone inhibitor cDNAs for studies of the molecular basis of the wound-Induced process of inhibitor synthesis. 

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