Serpin protease inhibitors in plant biology

Protease inhibitors of the serpin family are ubiquitous in the plant kingdom but relatively little is known about their biological functions in comparison with their counterparts in animals. X-ray crystal structures have provided crucial insights into animal serpin functions. The recently solved structure of AtSerpin1 from Arabidopsis thaliana, which has the highly conserved reactive center P2-P1' Leu-Arg-Xaa (Xaa = small residue), displays both conserved and plant-specific serpin features. Sequence homology suggests that AtSerpin1 belongs to serpin Clade B, composed of intracellular mammalian serpins, which is consistent with the lack of strong evidence for secretion of serpins from plant cells. The major in vivo target protease for AtSerpin1 is the papain-like cysteine RD21 protease, a match reminiscent of the inhibition of cathepsins K, L and S by the Clade-B mammalian serpin, SCCA-1 (SERPINB3). The function of AtSerpin1 and other serpins that contain P2-P1' Leu-Arg-Xaa (the 'LR' serpins) in plants remains unknown. However, based on its homology and interactive partners, AtSerpin1 and perhaps other serpins are likely to be involved in regulating programmed cell death or associated processes such as senescence. Abundant accumulation of serpins in seeds and their presence in phloem sap suggest additional functions in plant defense by irreversible inhibition of digestive proteases from pests or pathogens. Here we review the most recent findings in plant serpin biology, focusing on advances in describing the structure and inhibitory specificity of the LR serpins.     

Sulphhydryl protease inhibitors from pineapple plant stem

• 1.1. Pineapple stem extract, consisting of a mixture of the protease bromelain and sulphhydryl protease inhibitors, was fractionated by gel permeation chromatography.
• 2.2. Inhibitor-containing fractions were further resolved by ion exchange chromatography on DEAE-cellulose, giving 12 chromatographically distinct inhibitory fractions.
• 3.3. These 12 inhibitory fractions all show an inhibition specificity towards bromelain.
• 4.4. Reduction, S-carboxymethylation and refractionation of each of these inhibitory fractions gave, for each fraction, two separated peptides of ca 13 and 40 amino acids in length, respectively.
• 5.5. The amino acid compositions and the N-terminal sequences of these peptides show the inhibitors to be a closely homologous set. Both the constituent peptides of each fraction are microheterogeneous. Each DEAE-cellulose chromatogram peak contains a co-eluting set of iso-inhibitors.
• 6.6. Structural microvariations within these isoinhibitors have a minor influence on inhibitor activity towards bromelain.

     

Potential physiological role of plant glycosidase inhibitors

Carbohydrate-active enzymes including glycosidases, transglycosidases, glycosyltransferases, polysaccharide lyases and carbohydrate esterases are responsible for the enzymatic processing of carbohydrates in plants. A number of carbohydrate-active enzymes are produced by microbial pathogens and insects responsible of severe crop losses. Plants have evolved proteinaceous inhibitors to modulate the activity of several of these enzymes. The continuing discovery of new inhibitors indicates that this research area is still unexplored and may lead to new exciting developments. To date, the role of the inhibitors is not completely understood. Here we review recent results obtained on the best characterised inhibitors, pointing to their possible biological role in vivo. Results recently obtained with plant transformation technology indicate that this class of inhibitors has potential biotechnological applications.     

Proteinase inhibitors in plant biotechnology: A review

Possible utilities for natural inhibitors of proteolytic enzymes in plant biotechnology have been reviewed. Among the potential areas of use of the inhibitors are (1) construction of transgenic plants with increased resistance to insects and other pests and (2) development of procedures for biosynthesis of recombinant proteins. In the latter case, the inhibitors will serve to prevent the protein degradation by proteinases.     

Proteinase inhibitors in plant biotechnology: a review

Possible utilities for natural inhibitors of proteolytic enzymes in plant biotechnology have been reviewed. Among the potential areas of use of the inhibitors are (1) construction of transgenic plants with increased resistance to insects and other pests and (2) development of procedures for biosynthesis of recombinant proteins. In the latter case, the inhibitors will serve to prevent the protein degradation by proteinases.     

The adaptation of insects to plant protease inhibitors

Plants and herbivores have been co-evolving for thousands of years, and as a result, plants have defence mechanisms that offer protection against many herbivores such as nematodes, insects, birds and mammals. Only when a herbivore has managed to adapt to these defence mechanisms does it have the potential to become a pest. One such method of plant defence involves the production of protease inhibitors (PIs). These inhibitors are proteins that may be found constitutively in various parts of the plant, or may be induced in response to herbivore attack. PIs work at the gut level, by inhibiting the digestion of plant protein. This review focuses on insect herbivores and looks at the mechanisms involved in the role and function of PIs in plant defense against insects, as well as at the ability of well adapted species to overcome the effects of these plant PIs.     

Iridoids of garrya elliptica as plant growth inhibitors

Extracts from catkins of Garrya elliptica inhibit the growth of wheat embryos. The components responsible for this activity have been identified as the iridoids geniposide and geniposidic acid together with their aglucones.     

Gibberellin synthesis inhibitors affect electron transport in plant mitochondria

NADH oxidation and cytochrome c reduction rates in the electrontransport chain were determined for mitochondria isolated from leaves of matureEuropean black alder (Alnus glutinosa L.) and exposed to arange of concentrations of the growth retardants flurprimidol andpaclobutrazol.NADH oxidation and cytochrome c reduction were enhanced by low concentrationsofboth compounds whereas higher concentrations reduced electron transport. Thisisthe first report of gibberellin synthesis inhibitors affecting electrontransport in plant mitochondria and provides evidence for another potentialmodeof action of this type of growth retardant.     

Distribution of podolactone-type plant growth inhibitors in the coniferae

Plant growth inhibitors of the podolactone-type have been detected by bioassay in ten further species of Podocarpus. The most active extracts in P. elatus were from root tips, root cortex and very young leaves. Fifty-seven other conifers were examined for this type of activity. It is present in Cephalotaxus harringtonia where it is probably due to the presence of harringtonolide, which, like momilactone B from rice husks, shows podolactone-type inhibition of the growth of etiolated dwarf pea hooks.     

Quassinoids from Eurycoma longifolia as plant growth inhibitors.

Seven quassinoids including a new 12-epi-11-dehydroklaineanone were isolated from the leaves of Eurycoma longifolia (Simaroubaceae) as plant growth inhibitors or related compounds. The strongest activity was found in 14,15beta-dihydroxyklaineanone.     

Lichen acids,plant growth inhibitors from Usnea longissima

Eight components, depsides and orcinol derivatives which exhibit growth-inhibitory activity agai.     

The effects of spermidine synthesis inhibitors on in-vitro plant development

The spermidine synthesis inhibitors methylglyoxal bis-(guanylhydrazone) (MGBG) and dicyclohexylammonium sulfate (DCHA) were found to reduce growth and embryogenesis in wild carrot cultures. Cellular polyamine levels were also affected by the inhibitors, with spermidine levels being especially reduced by DCHA. Similarly, MGBG reduced organogenetic development of shoots on excised aspen hypocotyls. These data suggest that the polyamines, especially spermidine, play an important role in the growth and development of plants.     

Schiffs bases and derived secondary amines as plant growth inhibitors

Seventy-two Schiffs bases, 44 corresponding secondary amines, and 12 N-acetylated compounds were tested on their growth activity. Eighty-one compounds were active as growth inhibitors in at least one of three bioassays.     

Broomrape (Orobanche) seed germination inhibitors from plant roots

Two species (tomato and cucumber) which are not hosts to Orobanche crenata but which are hosts to other species of Orobanche not only failed to produce the compound required to trigger O. crenata to germinate but produced germination inhibitors which stopped germination even in the presence of a suitable stimulant. This suggested the possibility of using germination inhibitors to control at least some species of Orobanche. The question whether host species produce inhibitors as well as stimulants has not however been resolved.     

Schiffs bases and derived secondary amines as plant growth inhibitors

Seventy-two Schiffs bases, 44 corresponding secondary amines, and 12 N-acetylated compounds were tested on their growth activity. Eighty-one compounds were active as growth inhibitors in at least one of three bioassays.