Polyphenol oxidases in plants

Publisher Summary This chapter discusses the regulation of synthesis and transport of secreted proteins in cereal aleurone. It is one of the few digestive tissues found in plants, and the synthesis and secretion of hydrolytic enzymes by this tissue are controlled primarily by the plant hormones gibberellic acid (GA) and abscisic acid (ABA), and by the calcium ion. The aleurone cells from various cereals have the same basic structure and function and play the same role in germination-related processes. The most extensively studied aleurone enzyme is α-amylase. α-Amylase plays a role in the endosperm during germination; it is made in very large amounts in aleurone; it is easily assayed, purified, and detected on electrophoretic gels; it is very stable; and it consists of a single polypeptide chain. The mechanisms that regulate the intracellular transport and secretion of hydrolytic enzymes from the barley aleurone cell as well as the mechanisms involved in the targeting of proteins to subcellular compartments and the identity of these compartments are reviewed in the chapter.

Regulation of synthesis and transport of secreted proteins in cereal aleurone.

In agriculture, search for biopolymer derived materials are in high demand to replace the synthetic agrochemicals. In the present investigation, the efficacy of Cu-chitosan nanoparticles (NPs) to boost defense responses against Curvularia leaf spot (CLS) disease of maize and plant growth promotry activity were evaluated. Cu-chitosan NPs treated plants showed significant defense response through higher activities of antioxidant (superoxide dismutase and peroxidase) and defense enzymes (polyphenol oxidase and phenylalanine ammonia-lyase). Significant control of CLS disease of maize was recorded at 0.04 to 0.16% of Cu-chitosan NPs treatments in pot and 0.12 to 0.16% of NPs treatments in field condition. Further, NPs treatments exhibited growth promotry effect in terms of plant height, stem diameter, root length, root number and chlorophyll content in pot experiments. In field experiment, plant height, ear length, ear weight/plot, grain yield/plot and 100 grain weight were enhanced in NPs treatments. Disease control and enhancement of plant growth was further enlightened through Cu release profile of Cu-chitosan NPs. This is an important development in agriculture nanomaterial research where biodegradable Cu-chitosan NPs are better compatible with biological control as NPs “mimic” the natural elicitation of the plant defense and antioxidant system for disease protection and sustainable growth.

Cu-chitosan nanoparticle boost defense responses and plant growth in maize (Zea mays L.)

Activation of pro-phenoloxidase by the activating enzyme of the silkworm, Bombyx mori

Throughout the last decade, high pressure technology has been shown to offer great potential to the food processing and preservation industry in delivering safe and high quality products. Implementation of this new technology will be largely facilitated when a scientific basis to assess quantitatively the impact of high pressure processes on food safety and quality becomes available. Besides, quantitative data on the effects of pressure and temperature on safety and quality aspects of foods are indispensable for design and evaluation of optimal high pressure processes, i.e., processes resulting in maximal quality retention within the constraints of the required reduction of microbial load and enzyme activity. Indeed it has to be stressed that new technologies should deliver, apart from the promised quality improvement, an equivalent or preferably enhanced level of safety. The present paper will give an overview from a quantitative point of view of the combined effects of pressure and temperature on enzymes related to quality of fruits and vegetables. Complete kinetic characterization of the inactivation of the individual enzymes will be discussed, as well as the use of integrated kinetic information in process engineering.

Effects of combined pressure and temperature on enzymes related to quality of fruits and vegetables: from kinetic information to process engineering aspects.

Induction of polyphenol oxidase in germinating wheat seeds

Separate monophenolase and o-diphenolase enzymes in Triticum aestivum

Embryoless wheat (Triticum aestivum L.) half-seeds on incubation with gibberellic acid (GA3) showed a 2- to 2.5fold stimulation of monophenolase activity. The enzyme activity was not released into the incubation medium in GA3-treated half-seeds. The effect of GA3 was counteracted by the addition of abscisic acid (ABA) to the half-seeds. Adenosine-3',5'-cyclic monophosphate and its structural analogues were ineffective in increasing the monophenolase activity. Actinomycin D and cycloheximide showed no inhibitory effecton the monophenolase activity in controls as well as in GA3-treated half-seeds, but on the contrary caused a 2- to 3fold stimulation of enzyme activity similar to that observed in endosperm treated with GA3 alone. However, there was no additive or synergistic enhancement of monophenolase activity when GA3 was tested in combination with cycloheximide or actinomycin D. GA3- or cyclic AMP-treated half-seeds showed no stimulation of o-diphenolase activity.

Stimulation of polyphenol oxidase (monophenolase) activity in wheat endosperm by gibberellic acid, cycloheximide and actinomycin D.

Enzyme synthesis by conserved messengers in germinating wheat embryos

Application of GA3 and cyclic AMP to cowpea seedlings caused a 2–3 fold stimulation of RNAase activity, together with the augmentation of RNAase isoenzymes. Inhibitor studies indicated the requirement of fresh RNA and protein synthesis for enzyme stimulation.

Stimulation of ribonuclease activity and its isoenzymes in germinating seeds of cowpea (Vigna sinensis) by gibberellic acid and adenosine-3',5-cyclic monophosphate.

R.C. Sachar

Papers

Induction of polyphenol oxidase in germinating wheat seeds

Separate monophenolase and o-diphenolase enzymes in Triticum aestivum

Stimulation of polyphenol oxidase (monophenolase) activity in wheat endosperm by gibberellic acid, cycloheximide and actinomycin D.

Enzyme synthesis by conserved messengers in germinating wheat embryos

Stimulation of ribonuclease activity and its isoenzymes in germinating seeds of cowpea (Vigna sinensis) by gibberellic acid and adenosine-3',5-cyclic monophosphate.