Quote: Mike Mazur >I have been using a product containing harpin proteins that has been a >tonic for all orchids in my hobbyist's collection of 600 - 700 plants.
Harpins are derived from bacteria which attack plants, Erwinia, for example. They are the proteins which the bacteria uses to punch through the cell wall when mounting its attack. Plant cells have learned to recognise these and react quickly to their presence, which they do through what is called apoptosis, programmed cell death. Multicellular organisms have many strategies for managing invaders. Apoptosis is one of these. Cells that are infected or damaged are identified or self-identify, and this triggers a series of events which lead to cell death. Plant cells mostly keep apoptosis in house, as an unassisted suicide, so to speak. There are, however, various pervasive signals such as jasmonic acid, ethylene and, apparently, micro-RNAs which indicate the general presence of pathogens. All of these contribute to reducing the threshold at which the 'hypersensitive response' occurs, making the plant pro-active in dealing with bacterial invasion. Harpins trigger an immediate and local response, as discussed, but they are also reported to cause the affected cells to issue these more pervasive signals, preparing others in the plant to give their lives for the greater good. Whether it is a good thing to maintain a crop in such a state of nervous excitement is not really established. The harpins have been most studied in the Solanaceae - notably, tomatoes and tobacco - where there is good evidence that a pretreatment with harpins does help the plant to resist subsequent challenge with e.g. Pseudomonas. A gene (pflp) from one of these, the sweet pepper, accentuates the harpin hypersensitive response. It has been engineering into Oncidiums (and into rice, bananas, broccoli) to increase their resistance to infection. Earlier, I mentioned that soil contains an enormous number of micro-organisms, and that plants were under permanent attack from these. One person writing in response to this said that one should think of the poor human. We are an assemblage of around one hundred trillion cells. Only ten percent of these are human, and the rest are bacteria, fungi and so on that hitch a ride on us. ______________________________ Oliver Sparrow +44 (0)1628 823187 www.chforum.org _______________________________________________ the OrchidGuide Digest (OGD) [email protected] http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com
