Question:

  Thanks for describing cell-cell transport..:)) The analogy stands. Ever     wonder what causes your heart to beat? Yup. Fresh air. Seriously: vessels such as those supplying the heart are highly contractile, reducing their cross section by a factor of four or so under the influence of vasoconstrictive hormones. Transient events can cause waves of clamping, reducing circulation, causing pain and worse. Plant vessles just don’t have the plumbing: they are rigid tubes, designed to withstand great pressure. You can hear them collapsing with a stethoscope placed on the stem of a maize plant when the weather is very dry: click, click, pop.   Ok..But would you expect this to happen only partially as well as     cyclically? I would think the phenomenon would affect the plant as a   whole, not as one or two spots on a leaf which appear and disappear on a   daily basis. -Rod- A simple reply is that the antidote to senescence is twofold: folic acid – closely associated with photosynthesis – and feeding the roots, also the results of photosynthesis having provided food. A more complex answer is summed up in a word: dunno. I dunno; but t’ain’t heart disease.     Oliver Sparrow

Response:

o oOrchids" writes:  

o Thanks for describing cell-cell transport..:)) The analogy stands. o Ever   wonder what causes your heart to beat? o oYup. Fresh air. Seriously: vessels such as those supplying the heart oare highly contractile, reducing their cross section by a factor of ofour or so under the influence of vasoconstrictive hormones. Transient oevents can cause waves of clamping, reducing circulation, causing pain oand worse. Plant vessles just don’t have the plumbing: they are rigid otubes, designed to  withstand great pressure. You can hear them ocollapsing with a stethoscope  placed on the stem of a maize plant owhen the weather is very dry: click,  click, pop. True enough, but there there’s the temperature gradient from night to day..I suppose it’s possible that the expansion and contraction could should up as an Iscemic event..I don’t know..just letting my mind play.. o Ok..But would you expect this to happen only partially as well as   o cyclically? I would think the phenomenon would affect the plant as o a  whole, not as one or two spots on a leaf which appear and o disappear on a  daily basis. -Rod- o oA simple reply is that the antidote to senescence is twofold: folic oacid –  closely associated with photosynthesis – and feeding the oroots, also the  results of photosynthesis having provided food. A omore complex answer is  summed up in a word: dunno. I dunno; but ot’ain’t heart disease.     I Dunno either..remember I presented this only as a thought..:) -Rod- Rod & Susan Venger, Venger’s Orchids Homepage address http://www.usa.net/venger/ Listings Available – Email us for your copies The September Special is now available Order Line: 1-800-483-6437 —

Response:

Ischemia sishceamia. Plants transport water and nutrients entirely by osmotic potential. Upward water transport occurs when cells become less hydrated that the vessel that supplies them: they suck up water across the dividing membrane by exactly the same mechanism as sugar sucks water out of a slice of melon. The vessels feel suction and transmit this along their length. Roots, at the other end, become able to pull water in across membranes from the soil or whatever surrounds them: lo! Flow! And flow at about 1 metre per second in a wheat plant in the sun: it fair whizzes about. Sugars get moved about in much the same way. A cell – one of, say, an expanding pod – beings to take up sugars from the vessels which handle this kind of transport. The cell has a stronger concentration of sugar than the vessel, so water moves in from the vessel. Pressure transmits itself along, and so water and sugars start moving toward the growing pod. (This is why young leaves of plants like clover have drops of water hangig off their tips – they are dumping surplus water that they cannot evaporate.) The vessels are themselves rigid structures which have to withstand huge pressures: there can be a 50 atmosphere difference across a leaf cell-water vessel membrane. Ischaemia occurs when a vessel either contracts (due to hormonal influences) or is occluded. Occlusion is permanent in plant vessels are there is no clearance mechanism: it is how dutch elm disease kills elm trees. Transient contraction is impossible, as the architecture is not there. Damn. A lecture. However, a suggestion. Plants secrete hormones (cytokines) from their roots which then permeate the rest of the plant. Their presence prevents the plant tissue from moving into what appears to be its natural state, which is a condition known as senecence. When these hormones are cut off – when, for example, the stem is cut, the roots are starved or under fungal attack – then the hormones are no longer released. Senecence begins: a mass of enzymes are produced in the cell which break down anything mobile into a soup and make it available for transport. Trees which go yellow in Autumn are undergoing exactly this process of planned shut down. Wheat and maize plants turn on such ferociously hungry seeds that they literally starve the roots until the cease to produce the required hormones, precipitating a mass breakdown of material which gets shifted into the seed before the plant dies. In the order of 45% of the weight of a maize plant can end up in the seed. It may well be that orchids which have unhappy roots undergo a similar problem, with intermittant senescence when the probelm is similarly intermittant. Certainly, Paphs which have a poor root medium suffer just such a syndrome: no growth, yellowing leaves, sulks and senility.   Oliver Sparrow

Response:

j jFor the past few weeks the translucent spots only appear on the Phrag. jbesseae. They start to show just before the sunset, and the spots jexpand  overnight. Spots start to shrink in the morning and by 10 or j11am they are  all gone. They start to come back at 6 or 7pm. j jIt has nothing to do with heat. There’s no heat wave in the past two jweeks. It doesn’t matter if I fertilize or not. It doesn’t matter if I jexpose the plant to full morning sun or not. There’s no pest as far as jI  can tell. Some area have turned brownish but others haven’t. Some jsuggested that Phrag. besseae is very sensitive to water quality. I jtried  with filtered water, but it didn’t make any difference. j jAny help will be appreciated. I have a theory, Japheth, but a few questions: Does the area change in texture? Does the area get thinner in relation to the surrounding tissue? -Rod-

Well, because the area allows more light to get through, and the area looks paler comparing to "normal" tisuue, you can say that the texture changes, and the area does get thinner.

Response:

Japheth, j I have a theory, Japheth, but a few questions: Does the area change j in  texture? Does the area get thinner in relation to the j surrounding  tissue? -Rod- j jWell, because the area allows more light to get through, and the area jlooks paler comparing to "normal" tisuue, you can say that the texture jchanges, and the area does get thinner. Good enough. I can’t say for sure, and probably couldn’t explain to everyone’s satisfaction unless they have a detailed knowledge of human physiology, but it really sounds like "transient ischemia", only on a scale appropriate to Orchids. They do have a rudimentary circulatory system, via cell-to-cell transport of fluids and nutrients. Were part of the system to be "faulty", fluids may be draining but not replaced, resulting in thinning of the tissues. (Ischemia in a human is reduced blood supply to any tissue, resulting in oxygen deprivation, pain, some tissue damage…you may see the analogy) As to why this is happening on a daily basis, and on schedule, is more speculation. Perhaps a metabolic problem due to a genetic defect or something to do with nutrition…To carry the analogy a bit further, in a human heart, ischemia results from narrowing or spasms in the coronary arteries..a step further, the arteries block and myocardial tissue dies..a heart attack. On your leaves, the brown spots may well represent dead tissue caused by complete breakdown of fluid transport within the cells in certain areas. Bear in mind it’s only a theory, and I apologize if I’ve left more people scratching their head than not.:)) -Rod- Rod & Susan Venger, Venger’s Orchids Homepage address http://www.usa.net/venger/ Listings Available – Email us for your copies The September Special is now available Order Line: 1-800-483-6437 —

Response:

Translucent spotting on leaves is the classic first symptom of bacterial leaf spot diseases and a few fungal diseases as well.   Since it doesn’t progress from day to day, it is most likely a pathogen of something other than orchids.  Do you have any other types of plants that have spots (brown or black) where this could be coming from?  

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I received the following e-mail message from Rod. He said he posted it on the Internet, but for some reason I cannot find his posting. Just in case if you don’t see the posting either. Here’s what Rod thinks, (Thanks, Rod!) it makes sense because metabolism does slow down when it gets darker. I learned from personal communication that other people also have the same experience on Phrag. besseae. Is it common to Phrag besseae? Is it a genetic defect on all besseae, or just on some strain of besseae? If anyone out there has Phrag. bessae, could you tell us if you observe the same problem on your plants? I just had to find out if the article was still there, so I grabbed and enclosed it below. A biochemist I talked disagrees with me and thinks it’s a bacteria not normally found on Orchids, so the effect isn’t as bad as it might be. I don’t know. Anyhow, one POSSIBILITY is below. j I have a theory, Japheth, but a few questions: Does the area change j in  texture? Does the area get thinner in relation to the j surrounding  tissue? -Rod- j jWell, because the area allows more light to get through, and the area jlooks paler comparing to "normal" tisuue, you can say that the texture jchanges, and the area does get thinner. Good enough. I can’t say for sure, and probably couldn’t explain to everyone’s satisfaction unless they have a detailed knowledge of human physiology, but it really sounds like "transient ischemia", only on a scale appropriate to Orchids. They do have a rudimentary circulatory system, via cell-to-cell transport of fluids and nutrients. Were part of the system to be "faulty", fluids may be draining but not replaced, resulting in thinning of the tissues. (Ischemia in a human is reduced blood supply to any tissue, resulting in oxygen deprivation, pain, some tissue damage…you may see the analogy) As to why this is happening on a daily basis, and on schedule, is more speculation. Perhaps a metabolic problem due to a genetic defect or something to do with nutrition…To carry the analogy a bit further, in a human heart, ischemia results from narrowing or spasms in the coronary arteries..a step further, the arteries block and myocardial tissue dies..a heart attack. On your leaves, the brown spots may well represent dead tissue caused by complete breakdown of fluid transport within the cells in certain areas. Bear in mind it’s only a theory, and I apologize if I’ve left more people scratching their head than not.:)) -Rod- Rod & Susan Venger, Venger’s Orchids Homepage address http://www.usa.net/venger/ Listings Available – Email us for your copies The September Special is now available Order Line: 1-800-483-6437

Response:

Expanding and contracting spots is a new one on me! What follows should be taken with a large pinch of salt (or Physan  ) as it is plainly impossible to say anything firm from such limited information as can be packed into ASCII. One needs to see, to touch, to smell. This said, there is, however, a very nasty bacterial disease (Erwinia) which attacks Phalaenopsis (and also Chrysanthemums, its chief target.) This shows up as an area of translucence which spreads very rapidly: a dot to a square inch in one day, the whole leaf in a second, the whole plant (or all but the very mature parts of it) in the third. P. amabilis, sanderana, x intermedia and aphrodite seem particularly vulnerable to this plague. It also strikes Coelogynes – where an entire rhizome can be turned into a brown shell around a liquid core in a day or two – and, to a lesser extent, young Paphs and Cory. Paphs. I do not know anything about Phrags, so I cannot comment. Diagnostics are: exceptionally rapid onset, "liquidisation" of the effected tissue, streaks of liquidisation running up the leaf from the infection site, small white encrusted areas under the leaf where the infection began. Fungal attacks which lead to local rotting are nothing like this: it gallops and spreads everywhere, irrespective of external dampness, contact with the medium etcetera. It is particularly rampant when temperatures are high. It appears to be spread almost entirely by insect bites, notably by fruit-fancying mosquito species which actively promote the spread of rot so as to be able to feed on the resulting liquid goop. If you have an orchard in which plums are currently rotting…. The only treatment that seems to work lies in eliminating the infection and the vector. Getting rid of the mosquitoes are the easy bit. I hesitate to recommend the excision of leaves when it is far from clear that this is the source of your problem, but where Erwinia is the case, the best that one can achieve is a swift amputation; and hope. A weak solution of the antibiotic Erythromycin applied topically and to the exposed roots stops the infection in Phalaenopsis species, however, but as this has not been tested for its effects on plants – let alone, on orchids – caution is recommended.   Oliver Sparrow

Response:

j jFor the past few weeks the translucent spots only appear on the Phrag. jbesseae. They start to show just before the sunset, and the spots jexpand  overnight. Spots start to shrink in the morning and by 10 or j11am they are  all gone. They start to come back at 6 or 7pm. j jIt has nothing to do with heat. There’s no heat wave in the past two jweeks. It doesn’t matter if I fertilize or not. It doesn’t matter if I jexpose the plant to full morning sun or not. There’s no pest as far as jI  can tell. Some area have turned brownish but others haven’t. Some jsuggested that Phrag. besseae is very sensitive to water quality. I jtried  with filtered water, but it didn’t make any difference. j jAny help will be appreciated. I have a theory, Japheth, but a few questions: Does the area change in texture? Does the area get thinner in relation to the surrounding tissue? -Rod- Rod & Susan Venger, Venger’s Orchids Homepage address http://www.usa.net/venger/ Listings Available – Email us for your copies The September Special is now available Order Line: 1-800-483-6437 —

Response:

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