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Excretory System in plants
This is a simple question from a non-science student. For lanog, I have
wondered how plants get rid of wastes. As far as I know, plants get rid of unwanted water by transpiration. What happens to all the unwanted solids ? In other words, where is the excretory system of plants ? |
Internal waste dumps.
PvR schreef This is a simple question from a non-science student. For a long time, I have wondered how plants get rid of wastes. As far as I know, plants get rid of unwanted water by transpiration. What happens to all the unwanted solids? In other words, where is the excretory system of plants ? |
Plants do not really produce any solid, organic wastes. The main waste
product of photosynthetic plants in the light is oxygen gas, which escapes mainly through leaf stomata (tiny pores in the leaf surface). Water is not really a waste product, it just evaporates from leaves as a consequence of keeping stomata open to admit carbon dioxide gas required for photosynthesis. Photosynthetic plants make all their organic compounds from carbon dioxide gas, water and mineral nutrients absorbed mainly from the soil solution. Photosynthetic plants are autotrophs so differ markedly from animals, which are all heterotrophs. Heterotrophs gets their organic compounds by consuming other organisms. Heterotrophs have to digest the other organisms and usually produce some solid waste as a byproduct. Plants produce a wide variety of organic molecules that do not seem to play a direct role in their growth and development, such as caffeine, nicotine, latex, anthocyanins, etc. They are termed secondary compounds, secondary metabolites or secondary products and are believed to function mainly in defense against herbivores (animals that eat plants) or disease organisms. A few secondary compounds are pigments that color flowers and attract animal pollinators or color fruits and attract animals that disperse seeds. Red anthocyanin pigments can also act as "sunscreen" to protect leaves from radiation. The plant cell vacuole is sometimes considered the "trashcan" of the cell, and the secondary compounds and inorganic compounds that accumulate in vacuoles are considered waste. Heartwood, consisting of xylem that no longer functions in water transport, also accumulates secondary compounds that are sometimes considered waste. Those views seem obsolete given the defensive function of secondary compounds. David R. Hershey References The Secondary Metabolism of Plants: Secondary Defence Compounds http://www.biologie.uni-hamburg.de/b-online/e20/20.htm Plant Secondary Compounds http://www.nslc.wustl.edu/courses/Bi.../secondary.pdf Why Turn Red? The autumn leaf is toast, but it still redecorates http://www.sciencenews.org/articles/20021026/bob8.asp Vacuole (plants) http://www.kcl.ac.uk/kis/schools/lif...l/vacuole.html |
In article ,
Phred wrote: ISTR talk of some plants actually excreting excess salt (NaCl) as one method of tolerating saline conditions. Also, don't some plants actively excrete excess water in the process known as "gutation"? IIRC, some plants adapted to the seaside do excrete salt, or actually salty water this way. Others can store salt in cell vacuoles. Many plants will guttate pure water under appropriate conditions: wet soil and high humidity. Recently a genetic engineering project at U of Toronto and UC Davis produced salinity-resistant tomato plants that had a store-salt-in-vacuoles method from hm, could it be Arabidopsis? Maybe not. At any rate, with so much arable land losing its productivity from salinity increase due to irrigation, crop plants modified like this can be very useful. Also the possibility of irrigation or hydroponics with partly desalinated seawater is promising for some coastal arid regions. AFAIK, this is a fairly hot topic in crop research. |
In message , Phred
writes ISTR talk of some plants actually excreting excess salt (NaCl) as one method of tolerating saline conditions. Some mallows are glyphosate-resistant. Reading between the lines this is a side-effect of salt-excretion. -- Stewart Robert Hinsley |
wrote in message . .. In article , Phred wrote: ISTR talk of some plants actually excreting excess salt (NaCl) as one method of tolerating saline conditions. Also, don't some plants actively excrete excess water in the process known as "gutation"? IIRC, some plants adapted to the seaside do excrete salt, or actually salty water this way. Others can store salt in cell vacuoles. Many plants will guttate pure water under appropriate conditions: wet soil and high humidity. Recently a genetic engineering project at U of Toronto and UC Davis produced salinity-resistant tomato plants that had a store-salt-in-vacuoles method from hm, could it be Arabidopsis? Maybe not. At any rate, with so much arable land losing its productivity from salinity increase due to irrigation, crop plants modified like this can be very useful. Also the possibility of irrigation or hydroponics with partly desalinated seawater is promising for some coastal arid regions. AFAIK, this is a fairly hot topic in crop research. And what about the idea for a genetically modified floating seaweed - like the notorious Water Hyacinth - to float on the surface of the world's oceans producing some sort of edible or industrial oil which is easily cropped my mechanical harvesters. No fertilizers or soils needed. Surely some one is working on this idea. |
In article ,
Peter Jason wrote: And what about the idea for a genetically modified floating seaweed - like the notorious Water Hyacinth - to float on the surface of the world's oceans producing some sort of edible or industrial oil which is easily cropped my mechanical harvesters. No fertilizers or soils needed. Surely some one is working on this idea. Interesting notion. One problem with it is that to get a vascular plant to cope with that much salinity would be quite a challenge. Another is that the main limit to growth in marine ecosystems is basic nutrients like nitrogen and phosphorus, which are at an extremely low level -- they are rapidly taken up and incorporated into biomass. On the other hand, floating and emersed aquatic plants are extremely productive in fresh waters, where plant growth is limited by dissolved CO2 and by available light since the water isn't often clear to much depth. By having surfaces exposed to the air, these plants get around these limitations, and in the presence of plenty of nutrients grow explosively. They are excellent for removing nutrients from polluted waters, and there are already installations where artificial wetlands are used to purify water from livestock operations, sewage plants and storm sewer outflow. Another important application of this practice is in fish farming, which can generate huge amounts of pollution. By partly closing the system, this can be greatly reduced, and if the fish are herbivores, like tilapia and carp, the floating plants can be fed back to them. This is particularly valuable in arid or heavily populated regions. Duckweed (Lemna spp) is very high in good quality protein and is already being used in aquaculture and wastewater treatment to produce a protein feed supplement for fish, poultry and pigs. Here's a URL with links: http://ecosyn.us/ecocity/Links/My_Li...ckweed_01.html People are already considering the use of duckweed for "molecular farming", in which genetically engineered plants produce pharmaceuticals, much as genetically engineered bacteria have for decades. I have strong reservations about these practices because of the risk of contaminating the gene pool of crop and fodder plants with genes for toxic substances. Once they escape, you'll never get them back, and they could have disastrous consequences for the food supply. |
Actually there are a few species of flowering plants that are adapted to
growing in salt water and they are monocots too. They are commonly called "Seagrass". Check it out. They are not in the family Pontederiaceae though. wrote in message . .. In article , Peter Jason wrote: And what about the idea for a genetically modified floating seaweed - like the notorious Water Hyacinth - to float on the surface of the world's oceans producing some sort of edible or industrial oil which is easily cropped my mechanical harvesters. No fertilizers or soils needed. Surely some one is working on this idea. Interesting notion. One problem with it is that to get a vascular plant to cope with that much salinity would be quite a challenge. Another is that the main limit to growth in marine ecosystems is basic nutrients like nitrogen and phosphorus, which are at an extremely low level -- they are rapidly taken up and incorporated into biomass. On the other hand, floating and emersed aquatic plants are extremely productive in fresh waters, where plant growth is limited by dissolved CO2 and by available light since the water isn't often clear to much depth. By having surfaces exposed to the air, these plants get around these limitations, and in the presence of plenty of nutrients grow explosively. They are excellent for removing nutrients from polluted waters, and there are already installations where artificial wetlands are used to purify water from livestock operations, sewage plants and storm sewer outflow. Another important application of this practice is in fish farming, which can generate huge amounts of pollution. By partly closing the system, this can be greatly reduced, and if the fish are herbivores, like tilapia and carp, the floating plants can be fed back to them. This is particularly valuable in arid or heavily populated regions. Duckweed (Lemna spp) is very high in good quality protein and is already being used in aquaculture and wastewater treatment to produce a protein feed supplement for fish, poultry and pigs. Here's a URL with links: http://ecosyn.us/ecocity/Links/My_Li...ckweed_01.html People are already considering the use of duckweed for "molecular farming", in which genetically engineered plants produce pharmaceuticals, much as genetically engineered bacteria have for decades. I have strong reservations about these practices because of the risk of contaminating the gene pool of crop and fodder plants with genes for toxic substances. Once they escape, you'll never get them back, and they could have disastrous consequences for the food supply. |
In article ,
Cereus-validus....... wrote: Actually there are a few species of flowering plants that are adapted to growing in salt water and they are monocots too. They are commonly called "Seagrass". Check it out. They are not in the family Pontederiaceae though. Hm. Hadn't thought of those -- I guess because I've never lived near the sea. I wonder if anyone has worked out their mechanism for dealing with salinity, or is trying to engineer it into crop plants. Salt-tolerant grains and fodder grasses would be very valuable in both salinized soils and where irrigation water is high in salts. Google brought up half a million hits on the key seagrass research, but the few I looked at were mostly about the ecology of seagrasses and how they are indicators of both local and global environmental change. I'll have to search further. Thanks for the lead. |
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