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Carnivory in Byblis & Roridula without aid of bugs?


Greg Allan

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My biochemistry is a bit rusty; the way I see it is that phosphatases are enzymes that may help a plant absorb and uptake phosphates from prey by generating free phosphate groups, enabling a plant to derive the element phosphorous from prey.

However, most studies into plant digestive enzymes have looked at a different group of enzymes, proteases, which break down proteins into amino acids, which can be absorbed enabling a plant to derive nitrogen from prey. This is the group of enzymes that the simple gelatine film test look for; the proteases digest the protein, gelatine.

Generally, it's thought that as CPs grow in environments where nitrogen is scarce they trap prey it's to obtain this element, not phosphorous. So, even with phosphatase activity, Roridula spp. still need the activity of Pameridae spp (bugs) to process the nitrogen compounds in the prey (mostly proteins) into a form that the plant can absorb, bug poop!

No doubt some biochemists will shed more light on the discussion! :)

Vic

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No doubt the phosphorous compounds are of use to the plant, but the study in the paper doesn't investigate what the enzymes are doing or what the plant plant benefits are etc.; it just investigates the presence of the enzymes.

Perhaps the full version speculates further in the discussion?

Most plant fertilisers with phosphate are based on Ammonium Phosphates, so they also contain nitrogen. both of which are important plant nutrients.

Vic

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I will try to access the full version tomorrow. As I work in a university, I may be able to access the article for free when I'm at work. I've always found it difficult to believe that Byblis possess no powers of digestion. My gigantea, liniflora and lamellata plants are all very efficent insect catchers with both short and long tentacles which clearly secrete extra juices when they capture prey. I've always doubted whether these features can have evolved for no real reason.

Cheers,

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Having had the opportunity to read the entire paper (Thanks, you know who you are! :) ), it seems I was roughly correct in my assumptions! :)

The Conclusion section ends;

'Enzyme production by the plant and also by symbionts enables the release of inorganic phoshate from prey in P-limited habitats, this ability significantly increases plant fitness'

So, we are still left wondering to what extent P is limiting in CP habitats and as for the statement about significantly increasing 'plant fitness' it's speculation until you actually research and measure it! When biologists talk of a significant increase, it's usually an increase that's measured and statistically tested.

Interesting paper though.

Vic

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From a practical standpoint, one would look at grasses in the immediate vicinity of those CPs. Grasses, and cultivated grains get purplish leaves if there is a P deficiency in the soil. That's how we applied P in the vineyards in SA in the almost nutrient absent soils where our last development project was. Soil tests don't always answer the question since P can be present and not available to plants due to a variety of factors. So we'd plant maize or oats and irrigate with the same water as the grapes, and just keep adding P until the leaves of the grasses lost the purplish tinge. Grapes don't show P deficiencies near as quickly as grasses, so it was a quick and very practical test.

OK I know it's just trivia, but perhaps some one will remember this and look around while in one of those locations.

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Yes, the full article is extremely interesting. It suggests plants that produce phosphatases to aid digestion are certainly true carnivores. Representitives of several genera are tested (Aldrovanda, VFTs, Genlisea, Drosera, Utrics, Nepenthes, Drosophyllum, Byblis, Pings, Roridula, Brocchinia & Stylidium). It was found that Aldrovanda, VFTs, Genlisea, Drosera, Utrics, Nepenthes, Drosophyllum, Byblis & Pings all produce this enzyme on or around their traps. This on its own is surely compelling, if not conclusive, evidence that digestion of phosphate is of benefit to the plants (presumably, most other plants do not produce the enzyme). Roridula was found to produce the enzyme only in its epidermis, and the authors concluded that 'further research will show if the epidermis takers part in the utilization of prey'. Brocchinia only gave a very slightly positive reaction- 'no clear result'. The Stylidium produced no positive results, although the authors do intriguingly mention that someone called Darnowski in 2002 proved that some species of Stylidium are carnivorous as they can digest proteins. It was also interesting to read that proteases do not seem to occur in significant concentrations in at least some Utrics either- they seem to be reliant on phosphatases and arthropod mutualism, and that there is also evidence that Ping and maybe even Genlisea & Byblis flower stalks are carnivorous.

Clearly, this area requires further research. in the mean time, I am going to start feeding my Byblis again!

Thanks to Vic for your explanations and to the generous forum member who allowed me access to the article.

Cheers,

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Doug Darnowski presented his research results with Stylidium spp. at the ICPS Conference in Frostburg, Maryland in June this year. He was one of the conference's main organisers and a nice bloke too.

In summary, from memory (!!), he suggests that Stylidium spp. are carnivorous for part of their life, in that he has found protease activity in the glands on the flower stalks. Thus they could catch and digest prey at a time when demands on the plant for Nitrogen, during reproduction, are particularly high. He intends to do radio-label studies in the future in order to investigate whether the plants actively take up and make use of prey-derived nitrogen.

It's not as far fetched as it sounds, as many Stylidium spp. live in the same wet, acidic conditions as sundews in Australia and the glandular hairs catch many small insects in habitat. I await his results eagerly! :)

Vic

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