Category: science

Plant blindness

Posted on by andy.winfield

You may or may not of heard of the term ‘plant blindness’; it’s a phrase that we in the Botanic Garden have been hearing much more of in recent years and will continue to throw around in the future. It refers to the slow shutting off of plant knowledge from generation to generation resulting in an inability to acknowledge plants around us. The simple things that were once common knowledge, such as dock leaves used for nettle stings are becoming bred out of a collective instinct and plants are becoming irrelevant and annoying green things to many people.
I can remember when my eyes were truly opened. I noticed trees that I hadn’t before; as I walked along the street I started looking at the borders and the hanging foliage all around me. Before, I’m not sure what I looked out for in the streets, the pavement or the shops, who knows, but plants for sure changed my life and I see them changing the lives around me at the Botanic Garden. I think I could live to be three hundred and still find something in the plant world that fascinated me. This week I learnt about the incredible relationships between some species of orchid and ants. The ants don’t pollinate the orchid flower but hang around the plant living off an ‘extrafloral’ nectar secreted elsewhere; they then do everything to protect their food source and keep the plant safe. Plants and animals have these delicate relationships that allow both to flourish, and it’s fair to say that ours has become less delicate over the years.
Dandelion seed head
This change in the collective instinct of people has come about through successive generations becoming more urbanised with less plant interaction such as blowing a dandelion seed head, throwing a grass seed dart, eating wild blackberries or sticking cleavers to jumpers; children still do this but there are many who don’t and lose a connection with the plant world. The result of this is that education reduces the amount of plant learning, and in biology courses there is a main focus on the animal kingdom; there is a perceived lack of interest in the plant world. Things have become so bad that the Oxford Junior Dictionary removed words like ‘acorn’ and ‘buttercup’ preferring instead ‘broadband’ and ‘cut and paste’; they were seen as no longer relevant to a child’s life.
University of Bristol Botanic Garden
There is however, a great appetite among young people to be green, to recycle and mend the excesses of the generations that went before them; often students tell me it’s the biggest issue for them and they’d like to make a difference. How is a difference made? I think we can all make a simple difference by introducing plants to friends and relatives, opening eyes to the trees and weeds and the force of life going on around us and under our feet. It could be argued that many of the world’s problems can be solved with plants; forests, food, habitats are all areas that need experts, and while there are many graduates of zoology degrees there are few from plant sciences. This is changing with Universities now offering full plant science degrees; there are many jobs in plant sciences as governments and companies are beginning to see how important it is. Bristol University is launching a plant science degree starting in September 2019 based in the magnificent Life Sciences building with a group of world experts in the field of plant science. Of course, undergraduates will use the Botanic Garden as a second home and have access to all our knowledge and experience, we’re really looking forward to it. If you, a relative, son or daughter are interested click here to view the degree.
We all have a role to play in protecting our relationship with the natural world which can be played by simply talking about the plants we see to people. I’m always disposed to optimism and today’s

young people seem to be committed to green ways; this problem arose through successive generations and perhaps it can be cured in the same way, the passing down of knowledge as we go.

By Andy Winfield

The potential of honey: a highly topical application

Posted on by andy.winfield

By Helen Roberts

The one animal that springs to most people’s mind for eating honey is bears. Especially a particularly round individual who gets his hand stuck in the honey pot numerous times. However, many animals around the world, including raccoons, skunks, opossums and honey badgers, feast on honey. They brave the fury of the hive to not only get at the sweet sticky stuff, but for the protein obtained from eating the bees and larvae themselves. We humans are fussier and prefer to stick to just the honey, though some people will eat honey on the comb.

For centuries, honey has been recognised not only for its culinary uses but its medicinal uses, due to its antimicrobial properties. The potential scope of honey in medicine is vast and still developing despite its use since ancient times; the ancient Egyptians and Greeks commonly used honey to treat wounds. Research into the medicinal properties of honey is ongoing and not only restricted to its use in promoting wound healing, but also its potential as  an anti-inflammatory, anti-fungal, treatment for burns, aid in the treatment of chronic rhinosinusitis and combatant against the bacterial biofilms that can form in urinary catheters.

The sticky issue of Manuka honey

Manuka flowers (Leptospermum scoparium).
Photo credit: FlowerGirl on Flickr [CC BY-ND 2.0]

Manuka honey (MH) is a monofloral honey produced in New Zealand and is made exclusively by European honey bees from the flowers of the Manuka bush, Leptospermum scorparium. MH is also produced in other countries, such as Australia and even in the UK, although it could be argued that this is not the ‘real deal’, having not come from New Zealand. In fact, there is currently an acrimonious disagreement between Australian and New Zealand honey producers over the right to market MH. New Zealand producers want exclusive trademarks on MH and Australian apiarists are fighting this, arguing that MH has been used in Australia since 1831, 8 years before New Zealand even got European honey bees. The bitter battle ensues.

The ‘essence’ of Manuka honey

The unique antibacterial properties of MH are attributable to the organic compound called methylglyoxal (MGO), which comes from the conversion of dihydroxyacetone (DHA) – a simple carbohydrate that is found in the nectar of Manuka flowers. DHA is one of the markers used to grade MH on a scale known as the UMF, or Unique Manuka Factor. Manuka honey needs a minimum rating 10 UMF to be labelled as Manuka.

Microbiologist Dr Rowena Jenkins, Lecturer at Cardiff Metropolitan University, and her research team have discovered numerous health benefits of using MH, which has been supported by clinical trials. This is an opportune moment for research into non-antibiotic agents as more antibiotic resistant pathogens emerge. Jenkins and her team are particularly interested in how MH might help battle the most challenging infectious agents…the ‘superbugs’.

Meticillin-resistant Staphylococcus aureus (MRSA) is the ‘superbug’ many of us associate with health care facilities. Jenkins’ team is exploring how MH wipes out MRSA that have infected wounds sites by preventing the bacteria from dividing.  In addition, Jenkins highlighted the potential for MH to be used in combination with antibiotics to stop the growth of MRSA.

If you’re interested in learning more about the ongoing research into honey, on the 24th of August, Dr Rowena Jenkins will be a guest speaker at the University of Bristol Botanic Garden Science Picnic. Visitors can relax in the garden and engage with Rowena in an informal discussion about her ongoing research into the health benefits of honey. It’s a rare opportunity to mingle with the scientists working on the edge of cutting research. You can book your place at the University of Bristol’s online shop.

Helen Roberts is a trained landscape architect with a background in plant sciences. She is a probationary member of the Garden Media Guild and a regular contributor to the University of Bristol Botanic Garden blog.

References:

Adams, C.J., Manley-Harris, M. and Molan, P.C. 2009. The origin of methylglyoxal in New Zealand Manuka (Leptospermum scoparium) honey. Carbohydrate Research, 344(8):1050-1053.

Jenkins, R., Burton, N. and Cooper, R. 2011. Manuka honey inhibits cell division in methicillin-resistant Staphylococcus aureus. Journal of Antimicrobial Chemotherapy, 66(11): 2536-2542.

Roberts, A.E.L., Brown, H.L., Jenkins, R.E. 2015. On the antibacterial effects of Manuka honey: mechanistic insights. Research and Reports in Biology, (6): 215-224.

Mycoheterotrophs: the sly swindlers of the plant world

Posted on by andy.winfield

By Helen Roberts

New plant species are discovered all the time. But it is not typical for plants to be discovered in areas that have been meticulously surveyed. Last year, however, a thoroughly unusual species was found on an island in the Kagoshima prefecture, Japan [1].

Gastrodia kuroshimensis is a mycoheterotroph
discovered last year in Japan.
Photo credit:Kenji Suetsugu/Kobe University


Gastrodia kuroshimensis neither photosynthesises nor flowers. Certainly by no means an ornamental showstopper, it is undoubtedly odd looking with fleshy tubers, the absence of leaves and no flowers. In essence, it resembles a pathetic looking fungal protuberance. Strangely enough, it is not a fungus, but a vascular plant. The fact that it does not photosynthesise means it belongs to a peculiar group of plants that are called mycoheterotrophs, which get all or some of their nutrients from a host fungi attached to a vascular plant. The newly found species, Gastrodia kuroshimensis, is what is termed ‘fully’ mycoheterotrophic in that it depends entirely on its association with the fungus throughout its lifecycle. The relationship between it and the host fungi is not mutualistic – it takes all it needs while offering nothing in return. In other words, it’s a big fat cheat.

Mycoheterotrophs parasitise fungi, which are in turn getting their nutrients from a host plant. The fungi that are preyed upon by these cheaters are usually mychorrizal fungi, with mycoheterotrophs often parasitizing a specific arbuscular mycorrhiza (arbuscular mycorrhiza are those that penetrate the cortical cells of plant roots). In this sense, they are dissimilar to parasitic plants like dodder, which obtain their nutrients by directly taking what they need from the vascular tissue using an adapted root.

Who wants flowers?

The second interesting thing about Gastrodia kuroshimensis is that it is entirely cleistogamous, producing flowers that never blossom. Most plants also produce chasmogamous (cross-pollinating) flowers; it is extremely rare to find plants that are entirely cleistogamous. The term cleistogamy means ‘closed marriage’ and the plant produces flowers that are self-fertilised within closed buds. It is essentially a way of ensuring reproduction [2].

The evolutionary reasons are still a puzzle, but it is considered a way of safeguarding fertilisation if suitable pollinators are not around or they have somehow missed the plant or if environmental conditions are not conducive. It can also aid plants in adapting to local habitats, where both sets of maternal genes are passed onto the progeny, thereby removing harmful gene variants. Being cleistogamous also use fewer resources; flowers that are chasmogamous require more energy to produce. However, in most cases chasmogamous flowers are beneficial as they help to provide variability necessary for adaptation, hybrid vigour and negate the effects of deleterious mutations. The reasons for complete cleistogamy remain unresolved but the discovery of Gastrodia kuroshimensis may well help to answer some of these questions.

Other fungi tricksters

Other plants that fall under the mycoheterotrophic category are orchids, monotropes (a subfamily of Ericaceae), members of the Gentian family, certain liverworts and the gametophyte stages of ferns and clubmosses. Some are quite attractive if you like the look of fungal fleshy looking vascular plants with varying hues of red, white and cream. Some are even striped red and white and so commonly known as candystick. Whatever their appearance though, they are unquestionably interesting. But because or their size and rarity they often go unnoticed, lingering in the background like villainous free-loaders.

Mycoheterotrophs at the University of Bristol Botanic Garden

The inflorescences of toothwort in the pollinator display
this week at the Botanic Garden.
Photo credit: Andy Winfield

A wonderful example of a mycoheterotroph at the Botanic Garden is toothwort (Lathraea squamaria L.). It spends most of its time below ground, but in April it sends up aerial inflorescences about 20-25 cm tall. These were in their full glory in the garden a couple of weeks ago, but can still be seen (see photo) in both the pollinator display on the left as you walk in the main gate, or at the east gate.

Unlike Gastrodia kuroshimensis, toothwort flowers are bisexual and pollinated by bumble-bees.

Stop in over the weekend if you get a chance and have a look at this interesting plant.

Helen Roberts is a trained landscape architect with a background in plant sciences. She is a probationary member of the Garden Media Guild and a regular contributor to the University of Bristol Botanic Garden blog.


Sources:

[1] Kobe University. (2016). Plant discovered that neither photosynthesizes nor blooms.
< https://www.sciencedaily.com/releases/2016/10/161014092115.htm>

[2] Allaby, M. (2016). Plant Love: The scandalous truth about the sex life of plants. Filbert Press, pp. 98-103.

In the guts of bees

Posted on by andy.winfield

By Nicola Temple

We hear a great deal about the beneficial bacteria that live in our digestive system and commonly referred to as the microbiome, which help us turn indigestible materials into nutrients that we can absorb. There are countless probiotic products on the market that are meant to introduce more of these beneficial bacteria into our system, enriching our microbiome. However, humans and indeed mammals are not alone in having helpful microflora in the gut.

The microbes that inhabit the guts of social bees has been of particular interest recently. These microbial communities have been studied for their role in bee health, but also as a model organism to help understand the relationship between hosts and their gut microbes, potentially providing insight into our own system.

The specialised cast of microbes

The microbiome of bees is relatively simple, but very specialised. There are about eight to ten bacterial species, but different species of bee will carry different strains of these bacterial species. The bacteria are so specialised that a strain from one bee genus isn’t able to colonise the gut of a bee from a different genus. This suggests that these bacterial strains have been evolving with their hosts over a very long period of time.

Nest entrance of the stingless bee, Geniotrigona thoracica, is
from Malaysia. Photo credit: Eunice Soh.

Like us, these bacteria help the bees break down complex molecules through fermentation in order to make the nutrients available to the hosts. There’s also evidence that they might help to neutralise toxins in the gut. These friendly microbes also outcompete nastier pathogenic species that can make the host ill. For example, the gut microbes in bumblebees have been linked to lower levels of the parasite Crithidia bombi.

The gut microbes of non-social insects, including solitary bees, aren’t as specialised because they acquire them from their environment rather than from other members of their species. Among social bees, it is behaviours such as passing food between individuals and feeding larvae, that allow an exchange of microbes. However, these exchanges pass along the bad microbes as well as the good.  Beekeepers are painfully aware that pathogens can pass through a colony like wildfire. Social insects therefore need a very responsive system that helps keep these pathogens in check. And the key to this might be a very ancient relationship between the good microbes and the host bees themselves, which allows the bee’s immune system to quickly identify the less desirable critters.

A long-term relationship

Research published this week in the journal Science Advances suggests that five of the species of gut bacteria found in modern social bees have been evolving along with their hosts for about 80 million years. It was around this time that the first solitary bees began socialising with other bees – sharing nests and food resources and making concerted defence efforts. The descendants of these first social bees are the hundreds of species of honey bees, bumblebees and stingless bees that are alive today.
This finding not only shows that social creatures, such as bees and humans, transfer bacteria among each other during the same lifetime, they pass them along generations, enabling the microbiome and host to evolve together.

“The fact that these bacteria have been with the bees for so long says that they are a key part of the biology of social bees,” says Nancy Moran, a professor of integrative biology at the University of Texas who co-led the research with postdoctoral researcher Waldan Kwong. “And it suggests that disrupting the microbiome, through antibiotics or other kinds of stress, could cause health problems.”
The co-evolution of the gut bacteria and the bees is so closely linked, in fact, that the researchers found that when a new species of bee branches off in the evolutionary tree, a new strain of bacteria branches off with it. The result being that each of the hundreds of species of social bees alive today has its own specialised strains of gut microbes.

Human influence on this long-term relationship

It’s currently unknown how toxins introduced by humans, including pesticides, might affect the bee microbiome. There is recent evidence, however, that the prophylactic use of antibiotics by bee keepers in the US has resulted in some gut bacteria in honeybees developing antibiotic resistance.

References

Engel, P. et al. 2016. The bee microbiome: impact on bee health and model for evolution and ecology of host-microbe interactions. mBio 7 (2): e02164-15.

Kwong, W.K., Medina, L.A., Koch, H., Sing, K-W., Soh, E.J.Y., Ascher, J.S., Jaffe, R. & Moran, N.A. 2017. Dynamic microbiome evolution in social bees. Science Advances 3: e1600513.

Kwong, W.K., Engel, P., Koch, H. & Moran, N.A. 2014. Genomics and host specialization of honey bee and bumble bee gut symbionts. PNAS 111 (31): 11509-14.

Nematodes: the natural nemesis to slugs and other garden pests

Posted on by andy.winfield

By Alida Robey

Nematodes pop up from time-to-time on gardening programmes, but usually as something of an afterthought: “Oh, and of course if you don’t want to use pesticides you can always try nematodes.” A certain air of mystique has surrounded nematodes for some years now, but these environmentally friendly pest controllers warrant far more consideration than a mere afterthought!
Nematodes are in fact one of the most successful and adaptable animals on the planet. They are second only to the insects in their diversity of species, geographic spread and the range of habitats they can occupy. There are more than 15,000 known species of nematodes, more commonly known as roundworms, and likely thousands more that are yet to be described.
There are parasitic nematodes that live in the gut of animals, humans, birds and mammals. Other species are free-living in the soil, feeding on bacteria and garden waste. Some are parasitic on plants and may cause disease and crop devastation. But, as a gardener, I’m most interested in those species that are free-living in healthy soil and those that parasitise common garden pests.
Free-living garden nematodes are microscopic thread-like worms, which are scarcely visible without a microscope. (This is in marked contrast to the 9 metre long species, Placentonemagigantissima, which can be found in the placenta of the sperm whale!). In good nutritious soil there could be as many as 3 billion individuals per acre. They eat fungi, bacteria and algae. So, much like ordinary earthworms, they have a useful role in decomposing and recycling nutrients.

Biological control with a specific target

Parasitic species have an equally important role in the garden. With such a diversity of species, it is not surprising to find that there are nematodes that specifically parasitise slugs, ants, vine weevil, leather jacket, chafer grub – you name it! This means that a slug nematode won’t have any impact on anything but slugs – this isn’t always the case with other biological controls and rarely the case with chemical controls.
A wax moth pupa can be a host to thousands of
nematodes. The parasitised cadavers can be placed in
orchards to protect crops from pests such as citrus root and black
vine weevils.
Photo credit: Peggy Greb, US Department of Agriculture
It works like this: the juvenile nematodes are in the soil looking for a specific host. Once found, the nematode enters the body of the host and gives off  bacteria inside the host’s body. These bacteria multiply and cause blood poisoning and, eventually, death. The nematodes then feed on the body of the creature and multiply, sending a new generation off into the soil to find another host. When hosts are scarce, the nematodes naturally die off.

The practicalities of using nematodes

As nematodes are living organisms they have a very limited shelf life. They therefore need to be bought online, stored according to instructions and used very soon after delivery.
There are several UK suppliers of nematodes.
It is important to choose the correct nematode species for the right type of pest and to use them in the right conditions. The soil temperature has to be above 5oC (and remain so) and they should be applied only when the pests or their larvae are active. Nematodes are also light sensitive, so use them early morning or dusk, when light levels are low.
They come as a thick paste in a little sachet, which you need to dilute with water. Repeat applications may be needed.

The specifics:

Ants : Drench the nests between April and September.
Chafer grubs: Apply nematodes in August and early September.
Fruit flies, carrot root fly, onion fly, gooseberry sawfly and codling moth: All of these pests can be treated with a generic nematode mix called Nemasys Natural Fruit and Veg Protection Pest Control. You can use it as a general treatment after planting out and when the soil has warmed up, or to target specific pests when you see them, such as gooseberry sawfly caterpillars. These (and other caterpillars) need to have direct contact with the spray while they are on the leaves.
Leather jackets:  These are the larvae of the crane fly or daddy longlegs and attack the roots of grass in the lawn. Treat with nematodes in the autumn, when the adult daddy-long-legs are laying.
Slugs:  The nematode for slugs was discovered by scientists at the University of Bristol! An application early in spring will tackle the young slugs growing under the ground, which are feeding on humus. A single application should last for at least 6 weeks, which allows time for tender seedlings and young plants to get established. They can be applied until early Autumn.
If using on potatoes, apply them 6-7 weeks before harvesting , when the tubers are most likely to be eaten by slugs.
Slug nematodes are very efficient, enjoying the same wet environment so loved by the slugs themselves.
Vine weevils: An application in March will give much greater control of larvae when they are present – either March to May, or from July to October.
I have heard the anecdotes from many gardeners who have had good results using nematodes for ants, vine weevils and slugs. But in May 2016, the Royal Horticultural Society and BASF, the only UK manufacturer of nematodes, announced a one-year research project to put slug nematodes to the test.
So in May 2017, we should see just how well this little creature stacks up against the chemical and other treatments in tackling arguably our most annoying garden pest.

Alida Robey has a small gardening business in Bristol. For several years in New Zealand she worked with others to support projects to establish composting on both domestic and a ‘city-to-farm’ basis.

What lies below: how soil bacteria fight off sticky roots

Posted on by andy.winfield

By Nicola Temple

The first horror film I ever watched was Invasion of the Body Snatchers. The film was already dated by about 30 years when I saw it and so aspects seemed silly rather than scary. Yet, those alien plants still managed to evoke nightmares in my pre-teen imagination. Antagonistic plants have cropped up in numerous films over the years – from the musical menace in Little Shop of Horrors to the Devil’s Snare that entangles Harry Potter and his friends. Yet, the cinematic nightmare of being entwined and strangled by the (not so) local flora is based in some truth…if you’re a microbe.

Soil is alive with microbes – on the order of 100 million cells per gram of soil. Some of these are friendly microbes and some are less so. So, as plant roots seek out water and nutrients within the soil they must also be wary of what they encounter. The root tips are sheathed in specialised cells known as root border cells and these are the front line of defence. These cells launch themselves from the root tips and through the release of various chemicals, help to manipulate the environment around the extending root tips. They can attract and stimulate growth of helpful microbes and repel or inhibit the growth of others. 

Earlier this year, researchers at the University of Wisconsin, USA looked closely at how the root border cells of peas and tomatoes interact with the bacteria Ralstonia solanacearum.
R. solanacearum is a pathogen that affects a number of economically important plants, including potatoes, tomatoes, peppers, bananas and tobacco. It follows the chemical signals sent out by plant roots and finds natural openings or wounds within the root in order to invade the plant. Once inside, the bacteria replicate rapidly and take up residency in the xylem of the plant. Eventually, they block this important transport system of the plant and cause it to wilt and die.

A false coloured electron micrograph showing bacteria (blue)
tangled in the DNA-based trap (yellow).
Photo credit: Tran et al.
The Wisconsin researchers found that when the root border cells of both the peas and tomatoes encountered R. solanacearum, they released DNA. Surrounded by stands of sticky DNA, the bacteria become entangled. Unable to move, the bacteria die. It truly is the stuff of horror films.
Other friendlier species of bacteria didn’t induce this projectile DNA trap from the root border cells, which suggests that they are able to recognise the threat of R. solanacearum.

However, as is almost always the case with nature, there is always a counter attack. The researchers discovered that only 25% of the bacteria were dying in the plant’s sticky trap, so how were the rest managing to escape?

The Wisconsin group found that when R. solanacearum encountered the DNA, it triggered a release of an enzyme that cuts DNA. In other words, they were using molecular scissors to cut their way out of the trap.

And so the evolutionary arms race continues. It is those individual bacteria that produce more of the defensive enzyme that will escape the traps and replicate. Perhaps over evolutionary time, those that have limited capacity to produce the enzyme will be weaned out of the population, forcing the root border cells to improve their offensive game.

For scientists, this detailed understanding of how hosts interact with different pathogens could help them to develop disease-resistant plant varieties of these economically important crops.

For me, this insight into the quiet battles being fought below the ground give me an even greater appreciation for the fruits and vegetables I harvest from my small little garden – they have been hard-won!

The paper referred to is:
Tran TM, MacIntyre A, Hawes M, Allen C (2016) Escaping Underground Nets: Extracellular DNases Degrade Plant Extracellular Traps and Contribute to Virulence of the Plant Pathogenic Bacterium Ralstonia solanacearum. PLoS Pathog 12(6): e1005686. doi:10.1371/journal.ppat.1005686

Nicola Temple is a science writer and co-author or the book ‘Sorting the Beef from the Bull: The Science of Food Fraud Forensics’ . She dabbles in her small veg patch and regularly contributes to the University of Bristol Botanic Garden blog.