Man’s best friend now plant’s best friend too?
For thousands of years, dogs (domesticated descendants of wolves[1,2]) have been considered to be man’s best friend[3,4]. One of the ways that friendship has been manifested is the use of the dog’s highly-developed sense of smell to detect signs of disease in humans[5,6]. Since this is usually possible long before any more obvious symptoms may be evident to the diseased person, it may enable life-saving medical intervention for the individual concerned[7]. Now, there’s also evidence that a similar disease-detection role could be played by dogs in the service of plants (or, rather, for the humans who own the plants and who would/should use that information to treat the damaged botanics). The proof-of-principle for this comes from work by Julian Mendel et al.[8]. In this instance three dogs – one Belgian Malinois[9] and two Dutch Shepherds[10] – were trained to ‘sniff-out’ the presence of laurel wilt disease (caused by Raffaelea lauricola[11]) in commercially-important avocado (Persea americana[12]) trees. It worked, and importantly, enabled infection to be detected before visible symptoms would have alerted the human guardian of the trees to any problem. Identifying so-called presymptomatic trees should give time for interventions to be put in place to deal with the infection; when symptoms are obvious to humans it is usually at a stage where the disease is very difficult to control. The canine trio involved not only demonstrated the ability to locate laurel wilt–diseased avocado wood with high accuracy and speed, but were also capable of high levels of performance even in harsh weather conditions such as high heat and humidity. Is this a case of a dogs barking up the right tree[13]? Whatever, we predict more examples of this doggedly determined disease detection work in future.
Image from: Wikimedia Commons
References
Houseplants as human health monitors
Plants provide humans with many products and services that are not only important but essential to our existence. We don’t have space to catalogue all of those bountiful botanical benefits here (although we have done our best in this column over the years!). But we can showcase a new one, which may be a glimpse of the future in which houseplants[1] are not only a treat for the eyes – and a boost to our well-being[2,3] – but also act as “functional sirens of home health”[4]. Although the built environment – of which homes are a significant part – only accounts for 0.5% of the livable surface of the Earth[5], it is the habitat in which most humans live and is recognised as an “evolving microbiome incubator”[5]. Although humans share their homes with a myriad of microbes, some are harmful and implicated in sick house (or building) syndrome, an illness of the built environment[6,7,8]. Fungi that are particularly relevant to this malaise – and which are frequent house-dwellers – include species in such genera as Aspergillus[9], Cladosporium[10], Penicillium[11], and Fusarium[12,13,14]. Although they may largely be invisible to the casual observer, they produce volatile organic compounds (VOCs[15,16,17]) that can reduce indoor air quality[18,19], and have associated human-health implications. As envisaged by C Neal Stewart Jr et al.[20] houseplants – which are already commonplace companions of humans in their homes – would be engineered (yes, genetically via GM [genetic modification[21]]) to detect the presence of such microbes by reacting to the VOCs that they produce*. The simplest ‘phytosensor platform’ – the bio-engineered houseplant – could report the presence of the harmful fungi by producing a visible signal from green fluorescent protein (GFP)[22] in the plant tissues. The GFP would be synthesised in response to detection of the microbes’ VOCs. Once alerted to the fungal threat it would need to be treated appropriately, but at least the home-dweller would know it was present and have the choice to do something about it or not. As co-author of the paper[20] Rana Abudayyeh states, “Our work should result in an interior environment that is more responsive to overall health and well-being of its occupants while continuing to provide the benefits plants bring to people every day”[23]. However, as Stewart et al.[20] also recognise, we currently lack the tools to engineer many popular types of houseplants. Until such time as that is possible we either wait for this built environment transformative technology to come of age, or fill our homes in the meantime with easily-grown and engineered model plants such as tobacco and Arabidopsis. Cynically, one might envisage the situation where the technology will only be developed for annual plants, so that healthy-home-concerned humans would have to buy a new set of sensing-plants each growing season. Rumours that Monsanto (“a global modern agriculture company”[24]) – famously associated with forbidding the saving and re-use of its GM seed to sow the following years’s crop[25,26] thereby avoiding the need to repurchase from Monsanto – are investigating this potential new income stream are just that.
* This work builds upon successful field trials of phytosensing plants that respond to bacteria by glowing orange[27].
Image from: Wikimedia Commons
References
Top-up, and bottom-down effects of marine plankton
Members of the plankton[1,2] are so-called because they don’t have the ability to move against modest currents in the water bodies they inhabit, i.e. they ‘wander’ or ‘drift’ (as in the meaning of the Greek word from which they get their name[3]). These organisms quite literally ‘go with the flow’[4]. Plankton is broadly divided into two categories: phytoplankton (which have plant-like characteristics, including the ability to photosynthesise[2]), and zooplankton (which don’t[2]). Because of the photosynthetic ability of phytoplankton one might assume they play their important ecological roles in the upper-most, illuminated levels of their aquatic homes. However, this news item looks at roles of phytoplankton not only at the top of the ocean, but also in its very depths. First, and demonstrating one of the many interactions and exchanges between the ocean and the atmosphere[5,6,7], is the finding that infection of certain phytoplankters[8,9] by viruses[10] can have an impact upon global temperatures. Miri Trainic et al. demonstrate that infection of the coccolithophore[11]Emiliania huxleyi[12,13], by the rather unimaginatively-named E. huxleyi virus, strain 201 (EhV201)[14,15], causes an increase in sea-spray aerosol (SSA[16,17]) * formation[18]. In particular, they show that parts of the external chalky coverings of the alga – the coccoliths – are shed from infected cells and released into the atmosphere above the ocean. These tiny calcareous particles are highly reflective and therefore reflect some of the sun’s radiation back into space – before it can contribute to warming of the surface of the Earth. Somewhat balancing the global heat equation, the coccolith particles can also act as nuclei that can cause clouds to form. Some clouds help to trap radiation emitted from the surface of the Earth[19,20,21] preventing its escape into space, thereby contributing to the greenhouse effect[22,23]. Additionally, the coccolithofragments fall back down to the ocean very slowly, so persist as an effective and active component of the SSA for quite some time. As so often in nature, it’s the action of the tiny things that can have some of the biggest impacts**. So much for living – albeit unhealthy and maybe dying – phytoplankton at the top of the ocean. Importantly, and when dead, such aquatic organisms can also play an important role in the ecology of the planet from the ocean’s depths. We are reminded of this by Sara Zaferani et al.[24] who have examined the connection between diatoms[25,26] and mercury[27,28], a toxic heavy metal[29,30]. They have found that these unicellular members of the phytoplankton trap large amounts of mercury which thereby accumulates in the ‘diatom ooze’ that builds up on the seabed. Extrapolating from mercury deposits found around Antarctica, Zaferani et al. estimate that these algal remains have globally accumulated 22,000–84,000 metric tons of mercury since 1850 (when mercury pollution from human activity is judged to have begun). Until now it had been assumed that the majority of the mercury that entered the ocean ended up in the atmosphere. Rather than any suggestion that the diatoms are killed by the mercury (although mercury can affect functioning of algae, e.g. [3]), it is suggested that the sinking of the dead diatoms ‘scavenges’ the mercury dissolved in the ocean. Arguably, this mechanism – a sort of oceanic ‘mercury pump’[32] – may help to clean-up upper layers of the water column removing this highly toxic heavy metal to depths where it cannot harm phytoplankton (although quite what harm it may cause to benthic biota is another matter…). Now that this discovery is published one wouldn’t be surprised to learn that entrepreneurs are already planning how to scoop up this biological bonanza, recover the mercury, and begin the whole polluting heavy metal cycling of mercury all over again.
* Typically, and as you’d probably expect, SSA contains sea salt. Interestingly, the size and shape of the coccolith fragments enable them to sink at only one-twenty-fifth of the settling rate of sea salt, thereby enriching the atmosphere in this component[18].
** This adds an intriguing new dimension to this organism’s relationship to the atmosphere because formerly E. huxleyi had only been known to emit DMS (dimethyl sulfoxide[33]), a “climatically active volatile organic compound that can generate secondary aerosols through atmospheric photochemical oxidation”[18]. Those secondary aerosols can lead to cloud formation[34] and thereby exert an effect upon the Earth’s global heat balance[35]…
Image from: Wikimedia Commons
References
China, the Congo Basin and the POTUS[1]…
The commercial value from, and exploitation potential of, plant products to humans is huge and undeniable. One of the biggest – in the sense of most conspicuous – examples of this expropriation[2] of the planet’s plant-derived bounty is the timber trade. Here huge trees are felled and ‘repurposed’ for use in the construction industry[3], furniture manufacture[4], and a multiplicity of other uses[5]. However, as important as is the timber from the dead tree, intact trees and forests are also very useful, e.g. in combating global climate change, cleaning the atmosphere, preventing soil erosion, reducing violence, etc.[6,7,8]. Although the benefits of leaving trees and forests intact are well-established, humans have a yearning for the products that can come from exploiting such seemingly abundant natural resources. Inevitably, therefore, the world’s forests are under considerable threat[9], and their current and continued exploitation is problematic, particularly in the tropics. One example of today’s troubled tropical timber trade is the usage of the rainforests of the Congo basin[10,11]. Investigating this, Trevon Fuller et al. demonstrate that export of timber from the Congo basin area to China doubled between 2001 and 2015, with a positive relationship between Chinese logging activity and loss of tree cover in that region[12]. Furthermore, US demand for Chinese-made wooden furniture was positively correlated with Chinese timber imports from the Congo Basin. This study therefore shows how one country’s (the USA in this instance) demand for a product (furniture) can inspire businesspersons in another country (China in this case) to extract a natural product (timber) from a third geographical region (the Congo Basin). This dramatically demonstrates the “complex environmental and economic drivers surrounding trade and deforestation”. However, whilst that trade may appear to be a legitimate business activity (although there are concerns about how legal it all may be[13]), any loss of rainforest has consequences that affect us all, wherever we may be geographically. The magnitude of this particular timber trade – and all others – must be considered, and its sustainability – or otherwise – as a commercial practice managed for the good of the global community. Timber products are included amongst the items exported from China to the USA that face large increases in tariffs[14,15], and if such tariffs reduce the import of these items, then the second biggest rainforest on the planet – in the Congo basin – may be an unexpected beneficiary of this Sino-American ‘trade war’. And therefore a serendipitously[16] tariffic [sic.] triumph of Trumpism..? Although President of the US Trump has interesting views on many environmental issues[17,18] maybe in respect of protecting the world’s forests he is a true friend of the environment after all. [Or, maybe, American companies will just ‘fill the void’ by visiting the Congo basin and undertaking their own frantic, finance-fuelled, forest-felling and furniture-fabrication activities direct..?]
Image from: Wikimedia Commons
References
Chaffey N. 2019. Plant Cuttings, Annals of Botany123(3): iv–vii.
