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Plant of the Month 2019

Periodic Table

Launched in July 2017, the SCIence Garden brings to life a diverse array of plants representing SCI’s technical and regional groups. The Garden also showcases the connections between all areas of chemistry related science and highlights the intrinsic role played by natural resources and the environment in industry.

2019 – The International Year of the Periodic Table of Chemical Elements

2019 has been declared by the United Nations General Assembly and by UNESCO to be the International Year of the Periodic Table of Chemical Elements (IYPT). 2019 is a landmark year - 150 years since the discovery of the Periodic System by Dmitry Mendeleev and also the centenary of IUPAC (International Union for Pure and Applied Chemistry).

Celebrating the IYPT will raise global awareness of how chemistry promotes sustainable development and provides solutions to global challenges in energy, education, agriculture and health.

The SCIence garden will also be celebrating the IYPT, with various plants with names linked to chemical elements.

To find out more about the IYPT go to: https://www.iypt2019.org/.

Archive issues of the Horticulture Group newsletter, including Plant of the Month up to March 2017, can be found here.

August:
Sorghum bicolor, sorghum, great millet, Poaceae
Zea mays, corn, Poaceae

August in the Science Garden

Plant of the month August 2019: Zea mays, corn, PoaceaeAs summer reaches its peak, the ornamental grasses in a garden start to flower and add to the show and in the SCIence Garden the plants from the grass family are also reaching their ultimate heights!

Grown not just for their ornamental appearance but rather for their representation of several of the SCI technical interest groups are both black millet and corn (sweetcorn). Sweetcorn has featured as a plant of the month previously (September 2017) but sorghum was a new addition to the SCIence Garden in 2018 and is growing there again this year. Easily grown from seed, this plant is surprisingly ornamental for a crop plant.

It is estimated that this plant was first cultivated in north-eastern Africa from 5,000 to 3,000 BC. Ethiopia is today the country with the greatest genetic diversity of sorghum. It is probably no surprise therefore that with such a long history of domestication and cultivation that there are a slightly terrifying number of synonyms for this plant. Plant of the World Online (A Royal Botanic Gardens, Kew database) lists 177! The seeds that the SCIence Garden plants were grown from were listed as Sorghum nigrum –just one of those 177 synonyms.

When local common names are considered, the number of potential names this plant has expands astronomically! Some of the common names include the word millet, but millets are generally considered to be a separate crop to sorghum.

The publication of the IPCC report on Climate Change this month, recommended reducing consumption of meat and dairy based foodstuffs whilst increasing consumption of plant based foods. It therefore seems only right to choose a plant to write about this month that is a staple food for more than 500 million people across more than 30 countries.

Sorghum is grown widely in the more arid parts of Africa, Asia, Australia as well as North and South America and even Europe. It is well suited to these environments as it uses C4 carbon fixation thereby using one third of the quantity of water that C3 plants do. In America it is a bulk commodity grown for feeding livestock, whilst in the developing countries it is mainly grown by subsistence farmers.

It is mainly grown as an annual crop, but some strains are perennial, and certainly the one that has been grown in the SCIence garden has shown itself to be perennial.

The grain can be used to make flour, or popped (like corn), but can also be boiled and roasted. It can be used to produce beers and a sweet syrup is made from it in the southern United States. There are many material uses of the plant (fencing, weaving, fuel etc.) and it has been used in African traditional medicine as a remedy for hepatitis and to treat jaundice.

The International Crops Research Institute for the Semi-Arid Tropics conducts research for development in the drylands of Asia and sub-Saharan Africa. Sorghum is just one of the nutritious but drought-resistant crops it conducts research programs on. For much more information on their work see: http://exploreit.icrisat.org/profile/Sorghum/193 - opens in a new window.

July: Melaleuca citrina, bottlebrush, Myrtaceae

July in the Science Garden

Melaleuca - plant of the month July 2019Looking good in the SCIence garden this month is an Australian plant with showy red inflorescences that look like bottle brushes and indeed bottlebrush is the common name for this plant. The scientific name has changed multiple times since the plant was first formally described.

Although perhaps more familiar to many people as Callistemon, the current accepted generic name for this plant according to the World Checklist of Selected Plant Families is Melaleuca. This “lumping” of Melaleuca and Callistemon follows a paper from 2006 by botanist Lyn Craven, where it was argued that the differences between the genera did not warrant them being maintained separately. However, not all Australian Herbaria have taken up this system.

Named Melaleuca citrina in 1802, this species was already reasonably widespread in cultivation in Britain by then, but to add even more confusion to the picture it was then known as Metrosideros citrina after an illustration was published in Curtis’ Botanical Magazine in 1794. This was one of the first Australian plants to be grown in Britain after being brought here by Joseph Banks in 1770.

The flower spikes, for which the plant gets its common name of bottlebrush, are made up of many individual small flowers. The petals are actually very short and insignificant and it is the coloured filaments which bear pollen on the anthers at their tips that make up the showy part of the flowers that give the plant the common name.

Melaleuca - plant of the month July 2019When the leaves are crushed they give off a citrus like odour. The major components of the essential oil derived from the leaves are 1,8-cineole and α–pinene. The essential oil shows strong antibacterial properties against a range of gram positive bacteria.

This plant, along with others in the myrtle family, contains another interesting chemical called leptospermone. This substance was first identified in 1927 and later isolated from a range of plants in the 1960’s. However it was not until 1977 that it was first isolated from a plant of Melaleuca citrina (then known as Callistemon citrinus) growing in California. A researcher working for the Stauffer Chemical Company observed that very few plants were growing under these bottlebrush bushes. He took soil samples from underneath the plants and eventually identified the herbicidal component. However, it was not potent enough to be of practical use. A discovery research programme followed, based on the structure of leptospermone and the final outcome was the herbicide mesotrione, known under the brand names Callisto and Tenacity. This substance acts by inhibiting the plant enzyme 4-hydroxyphenylpyruvate dioxygenase (4-HPPD). This enzyme is involved in carotenoid biosynthesis. Without carotenoids to protect the chlorophyll in the leaves, sunlight degrades the chlorophyll and the plant dies.

Cineole also known as eucalyptol plant july 2019
α-pinene Plant July 2019
Leptospermone plant july 2019 Mesotrione
1.8-cineole (also
known as eucalyptol)
α-pinene Leptospermone Mesotrione

June:
Digitalis purpurea, common purple foxglove, Plantaginaceae
Digitalis lanata,
woolly foxglove, Plantaginaceae

June in the SCIence Garden

Purple foxgloveBoth the common purple foxglove and the woolly foxglove are currently flowering in the SCIence Garden, and the purple foxglove in particular is making itself at home, seeding around where it is most happy.

Whilst the story of the development of the drug digoxin starts with the common purple foxglove, it is the woolly foxglove that is widely grown today for the production of this powerful drug.

Woolly foxgloveIn the latter part of the 18th Century, William Withering, a physician and member of the Lunar Society, became interested in the case of a lady who recovered from a severe case of dropsy after taking a herbal mixture. After extensive investigation he found that the purple foxglove was the plant responsible for the seemingly miraculous recovery of the patient. He began experimenting with foxglove to treat other patients and found it to be very successful with patients suffering from what we now know to be congestive heart failure (dropsy). It was not until the 1930’s that scientists at Burroughs Wellcome isolated the active principle, digitoxin, from the foxglove and determined its structure.

Digitoxin is a cardiac glycoside and works by strengthening and slowing the heart beat. It is still available today, but a related molecule, digoxin, isolated from the woolly foxglove, Digitalis lanata, is much more widely used. The additional hydroxyl subsituent on the steroid ring system renders it more potent and also more rapidly excreted from the body, thus increasing the therapuetic index (and hence safety).

 Digoxin - plant of the month June 2019  Digitoxin - Plant of the month
 Digoxin  Digitoxin

April: Citrus mitis, Calamondin, Rutaceae

April in the SCIence Garden

Citrus mitis, Calamondin, RutaceaeThe calmondin orange plant in the SCIence garden is looking at its most ornamental this month, with a proliferation of small, ripe, tangerine-coloured fruits decorating it. It is growing in a large pot, on the terrace directly outside the Council Room. During the past winter, the temperature on this terrace, in the vicinity of this particular plant, has not dropped below 4°C although this hardy citrus would be capable of surviving lower temperatures.

Labelled as Citrus mitis here at the SCIence Garden, because that is the name it was purchased under, this is a plant with a confusing history that continues into the present! Variously known as Citrus x mitis, x Citrofortunella microcarpa, x Citrofortunella mitis, these synonyms have been superseded by Citrus x microcarpa, as a revision of the genus Fortunella has sunk this group of species into the genus Citrus. However, elsewhere, calamondin has been used to describe Citrus madurensis (syn. Citrus japonica). Whatever the scientific name, this is just one of many citrus with a complex history grown for their fruit. A recent paper in Nature(i) attempts to unravel some of that history using genomics.

 Genealogy of major citrus genotypes

Genealogy of major citrus genotypes.

Image from G A Wu et al. Nature 554, 311–316 (2018) doi:10.1038/nature25447 This work is licensed under a Creative Commons Attribution 4.0 International (CC BY 4.0) licence

Calamondin are also known as calamansi, golden lime and Philippine lime amongst a wealth of other common names, so these are no more helpful than the scientific names! However, they do give us some idea that this is a sour rather than sweet fruit and that they are very popular in the Filipino cuisine. They are used when still some way short of fully ripe to season dishes such as Siomai (filled wonton wrappers). Both the juice and essential oil from the rind of this fruit have been repeatedly analysed to look at the chemical profiles. An analysis of the volatile components of the peel oil, published in 1996, identified 56 different components, with limonene being by far the major component at 91%.(ii)

Researchers have been looking for uses of the by-products of juice and oil extraction from the citrus industry, and a recent paper from an SCI publication, The Journal of the Science of Food and Agriculture, describes the chemical and physicochemical characterisation of these by-products.(iii) Read the SCI news article "Orange juice waste turned into valuable products".

And since it is the International Year of the Periodic Table of Chemical Elements, this piece would not be complete without mention of at least one element.

Citrus mitis, Calamondin, RutaceaeMany pests and diseases affect the global citrus industry. One such is Citrus greening – spread by aphids – which is threatening the Citrus industry particularly in Florida. But pest control and disease prevention is not a new challenge for this industry. I wanted to share with you a paper I found from 1938, entitled “The effect of lead arsenate and copper carbonate sprays on the quality of oranges”.(iv) Working in South Africa, the authors were using plant protective agents, commonly in use at the time to control pests such as false codling moth, the Mediterranean fruit fly, the Natal fruit fly and the American bollworm. You will be pleased to learn that neither lead nor copper were present in the fruit juice at levels higher than in unsprayed fruit and that the levels of arsenic in the fruit juice were “negligible”.

Plant protection has come a long way since the 1930’s. Nowadays, it is usual in commercial orchards to follow an Integrated Pest Management approach. Cultural controls, monitoring for pests, release of beneficial predatory insects as well as spraying of synthetic or natural pesticides are all used in combination to achieve the best control possible. Thankfully blanket spraying with substances such as lead arsenate are a thing of the past.

(i) Wu GA et al, Nature, 2018 Feb 15, 554 (7692) 311-316 doi: 10.1038/nature25447

(ii) Moshonas MG & Shaw PE, J Agric. Food Chem, 1996, 44, 1105-1107

(iii) Pacheco, MT et al, J Sci Food Agric, 2018, 99, 2, 868-876 doi: 10.1002/jsfa.9257

(iv) Raimund H. Marloth & F.J. Stofberg (1938) The Effect of Lead Arsenate and Copper Carbonate Sprays on the Quality of Oranges, Journal of Pomology and Horticultural Science, 16:4, 3-345, DOI: 10.1080/03683621.1938.11513523

March: Clianthus puniceus Albus, White lobster claw, White kaka beak, gutukākā, Fabaceae

March in the SCIence Garden

Clianthus puniceusThis month, for the International Year of the Periodic Table of Chemical Elements, it seems apt to celebrate the element nitrogen as plants spurt into fresh green growth all around us. Essential for all living things, including plants of course, nitrogen is a vital component of DNA, RNA and the amino acids that link together to form proteins. Nitrogen is element no. 7 in the periodic table and is a diatomic gas at room temperature and pressure. However, plants typically take up nitrogen in the form of nitrates, which are made available to them in a variety of ways.

Lightning strikes provide the energy required to break the nitrogen-nitrogen bond, enabling nitrogen atoms to react with atmospheric oxygen to form nitrogen oxides which combine with rainwater to form nitric acid. Nitrogen can also be “fixed” into ammonia by the action of enzymes called nitrogenases. The ammonia is then assimilated via further enzymatic reactions into higher nitrogen compounds. Nitrogenases can be found in micro-organisms such as cyanobacteria and also in symbiotic bacteria that live in root nodules of particular plants. Root nodules with nitrogen fixing bacteria are widespread in the legume family, but also in some 25 other genera spread across 8 plant families.

Industrially, the most important process that converts atmospheric nitrogen into “usable” nitrogen is the Haber-Bosch process. Nitrogen is reacted with hydrogen gas in the presence of a catalyst at extreme temperature and pressure. The largest use today for this fixed nitrogen is fertiliser, although initially it was used in the production of explosives.

Clianthus

The plant growing in the SCIence garden, chosen to represent the element nitrogen is Clianthus puniceus ‘Albus’ in the legume family, Fabaceae. It is to be found growing up against the wall on the left of the “sunken room” towards the tropical looking Fatsia. It has pinnate evergreen leaves, a slightly sprawling habit and beautiful creamy white flowers, which resemble a lobster’s claw or a parrot’s beak depending on your perspective. The flowers will be on show through March and hopefully into April depending on the weather. It is a white flowered variety of the normally pink/red-flowered species which originates from New Zealand. Clianthus puniceus is listed as Endangered on the global IUCN red list and as Nationally Critical by the Department of Conservation in New Zealand. Formerly more widespread, the sole remaining location where it grows in the wild is Moturemu Island in Kaipara Harbour on the northwest coast of New Zealand’s North Island.

Like many plants in the legume family, Clianthus plants have root nodules containing nitrogen fixing bacteria. In addition to using the fixed nitrogen for growth, the plants produce a range of nitrogen containing specialised metabolites. These molecules act as a nitrogen stores, but also play a defensive role. Canavanine, a non-proteinogenic amino acid, is one such nitrogen containing molecule. It has only been found in leguminous plants, nearly all of which are in the sub-family papilionoideae. Canavanine has been isolated from the whole plant, but the concentration is highest in the seeds. It has been shown to function as a nitrogen store, but also exhibits allelochemical properties, inhibiting the germination and growth of other plants and organisms. It has also been shown to defend the plant against insect predation. It has a very similar structure to the proteinogenic amino acid arginine, and is therefore not surprisingly a potent arginine anti-metabolite. When incorporated into proteins mistakenly instead of arginine, it can render them non-functional, thus proving to be toxic to whatever has ingested it.

Other leguminous plants in the sub-family papilionoideae growing in the SCIence garden at Belgrave Square include Coronilla valentina subsp. glauca 'Citrina' and Laburnum x wateri 'Vossii'. So when you are at Belgrave Square, take a look at these plants in the garden but please don’t eat any part of them!

 arginine  
 arginine  canavanine

Further reading:

Dawson J.O. (2007) Ecology Of Actinorhizal Plants. In: Pawlowski K., Newton W.E. (eds) Nitrogen-fixing Actinorhizal Symbioses. Nitrogen Fixation: Origins, Applications, and Research Progress, vol 6. Springer, Dordrecht

The Biological Effects and Mode of Action of L-Canavanine, a Structural Analogue of L-Arginine; Gerald A. Rosenthal; The Quarterly Review of Biology, Vol. 52, No. 2 (Jun., 1977), pp. 155-178

February: Eranthis hyemalis Winter aconite, Ranunculaceae

February in the SCIence Garden

eranthisIn the bleak months of winter, I find myself searching for signs that there is still life out there in the garden. What surer sign can there be than the vibrant yellow and green of winter aconites? These low slung beauties are in the buttercup family and join the winter flower parade with their relatives the hellebores. But have you ever considered the hidden depths of the humble winter aconite?

Like many members of the buttercup family, this plant is toxic if ingested. Eranthin, an oxepinochromone, was isolated by a researchers in Germany in 1979 along with a glucoside derivative. Recent studies have reported the isolation of other 4H-chromenone glycosides which also have cardiac activity.

But perhaps, the most striking substance isolated from this plant is EHL – Eranthis hyemalis lectin. It was the first lectin that was isolated from plants of the buttercup family, Ranunculaceae. Lectins are carbohydrate binding proteins that agglutinate erythrocytes (make red blood cells clump together). Some lectins, such as ricin, act as Ribosome Inactivating Proteins (RIPs) and are extremely toxic. These RIPs cause the halt of protein synthesis and thus cell death. EHL is one such of these RIPs. Due to their cytotoxic effect, there is much interest in RIPs as potential anti-cancer and anti-viral agents.

eranthin diagram 01  Cimicifugin glycosides diagram 02  Eranthin glycosides diagram 03 
 eranthin  Cimicifugin glycosides  Eranthin glycosides

As botanists started to investigate the detailed evolutionary relationships of plants within families, there was uncertainty as to where the genus Eranthis should be placed. Based on morphological characters alone, it had been thought to be more closely related to the genus Helleborus. However, recent molecular studies have revealed that it is more closely related to Actaea than to Helleborus as previously thought.

eranthisWinter aconites have also been used to study the detailed mechanism involved in the thermonastic movements of petals, sepals and tepals. Thermonastic movements are those that happen in response to the plant experiencing a temperature change. You may have noticed the opening of crocus and tulip flowers during the day as the temperature rises and their closure again as the temperature falls but have you ever wondered how the plant knows what the temperature is? Or how the flowers actually open? Some of the details such as the changes in the electric potential differences across the plasma membrane in cells of tepals have been investigated in winter aconites.

So as you marvel at the carpets of winter aconites you see this winter, or at those in the SCIence garden, spare a moment for the humble plant playing its own important role in furthering the understanding of plant development and the future of medicines from plants.

Further reading:

McConnell, M. (2016) A study of the structure and biological activity of the Eranthis hyemalis type II ribosome inactivating protein. Ph.D. thesis, Canterbury Christ Church University.

Kopp, B. , Kubelka, E., Reich, C., Robien, W. and Kubelka, W. (1991), 4H‐Chromenone Glycosides from Eranthis hyemalis (L.) SALISBURY. Helvetica Chimica Acta, 74: 611-616. doi:10.1002/hlca.19910740318

Junior, P. Eranthin und eranthin-β-D-glucosid: zwei neue chromone aus Eranthis hiemalis. Phytochemistry 1979, 18, 2053.

Compton, James A., and Alastair Culham. Phylogeny and Circumscription of Tribe Actaeeae (Ranunculaceae). Systematic Botany, vol. 27, no. 3, 2002, pp. 502–511.

Hejnowicz, Z. , Trebacz, K. and Sievers, A. (1995), Temperature-dependent changes of electric potential differences on opposite sides of the tepals of Eranthis in relation to thermonastic responses. Plant, Cell & Environment, 18: 471-474.

January: Hedera helix, English ivy, Araliaceae

January in the SCIence Garden

Hedera helix silver king labelJanuary’s plant, which is growing in the tall black planters in the area around the pond behind the garden room, is Hedera helix ‘Silver King’. A good climbing and trailing ivy with silvery white (as you might expect from the name) variegation. It will grow in semi-shade – which is much needed for this particular spot in the SCIence garden and is evergreen, providing some interest to the planters all year round. The typical leaf has five lobes, with the central lobe being about twice as long as the outer lobes.

Hedera, the genus to which English ivy (Hedera helix) belongs, is one of 43 genera in the family Araliaceae. Fatsia, of which there is a large plant growing in the main SCIence garden, is also in this family. Hedera itself is quite a small genus, with just a handful of species. Fatsia in flowerThese species are native to central, southern and western Europe, Macaronesia, north-west Africa and across central and southern Asia to Japan and Taiwan.

Fatsia in flower (right)

Ivy has adhesive, aerial roots that are only found on the juvenile form, which also differs from the mature form in leaf shape. The flowers of the mature ivy provide a fantastic nectar supply for insects, particularly in months when there are few alternatives. The berries also have great wildlife value, as a source of winter food for birds.

Silver, element no. 47, sits in group 11 of the periodic table. Evidence near ancient mine workings in Turkey and Greece show that silver mining was taking place around 3000 BC. Silver mining continues to this day with the top producing countries being Mexico, Peru and China.

Hedera helix silver kingMetallic silver, which is relatively soft and shiny, tarnishes slowly in the air, forming a black coating, made of silver sulfide. This is formed as sulfur compounds in the air react with the surface of the silver.

Hedera helix with silvery white variegation (left)

Silver is of course the major component (92.5%) of Sterling Silver, used for making jewellery and silver tableware. The remainder is normally copper.

Other than jewellery and tableware, silver (and compounds thereof) is used for a wide variety of applications from dental alloys, to printed circuits and in photography. Silver is antibacterial and its use in plasters and clothing is becoming increasingly popular. It is even woven into the fingertips of gloves so that wearers can still use touchscreen devices!

For more information about silver visit: http://www.rsc.org/periodic-table/element/47/silver.

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