Crocosmia, invasion, diabetes and obesity

The rich flora of southern Africa has provided us with many garden plants, including members of the iris family that naturalise readily [1]. Among the most popular of these plants is montbretia, or coppertips (Crocosmia x crocosmiiflora – a cross of C. aurea and C. pottsii [2]), the result of horticultural inter-breeding and now popular world-wide for its attractive foliage and, especially, its orange-red flowers.

Montbretia has two methods of reproduction: fertilisation of the flowers by insects (and, in some closely-related Crocosmia plants, by wind or humming birds) to produce seeds; and vegetative reproduction, where each plant produces stolons, or runners, that form new plants when roots and leaves grow from nodes.

Flowering occurs over a period of days, with the first flowers at the base of the spike and then sequentially towards the tip, the production of seeds following the same sequence. This habit ensures that some flowers are likely to be fertilised during optimal conditions for pollination, and the seeds, similarly, are produced over time to ensure that dispersal is optimal. This flowering habit is a feature of many plants, but it is important to recognise that it evolved to the advantage of the plant a very long time before humans appeared. It was not designed by, and for, gardeners.

Vegetative growth by stolons ensures local colonisation and many gardeners like to divide dense clumps, as they tend to choke off other plants (a measure of the success of the strategy). Each individual montbretia grows from a corm and this develops after the successful germination of seeds and the growth of the first colonising plant. It is likely that the casual disposal of corms, rather than the spread of seeds, allowed montbretia (coppertips) to be such a successful coloniser of natural habitats, frequently forming large and vivid clumps on embankments and in coastal regions [2]. When established, its growth habit ensures its spread and it may now be regarded by some as a "wild flower".

 

Each corm is a store of starch grains produced synthetically after photosynthesis and this store allows the growth of leaves and stems at the beginning of the growing season. It is also used in shorter time scales to allow the efficient metabolism of the plant. Starch grains that are stored by plants for months often have their surface eroded [3], resulting from the action of naturally-occurring enzymes involved in releasing easily-metabolised sugars from the more complex starch. Among these is α–amylase and this enzyme is disabled in montbretia corms by the presence of a compound called montbretin. This ensures that starch grains are retained in good condition during resting phases, montbretin being of less significance when starch is being metabolised.

The presence of montbretin, the metabolism of the plant, the succession of flowers and seeds, and the vegetative spread by stolons, are all extraordinary adaptations that make montbretia such a successful plant and an effective invader. In addition, montbretia has recently received attention in the world human health, something which always results in wide publicity. It has been discovered that montbretin not only serves to protect starch grains from the action of α–amylase in Crocosmia corms, but may also inhibit the action of these enzymes in humans, something that offers the possibility of new drug treatments against diabetes [4]:

Type 2 diabetes mellitus is a condition that affects well over 320 million people worldwide and is closely associated with obesity. Among the oral antidiabetic drugs used for its treatment are the α-glucosidase inhibitors, which prevent hyperglycosemia by slowing digestion of starch and malto-oligosaccharides in the gut. Partial hydrolysis of starch is accomplished by salivary α-amylase, with principal cleavage provided by human pancreatic α-amylase (HPA) within the gut, generating linear and branched malto-oligosaccharides. These in turn are broken down to glucose by α-glucosidases that are anchored in the epithelium of the small intestine..

..Selective inhibition targeted at only HPA, the enzyme at the top of the starch digestion pyramid, could be used to quantitatively modulate blood glucose levels by restricting or even shutting down starch degradation, thereby minimizing the specificity problems that arise with currently available α-glucosidase inhibitors.

This is written in the technical language of a scientific paper, but Williams, Zhang et al. [4] then describe the selective nature of montbretin A (MbA) and its possible value in medicine:

Because MbA is such a potent inhibitor and is easily isolated from the corms of a readily grown plant (Crocosmia sp.), it has potential as a new agent for controlling blood glucose levels in diabetics and obese patients. 

So, the mechanism that evolved in Crocosmia to conserve starch grains is one in which the pharmaceutical industry is likely to show a great deal of interest, given the numbers of diabetics and the "epidemic" of obesity in many countries. This medical application could lead more people to think about the evolution of Crocosmia and its Natural History, helping us to move away from our dominant anthropocentric view and towards a sense of wonder in the capabilities of all living organisms. 

Well, it should do.

[1] Mark Van Kleunen, Steven D. Johnson and Markus Fischer (2007) Predicting naturalization of southern African Iridaceae in other regions. Journal of Applied Ecology 44: 594-603.

[2] http://www.nonnativespecies.org/factsheet/factsheet.cfm?speciesid=1040

[3] A. T Modi and R. Mare (2016) Alpha amylase activity and sprouting during short term storage of taro corms. Journal of Agricultural Science and Technology 18: 1053-1063.

[4] Leslie K. Williams, Xiaohua Zhang + 11 authors (2015) The amylase inhibitor montbretin A reveals a new glycosidase inhibition motif. Nature Chemical Biology: published online 27th July 2015 DOI 10.1038/NCHEMBIO.1865.

The best coffee?

Like many people, I enjoy drinking coffee. My preference is for lightly roasted beans and I don't mind whether the coffee is made using a French press, a filter, or a commercial coffee machine. 

World-wide demand is such that many countries now produce coffee beans and the resultant crops vary in quality, depending on whether they are grown at altitude, as an understory in forests, in intensive plantations, or by other farming methods. Coffea arabica, the most widespread coffee plant, comes originally from north-east Africa and its global spread has brought problems, with much effort being given to controlling coffee borer beetles and other pests. Spraying of the crop is sometimes needed as there is often no natural biological control of the pests, and monoculture provides optimal conditions for pest transmission.

Ripe "cherries" are red, those that are over-ripe are dull brown-red and those that are yet to ripen are green (see above), so hand picking is often the best method of collection. The bean that we roast is contained within the cherry and, in the picture below, a cherry has been halved and the two beans it contains partly removed. The pulp and mucilage that surrounds each are obvious, as is the white parchment-like coating of the bean itself.

Coffee beans only develop their flavour upon roasting so they must first be extracted from the cherry.  As in many fruits, the soft pulp evolved to protect the bean (seed) from drying, or abrasion, and the mucilage layer provides an extra barrier that also allows easy penetration of the shoot when the seed germinates. Mucilage has many functions in Nature [1] and the layer is important in allowing the production of the famous Kopi Luwak from Indonesia [2]:

Although Kopi Luwak.. ..comes from the Indonesian islands of Java, Sumatra and Sulawesi, it is not its exotic location of origins but rather its unusual and quite unexpected method of production which contribute to its mystique and price. The desire to consume unique food products is a characteristic of passionate coffee drinkers.

So, what is the method of production of Kopi Luwak? The skin and pulp of ripe coffee cherries are naturally sweet and are thus attractive as foods for a number of vertebrates. Among these, the African civet feeds on coffee cherries in north-east Africa, the original home of the plant, utilising the pulp and then depositing the beans, protected largely by the mucilaginous coat, in their faeces. This passage is the basis of the production of Kopi Luwak, and begins with the collection of faeces of palm civets (below, upper) that climb trees and eat the beans in situ. They would originally have fed upon the many other forms of fruit available, but the arrival of coffee plantations provided a new, and concentrated, source of food. Coffee beans are retrieved from the palm civet faeces (below, lower) and are then washed and prepared for export. The collection of faeces from the wild has now been superseded by a battery-farming approach [3], with caged civets being fed coffee cherries, but the beans that have passed through civets are still a very tiny part of the total market for coffee beans. The same is true of coffee beans that pass through Jacu birds [4], that rival the fame of Kopi Luwak.

Ingestion of fruits results in the dispersal of seeds, but there are many other methods for this essential process that are more familiar to us:

- Coconuts falling into the sea and being carried large distances to other islands

- The winged seeds of sycamore that we used as "helicopters" when we were children

- The "clocks" of dandelions, with each seed having a parachute

- The explosive pods of gorse that fling seeds large distances

- Seeds of avens with hooks that attach to animal fur

These are just a few examples of a large number of dispersal mechanisms that have evolved and all readers will know of others. However, the passage of seeds through animal guts is less familiar to us, yet we eat many berries and pay little attention to what happens to the seeds they contain. The purple droppings that result from birds eating blackberries, elderberries and other fruits are more familiar, especially to car owners in late summer, but we are less aware that the droppings often contain seeds and that these are deposited in fertiliser, far from the parent plant.

Anna Traveset has reviewed the effect of frugivores (birds, non-flying mammals, bats, reptiles, fishes) on the germination of seeds that pass through the gut of animals and concludes [5]:

In addition to moving seeds from the parent plant to sites that can be suitable for recruitment and seedling growth, frugivore seed dispersers have the capacity to modify the germination patterns of many plants by varying the potential germinability of seeds, the rate of germination, or both.

The effect on germination is complex and depends on many factors, varying also from individual to individual. Each plant is likely to produce many seeds, so the main beneficial effect of having fleshy fruits is dispersal, just as it is for the other mechanisms listed above. All worth thinking about when eating strawberries, or when savouring a cup of Kopi Luwak, This unusual coffee is yet another example of the extraordinary power of evolution and of the ingenuity of humans in taking advantage of natural processes. Is it the best coffee though?

[1] http://rwotton.blogspot.co.uk/2015/08/we-cant-exist-without-slime.html

[2] Massimo F. Marcone (2004) Composition and properties of Indonesian palm civet coffee (Kopi Luwak) and Ethiopian civet coffee. Food Research International 37: 901-912.

[3] https://www.theguardian.com/lifeandstyle/wordofmouth/2013/sep/13/civet-coffee-cut-the-crap

[4] http://modernfarmer.com/2013/10/flight-jacu-bird/

[5] Anna Traveset (1998) Effect of seed passage through vertebrate frugivores' guts on germination: a review. Perspectives in Plant Ecology, Evolution and Systematics 1/2: 151-190.

Garden plants, seeds and being unnatural

Flowering plants produce seeds and these are dispersed away from the parent plant, many mechanisms having evolved for this purpose. These mechanisms range from winged seeds, to those with parachutes, plants having “pepperpots” to scatter seeds, to those that use explosive discharge. Wide-ranging dispersal is achieved after attachment to, or ingestion by, animals, and seeds may also be carried very long distances by wind and water. Providing conditions in newly-colonised regions are suitable for development, plants are then able slowly to increase their range. With changes in climate, and the movement of continents, through geological time, flowering plants have been very successful in colonising almost all terrestrial habitats and even some aquatic ones. This success is not the result of dispersal ability alone, but also of mutations in their genetic structure, resulting in adaptations of both structure and physiology. As a result, flowering plants are found in deserts, on mountains and in high latitudes as well as the profusion of types we find in temperate and tropical regions.

When early humans began to cultivate some of the wild plants around them, they began to select those that could be bred to produce crop plants, this being accompanied by a reduction in diversity, as the natural community was managed by our farming practices. Yet further along in human evolution, when we started having plants for decoration, even more selective breeding was undertaken and, as humans began to migrate, it was possible to take the seeds of plants that we liked, or needed, with us. That is the background to the work of botanical collectors who, for centuries, journeyed to find new wild plants in distant countries and then bring their seeds back for cultivation. The extent of such deliberate imports is unique to the activities of humans; no other organisms do this.

Many gardeners are familiar with the huge array of types of garden flowering plants that are available (and we not only propagate from seeds), but less familiar with their origins. Below are some suggested plants for borders given by Anna Pavord, the excellent writer on gardening [1]; the types of borders (Anna Pavord’s headings) being for gardens in temperate Europe. The scientific names of plants are given, together with their common names and varieties (the latter resulting from selective breeding by horticulturalists) and the original geographical locations of the parent plants [2]:

Cottage-garden border

Viola labradorica (Purple-leaved violet) - North America, Greenland

Bellis perennis (Double daisy) - Europe, Turkey

Camassia leichtlinii (Quamash) - North America

Aquilegia vulgaris (Columbine) - Europe

Daphne x burkwoodii - Europe, North Africa, Asia

Geranium pratense (Meadow cranesbill) - Europe, Central Asia, China

Paeonia Sarah Bernhardt (Peony) - Europe, Asia, North America

Salvia sclarea (Vatican sage) - Europe, Central Asia

Thalictrum delavayi (Meadow rue) - Western China

Campanula lactiflora (Milky bellflower) - Caucasus, Turkey

Gypsophila paniculata (Baby’s breath) - Europe

Lychnis coronaria (Rose campion) - Europe

Of these twelve plants, eight (67%) have European origins and one further has a wide distribution with many European relatives. A characteristic of cottage gardens is their “naturalness” and the recommendations above contain cultivars of wild flowers likely to be found in close proximity to the garden, cottages being characteristic of the countryside - at least, that is the image to be created. The planting is boosted by the appearance of plants that are not part of the natural flora of Europe.

A scheme for scent

Lilium candidum (Madonna lily) - Europe

Narcissus jonquilla (Jonquil) - Spain

Thymus x citriodorus (Lemon thyme) - Garden origin

Lavandula angustifolia (Lavender) - Mediterranean

Rosmarinus officinalis (Rosemary) - Mediterranean

Pelargonium Mabel Grey - ?South Africa

Iris graminea - Spain to Russia + Caucasus

Dianthus Prudence (Pink) - Europe, Asia, South Africa

Thymus serpyllum (Wild thyme) - Europe

Hemerocallis citrina (Daylily) - China

Daphne odora - China, Japan

There are eleven plants in this list, with seven (64%) that originate in Europe. In two cases (Pelargonium and Dianthus), the origins are vague as the possible parental stocks have a worldwide distribution.

A tropical summer border

Ensete ventricosum (Banana palm) - Ethiopia to Angola

Cleome hassleriana (Spider flower) - Southern South America

Canna indica (Indian shot plant) - South America

Argyranthemum frutescens - Canary Islands

Pelargonium Royal Oak - ?South Africa

Aeonium arboretum - Morocco

Felicia amelloides (Blue daisy) - South Africa

Cosmos Sensation - Mexico

Nicotiana sylvestris (Tobacco plant) - Argentina

Ricinus communis (Castor oil plant) - North Africa to West Asia

Given that the intention is to create a tropical summer border, it is no surprise that none of the plants originate in Europe and, indeed, many can only be grown outdoors during summer, as they cannot tolerate cold temperatures. This is another feature of the power of humans in gardening - we not only use transplantation of species, but choose where, and when, to locate them. There is a wide geographical spread of origins, including one representative found solely on an island chain.

A bold desert bed

Datura (Brugmansia) x candida (Angels’ trumpets) - Garden origin

Gazania uniflora - Tropical Africa

Agave Americana - Mexico

Fuchsia Thalia - Central and South America

Begonia rex (King begonia) - Himalayas

Phormium tenax (New Zealand flax) - New Zealand

Aeonium arboretum - Morocco

Kniphofia caulescens (Red hot poker) - South Africa

Eucalytus niphophila (Alpine snow gum) - Australia

Crassula falcata (Aeroplane propeller) - South Africa

Echeveria gibbiflora - Mexico

Yucca whipplei (Our Lord’s candle) - USA, North Mexico

As would be expected, there are no representatives from Europe in this list and the geographic spread is even wider than for the tropical summer border. It is worth pointing out that some desert plants cannot be grown outdoors in most of Northern Europe and fanciers of cacti and some succulents will need heated greenhouses for their collections. This is an example not only of human ability to transplant, but also to change the environment in which the imported plants grow.

Although a very large number of plants have been collected for gardens, some have escaped and invaded surrounding areas, mingling with the native flora. This represents a reverse of the position of weeds (wild, native plants) in gardens and, while many of the invaders from gardens provide an excellent “show”, some have habits which mean that they become a nuisance, sometimes dominating, and excluding, local plants that would not have to compete under natural conditions with these very recent invaders. There are many examples and I’ll just mention three.

Hedychium gardnerianum (Kahili Ginger - below, top) is native to the Himalayas and is a striking plant which has been imported both for its foliage and for its scented spikes. It produces sticky seeds that aid dispersal in its natural habitat and these also provide one of the means that encourage its spread elsewhere. It has become a serious invasive pest in several areas of the world and, once present, is difficult to remove. The same can also be said of my other two examples: Impatiens glandulifera (Himalayan Balsam - below, middle) and Fallopia japonica (Japanese Knotweed, below, bottom). As its common name suggests, I. glandulifera is, like H. gardnerianum, a native of the Himalayas and shares the same high dispersal ability. The balsam has attractive pink flowers which appeal to gardeners, and its success in dispersal results from the explosive release of seeds that scatter from the parent plant. As riparian zones of streams and rivers are especially favoured by these invading plants, the flowing water provides another excellent means of dispersal, as the seeds are carried downstream after being shot out.

F. japonica colonises many habitats.  A hollow-stemmed plant, it shows rapid growth and produces many leaves, giving effective ground cover and, with its height, a means of hiding unattractive or derelict areas. Vegetative growth by means of rhizomes ensures that there is strong lateral spread and only a small section of rhizome is needed for the successful growth of a new plant, the rhizomes possessing such strength that they can cause damage to buildings and any solid structures with which they come in contact. Once established, Japanese Knotweed is very difficult to kill and it is such an effective plant that special operatives may be necessary to remove it.

The collection of seeds from plants that grow in very distant regions, and then bringing them to countries that are highly unlikely to be colonised naturally, is a means of dispersal that is markedly unnatural. It should therefore not surprise us when some plants - and animals - "escape" and reach pest levels. They have been transplanted from the regions where they evolved over millions of years and where they are part of different, complex communities that contain natural controls.  It is another result of humans needing to modify Nature, rather than feeling part of it.

[1] Anna Pavord (1994) The Border Book. London, Dorling Kindersley.

[2] Christopher Brickell [Editor-in-Chief] (1996) The Royal Horticultural Society A-Z Encyclopedia of Garden Plants. London, Dorling Kindersley.