Category Archives: Bite-sized Science

Suggestions needed for the ten best of everything: plants for botanists

Three plant species for my ten best of everything: wheat, pine and arabidopsis

Three plant species for my ten best of everything: wheat, pine and arabidopsis

Some time ago, I started on an AoBBlog post (or maybe posts) on ten plants that all botanists should know quite a lot about. Criteria for inclusion on my list include, at the least, importance in the environment, importance to people as food or culturally, scientific interest, global nature, and evolutionary position. Together, the species (genera? even families?) chosen should illustrate a wide range of botany and complement each other. So, here I give my current list of starters; the order is computer-sorted random.

Wheat (or rice)

Arabidopsis

Drosera (or Pinguicula)

A legume – but which one? Acacia? Arachis? Trifolium? Pisum? Glycine?

Physcomitrella (or Sphagnum or another non-vascular plant)

Wollemi pine (Ponderosa pine?)

Rose

Banana

Lycopodium

Oak

I’m deliberately not including reasons for my choices here – they will be included in the final posts – but suggestions of what I have missed would be welcome – along with those species that should not make the cut and should be replaced. I suppose I could stretch to a dozen species if needs be.

Comments below please!

Carving in Perugia: the cultural importance of three families of my top ten species

Carving in Perugia: the cultural importance of three families of my top ten species

My favourite colour is structural colour

Colours of a Peacock Head

What do peacocks, CDs and certain plants have in common? They all have multi-coloured parts – feathers, surfaces or petals – which change their hue depending on the angle you look at them. This physical phenomenon in which an ordered repeating surface structure rather than a pigment gives an object its colour is called iridescence.

Iridescence has evolved multiple times in plants and occurs in a lot of land plant families, from angiosperms to algae and ferns. It can impact on how insects and animals see plants. Dr Heather Whitney, a plant scientist from Bristol University, was awarded the President’s Medal of the Society of Experimental Biology (SEB) last week for her novel and interdisciplinary work. Heather studies how plant surfaces become iridescent and how iridescence influences plant-animal interactions.

Heather started her presentation by talking about how she became interested in her study field. When she went to the Botanic Garden she noticed that even though most flowers of Hibiscus trionum (pictured below) were creamy white, their centre had an oily sheen. So she decided to look at the petals with an electron microscope and realised that the surface looked very structured: The oily sheen on the petals is caused by iridescence.

Hibiscus trionum flower closeup

One way to proof that a flower’s colour is created by iridescence is to replicate the petal structure in epoxy resin, which makes the clear resin shine blue when looked at from a certain angle. This is why iridescence is also called a “structural colour”.

Ophrys speculum

One function of iridescence in plants is to make them more appealing to pollinators. An example is the “sexually deceptive orchid”, Ophrys speculum (pictured right). It pretends to be an animal by mimicking the wings of a female wasps. Similarly, Moraea villosa copies the iridescence of pollinating beetles.

If, like me, you now feel inspired to plant iridescent species in your garden, why not start with tulips?
Iridescent Tulip

Image Credits
1. Peacock Head by Cuatrok77 at Flickr. This image licensed under a Creative Commons by licence.
2. Hibiscus trionum flower closeup by la la means I love you. This image licensed under a Creative Commons by-sa licence.
3. Ophrys speculum (plant) by Hans Hillewaert. This image licensed under a Creative Commons by-sa licence.
4. Iridescent Tulip by Anne Hornyak at Flickr. This image licensed under a Creative Commons by-sa licence.

The Enormous Influence of Microscopic Marine Plants

Diatoms

Diatoms by Randolph Femmer / USGS Library of Images From Life via pali_nalu@Flickr

Many phytoplankton share a common feature with their larger non-aquatic cousins, the land plants: chloroplasts. Therefore they are also united in their ability to photosynthesize and their environmental requirement of sunlight. Phytoplankton occupy the surface waters of our oceans where sunlight can penetrate. They account for more photosynthesis, carbon dioxide fixation and oxygen production than all the worlds rainforests combined. As the primary producers of the oceans they provide the basis of the oceanic food chain and have contributed to the evolution of the largest living creatures on earth. Phytoplankton feed zooplankton and these minute organisms in their billions make up the diets of hundred ton whales, alongside other filter feeders. Many predatory fish such as mackerel and tuna feed upon these filter feeders, which we humans in turn enjoy.

The range of darks blues, bright turquoise hues to deep greens of the world’s oceans is attributable to the range of different compositions of microscopic algae populating different regions. This is also true when more unusual areas of colour such as pinks and reds appear – a result of algal blooms. This spectrum of colours is due to the variety of photosynthetic pigments present in the microscopic organisms. Despite their beauty, not all of these blooms are beneficial to life. Some produce toxic compounds that in high concentrations can exert harmful effects on both the marine and coastal life. For example Karenia brevis secretes neurotoxins potent enough to lead to fatalities of marine life and birds which feed upon them. However algal blooms need not produce toxins to be fatal. Unusually large numbers of phytoplankton in an area can tip the balance from providing vast quantities of food for feeding marine life to producing a fatal depletion of oxygen.

Stirring Up a Bloom off Patagonia by NASA Goddard Photo and Video

Prior to seeing these organisms at higher magnifications it is too easy to instinctively imagine the constituent parts of algal blooms as relatively undifferentiated globular organic material. The reality of their cellular architecture couldn’t be further from this depiction. Magnified several hundred times the intricate structure of individual unicellular plants is revealed to be highly structured, some with crystalline characteristics reminiscent of snowflakes drifting in the water. Upon first glance at a collection of micrographs, the diversity and complexity between species appears potentially infinite in their highly differentiated conformations. This is just one example of how in nature the closer you look, the more intricate organization presents itself in surprising forms.

Images

Diatoms by Randolph Femmer / USGS Library of Images From Life via pali_nalu@Flickr. Licenced under a Creative Commons BY-NC licence.
Stirring Up a Bloom off Patagonia by NASA Goddard Photo and Video. Licenced under a Creative Commons BY licence.

The Vacuole: not just an empty hole!

The vacuole is the largest organelle of a plant cell. It accumulates proteins, ions and secondary metabolites while providing turgor for cell growth via water content. It is also a major site for the degradation of macromolecules. A full understanding of the vacuole’s roles in salt and metal ion accumulation and water uptake are hot topics in current research. It is a necessity to understand these processes for potential exploitation in production of future stress tolerant crops. How the vacuole is made and where it comes from remain unanswered questions. What we do know is a plant without vacuoles is a dead plant (Rojo et al 2001)!

The simplest view is of a single vacuole fulfilling all roles. However, to achieve such a diverse set of functions, specialised vacuoles must exist; a single vacuole cannot function as a storage compartment and dustbin at the same time! Lytic Vacuoles (LVs) are hydrolytic, acidic compartments responsible for the breakdown of a variety of macromolecules, while Protein Storage Vacuoles (PSVs) accumulate proteins in storage organs such as seeds. Up until a few years ago it was thought these two vacuole types could coexist. It now appears their coexistence in a single cell is a rare occurrence (Frigerio et al 2008). PSVs are only found in seeds, whilst LVs are prominent in vegetative tissues. Interestingly, the PSV alters it’s identity and function to become an LV during development (Marty 1999 and Zheng et al 2011).

One way researchers identify different vacuoles is by visualising proteins at the vacuolar membrane, such as aquaporins. Aquaporins are membrane channels that transport water and other small molecules; some of which do so at the vacuolar membrane, the tonoplast. These are called Tonoplast Intrinsic Proteins (TIP) and are used as vacuole ‘markers’. In the model plant Arabidopsis thaliana, 10 TIP isoforms exist (Johanson et al 2001). Different isoforms are expressed at different stages of development and in different plant organs. The most recent expression map of these isoforms to date uses translational fluorescent protein fusions to highlight isoforms at different tissues in the root (Gattolin et al 2009). By having an expression map of TIPs, researchers can begin to understand functional differences between isoforms, which could have different roles in water uptake.  The most common markers are TIP3;1 which exclusively labels PSVs in the developing embryo, and TIP1;1 which labels LVs post germination.

Stained plant cells

Left: Arabidopsis leaf epidermal cells, LV tonoplast shown in green using fluorescently tagged TIP1;1. Right: Mature Arabidopsis embryo cotyledon cells, PSV marked using fluorescently tagged TIP3;1 (http://www.illuminatedcell.com/Vacuolarsystem.html)

Confocal microscope images using these markers have most recently been compiled in video form, with a chirpy accompanying song in which the vacuole introduces itself. Created by Dr Anne Osterrieder of Oxford Brookes University in collaboration with Dr Lorenzo Frigerio and PhD student Charlotte Carroll at the University of Warwick; the video and accompanying song are part of a series of organelle teaching aids. Enjoy!

You can read more about vacuoles at The Illuminated Cell, who kindly provided the image of the tagged plant cells.

References

FRIGERIO L, HINZ G, ROBINSON D.G. (2008). Multiple vacuoles in plant cells: rule or exception? Traffic 9:1564-1570. doi:10.1111/j.1600-0854.2008.00776.x

GATTOLIN S, SORIEUL M, HUNTER P.R, KHONSARI R.H, FRIGERIO L. (2009) In vivo imaging of the tonoplast intrinsic protein family in Arabidopsis roots. BMC Plant Biology 9:133. doi:10.1186/1471-2229-9-133

JOHANSON U., KARLSSON M., JOHANSSON I., GUSTAVSSON S., SJOVALL S., FRAYSSE L., WEIG A.R., KJELLBOM P. (2001) The complete set of genes encoding major intrinsic proteins in Arabidopsis provides a framework for new nomenclature for major intrinsic proteins in plant. Plant Physiology 126:1358-1369. doi:10.1104/pp.126.4.1358

MARTY F. (1999) Plant Vacuoles. Plant Cell 11:587-600. doi:10.1105/tpc.11.4.587

ROJO E, GILLMOR S, KOVALEVA V, SOMERVILLE C.R, RAIKHEL N.V. (2001) VACUOLELESS1 Is an Essential Gene Required for Vacuole Formation and Morphogenesis in Arabidopsis. Developmental Cell 1:303-310. doi:10.1016/S1534-5807(01)00024-7

ZHENG H. and STAEHELIN A.L. (2011) Protein Storage Vacuoles Are Transformed into Lytic Vacuoles in Root Meristematic Cells of Germinating Seedlings by Multiple, Cell Type-Specific Mechanisms. Plant Physiology 155:2023–2035. doi:10.1104/pp.110.170159