The starchy endosperm of wheat, Triticum aestivum, has three major components: protein, starch and cell wall polysaccharides, which are are not homogenously distributed across the tissue. Using antibodies for specific gluten protein types, Tosi et al. find that quantitative and qualitative gradients in gluten protein composition are established during grain development. These gradients may be due to the origin of subaleurone cells, or could result from the action of specific regulatory signals produced by the maternal tissue on specific domains of the gluten protein gene promoters.
The origins of the economically important tetraploids in Arachis (including peanut) have largely been studied; however, the polyploidization pathway through which they arose still remains unknown. Lavia et al. make a detailed cytogenetic analysis of the recent, spontaneously originated triploid cytotype of A. pintoi and find that this cytotype arose by autopolyploidy. The occurrence of unreduced gametes strongly supports sexual polyploidization as the most probable mechanisms involved in the origin of polyploid species of this genus.
I’ve learned a lot from a new article in AoB PLANTS, the Open Access sister Journal to Annals of Botany. It’s Green love talks; Cell-cell communication during double-fertilization in flowering plants by Tomokazu Kawashima and Frederic Berger and it shows how things get really interesting when simple analogies break down. The paper is a review of recent research on cell signalling and how it works to ensure successful fertilisation of flowers by pollen. Borrowing from the title, it’d be easy to try and conjure up a start like: “Experts have got it right, the key to a successful relationship is communication.” But Kawashima and Berger show that there are times when anthropomorphising plants can effectively hide what is so fascinating about them.
The issue is how does signalling work to get the male material into the female reproductive cells to start the seed making process? I’ve had the talk, so I know that it’s a matter of delivering sperm to the egg, so it’s just a case of making sure that the female organs signal they’re receptive, yes? In the case of angiosperms, flowering plants, it’s more complex. You need two male gametes to fertilise two parts of the female. There’s a central cell and within that there’s an egg cell.
This has been source of a puzzle for plant scientists. There are two female cells, so presumably there are two male cells, yet they’re coming from the same source i.e. a pollen grain that’s landed on the stigma and germinated there. How does the plant stop the wrong male cell getting to the wrong female one?
The answer found from studies of flowers, including Arabidopsis thaliana, is a surprise. They’re not two types of male cell. As the authors report, advances in high resolution imaging mean that they can identify that the two male cells are identical. All the hard work seems to be done by the female parts of the plant. Cells surrounding the egg cell produce proteins to attract the pollen tubes, and signalling between the female cells makes sure everything is delivered to the right place.
To be honest, some of the language in the paper is daunting. Being a human I’m used to the idea that plants are passive. No doubt, Kawashima and Berger would emphatically disagree. There’s a lot going on in a pollinated flower and the uses of various terms and proteins can be dizzying. What they show is that the signalling is complex. When you think about the scale of the operations it’s hard to see how so many proteins can be shuffled, ordered and directed to make everything happen. Far from silence, it looks like there’s a well-orchestrated chemical symphony being played in the cells that makes the double-fertilization possible. Keeping on top of all the detail means that the paper is not light-reading. It can however be rewarding reading.
The best papers don’t simply answer questions, they also open up new avenues of research. Here Kawashima and Berger are extremely helpful. If you’re looking for something to research in signalling then the authors have erected big signposts in the conclusion with big arrows marked ‘mysteries this way’. If you’re looking for a departure point into cell-cell signalling, then this looks like a helpful guide to where the interesting puzzles in mechanisms are.
Plants are people too? Well, before you put in the call to have me taken me away, let me explain where I’m coming from. Way back in 2003, when I was an undergraduate in plant science at the University of Edinburgh, one of our Professors, Tony Trewavas, published a paper in Annals of Botany titled ‘Aspects of Plant Intelligence.’ Controversial as it was, like all good science it questioned the status quo and provided a wealth of evidence to support its central claim that plants are intelligent organisms, despite their sessile, seemingly passive lifestyle.
Professor Trewavas’ paper got me thinking about the wider social and ethical implications of plant intelligence and I wrote my new book, Plants as Persons: A Philosophical Botany, as my response to the thought provoking ideas. First and foremost I wrote ‘Plants as Persons’ because I wanted to find out why it is that we generally view plants as passive and unintelligent and why we don’t include them within our moral responsibilities. These are positions we might well think of as ‘normal’, I knew that other cultures had very different views plants. I wanted to also understand how these perceptions influenced people’s behaviour towards plant life.
In order to try and tackle these questions, the book surveys a very wide range of disciplines and bodies of thought, from ancient Greek writings on nature, through the history of botany, Christian scripture, the Hindu Vedas to scholarship on Indigenous animist cultures and the growing scientific literature on plant neurobiology.
The first three chapters look at this ‘exclusion’ of plants from the moral sphere in western philosophy. The basic argument runs that plants were deliberately excluded from the moral sphere through by the influential trinity of Plato, Aristotle and the Bible because it was decided that the faculties which humans or animals possess are somehow radically different and therefore superior to those plants possess. To back up such claims, plants are portrayed as lesser forms of life with lesser faculties, lacking in sensation, movement and crucially the defining human faculty, intelligence. Interestingly it is always humans evaluating themselves as the superior organism! Time and time again, this portrayal of passive plants is connected with a need to claim the natural world purely as a passive human ‘resource’ (as happens in Plato, Aristotle, the Bible) rather than as an equally valid, locus of being.
For me, this process of exclusion only really became clear when I researched more into other cultures (including Indigenous animists) where plants are related to as proper persons (with all the respect that deserves) as well as being resources. This view of plants stems largely from a sense of kinship – a pre-Darwinian appreciation of common ancestry, with all creatures recognised as coming from, and returning to, the Earth. It also arises from the practical fact that (as anyone who works closely with plants sees) plants obviously actively live their lives. They grow in incredible places, they sense and communicate, they are pretty self-sufficient, they live and flourish, reproduce and die – a view that is corroborated by much recent evidence in the plant sciences.
This subtle change from a stance of exclusion to one of inclusion has important consequences. Rather than behaving towards plants as resources which are available to humans to do as they see fit, with little restraint, plants become appropriate recipients of care and respect in their own right, regardless of whether they are ‘useful’ or not. Indigenous peoples express this relatedness and responsibility towards plants by including them within their family ties. Viewing the grey mangrove (Avicennia marina) in Australia’s Northern Territory as her ‘most senior paternal ancestor’, a Yanyuwa woman, Annie Isaac, behaves towards them with all the respect due to elder family members. Most importantly this means that the mangrove habitats are not treated as a vacant space, or as a commodity which must prove its economic worth. They are places that are full of persons which must be considered when making land management decisions. As we move deeper into the human dominated era now known as the ‘anthropocene’, perhaps we could use such relationships as a guide for translating our increasing knowledge of plant intelligence into our actual behaviour towards plants and the ecosystems they underpin.
Royal Botanic Garden Edinburgh
There is considerable discord among treatments of the Velloziaceae despite the large amount of data that exists for this family. Mello-Silva et al. undertake analyses of 48 species representing all ten genera, including data on DNA sequences from the atpB-rbcL spacer, trnL-trnF spacer, trnL intron, trnH-psbA spacer, ITS ribosomal DNA spacers and morphology. The results imply recognition of five genera (Acanthochlamys (Xerophyta (Barbacenia (Barbaceniopsis, Vellozia)))), solving the long-standing controversies among recent classifications of the family. They also suggest a Gondwanan origin for Velloziaceae, with a vicariant pattern of distribution.
The bacterium Xylella fastidiosa, responsible for Pierce’s disease of grapevine, colonizes the xylem conduits of vines. Chatelet et al. examine the xylem structure of several varieties of grapevine, Vitis vinifera, and other plants to determine if anatomical differences might explain some of the differences in susceptibility to infection. They find that tolerant vines have narrower vessels and more parenchyma rays in their stems than susceptible ones, possibly restricting bacterial movement at the level of the vessels.
Polyploidy is a major evolutionary force generating new plant species. Hunt et al. explore the dynamics of allopolyploid speciation in the western Mediterranean rock fern Asplenium majoricum at a site where it occurs sympatrically with its diploid parents and their diploid hybrid. Analysis of genetic diversity in allotetraploid and progenitor populations shows recurrent formation of hybrids and polyploids, but polyploid populations have established successfully only in geographic isolation from diploid parent taxa.
I was in London earlier this week for an editorial meeting with many of the Annals of Botany members. As part of it, I took my first trip to Kew. So long as you’re not thinking, you can take a pleasant stroll around the gardens in two or three hours. There’s some nice shaded paths beneath the trees and some well-sculpted displays. If you stop and start thinking “Hey! Almost every one of these trees is different from its neighbours, how much effort is it to keep them all growing and healthy?” then you’ll need days. I took a few photos there and had the odd experience of one coming out as I expected it too. Usually I take dozens and try and find one I can rescue into something viewable.
This is a Wollemi Pine. It’s found in Australia, but not very often as there’s fewer than 100 of them in the wild. It was also, till 1994, thought to be extinct as it was only known from fossils. It wasn’t till less than 20 years ago a stand of them was found 60 miles out of Sydney. Professor Carrick Chambers, director of Sydney’s Royal Botanic Gardens, said at the time of the discovery that it was “the equivalent of finding a small dinosaur still alive on Earth”.
Why are sterile anthers and carpels retained in some flowering plants, given their likely costs? Yu et al. study a cryptically dioecious species, Petasites tricholobus, in which male and female plants each have two floret types that appear pistillate and hermaphroditic. Sterile female structures in male florets are found to be essential for secondary pollen presentation, which significantly enhances pollen dispersal, whilst sterile hermaphroditic florets on female plants attract pollinators by producing nectar. Sterile pistillate florets on male plants, however, do not contribute to floral display and are only found in about 55 % of plants, suggesting that they may be vestigial and will disappear over time.
… well, it’s not a plant! And how predictable! The Top 10 new species of 2010 includes no plants. However, before all readers of this column jointly and severally get incensed, we must ask the obvious question: were any new plants discovered in 2010? Let me see: oh yes, there were! In fact, ‘On average, 2,000 new plant species are discovered each year’ and a small selection can be seen on the RBG Kew site at http://www.kew.org/news/science-conservation-news/discovery/discovered-2010/index.htm. So, why were there no plants – and here I mean proper plants, members of the Kingdom Plantae – in the top 10? Are plants not photogenic? Are they not useful? Were would we be without them? Why are they so unappreciated? Is it that they don’t move? (See first article in this month’s collection if still in doubt!) In the so-called top 10 were a large monitor lizard, a jumping cockroach, Titanic-eating bacterium, a duiker (type of antelope), Darwin’s Bark Spider, a T. rex leech, a pancake batfish, a mushroom that fruits underwater, and a bioluminescent fungus. I suppose the fungi have the virtue of being ‘not animals’. The lizard is frugivorous so at least has a plant association, as does the no-doubt herbivorous duiker. The only organism with anything like half-decent plant credentials is the pollinating cricket (http://species.asu.edu/2011_species05; whose pollinating activity was announced to the world in an article in this very journal: Annals of Botany 105: 355–364, 2010), but which was dismissively described as a ‘pollinating cockroach’ in the news item at http://www.physorg.com/news/2011-05-scientists-species.html! That notwithstanding, this top 10 is pure phytophobia and will not – indeed, must not – be tolerated. So, I urge you all to get voting now for the 2012 list of the top 10 new species from 2011 at http://species.asu.edu/species-nomination, and let’s try to get a plant into the top 10! Maybe next year might be better anyway because the IISE (the University of Arizona’s International Institute for Species Exploration), the organisation that runs the top 10, has recently been partnered by AIPC (the Italian Carnivorous Plants Association). Why might this help? Well, a new pitcher plant Nepenthes attenboroughii (pictured above) was one of the previous year’s top 10 new species (http://species.asu.edu/2010_species01). And at least carnivorous plants do something… Finally, for those who’d like to see the ‘pollinating cockroach’ in action, the IISE helpfully provide a ‘click here’ link (http://news.bbc.co.uk/1/hi/8391540.stm) ‘to see video of the cricket pollinating the orchid provided by the BBC’ [one imagines it will also pollinate orchids provided by other news agencies(!)].