Plant Cuttings

A tiny silver bullet^[1] for cut flowers?

The cut flower industry – wherein stems of intact growing flowering plants are removed, and transported from their place of growth to a place of purchase by a customer and ultimately displayed in a vase (“a container for holding flowers”^[2]) containing water – is big business*. In the UK in 2006 it was estimated to be worth approx. £2 billion annually (about the same as the UK music industry at that time…)^[3]. And globally, the flower trade – which phrase includes not just cut flowers – was worth US$101.84 billion as long ago as 2003^[4]. Undeniably, that’s a lot of money to those who sell the cut flowers, and a considerable outlay by those who purchase them. And, as a purchaser, you would like to be (re)assured that those carefully-selected blooms stay alive as long as possible once brought home, or gifted to the recipient. For many years the life of those blooms has been extended by the use of so-called ‘flower food’. Often supplied as a sachet with the blooms themselves, this food contains organic compounds that act to variously inhibit microbial growth, reduce pH of the vase water, and provide the plant with a ready-made organic energy source^[5,6]. Although one might scoff at the necessity for such potions – yet another money-making scam/add-on that increases the cost of those already-too-expensive blooms? – they are necessary and do work, according to The British Florist Association^[7]. In case you think that source may not be as independent as you’d like for a scientifically-robust, evidence-based adjudication, the same conclusion was also reached by Melanie Pinola at LifeHacker^[8] who researched several ‘cut-flower-life-prolonging’ interventions** Although use of such chemical additives to prolong ‘vase life’ is important for any cut flower, it is arguably more so for those flowers with short vase lives, such as peonies^[9,10]. In an attempt to maximize vase life of Paeonia lactiflora^[11,12], Daqiu Zhao et al.^[13] investigated use of nano-silver – particles of silver that are typically 25nm in diameter^[14,15] – which has demonstrable anti-microbial properties^[16,17]. Amongst a number of physiological and biochemical changes, nano-silver application led to an increase in vase life of 4 days – a 50% increase on ‘non-nanotech’d’ stems. In part this was related to inhibition of growth of bacteria (which blocked the cut stem-ends of non-treated flowers), and induction of aquaporin genes. Aquaporins are membrane-located “highly regulated channels controlling plant water relations”^[18,19]. Changes in the activity of aquaporin genes is suggested to have helped in “maintaining the water balance” of the cut flowers***. I wonder if you could achieve the same effects with gold nanoparticles? Or would that be construed as gilding ^[20,21] the, err, lily^[22]?

* But also an industry that raises major concerns over its environmental-sustainability^[23] and ‘green’ credentials^[24,25].

** For an illustrated guide to the life-sustaining worth of such compounds, the American Chemical Society has a helpful video ^[26] that accompanies Compound Interest’s^[27] Andy Bunning’s infographic on the subject ^[28].

*** Having prolonged the life of your peonies, what if you’ve not that happy with the flower’s colour? Well, there is apparently some scope for changing this by alterations to pH. Their pink flower colour comes from the pigments the flowers contain – in particular peonin (an anthocyanin pigment^[29,30]), whose colour – ranging from blue to red – is pH-dependent ^[31]. However, it’s probably not as straightforward as this might suggest; the ratio of at least six anthocyanins – including peonin – contributes to the wide range of flower colours in the different cultivars of Paeonia suffruticosa^[32]. Whether colour change of what one assumes are vacuole-located pigments can be effected by alteration to the pH of the water in the vase is not known – maybe this could be taken further as a student project idea? If you’re just not happy with your peonies (in which case why are you bothering with them in the first place..?), you might like to experiment with a form of allelopathy (“chemical inhibition of one species by another”^[33,34]). When placed in a vase with cut flowers of a different species, such as roses and tulips, cut daffodils (Narcissus pseudonarcissus^[35]) can cause their non-Narcissus neighbours to wilt prematurely^{[36, 37]}. By contrast, daffodils delayed senescence of cut iris flowers ^[38,30]. Another series of student projects – for those of a more phytomurderous persuasion..?.

[Ed. – if your interest in cut flowers has been whetted by the above, you may be interested to know that genome sequences and analyses for Rosa chinensis^[40,41] have been published by L. Hibrand Saint-Oyant et al.^[42] and Olivier Raymond et al. ^[43], with a commentary thereon by Aureliano Bombarely ^[44]. Why mention roses in connection with this news item? Roses are amongst the ‘top 10’ cut flowers ^[45,46].]

Image from: Wikimedia Commons

New form of photosynthesis that’s above par^[1]

PAR is the acronym^[2] for Photosynthetically-Active Radiation^[3], and refers to light with wavelengths of 400 – 700 nm ^[4], the so-called visible spectrum, from red to violet^[5,6]. PAR is photosynthetically-active because it encompasses the range of wavelengths absorbed by pigments involved in photosynthesis – Chlorophyll a (Chl a) and various accessory pigments^[7,8], including Chlorophylls b, c, and d, and carotenoids. Although a wide range of wavelengths within that PAR band are absorbed by the multiplicity of pigments involved in photosynthesis, the energy associated with that radiation is ultimately passed to Chl a molecules that are at the reaction centres of the two photosystems (PSs^[9,10,11]) that drive photosynthesis. The Chl a that drives the energisation of the electrons in photosynthesis also, and importantly, absorbs light in its own right, maximally at 680 nm (in PS II) and at 700 nm in PSI, both of which are visible red wavelengths. Once absorbed by, or/and transferred to, Chl a this light energy is ultimately used to facilitate production of ATP (Adenosine TriPhosphate^[12,13,14]) and NADPH (Nicotinamide Adenine Dinucleotide Phosphate Hydrogen^[15,16]) in the so-called light reactions of photosynthesis (more formally, the light-dependent reactions^[17]). This ATP and NADPH subsequently participates in the light-independent reactions of photosynthesis^[18] – formerly termed the dark reactions^[19] – in which carbon dioxide is enzymically-incorporated into organic molecules for growth, etc. of the plant. Although PAR is a term that refers to the oxygen-producing form of photosynthesis engaged in by members of the Plant Kingdom^[20], it is also relevant to the photosynthesis undertaken by algae and seaweeds (the ‘old-fashioned’ Kingdom Prot(oct)ista^[21]), and oxygenic photosynthesis by specialised bacteria known as cyanobacteria (formerly, or still known nowadays – by those of us of a certain age and taxonomic preference – as ‘blue-green algae’^[22,23]) within the Domain Bacteria^[24,25]. And that view of photosynthesis all seemed nice and tidy and straightforward, is found in the textbooks, and is what we teach our students in the belief that this was the situation in nature. The cosy status quo was shaken-up a little a few years ago by discovery of a new chlorophyll – Chlorophyll f (Chl f) – isolated from cyanobacteria in stromatolites ^[26,27] in Australia by Min Chen et al.^[28] which absorbed and used light beyond the PAR range, at 706 nm. However, it had been presumed that Chl f was an accessory pigment, the ultimate driver of photosynthetic-energisation of electrons in those microbes – and as in all other oxygenic photosynthetic organisms – was Chl a. Indeed, so entrenched was this view of photosynthesis that a ‘red limit’^[29,30] was believed to exist which restricted photosynthetic electron-energising to wavelengths no greater than 700 nm (which light is red). Certainly, it did not extend to use of far-red light beyond 700 nm that Chl f absorbs. That view has now been seriously challenged by work from Dennis Nürnberg et al.^[31] using the cyanobacterium Chroococcidiopsis thermalis^[32,33]. When grown under 750 nm far-red illumination, photosystem II of the blue-green operated with 745 nm wavelength (solely down to Chl f), and at 727 nm for photosystem I, which may be due to Chl f (or Chl d, but – and importantly – a longer-wavelength-absorbing Chl than Chl a). Although Chl f in these complexes also acted in a light-harvesting capacity, the crucial observation is that far-red wavelengths – beyond the red limit of photosynthesis – were sufficient to drive the photochemistry of photosynthesis in these organisms. Even though Chl f can absorb at wavelengths in excess of 760 nm, the authors propose that 727 nm may be the ‘second red limit’ for photosystem II functioning. This new form of photosynthesis appears to be advantageous for organisms living in nature in deeply shaded environments where such far-red light naturally occurs. Other commentators suggest this discovery may be relevant to our searches for extra-terrestrial photosynthetic lifeforms, maybe on Mars^[34]. Mr Cuttings’ take on this is much closer to home, and relates to recent – and on-going – discussions about where life began on Earth (e.g. ^[35,36]), and hydrothermal vents^[37,38] in particular. Although they are high temperature, high pressure environments devoid of surface – sun-derived – light, deep-sea hydrothermal vents may have their own in situ illumination. That radiation, so-called geothermal radiation, is long wavelength – beyond the visible spectrum and therefore PAR – and is comprised of the electromagnetic radiation given off by hot objects in those high-temperature regions^[39,40,41]. Maybe primitive organisms evolved in such places with molecules that absorbed and exploited the long-wavelength light in an early version of photosynthesis. Some of those may have given rise to extant unicells such as Chroococcidiopsis thermalis, and others may have been the precursors of organisms that became the chloroplasts of eukaryotic cells via the operation of the Serial Endosymbiotic Theory^[42,43]. Subsequently, those radiation-absorbing pigments diverged and changed in response to visibly-lit environments giving rise to Chls a, b, and other accessory pigments, etc…. Thus, this exciting (yes, pun recognised and fully justified…) 21^st century research may help to support the case for hydrothermal vents being the ‘cradle of life’ on Earth many billions of years ago*. In any event, textbooks will need to be amended to accommodate this new form of photosynthesis.

* Exploitation of this discovery could also help in generating plants that can use a greater proportion of the sun’s radiation than at present. For example, Rienk van Grondelle and Egbert Boeker argue that re-engineering plants to better exploit wavelengths from 700 to 900 nm is worth investigating^[44]. Or one could just try to make better use of long-wavelength-absorbing pigments apparently already present in sunflowers^[45]. Such enhanced photosynthesis and increased crop productivity might go a long way to eliminating food security issues ‘at a stroke’. Alternatively, why not engineer bacteriochlorophylls^[46] into our crop plants? These molecules (one can’t call them pigments since they absorb non-visible wavelengths), that can use irradiation up to 1050 nm wavelength^[47,48], might be another as-yet-unexplored microbe-higher plant ‘symbiosis’..?

Image from: Wikimedia Commons

Big news items this month

Mr Cuttings recognises that the two news items above are longer than usual for this column. That’s because they appear in a summer-time issue of the Annals of Botany and represent his notion of vacation reading for the intelligently phytocurious. Happy holidays! However, to redress the balance somewhat, here’s a really short item…

Raising awareness of plant blindness

Readers of this column will know that there is a problem with the inability – or unwillingness – of people generally to appreciate plants. This is the well-recognised phenomenon of plant blindness^{[1,2,3,4,5,6]}. Although we’ve talked about it before in Plant Cuttings items (e.g. ^[7,8,9,10]), it’s now time to go visual. To that end I’d shamelessly like to showcase the work of one of my university’s undergraduates. Benedict Furness, an Honours Biology student, produced a video about plant blindness that deserves to be seen by an audience wider than those select few at his alma mater^[11] Bath Spa University^[12,13]. Benedict has kindly agreed to allow the video – viewable at ^[14] – to be shared with readers of this column. Produced as part of his coursework it eloquently articulates the problem of plant blindness and suggests ways in which this can be overcome. Please watch it, and share it in the hope that we can all help to make a difference to this issue. Should you want to follow-up on the video, Benedict can be contacted via eMail at ^[15].

Image from: Wikimedia Commons

Some more summer (and autumn…) reading

Finally, news of two new journals. Although neither is strictly a botanical or plant science publication, they both cover plant science-relevant topics. First is The Cell Surface^[1]. Published by Elsevier, The Cell Surface “is a highly multidisciplinary journal focused on aspects of the cell wall across all relevant disciplines, in the major groups of organisms that have cell walls: Bacteria [Mr P Cuttings’ emphasis*]; Plants [Mr P Cuttings’ emphasis*]; Algae; Oomycetes; Fungi; Unicellular parasites.” For the view of the Editor-in-Chief and Associate Editors on this new publishing venture, visit ^[2]. And, as a good example of the journal’s cross-Kingdom, multi-disciplinary scope and credentials, check out Jean-Daniel Julien and Arezki Boudaoud’s article entitled “Elongation and shape changes in organisms with cell walls: A dialogue between experiments and models”^[3]. Second is news of People and Nature, the sixth journal published by the British Ecological Society^[4]. Plants and Nature will be “a broad-scope, open access journal publishing work from across research areas exploring relationships between humans and nature”, and whose ‘strapline’^[5,6] is “a journal of relational thinking”. When this news item was written People and Nature had yet to publish its first issue, but we wish it – and The Cell Surface – well in their laudable aims, and worthy endeavours. We will take a keen interest in their growth and development. In particular, we’ll be interested to see how People and Nature ‘squares up’ [^[7], numbered definition 5] to last year’s new cross-disciplinary journal PPP (Plants, People, Planet^[8]), which appears to cover similar – albeit more plant-focused – territory...

* Emboldened because they are plants, or photosynthetic organisms, and therefore of direct relevance to botanists; italicised because these are groups of organisms that ‘interact’ in myriad ways with plants, some beneficially, others less – or not – so…

Image from: Wikimedia Commons