A tiny silver bullet 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”) 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…). And globally, the flower trade – which phrase includes not just cut flowers – was worth US$101.84 billion as long ago as 2003. 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. 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. 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 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. In an attempt to maximize vase life of Paeonia lactiflora, Daqiu Zhao et al. investigated use of nano-silver – particles of silver that are typically 25nm in diameter – which has demonstrable anti-microbial properties. 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”. 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 the, err, lily?

* But also an industry that raises major concerns over its environmental-sustainability and ‘green’ credentials.

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

*** 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), whose colour – ranging from blue to red – is pH-dependent. 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. 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”). When placed in a vase with cut flowers of a different species, such as roses and tulips, cut daffodils (Narcissus pseudonarcissus) can cause their non-Narcissus neighbours to wilt prematurely. By contrast, daffodils delayed senescence of cut iris flowers. 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 have been published by L. Hibrand Saint-Oyant et al. and Olivier Raymond et al., with a commentary thereon by Aureliano Bombarely. Why mention roses in connection with this news item? Roses are amongst the ‘top 10’ cut flowers.]