Contemporary Citation Classic: Broadley MR, White PJ, Hammond JP, Zelko I, Lux A (2007) Zinc in plants. New Phytologist 173, 677-702. https://doi.org/10.1111/j.1469-8137.2007.01996.x
Philip White writes: Last year, I compiled a list of contemporary Citation Classics in Plant Sciences. In addition to identifying these papers, I wanted to reveal something about the social context in which they were written. So, I have asked Martin Broadley (University of Nottingham, UK) to comment on this article, to which I contributed. I have fond memories of writing this review. I had just moved to Dundee to lead the Environment Plant Interactions Programme at the Scottish Crop Research Institute (SCRI) and was living in a flat with spectacular views over the Tay, where I recall we wrote intensively for several days. But I shall let Martin tell his story…
Fond memories indeed. This zinc review was our sixth in a series of reviews of elements in plants, whose conceptions began in the early days of mine and Philip’s interactions at Horticulture Research International, in the late 1990s. Our first review was on caesium (White and Broadley, 2000), the second on chlorine (White and Broadley, 2001), and the third on calcium (White and Broadley, 2003). Having got bored with the letter “C”, and academic monogamy, we then branched out into silicon (Hodson et al., 2005), selenium (Broadley et al., 2006) and zinc (Broadley et al., 2007). Some of the inspiration for these later reviews came as we started to get more interested in the roles of fertilisers in improving crop quality for human nutrition, but also as our collaborative networks expanded.
For the zinc review, beyond the standard narrative sections (for which, admittedly, most of the citations have probably accrued), my primary recollection was being driven by an urge to pull together several distinct areas of literature. For example, we developed a conceptual framework to describe zinc in terms of its subcellular abundance, together with predicted zinc-binding domains, based on analogy with bacterial and human studies. John Hammond (now at the University of Reading) contributed substantially to the bioinformatics work in this section. We then compiled a substantial literature on the kinetics of zinc uptake by roots, from which we hypothesised potential pathways of root uptake and transport in plants. The section of the review of which I am still most proud was a phylogenetic analysis to identify evolutionary trends in zinc accumulation by plants. The dénouement of this section was an exhaustive list of plant species that hyperaccumulated zinc (and their many synonyms!). We concluded our review with a secondary data analysis of transcriptomes from hyperaccumulator plants, together with some beautiful anatomical images of roots from Ivan Zelko and Alexander Lux at Comenius University, Bratislava, who had recently observed peri-endodermal suberisation in the root cell walls of a species of hyperaccumulator, Noccaea caerulescens. The evolutionary/adaptive significance of this has yet to be resolved. I feel exhausted just thinking about it all these days!
A question Philip and I got asked (a lot) back then, as we embarked on these lengthy reviews, was “Why?”. Such reviews didn’t count as ‘outputs’ for any projects. We didn’t even have funded projects on zinc, nor most of these elements, back then. Citation counting was not yet a thing. What were we thinking?
They were certainly a labour of love. Philip and I used to sit together for hours, in many settings, discussing plant nutrients. Each review had a different origin in time and space. Each took on a life of its own, as we explored, indulged, and weaved together mutual areas of interest. All of the reviews were similar in that we riffed and argued constantly as we tried to frame past studies in the context of future research aspirations. Philip was typically the more scholarly and encyclopaedic (and argumentative); I was more interested in linking fields. Music had been a big part of our earlier lives; writing together at high intensity had many obvious parallels. We both looked to Dylan for inspiration – although Philip is probably closer to John Cooper Clarke and I’m more of a sucker for a cheesy tune (Jeff Lynne?). I’ve since come to learn of a beautiful, untranslatable, German word, Sehnsucht, which describes intense feelings of ‘longing’, or ‘nostalgia for the future’. I think that was part of it.
I remember once being advised, by a very highly cited scientist, that review articles should be left to those who are acknowledged leaders in their fields. I couldn’t disagree more strongly, then and now. They were a wonderful learning experience for me as an early career researcher (ECR) and I shall be forever proud of my part in their synthesis. I hope that others have found them useful in some way.
Would I recommend other ECRs to embark on these types of review? A cautious yes, time and energy permitting, they helped my career especially in the days before grant successes came. But, academic landscapes change, expectations are greater in terms of primary outputs and engagement with other media, days pass faster, the urgent takes precedence over the important most of the time. Since this review in 2007, I have adopted a more pragmatic approach to writing reviews, with a single type of secondary data analysis per paper, and I tend to advise students likewise (e.g. Broadley and White, 2010, 2012; Kumssa et al. 2015; Joy et al., 2014, 2016). Today, I started to plan an (invited) review paper with two final year PhD students based in Malawi who are working on selenium. I’m channelling past reviewing experiences with them, but we’re all thankful for having a strict journal word-limit on this occasion!
“Ah, but I was so much older then. I’m younger than that now” (My Back Pages, Bob Dylan, 1964). Maybe Philip and I shall renew our reviewing vows again one day, but that’s definitely not yet a promise.
Broadley, M. R., & White, P. J. (2010). Eats roots and leaves. Can edible horticultural crops address dietary calcium, magnesium and potassium deficiencies? Proceedings of the Nutrition Society, 69(04), 601–612. https://doi.org/10.1017/S0029665110001588
Broadley, M. R., & White, P. J. (2012). Some elements are more equal than others: soil-to-plant transfer of radiocaesium and radiostrontium, revisited. Plant and Soil, 355(1-2), 23–27. https://doi.org/10.1007/s11104-012-1163-1
Broadley, M. R., White, P. J., Bryson, R. J., Meacham, M. C., Bowen, H. C., Johnson, S. E., … Tucker, M. (2006). Biofortification of UK food crops with selenium. Proceedings of the Nutrition Society, 65(02), 169–181. https://doi.org/10.1079/PNS2006490
Broadley, M. R., White, P. J., Hammond, J. P., Zelko, I., & Lux, A. (2007). Zinc in plants. New Phytologist, 173(4), 677–702. https://doi.org/10.1111/j.1469-8137.2007.01996.x
Hodson, M. J., White, P. J., Mead, A., & Broadley M. R. (2005). Phylogenetic Variation in the Silicon Composition of Plants. Annals of Botany, 96(6), 1027–1046. https://doi.org/10.1093/aob/mci255
Joy, E. J. M., Ahmad, W., Zia, M. H., Kumssa, D. B., Young, S. D., Ander, E. L., … Broadley, M. R. (2016). Valuing increased zinc (Zn) fertiliser-use in Pakistan. Plant and Soil, 411(1-2), 139–150. https://doi.org/10.1007/s11104-016-2961-7
Joy, E. J. M., Ander, E. L., Young, S. D., Black, C. R., Watts, M. J., Chilimba, A. D. C., … Broadley, M. R. (2014). Dietary mineral supplies in Africa. Physiologia Plantarum, 151(3), 208–229. https://doi.org/10.1111/ppl.12144
Kumssa, D. B., Joy, E. J. M., Ander, E. L., Watts, M. J., Young, S. D., Rosanoff, A., … Broadley, M. R. (2015). Global magnesium supply in the food chain. Crop and Pasture Science, 66(12), 1278. https://doi.org/10.1071/CP15096
White, P. J., & Broadley, M. R. (2000). Tansley Review No. 113, Mechanisms of caesium uptake by plants. New Phytologist, 147(2), 241–256. https://doi.org/10.1046/j.1469-8137.2000.00704.x
White, P. J., & Broadley, M. R. (2001). Chloride in Soils and its Uptake and Movement within the Plant: A Review. Annals of Botany, 88(6), 967–988. https://doi.org/10.1006/anbo.2001.1540
White, P. J., & Broadley, M. R. (2003). Calcium in Plants. Annals of Botany, 92(4), 487–511. https://doi.org/10.1093/aob/mcg164