Teachers Notes - Dr Lloyd Evans

Dr Lloyd Evans

Plant scientist

Contents

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Introduction

Dr Lloyd Evans was interviewed in 2003 for the Interviews with Australian scientists series. By viewing the interviews in this series, or reading the transcripts and extracts, your students can begin to appreciate Australia's contribution to the growth of scientific knowledge.

The following summary of Evans's career sets the context for the extract chosen for these teachers notes. The extract discusses his work on the physiology of flowering in plants. Use the focus questions that accompany the extract to promote discussion among your students.

Summary of career

Lloyd Evans was born in New Zealand in 1927. He began his studies at the University of New Zealand where he earned a BSc in 1949 and an MAgSc in 1950.  During these years his interests combined pure science with agriculture.

He won a Rhodes Scholarship to Oxford University and completed a DPhil in 1954, looking at the interaction between clay particles and soil organic matter. He continued to have an interest in agriculture and plants and after his time in Oxford went to the California Institute of Technology (Caltech). Caltech had the world’s first phytotron – a laboratory where a substantial number of plants can be grown under very closely defined conditions – in which Evans began his life’s work researching plant photoperiodism.

His model system was Lolium temulentum, darnel ryegrass, which will flower given one long day. Using Lolium, he has looked at a variety of questions including how plants sense and respond to day length, what messages are sent from the leaves (that perceive it) to the shoot apex (that reacts to it) and how the apex shifts from leaf to flower formation. 

In 1956 Evans arrived in Canberra to take up a position at CSIRO's Division of Plant Industry. He was recruited by Sir Otto Frankel, Chief of Plant Industry at the time, to help create an Australian phytotron in Canberra.  The phytotron was officially opened by Prime Minister Sir Robert Menzies in 1962.  Evans served as Chief of Plant Industry from 1971 to 1978.  On his retirement in 1990 he became an Honorary Research Fellow of the Division.

Evans has had a long-standing interest in international agriculture. He served as a member of the Technical Advisory Committee to the Consultative Group on International Agriculture Research from 1978 to 1983, on the Board of Trustees of the International Rice Research Institute (IRRI), Philippines, from 1984 to 1989 and on the Board of Trustees of the International Wheat and Maize Improvement Center, Mexico, from 1990 to 1995. His interest and expertise was instrumental in the development of a phytotron at IRRI in 1970. From 1977 to 1978 he served as the President of the Australian and New Zealand Association for the Advancement of Science.

In addition to numerous research papers, Evans has written three books and edited a number of others. His Crop Evolution, Adaptation and Yield (1963) and Feeding the Ten Billion (1998) have been globally influential with both agricultural researchers and policy makers.

He was elected a Fellow of the Australian Academy of Science in 1971 and served as President from 1978 to 1982. He became a Fellow of the Royal Society in 1976.

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Extract from interview

From leaf growth to flower: daylength and on-off switches

I think now is the time to explain briefly, in layman's terms, your work on the physiology of flowering, one of the two principal lines of research which brought you international recognition and acclaim. Before this interview you wrote to me that 'questions about how plants sense and respond to daylength and the messages sent from the leaves that perceive it to the shoot apex that reacts to it, and how the apex shifts from leaf to flower formation' have dominated your life in science. Could you now tell us a little bit more about that?

Well, I found a suitable test plant, Lolium temulentum, which I am still working on. It is just an ordinary grass, darnel, the 'tares' of the Bible. It is a weed of wheat crops. It flowers at about the same time as the wheat crop and its seeds are about the same size as wheat seeds so it gets propagated along by being sown with the next lot of seed. But they may carry a fungal disease (not ergot) which can cause blindness and madness in people. In biblical times you separated the tares from the grain, and people in the Middle Ages knew that they needed to pick the seeds of tares out of the wheat samples before they made a loaf of bread or something like that. This old plant, well known in biblical times, has been a wonderful experimental plant for me.

For the first five to six weeks we grow our plants in short days, going into darkness at 4 pm, and they remain vegetative. But keeping the light on till midnight tonight, say, is enough to make this plant flower. Chailakhyan's explanation was that the leaf makes a long day floral hormone which goes off down to the shoot apex and switches it on. But there is an alternative explanation, that the leaf, in short days, is making something that stops the plant from flowering, and as soon as you give it a long day, away it can go. Flowering physiologists had not resolved which alternative was correct.

One of my early experiments in Canberra, even before I got set up with the phytotron and had more space, was to test those alternatives. So I would have a plant with one leaf out getting the long day, and at the same time all the other leaves wrapped up for the night in aluminium foil, which involved a lot of labour. Then I could cut off the one leaf, or the other leaves, at various times and see what the result was. The conclusion from the experiment was clearly that both processes operated. There was a message from the long-day leaf to the shoot apex, switching it on, and there was a message from the short-day leaves that reduced the flowering response or would stop it, in the absence of any positive stimulus.

I got into hot water with the high priest of flowering physiology, Anton Lang – a good friend of mine and colleague but we traded punches quite a lot – who 'gave me the works' in his criticism. But subsequently, 15 years later when he had convinced himself that my finding was correct, he was gracious enough in defeat to send me a postcard saying, 'In hindsight I should have done the anti-florigen grafts at the same time as we did the pro-florigen grafts.' His approach was not my kind of experiment but to graft different plants together, grafting the leaves from one plant that had had short days onto a plant that had not, or vice versa.

That was one question. We then were able to consider how fast this message moved. By cutting the sheaths at different heights and so on, we could work out when it arrived at the shoot apex. So that was the time when we should look for changes at the minute shoot apex. That work has been very productive. I have had a lot of colleagues in it – in all my work, really – but particularly all through that.

Defining the hormone messenger

The next question was what the messenger is, what it is that switches on the shoot apex to make leaves instead of flowers, and as I have said, we are getting towards that now.

In fact, Anton Lang was the person who set me on that trail. In 1956, just before I left America, he did an experiment with a small sample of a newly available plant hormone, gibberellic acid, which he put on his favourite experimental plant. The plants flowered in short days, and he was so excited that he called me over to see them in the glasshouse. I got so excited that on my way to Australia I visited ICI in England and they gave me a small sample – it was unobtainable otherwise. As soon as I could I tried it out on my Lolium, and it made them flower in short days. But there are now 150 different gibberellins and only a few of them cause the plant to flower. That is partly what we are working on at the moment, and that is where in recent years I have had a lot of very fruitful collaboration with Lew Mander, who is the world's authority on running up different gibberellins.

Does he make them, or just isolate them?

He makes them. If you want an exotic one he'll think hard – he's still thinking about some of the ones we have asked him for – but mostly after a while he's been able to supply us with all sorts of them, including some artificial ones.

So you have some idea of which ones work and which don't?

Well, around 1990, about the time I retired, we were concentrating on defining which parts of the molecule are important. It is quite a complex molecule, with four rings and various hydroxyl groups attached here and there. It depends very much on where the hydroxyl groups are. For example, if it is a hydroxyl group on carbon 2, no flowering. On carbon 3 and not on carbon 2, very good flowering. So Lew has been able to present us with all sorts of opportunities for defining the important elements of the structure.

There are various things we couldn't explain. For example, the two gibberellins that are most effective for making the plant elongate, GA1 and GA4, are not effective for making it flower. That is what we have been working on recently. We think a paper by a Japanese group has given us a key to why some of these gibberellins work, when some that we would expect to work don't work. That is just the way it often happens in science: there was an incidental observation to which the Japanese did not attach any significance in their paper because they were looking at other things. As Rod King, my colleague in all this work, and I read the paper – independently – we each thought immediately, 'Ah! That would be very helpful for us if the same thing applies in Lolium.'

An edited transcript of the full interview can be found at http://www.science.org.au/scientists/interviews/e/le.

Focus questions

  • Scientists often look for competing alternatives which could explain natural phenomenon. Evans discussed two possible explanations as to how plants begin to flower, both of them involving chemical messengers. How do his two explanations differ?
  • Animals also use chemical messengers to control life processes. Can you name some of these and how they influence animal biology?

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Activities

Select activities that are most appropriate for your lesson plan or add your own. You can also encourage students to identify key issues in the preceding extract and devise their own questions or topics for discussion.

  • Flowering phenology: How do plants know when to flower? (Arizona State University)
    Students learn about the importance of the timing and duration of flowering events. They look at the significance of flowers to plant reproduction, as a food source for animals and as an indicator of environmental conditions.
  • Flowering (Kimball’s Biology Pages, USA)
    Ask students to read about florigen and the flowering response and then  write a brief report on what they have learned. Contains link to information on Photoperiodism.
  • Evans does basic plant research, although his work may be used by plant breeders who do applied research to improve crop species. Ask students to read Why do basic research? (National Institute of General Medical Sciences, National Institutes of Health, USA) and debate the merits of both kinds of scientific research.

Keywords

flower
gibberellins
hormone
photoperiodism
vegetative growth

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