Genetic engineers try for green revolution

Press, 30 April 1981, Page 27

Genetic engineers try for green revolution

Reprinted front the “Economist” In the audience at a recent Royal Society meeting in London on the use of genetic engineering techniques to breed plants was a man who could have told the assembled scientists that they were being much too conservative. Many of the things which they were saying would take years more of research to achieve — such as improved resistance to salinity — were further advanced than they imagined.

The quiet observer was Mr Martin Apple, of a Californian company called the International Plant Research Institute. His reticence about 1.P.R.1.’s own progress was perhaps understandable. One possible explanation is that the company fears its ideas will be stolen (few patent applications have been filed so far for precisely this reason.) The competition in the field of plant genetics is increasing. At least two other outfits are being formed to work as private research centres (much like 1.P.R.1.) to commercialise the improved plants expected to spring from university laboratory research. Large companies, especially those .in the food-processing industry, are beginning to put money into such research. A second reason for Mr Apple’s reticence may be that the claims 1.P.R.1. is about to make (in a promised colour brochure) abouf its progress far exceed the actual results it has achieved so far. The claims themselves? Nothing outside the limits of what should be just possible with today’s techniques. Nothing that rivals in the field deem to be utterly impossible — though they express considerable scepticism. Take the claims in ascending order of importance: Potatoes from seed. Potatoes are normally grown from tubers, because the highyielding strains do.not produce a lot of seeds. 1.P.R.1. says it has managed to combine the high yields of traditional potato varieties with the good seed-producing characteristics of others. It says it has sizeable acreages of these seed-grown potato plants (where?) that are producing much more than the 24 tonnes to 36 tonnes of potatoes per hectare considered a good yield in conventional fields.' Disease-resistant cassava. This staple plant of large parts of the Third World transmits an in-built virus that stunts its growth and limits its yield to an average of six to 10 tonnes a hectare. 1.P.R.1. says it has developed a virus-free ’‘germ plasm” (cellular material) that could double cassava yields. It is working to develop plants with yields five to eight times higher.

'A spin-off from this work is a test kit for typical plant viruses that can be (reliably) used in the field to tell a- farmer within a day just what his problems are. The kit may well be 1.P.R.1.’s first commercial product.

Super-wheats. By starting from a desert (i.e., drought-reistant) grass and then conferring on it the ability to grow giant wheat heads. I.P.R.T. claims to have developed a super-wheat. Some of the individual heads of wheat at its laboratories are over 25cm long. Now I.P.R.T. is working to iniect other characteristics, like a branched head, more seed florets across each branch, and multiple stems from each seed,, while at the same time retaining the great length of the first mutant examples. Some laboratory examples of steps towards this goal exist. They should also be droughf-resistanf inheriting this characteristic of the desert grass. That, at least, is the hone. There is, as Mr Apple is the first to admit, still a large amount of hit and miss in this area cf research. There is still no data on the likely over-all yields per hectare of these super-wheats, especially if their protein levels are increased (another nart of the I.P.R.T. research). Much less is there any indication whether these super cereals will bake into good bread. Resistance to salinity. I.P.R.T. claims to have cracked the genetic code of the genes that make t some nlants more tolerant of salt than others — no mean feat, as there may be six to eight or more genes involved. I.P.R.T. says it has already developed the beginnings of a new salt-tolerant strain of Jomatoes, that aro

also tastier and better nutritionally. Now it is working on the much more difficult task of improving the salt tolerance of - maize (normally very sensitive to salt) as well as other new plants like superwheat. The key laboratory technique used by 1.P.R.1., in common with all leading plant-genetics researchers, is protoplast fusion. In this, the walls of the cells have to be broken down to free genetic material for manipulation. After the material with the characteristics desired — say virus-free mutant genes in cassava — has been selected comes the really hard part: persuading the handful of cells to regrow . into a usable and fertile plant. The trick involves regeneration from a blob of cellular material called a callus culture. It is performed in a' small, flat culture dish on a growth medium in a room kept warm with bright sun lamps. It can be done relatively easily with some plants, like carrots and tobacco. It is now done more or less routinely in advanced laboratories with maize. The technique is much more difficult ■to work with other cereals, whose cell walls are very hard. 1.P.R.1. claims it has regenerated fused protoplasts of wheat as part of its super-wheat development. If so, that is probably a world first. However, it is not yet known whether what grew was a useful plant or — the ultimate test — a fertile one that would reproduce itself from seed. Working with this technique has the advantage of quite extraordinary speed. It is possible to screen the whole process of crossing two plants (or two genetic characteristics) in not much over two months. In a normal plant-breeding process, that can take at least one growing year and, for some plants, much,longer. It is for this reason, above all others, that claims of rapid progress have to be listened to.

For 1.P.R.1. to have come up with so much in such a short space of time suggests either great laboratory skill or amazing luck. It will only be when 1.P.R.1.s newly developed plants (or those from any other advanced plant researcher) have been put into the hands of traditional plant breeders for extended test that the claims will be properly assessed. Another goal for plant geneticists is the is the expansion of plants’ ability to gather their own nitrogen, as a substitute for energy-costly fertiliser. In the short term, researchers are hopeful about boosting the natural talents of legumes — a plant family which includes peas, soya beans and clover — to take nitrogen from the air and transform it into the ammonia they need for growth. But the big pride — transferring this nitro-gen-gathering ability to other plants — still looks a long way in the future, even to optimistists.

Legumes work their nitrogen-gathering trick by teaming up with bacteria, called rhzobia which normally live in the soil. It is the bacteria which do the actual work of transforming nitrogen from the air into ammonia. But ‘they cannot work alone. Rhizobia will “fix” nitrogen dependably only when enclosed within outgrowths of the legume’s roots called nodules. Exactly how these nodules are formed — and how they induce the bugs to take on the task of making the ammonia needed by the plant — remains something of a mystery. Full understanding of that mystery could provide the key to endowing other families of

plants with the ability to fix nitrogen. The facts now beginning to emerge from researchers’ laboratories are tantalising. One discovery with immediate application is that some rhizobia are more efficient at fixing nitrogen than others. The efficient ones have a special enzyme which allows them to gather energy from the hydrogen normally wasted as a by-product of ammonia synthesis. This means they require less “food” to be secreted into the nodule by the plant for each bit of nitrogen transformed, so leaving the plant with more energj r for its own growth.

Researchers are now working on ways to get legumes to take up these extra-efficient rhizobia into their nodules as they grow in the field. So far their attempts have met with little success. The naturally occurring, nonefficient rhizobia are simply too good at competing for the cushy spots in the nodules. But scientists are now hoping to use gen-etic-engineering techniques to introduce the efficien-cy-boosting enzyme into rhizobia which could compete for incorporation into legume nodules. Results could come soon.

Another approach to improving the nitrogen-fixing efficiency of legumes is to tamper with the controls which turn ammonia synthesis in the nodule on and off. Here the hope is to enable farmers to add growth-boosting nitrogen fertiliser to the soil without causing legumes to shut down their own am-monia-making nodules — as most of today’s legumes lazily do. But tapping this technique will require more detailed knowledge of the exact way plant and bacteria interact in nitrogen - fixation.

Even more knowledge will be required for the biggest prize of all — transferring nitrogen-fix-ation ability to other plants. This would allow plants to be grown with less nitrogen fertiliser while keeping yields yigh. Three approaches are now being tried. One is convincing freeliving, nitrogen-fixing soil bacteria to attach themselves to plant roots. Some bacteria, unlike rhizobia, fix nitrogen while living freely in the soil — without needing to be incorporated into nodules. They can sometimes even be convinced to attach themselves to the outside of a plant’s roots. Researchers at the University of Wisconsin are trying to make such bacteria do ’the work of fertilising Com. But sceptics wonder if the loosely bound associations of plant and bacteria will do more than attract scavenging soil organisms. Another approach is convincing other types of plants to form rhizobia contain! n g nodules. Encouragement for this task comes from one known (non-leguminous) tropical plant which does form nodules. But researchers will have to learn more about how plant and bacteria work together to form nodules before such a scheme seems thoroughly feasible. The third approach .is providing plants with their own, “in-cell” nitro-gen-fixing capability. This is the most ambitious of the nitr o g e n-fixing schemes. Achieving it would require full knowledge of the enzymes which transform nitrogen into ammonia, and the genes which control the enzymes. It would require a way of introducing genes from a bacteria into a plant cell, and of convincing all the genes to work together properly. And it would require a way of protecting the nitrogen r fixing enzymes from, among other things, the fixation-stopping effects of oxygen — a byproduct of the photosynthesis which fuels plant cells. :