Nature-De Wit-Mackey-2002 Comment

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antimony atoms among all the silicon atoms clusters is random. This suggests that over- they will also be important in increasing our
coming carrier saturation at very high dopantin the crystal is like searching for the prover- understanding of a wide range of complex
bial needle in a haystack. To ‘see’ the anti- concentrations will be a major challenge. materials.
Seeing is frequently the first step towardsmony dopant atoms, the researchers adapted Paul S. Peercy is at the College of Engineering,
a powerful technique — scanning transmis- understanding. This first, unambiguous University of Wisconsin, 1415 Engineering Drive,
5sion electron microscopy observation of single atoms bonded inside a— to image almost Madison, Wisconsin 53706-1691, USA.
all the antimony atoms in the silicon crystal, bulk solid environment has wide-ranging e-mail: [e-mail]
implications for the analysis of single atoms 1. Voyles, P. M., Muller, D. A., Grazul, J. L., Citrin, P. H. &even individual antimony atoms.
Gossmann, H.-J. L. Nature 416, 826–829 (2002).The first critical step was to prepare thin and of clusters of two, three or four atoms —
2. 2001 International Technology Roadmap for Semiconductors
crystals — only 9 or 11 atoms thick — lack- and for our efforts to understand the struc-
(Semiconductor Industry Association, 2001);
ing any surface or near-surface disorder that ture of impurities and alloy constituents in www.semichips.org/pre_technology.cfm
1 3. Gossmann, H.-J., Rafferty, C. S. & Keys, P M. at. Res. Soc. Symp.could scatter the incoming electron beam of crystalline solids. Voyles et al.’s results are
610, B1.2.1–B1.2.10 (2000).
the scanning transmission electron micro- important in understanding the distribution
4. Packan, P. A. Science 285, 2079–2080 (1999).
scope and prevent it from being guided of impurities in silicon at an atomic level; 5. Pennycook, S. J. & Narayan, JA. ppl. Phys. Lett.45, 385–387 (1984).
through the channels formed by the rows of
atoms in the lattice. The cross-section (or
probability) for electron scattering increases Plant biology
1.7with the atomic number Z, , as Z , so an anti-
mony atom, with Z451, scatters electrons On guard
nine times more strongly than a host silicon
atom with Z414. By detecting the intensity Pierre J. G. M. de Wit
1of the scattered electrons, Voyles et al. could
readily distinguish rows in the atomic lattice Microorganisms that infect plants must suppress their hosts’ defence
that contained a single antimony atom from mechanisms before they take up residence. But some plants use molecular
rows containing only silicon atoms (Fig. 1). guards to sense when they are being manipulated by pathogens.
From these elegant measurements, Voyles
et al. conclude that the electrically inactive s a rich source of sugars and amino nisms such as strengthened cell walls and
atoms are grouped in clusters containing two antimicrobial compounds, as well as activeacids, plants attract a variety of intrud-
antimony atoms. But their measurements Aers, from viruses, bacteria and fungi to healing responses. Only a few microbes can
also revealed that the basis on which impurity breach these ‘basal’ defences, and are theninsects. To protect themselves, plants have in
dopant atoms remain isolated or form small their armoury of passive defence mecha- fought by the plant’s innate immune system.
Agriculture
Champagne surprise
Pinot noir is an important grape their skin: using tissue culture, the
variety that is used for making wine, authors regenerated whole plants
including champagne. It is derived from Pinot Meunier L1 cells. As well
from an ancient strain that has been as having hairy leaves, these plants
cultivated for maybe 2,000 years. were semi-dwarfed — they were
Cultivated grapevines (Vitis vinifera ) shorter and stockier than usual. This
are usually reproduced from cuttings, provided a clue about which gene
so all individuals are genetically might be mutated. Sure enough, it
identical. But sometimes mutations turned out to be the grapevine
arise, and long ago this resulted in the equivalent of the gene that, when smaller. Of course this only occurs if this hormone may ensure that the
generation of another champagne mutated, causes dwarfing in wheat. all cells are mutant; if the mutation later-arising structures become
grape variety, Pinot Meunier (pictured Gene sequencing showed that the is limited to the epidermis the only tendrils rather than flowering stems.
here), from Pinot noir. Pinot Meunier gene had a similar mutation in the change seen is increased hairiness Gibberellic acid was known to
plants are genetically indistinguish- L1-cell plants and in dwarfed wheat. — gibberellic acid presumably also influence flowering in other plant
able from Pinot noir in most cells, but What does the gene do? It was suppresses hair growth. species, but this function is
their outer layer, the ‘L1’ epidermal first identified and cloned from the There was one more surprise apparently new. Interestingly, tendrils
cell layer, is different — meaning that thale cress Arabidopsis thaliana, and from Boss and Thomas’s study: in the in some plants such as peas have a
Pinot Meunier has a furry surface on named GA INSENSITIVE because of L1-cell plants, tendrils were replaced different origin — they are modified
its leaves whereas Pinot noir does the effect on the plant of mutating it. by flowering stems. Normally, a new leaflets rather than flowering stems.
not. Elsewhere in this issue ( Nature It is a regulatory gene that normally shoot produces several bunches of New knowledge about hormone-
416, 847–850; 2002), Paul K. Boss keeps a brake on plant growth; the flowers (and thus grapes) opposite response genes may allow us to
and Mark R. Thomas describe the brake is released by gibberellic acid the first few leaves, and tendrils fine-tune both the vegetative
precise mutation that causes this (GA). Thus the plant can regulate its opposite leaves that form later. The architecture of grapevines, and how
difference. Surprisingly, it is the growth by controlling the production tendrils anchor the vine as it grows in many bunches of grapes they
grapevine equivalent of the ‘dwarfing’ and location of this hormone. Some search of light. But in the semi- produce. David R. Smyth
mutations used to increase wheat mutations in the gene disrupt the dwarfed mutant, flowering stems David R. Smyth is in the School of
yields during the green revolution. encoded protein so that gibberellic continued to form in place of tendrils. Biological Sciences, Clayton
Boss and Thomas started by acid no longer releases the brake on Presumably, the explanation is again Campus, Monash University,
producing grapevines that carried growth. This means that the brake is that the plants cannot respond Victoria 3800, Australia; e-mail:
the mutation in all their cells, not just permanently on, and the plant is correctly to gibberellic acid. Normally, [e-mail]
NATURE | VOL 416| 25 APRIL 2002| www.nature.com 801
© 2002 Macmillan Magazines Ltd
CEPHAS/KEVIN JUDDnews and views Pseudomonas
a b syringaeSusceptible Resistant
DeliveryArabidopsis Arabidopsis
plant of Avr plant
proteins
RPM1 Inside
Avr AvrRIN4 RIN4 cell
100 YEARS AGO
Our present state of civilisation has of
necessity resulted in an annual increase in
RPM1the amount of capital borrowed by man from Avr InsideRIN4AvrRIN4the store of energy accumulated by our earth cell
in bygone times, and the diversion of this PP
capital to uses for which the world’s annual
income of solar energy was formerly Less pathogen growth
Suppress basal defences Hypersensitive responsedeemed adequate. An instance of this
More pathogen growth (local cell death)
tendency is afforded by the experiments of
Dr. Selim Lemström, of Helsingfors, on the
3uses of electricity in stimulating the growth Figure 1 At the crossroads of disease resistance and susceptibility. Mackeety al. studied the
of cereals, vegetables and other plants… The Arabidopsis thaliana resistance (R) protein RPM1, and the Pseudomonas syringaeavirulence (Avr)
investigation seems to have been suggested proteins AvrRpm1 and AvrB. (P. syringae infects A. thaliana leaves.) The authors found that the two
in the first instance by an attempt to connect bacterial proteins can bind to the plant protein RIN4, tag it with phosphate groups (circled ‘P’) and
the luxuriant growth of plants in high upregulate its concentration and its activity as a negative regulator of plant basal defence
latitudes with the influence of electric mechanisms. a, In susceptible plants, this downgrading of plant defences results in the spread of the
currents associated with the Aurora Borealis. bacterium. b, Resistant plants make use of the RPM1 protein to sense these manipulations of RIN4 by
The experiments showed that for plants the bacterial Avr proteins, activating the hypersensitive response which prevents bacterial spread.
growing on arable land of medium quality Figure modified from ref. 3.
an increase of 45 per cent. in the crops is
5
obtainable; but the better the field is The innate immune response is well descri- interactions , and so are expected to allow
ploughed and cared for the greater will be bed genetically by what is known as the R proteins to lock directly onto Avr proteins,
1
the increase. On poor soil the effect is trifling. gene-for-gene model , because it requires a although (despite much