Biotechnology and Ecology of Pollen: Proceedings of the International Conference on the Biotechnology and Ecology of Pollen, 9–11 July, 1985, University of Massachusetts, Amherst, MA, USA

528 Pages·1986·0.87 MB·English

by  M. B. Singh

Biotechnology and Ecology of Pollen
Biotechnology
and Ecology of Pollen
Proceedings of the International Conference on the
Biotechnology and Ecology of Pollen, 9-11 July 1985
University of Massachusetts, Amherst, MA, U .S.A.
Edited by
David L. Mulcahy, Gabriella Bergamini Mulcahy
and Ercole Ottaviano
With 141 Figures
Springer -Verlag
New York Berlin Heidelberg Tokyo
David L. Mulcahy Ercole Ottaviano
Gabriella Bergamini Mulcahy Department of Genetics
Department of Botany and Microbial Biology
University of Massachusetts University of Milano
Amherst, MA 01003 Milano 20133
U.S.A. Italy
Library of Congress Cataloging in Publication Data
Main entry under title:
Biotechnology and ecology of pollen.
Proceedings of the International Conference on Biotechnology and Ecology of
Pollen, held at University of Massachusetts, July 9-11, 1985.
Bibliography: p.
Includes index.
1. Pollen-Congresses. 2. Biotechnology-Congresses.
I. Mulcahy, David L. Il. Mulcahy, Gabriella Bergamini.
IH. Ottaviano, Ercole. IV. International Conference
on Biotechnology and Ecology of Pollen (1985 : University
of Massachusetts at Amherst) V. Series.
QK658.B57 1986 582'.0463 85-30357
© 1986 by Springer-Verlag New York Inc.
Softcover reprint of the hardcover Ist edition 1986
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ISBN-13: 978-1-4613-8624-7 e-ISBN-13: 978-1-4613-8622-3
DOI: 10.1007/978-1-4613-8622-3
DEDICATION
This volume is affectionately and respectfully
dedicated to the memory of
G. Sarfatti
and
R. A. Brink
for their outstanding contributions to the study of pollen
and to
Helen Vogel Mulcahy
for her many contributions to tw6 of the editors.
Preface
In Recognition of the Forgotten Generation
D. L. MULCAHyl
Pollen was long believed to serve primarily a single
function, that of delivering male gametes to the egge A
secondary and generally overlooked value of pollen is that
it serves to block the transmission of many defective
alleles and gene combinations into the next generation.
This latter function comes about simply because pollen tubes
carrying defective haploid genotypes frequently fail to
complete growth through the entire length of the style.
However, the beneficial consequences of this pollen
selection are diluted by the fact that the same deleterious
genotypes are often transmitted through the egg at strictly
mendelian frequencies (Khush, 1973). Gene expression in the
pollen might thus at least appear to be a phenomenon of
trivial consequence. Indeed, Heslop-Harrison (1979) rightly
termed the gametophytic portion of the angiosperm life
cycle, the "forgotten generation." This neglect, however,
came about despite subtle but constant indications that
pollen is the site of intense gene activity and selection.
For example, Mok and Peloquin (1975) demonstrated that
relatively heterozygous diploid pollen shows heterotic
characteristics whereas relatively homozygous diploid pOllen
does not. This was proof positive that genes are expressed
(that is, transcribed and translated) in the pollen.
1 Department of Botany, University of Massachusetts
Amherst, MA 01003, USA
viii
However, the implications for pollen biology of even
this recent and well known study were not widely recognized.
In order to study the consequences of gene expression in the
pollen, we have to go back to work of Ter-Avanesian, first
published in 1949. He determined that progeny resulting
from rapidly growing pollen tubes differed from those of
unselected pollen tubes, and, as shown in later
investigations, these differences have a genetic basis.
This single conclusion holds two important implications.
First of all, since the pollen used in each of Ter
Avanesian's experiments came from single plants, the genetic
differences among which he was selecting must reflect post
meiotic gene expression. Secondly, because selecting among
different pollen genotypes modifies the resultant
sporophytic generation, we must conclude that some of the
genes which are expressed, and thus subject to selection, in
the pollen, must be expressed also in the sporophtye. In
other words, the set of genes which are expressed in the
gametophyte must overlap the set expressed in the
sporophyte. Subsequent studies confirmed both of these
conclusions.
When the overlapping relationship between gametophytic and
sporophytic genotypes was first quantified (Tanksley, Zamir,
and Rick, 1981), it was determined that 18 out of 30, or
60%, of the structural genes which are expressed in the
sporophyte of Lycopersicon esculentum are expressed also in
the pollen. In addition to these 18 genes expressed in both
parts of the life cycle, one other was expressed only in the
pollen. Thus 18/19, or 94.7% of the genes which are
expressed in the pollen are expressed also in the
sporophyte. More recently Mascarenhas and colleagues have
measured genetic overlap in other species. Extending their
survey to a very large fraction of the structural genes
expressed in either phase of the life cycle, they detected
20,000 types of mRNA in pollen and 30,000 in the stern of
Tradescantia paludosa. In a conclusion which was strikingly
close to that reached by Tanksley, Zamir, and Rick, they
found that approximately 60% of the structural genes which
are expressed in the sporophyte are expressed also in the
pollen, and fewer than 15% of the genes expressed in the
pollen are not expressed in the sporophyte (Willing and
Mascarenhas, 1984~ Mascarenhas, et al., this volume).
Comparable figures on genetic overlap were obtained by Sari
Gorla, et al., (this volume) with ~ ~ and by G. F.
Moran (CSIRO Div. of Forest Research, Canberra, ACT,
Australia) with ~ radiata (G. Moran, pers. comm.).
Before evaluating the implications of these measurements of
overlap, recall that the extraordinary adaptability of
microorganisms is based on two characteristics: haploidy and
large population sizes. Both of these characteristics are
found, not only in microorganisms, but also in pollen. Thus
gametophytically expressed genotypes should be as responsive
to selective pressures as are those of microorganisms. More
significantly, the extensive overlap between
gametophytically and sporophytically expressed structural
genes means that also 60% of the sporophytic genome is
subject to a microbial type of selection. Certainly this
holds important implications for both basic and applied
studies. In fact, it may represent a rapid, inexpensive,
and effective method of screening genotypes for stress
resistance. Obviously, this would hold substantial
implications for both basic and applied studies.
When many of the participants of the present symposium met
at Lake Garda in Italy, in 1982, most of the above facts on
gene expression in pollen were known, although precise data
were few. Other topics discussed then were self
incompatibility, the movement of pollen in populations,
pollen transformation, physiology, and competition. Today,
we possess clear evidence that a majority of the structural
genes which are expressed in the sporophytic portion of the
life cycle are expressed, and thus exposed to selection also
in the pollen. POllen should thus provide a major access
point in natural and artificial manipulation of the
sporophytic genome. Examples of this type of selection,
dealing with heavy metals, herbicides, and pathotoxins are
presented in this volume. Other subjects in the realm of
x
pollen biology and biotechnology are still undecided. Self
incompatibility (at least in the eyes of somel) is an
unsettled issue. Pollen mediated transformation is a field
of intense activity because of its potential applications,
and pollen physiology continues to be a rich lode for basic
and applied studies. It now holds, among other things, the
promise of effective gametocides, and thus, new hybrid
crops. In the field of ecology, as much as in any other,
recent studies have provided precise measurements of
phenomena only hypothesized three years ago. Here too, the
significance of pollen competition and selection seems to be
at least as great as early speculations suggested.
Furthermore, phenomena such as negative interactions between
pollen tubes within styles, first hinted at in 1980 (see
Sari-Gorla and Rovida, 1980) are now clearly indicated in
several studies (see Snow; d'Eeckenbrugge; and Hessing; all
in this volume.
If our next meeting, perhaps four years from now, is marked
by progress comparable to that made in the past three years,
pollen biology and biotechnology will be ready to make
substantial contributions in some both basic and applied
areas of study.
References
Heslop-Harrison, J. 1979. The forgotten generation: some
thoughts on the genetics and physiology of angiosperm
gametophytes. In: D.R. Davies and D.A. Hopwood (editors).
Proceedings of the fourth John Innes Symposium. John Innes
Inst., Norwich.
Khush, G.S., 1973. Cytogenetics of aneuploids. N.Y.,
Academic Press.
Mok, D.W.S. Peloquin, S.J. 1975. Three mechanisms of 2n
pollen formation in diploid potatoes. Canad. Jour. Gen.
Cytol. 17, 2l7-225.i
Sari-Gorla, M., Rovida, E., 1980. Competitive ability of
maize pollen. Intergametophytic effects. Theor. Appl.
Genet. 57, 37-42.
Tanksley, S., Zarnir, 0., Rick, C.M. 1981. Evidence for
extensive overlap of sporophytic and garnetophytic gene
expression in I.ycopersicon esculenturn. Science 213, 453-
455.
Ter-Avanesian, D.V. 1949. The influence of the nurnber of
pollen grains used in pollination. Bull. Appl. Genet.
Plant Breeding Leningrad 28, 119-133.
Willing, R. P., Mascarenhas, J.P. 1984. Analysis of the
cornplexity and diversity of rnRNSa frorn pollen and shoots of
Tradescantia palludosa. Plant Physiol. 75, 865-868.
Acknowledgments
Since the strength of a scientific meeting depends primarily on the
presentations of the participants, the first acknowledgements must be to
the speakers at this meeting. They are to be congratulated, not only on
the quality of the talks themselves, but, to an even greater extent,on
the very substantial scientific progress made in the last three years.
Beyond the scientific presentations, several industries, Ciba-Geigy
Incorported, DeI Monte Corporation, Funk Seeds International, Monsanto
Agricultural Products Co., Pfizer Central Research, and Pioneer Hi-bred
International Inc., provided essential financial support. Other support
came from the National Science Foundation sections of population biology
and developmental biology, and also from the University of
Massachusetts, at Amherst. Ultimately, the actual progress of the
meeting was, to a very great extent, dependent on the energy, ability,
and cooperation of the staff and students in the Department of Botany,
University of Massachusetts. These include Sally Klingener, Douglas
MacMiIlan (an outstanding candidate for graduate school), Carol
Mardeusz, and graduate students Patty Shesgreen, Jennifer Ramstetter,
Douglas Robertson, Jeanne Curry, Lisa Webber-Barnes, and Jean Starobin.
To each of these, institutions and colleagues alike, we extend, not only
thanks, but, once more, congratulations.
The Editors