The Botanical Review 66(1)
Interpreting Botanical Progress
January-March 2000
A Revised Classification of Apocynaceae s.l.
Mary E. Endress and Peter V. Bruyns...........................1
Heterochrony in Plant Evolutionary Studies Through the
Twentieth Century
Ping Li and Mark O. Johnston..................................57
Role of Superoxide Dismutase in Combating Oxidative Stress
in Higher Plants
Sarmistha Sen Raychaudhuri & Xing Wang Deng...................89
Crown Gall Disease and Agrobacterium Tumefaciens: A Study of
the History, Present Knowledge, Missing Information, and Impact
on Molecular Genetics
Helen Stafford................................................99
Constraints and Trade-Offs in Mediterranean Plant Communities:
The Case of Holm Oak-Aleppo Pine Forests
M.A. Zavala, J.M. Espelta, and Javier Retana.................119
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A Revised Classification of Apocynaceae s.l.
Mary E. Endress and Peter V. Bruyns
Institute of Systematic Botany Bolus Herbarium
University of Zurich University of Cape Town
8008 Zurich, Switzerland Rondebosch 7700, South Africa
1. Abstract
The Asclepiadaceae, as traditionally defined, have repeatedly been
shown to be an apomorphic derivative of the Apocynaceae. It has
often been recommended that the Asclepiadaceae be subsumed within
the Apocynaceae in order to make the latter monophyletic. To date,
however, no comprehensive, unified classification has been established.
Here we provide a unified classification for the Apocynaceae, which
consists of 424 genera distributed among five subfamilies:
Rauvolfioideae, Apocynoideac, Periplocoideae, Secamonoideae, and
Asclepiadoideae. Keys to the subfamilies and tribes are provided,
with lists of genera that (as far as we have been able to ascertain)
are recognized in each tribe.
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Heterochrony in Plant Evolutionary Studies Through the Twentieth Century
Ping Li and Mark O. Johnston
Department of Biology
Life Sciences Centre
Dalhousie University
Halifax, Nova Scotia
B3H 4J1 CANADA
I. Abstract
The evolution of plant morphology is the result of changes in
developmental processes. Heterochrony, the evolutionary change in
developmental rate or timing, is a major cause of ontogenetic
modification during evolution. It is responsible for both inter-
and intraspecific morphological differences. Other causes include
heterotopy, the change of structural position, and homeosis, the
replacement of a structure by another. This paper discusses and
reviews the role of heterochrony in plant evolution at the organismal,
organ, tissue, cellular and molecular levels, as well as the relationships
among heterochrony, heterotopy and homeosis. An attempt has been
made to include all published studies through late 1999. It is
likely that most heterochronic change involves more than one of the
six classic pure heterochronic processes. Of these processes, we
found neoteny (decreased developmental rate in descendant), progenesis
(earlier offset) and acceleration (increased rate) to be more commonly
reported than hypermorphosis (delayed offset) or predisplacement
(earlier onset). We found no reports of postdisplacement (delayed
onset). Therefore, while rate changes are common (both neoteny and
acceleration), shifts in timing most commonly involve earlier
termination in the descendant (progenesis). These relative frequencies
may change as more kinds of structures are analyzed. Phenotypic
effects of evolutionary changes in onset or offset timing can be
exaggerated, suppessed or reversed by changes in rate. Because not
all developmental changes responsible for evolution, however,
result from heterochrony, it is proposed that plant evolution be
studied from a viewpoint that integrates these different
developmental mechanisms.
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Role of Superoxide Dismutase in Combating Oxidative Stress
in Higher Plants
Sarmistha Sen Raychaudhuri and Xing Wang Deng
Plant Molecular Biology Laboratory Department of Biology
Department of Biophysics, Molecular Osborne Memorial Laboratories
Biology, and Genetics Yale University
University of Calcutta 165 Prospect Street
92 APC Roy Road New Haven, CT 06511, USA
Calcutta 700009, India
1. Abstract
Superoxide dismutase (SOD) isozymes are compartmentalized in higher
plants and play a major role in combating oxygen radical mediated
toxicity. In this review we evaluate the mode of action and effects
of the SOD isoforms with respect to oxidative stress resistance
correlating age, species, and specificity of plants during development.
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Crown Gall Disease and Agrobacterium Tumefaciens: A Study of
the History, Present Knowledge, Missing Information, and Impact
on Molecular Genetics
Helen Stafford
Biology Department
Reed College
Portland, Oregon 97202, USA
1. Abstract
The production of crown gall tumors in plants caused by Agrobacterium
tumefaciens represents a unique disease involving the transfer of
DNA from the bacterium to the nucleus of the plant. Vital aspects
of this transfer are still being studied.
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Constraints and Trade-Offs in Mediterranean Plant Communities:
The Case of Holm Oak-Aleppo Pine Forests
M.A. Zavala(1), J.M. Espelta(2), and Javier Retana(2)
(1)Department of Ecology (2) CREAF
& Evolutionary Biology Autonomous University of Barcelona
Princeton Univeristy E-08193 Belllaterra (Barcelona)
161 Guyot Hall Spain
Princeton, NJ 08544, USA
1. Abstract
In this paper we review those aspects that are relevant to the
development of a mechanistic ecological theory to account for the
structure and dynamics of Mediterranean forests, focusing our
attention on mixed forests of holm oak (Quercus ilex L.), a shade-
tolerant, slow-growing species that resprouts vigorously after
disturbance, and Aleppo pine (Pinus halepensis M.), a fast-growing,
nonresprouting, shade-intolerant species. The main objectives of
this report are: to introduce some of the primary features of these
forests, showing their structural complexity and historical
peculiarities; to show that much of this complexity can be conceptually
reduced to two main factors of variation, soil-moisture gradients
and a complex interaction of historical management and disturbance
regimes; and to contrast the unique features of Mediterranean systems
with other communities that have inspired generalization in ecology.
Plants in Mediterranean-climate regions must face several environmental
constraints during their life cycle: water limitation, competition
for light, and a complex set of disturbance regimes, mainly fire,
herbivory, and human exploitation. The response of co-occurring
species to a given set of environmental constraints depends on a
combination of physiological and morphological traits. In holm
oak-Aleppo pine forests, the lower limit of distribution along a
soil-moisture gradient appears to be controlled by dry-season water
stress on seedling performance, and the upper limit seems to be
controlled by shade tolerance relative to competitors. The processes
that generate and maintain these patterns are related to the
responses of the two species to the water and light environments
that result from interacting gradients of disturbance and resource
availability.
The dynamics of mixed holm oak-Aleppo pine forests may be represented
along two major environmental axes: water availability and light
intensity; namely, time since last disturbance. At the regional
scale, the presence of holm oak and Aleppo pine is expected to
be driven mainly by the precipitation regime, with the proportion
of Aleppo pine increasing toward the driest border and with
holm oak being the dominant species in areas with higher precipitation.
Changes of dominance of holm oak and Aleppo pine also respond to
water availability at the local scale. In this case, variations
between species depend on different factors in a complex way,
because reduced soil-moisture levels may result either from low
precipitation or from topography and edaphic features. The dynamics
of holm oak-Aleppo pine forests are also determined by temporal
changes in canopy closure; that is, forest recovery after disturbance.
In this case, the proportion of Aleppo pine would increase in
recently disturbed stands (i.e., with high light intensity reaching
the forest floor), whereas regeneration of holm oak would be dominant
under partially closed canopies.
Theories of forest dynamics developed in humid regions may apply
only poorly to Mediterranean plant communities, where vegetation
change is qualitatively or quantitatively different. Thus, succession
in temperate forests appears to be driven by differences in light
availability and shade tolerance; but in Mediterranean plant
communities, water limitation is of greater importance for the
distribution of forest species. In Mediterranean landscapes the
interaction of life-history strategies with changing environments
is difficult to infer from observational and experimental studies.
A mechanistic approach, in which competition or plant performance is
measured as a function of resource availability, seems more feasible.
The idea should be to develop multispecies models calibrated specifically
for Mediterranean forests in a combined program of modeling, field
research, and experimentation.
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