Sieve-Element Characters of Ticodendron

4 Pages·1991·3.2 MB·

by  H-Dietmar Behnke

SIEVE-ELEMENT
H.-Dietmar Behnke^
CHARACTERS
OF TICODENDRON
1
Abstract
&
Among
the families of Hamamelidae, Ticodendron incognitum Gomez-Laurito Gomez P. contains S-type sieve-
element plastids, the specifics of which (diameter and starch grains) would place within or close to Betulaceae/
it
Corylaceae. The absence of persistent, nondispersive P-protein bodies in the sieve elements of Ticodendron excludes
the families of the Urticales and the Fagaceae, regularly containing persistent P-protein bodies, from the of
all
list
closest relatives.
its
Sieve-element characters, information ob- sectioning and eventual photographing with a trans-
i.e.,
tained with the transmission electron microscope mission electron microscope.
on sieve-element plastids, phloem proteins, and oth- Part of the prefixed material was dehydrated
er morphological features, have largely been used with ethanol, embedded into histowax, sectioned
to delimit higher taxa within angiosperms (Behnke, with a sliding microtome, stained with resorcin blue,
1981a), but in a few cases were also helpful to and screened with a light microscope,
assign single genera to a family {Lophiocarpus:
Behnke, 1974; Halophjtum: Hunziker GENERAL DESCRIPTION OF THE ShOOT
et
al.,
1974; Hectorella: Behnke, 1975; Swartzia:
Transverse sections of the shoot sample studied
Behnke, 1981b; Geocarpon: Behnke,
1982).
show
composition as follows Figs. 1-3): the
its (cf.
The unknown
taxonomic
hitherto position of the
innermost part occupied by the pith (Fig. 1: Pi)
is
newly described genus Ticodendron (Gomez-Lauri-
parenchyma and
containing thin-walled large
cells
&
Gomez
1989a, and probable
to P., b) rela-
its
marginal, shizogenous secretory sacs surrounded
Hamamelidae
tionships to various families of the
The
by
six epithelial cells (Fig. 1: o). length of
prompted an
investigation of sieve-element char-
its
these sacs, however, restricted to about three to
is
acters. Moreover, a survey of the sieve-element
The
Avc times their width. outermos.t^p.it.h .ce„ll,s,
r r 1-1 r ,.
, 11 1 1hamamelidaean -I-
characters oi oi the lamilies
all
_
, . ,
those bordering the xylem, often have
lignified
i.e.,
(Behnke, 1989) both a comparison with
facilitates
wa
ceil Us.
11
and asks for a complementation by data from 77-
The
xylem, phloem, sclerenchyma, and cortex
dend
ron
make
up distinct layers proceeding toward the pe-
The
riphery of the section. shoot protected by
is
Material and Methods
The
a periderm four to six cells broad (Fig. 1: Pe).
Shoot parts of a sapling of Ticodendron incog- presence of a periderm, as well as the extent and
&
nitum were collected Costa Rica (Bello Haber the arrangement of xylem and phloem, demon-
in
9809\
divided with a razor blade into longitudinal strate that this shoot part already in secondary
is its
and immediately immersed growth The xylem X) shows
sections, into a fixative period. (Fig. 1: a strict
containing paraformaldehyde and glutaraldehyde radial arrangement of rather small and evenly
its
may
The
(Karnovsky, 1965). samples were mailed to sized cells interspersed by vessels, which be
the author's laboratory, placed for 3 hr. in fresh twice as broad as the other elements but do not
M
Karnovsky's fixative, washed with 0.1 sodium greatly disturb the radial array (Figs. 2, 3: X).
1%
cacodylate bufTer, postfixed for hr. in buf- Small multiseriate rays, in cross sections only one
1
fered OsO^, dehydrated in acetone, embedded and cell broad, are found at regular intervals. In a few
polymerized in an Epon-Araldite mixture, and pro- parts of the studied shoot sample, the phloem (Figs,
cessed according to standard methods for ultrathin 1, 2: P) reflects origin from radially aligned
its
The E
This study was supported by grants from the Deutsche Forschungsgemeinschaft. author grateful to B.
is
'
Hammel, Missouri Botanical Garden, for providing stem material of Ticodendron.
^ Zellenlehre, Universitat Heidelberg, Im Neuenheimer Feld 230, D-6900 Heidelberg, Federal Republic of Germany
Ann. Missouri Bot. Card. 78: 131-134. 1991
—
132 Annals of the
Garden
Missouri Botanical
%wl'
J
»
—
Figures 1-7. TLcodendron incognitum. 1. Cross section of young shoot with periderm (Pe), cortex (C), phloem
—
xlOO.
(P), xylem (X), and pith (Pi). Cortex and pith contain secretory elements (o); 2. Detail of cross-sectioned
vascular cylinder showing part of secondary xylem with vessels (X), phloem delimited against the cortex by sclerenchyma
—
(S), and a pericycle made up of transparent cells (*); x 230. 3. Part of cross-sectioned phloem with numerous thick-
—
walled sieve elements (s) and black tannin cells (T); oblique sieve plate between arrows; x 500. 4. Longitudinal
x570.
section through phloem with many parallel-aligned sieve elements (SE) with sieve plates between arrows;
—
TEM
many x
5, 7. S-type sieve-element plastids with small to medium-sized starch grains (s); 30,000. 6. longitudinal
Volume Number Behnke
78, 133
1
1991 Ticodendron Sieve-element Characters
cambial initials. The cambial layer itself is rather and are enucleate when mature. Plastids and mi-
small and difficult to delimit. tochondria are ahout the only organelles present
The sclerenchymatous sheath (Fig. 2: S) consists and reside at the periphery of the whereas
cells,
of mostly one layer of thick-walled fibers, but Ion- filaments of P-protein are dispersed throughout the
gitudinal sections indicate that thinner-walled stone sieve element (Fig. 6: *) and are also trapped within
do occur rather frequently, probably bridging the sieve pores
cells
A The
the gaps between different fiber groups. one- sieve-element plastids contain starch grains
celled pericyclic layer of clear parenchymatic cells only and thus belong to the S-type. Their average
adjoins the sclerenchyma toward the periphery of diameter about /zm, and they contain an av-
is 1
the shoot (Fig. 2: *). erage of eight round or ovoid starch grains. How-
The composed parenchyma much among
cortex of small ever, there variation Ticod-
size
is is
cells and numerous large secretory cells (Fig. 1: e/iC?roAi sieve-element plastids (compare Figs. 5 and
C, o). Compared to the pith secretory sacs, these 7); diameters range from 0.7 to 1.5 ^m.
much No
are shorter, their extension being almost the persistent or nondispersive P-protein bodies
same in all directions. were found in the investigated sample. All mature
The content of the pith and cortex secretory sieve elements screened contained P-protein, the
elements seems to be mucilaginous. In addition, filaments of which were more or less evenly dis-
small cells containing tanninlike substances (Fig. persed over the cell lumina (Fig. 6: *).
T) are frequently found the cortex and are
3: in
also present in other tissues (see black cells in COMPARISON OF THE TiCODENDRON SlEVE-ELEMENT
all
Figs. 1-3). Crystal cells (containing clustered crys- CHARACTERS TO THOSE OF Putatively
abundant RELATED TaXA
tals) are in the cortex but are also fre-
quent phloem and
in the in the lignified pith cells,
The
sieve elements of Ticodendron contain
which border the innermost xylem.
S-type plastids as do the great majority of dicot-
yledons, including of the hamamelidalean fam-
all
SlEVE-ELEMENT CHARACTERS
The
(Behnke, 1981a, 1989). plastids of Tico-
ilies
The phloem Ticodendron composed dendron
of of sieve are smaller .0 fxm) than the total average
is 1
(
elements (Fig. 3: companion cells (Fig. 6: CC), of S-type plastids (1.4 )um, based on 1,400 S-type
s),
and phloem parenchyma Comparatively many species). The families that contain S-type plastids
cells.
of the parenchyma cells, including those in phloem with an average diameter between 1.2 and 0.8 fim
28 hamamelid
rays, contain tanninlike substances (Fig. 3: T) include 2 of the families of putative
1
6-10
With a diameter of /im, sieve elements of alliance, five of the six families making up the
Ticodendron are very narrow; their length about Fagales and of those in the Urticales (Behnke,
is all
80-100
Secondary sieve elements are some- 1989).
fxin.
what smaller than primary ones and are more reg- Variation in the morphological features of the
4 Ticodendron
ularly aligned (see Fig. with sieve plates aligned starch grains of outside that of
falls
between commonly
arrows). Sieve plates are re- the families of Urticales; their starch grains are
stricted to the end walls and have their pores ar- larger and fewer (compare Figs. 6 and 7 with
figs,
ranged in a single sieve area (simple sieve plate). 6.5 and 6.6 in Behnke, 1989). Also, with the
The position of the sieve plate in general at right exception of the Cannabaceae, of the Urticales
is all
angles to the lateral wall, and only in some cases sieve elements contain a specific globular nondis-
much inclined (Fig. between arrows). The pore persive P-protein body (see 6.1 in Behnke,
is 3, fig.
diameter about 0.5 fxm (Fig. 6, arrows), mostly 1989), lacking in Ticodendron.
is
Among
occluded by heavy callose collars (due to unfavor- the families of Fagales, the Nothofaga-
able conditions during tissue preparation of the ceae differ by their larger-sized plastids and the
sample Fagaceae by compound-spherical nondisper-
used). their
As seen with the transmission electron micro- sive protein bodies found in species studied so
all
scope, sieve elements have comparably thick walls far. Betulaceae and/or Corylaceae would have the
section through part of phloem with two sieve elements (SE) and a companion (CC). The sieve elements contain
cell
many
S-type plastids (S) and evenly dispersed filaments of P-protein (*). Sieve pores (arrows) are almost totally
x
occluded by callose deposits (white wall parts) and arranged into simple sieve plates; 5,000.
134 Annals of the
Garden
Missouri Botanical
closest similarities in their sieve-element charac- porting its inclusion into Leguminosae-Papilionoi-
13-
deae. Iseleya 2: 16.
The Betulaceae the sense of Cron-
ters. (e.g., in
s.l.
1982. Geocarpon minimum: sieve-element
.
1981, or Takhtajan, 1987) have S-type plas-
quist,
plastids as additional evidence for inclusion in the
its
tids with an average diameter of 1 .2 fxm and about Taxon 45-47.
Caryophyllaceae. 31:
five medium-sized starch grains. If Corylaceae are 1989. Sieve-element plastids, phloem pro-
.
and Ha-
held to be a separate family (e.g., Dahlgren, 1989), teins, the evolution of flowering plants. IV.
&
mamelidae. Pp. 105- 128 in P. R. Crane S. Black-
their plastid characters (diameter 1.1 /im; about
more and
(editors), Evolution, Systematics, Fossil
eight starch grains) would nicely with those of
fit
History of the Hamamelidae, Volume Systematics
1.
Ticodendron. However, considering the compar-
Association Special Volume 40A. Clarendon Press,
wide range of measurements on which av- Oxford.
atively
An
Cronquist^A. 1981. System^of Flow-
Jntegrated
erages are based, none of the discussed families
New
ering Plants. Columbia Univ. Press, York.
would seem
inappropriate.
Dahlgren, G. 1989. The Dahlgrenogram. System
last
Based on sieve-element data, Ticodendron 249-260
its of classification of the dicotyledons. Pp. in
would best within Betulaceae/Corylaceae, only K. Tan (editor), The Davis and Hedge Festschrift.
if
fit
Edinburgh Univ. Press, Edinburgh.
hamamelid families are considered. obvious
It is
&
G6mez
G6mez-Laurito, L. D. P. 1989a. Ticoden-
J.
that a positive alignment of Ticodendron cannot
dron: a new tree from Central America. Ann. Mis-
be given on only sieve-element characters; these
1148-1151.
Card
souri Bot. 76:
&
A
characters can only be used to favor or exclude 1989b. new hamamelid element
341-342
taxonomic made on account from Central America. Pp. in P. R. Crane
proposals for a position
&
Blackmore Evolution, Systematics,
S. (editors),
many
of other characters.
and Hamamelidae, Volume
Fossil History of the 2.
Systematics Association Special Volume 40B. Clar-
Literature Cited endon Press, Oxford.
&
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114-119.
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A
KarNOVSKY, M. 1965. formaldehyde-glutaralde-
J.
1975. Hectorella caespitosa: ultrastructural
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hyde
fixative of high osmolality for use in electron
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its
137A-138A.
microscopy. 27:
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PL 31-34.
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.
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