Abstracts of Papers - Harvard Forest - Harvard University

its acentric position throughout later stages of
sporogenesis. The plastid migrates later in the
tetrad stage from its meiotic position parallel to
the distal surface to a position perpendicular to the
distal surface with one tip in close proximity to the
proximal MTOC. The proximal microtubule system
reaches its maximum development by the end of the
tetrad stage and all micrographic evidence of it is
lost in the maturation stages of late sporogenesis.
BRUCK, DAVID K. and DAN B. WALKER. Department
of Biology, UCLA, Los Angeles, CA 90024
- Epidermal commitment in the Citrus embryo.
At the 30-60 celled globular stage of embryogenesis
in the rough lemon (Citrus jambhiri), a central core
of cells dividing in random planes is surrounded by
cells whose anticlinal walls predominantly radiate
out from the core. Not until a globular stage con-
taining 150-200 cells, however, are periclinal divi-
sions in the peripheral cells eliminated. Thereafter
the convoluted surface becomes smooth as the proto-
dermal cells are layered and tabular. The thick
cuticle of the mature lemon epidermis is not obser-
vable during embryogenesis under conventional histo-
logical stains. Whether the layering of the surface
cells is truly a reflection of commitment to epider-
mal ontogeny is one subject of our investigations.
Our experimental evidence to date indicates that
once the epidermis is determined, except for rare or
specialized circumstances, the subepidermal tissue
lacks the competence to redifferentiate as epidermal
even if put in the position and environment of an
epidermal cell. Removal of epidermal cells in
various organs (stems, leaves, floral organs) at
various developmental stages has resulted in a
replacement of the epidermis with wound callus or
periderm rather than epidermal regeneration by sub-
epidermal tissue. To test if embryos at sufficient-
ly early stages of tissue commitment can be induced
to regenerate a protoderm from subsurface cells, we
have surgically removed the protoderm from intact
embryos. Surgical procedures and subsequent growth
of embryos required the development of an in vitro
culture system where the lemon embryos were grown
in nurse ovules of citron (Citrus medica).
BUNTMAN, D.J.* and H.T. HORNER. Department of
Botany, Iowa State University, Ames, IA 50011.
- Microsporogenesis of normal and ms3 mutant soybean
(Glycine max).
The Ms3 genetic male sterile soybean anther is compared
with its normal line by using light, scanning,
and transmission electron microscopy. Floral development,
with the exception of androecium development,
is similar between normal and ms3 lines. The first
difference between normal and ms anther development
is observed in the tapetum. At Lhe early meiocyte
stage ms mitochondria appear abnormal. The ms
tapetum then becomes more disorganized and breais
down prematurely. Tetrads are not released and subsequently
abort. These events are accompanied by the
accumulation of large amounts of an unidentified
refractive material interior to the parietal cells.
CALVIN,* CLYDE L. and M. CAROL ALOSI. Department
of Biology, Portland State University, Portland,
OR 97207 and Department of Botany, University of
Cal iforni a, Berkel ey, CA 94720 - Devel opmental
Developmental and Structural Section 17
anatomy of thd epidermis of the dwarf mistletoe,
Arceuthobium tsugense.
The developmental anatomy of the epidermis of
Arceuthobium tsugense (Rosendahl) G.N. Jones was
studied using both light and scanning electron
microscopy. Aerial shoots of the dwarf mistletoe may
reach a height of 10 cm or more, but most are
somewhat shorter. In recently emerged shoots the
decussately arranged leaves of adjacent nodes overlap,
concealing the stem. As internodal elongation
continues, stem segments gradually become visible.
The leaf pairs, which are joined at their bases, stop
their development early. In mature stems they appear
as small boat-shaped structures surrounding the nodes.
No trichomes were present on the shoots examined at
any stage of development. Stomates are present on
stems and leaves. On the latter, they are most
abundant on the keeled midregions of abaxial leaf
surfaces. The longitudinal axes of stomates are
oriented perpendicular to the stem,axis. Guard cells
are partially covered by over-aching subsidiary cells,
producing a small antechamber just above the stomatal
aperture. Substomatal chambers are small to absent
and contiguous tissues have a paucity of intercellular
spaces. As development continues, the epidermis is
covered by a very thick cuticular layer and stomates
becomes occluded. Subsequently, subepidermal cells
also secrete cuticular material, isolating sections
of epidermal tissue that become necrotic. The changes
outline constitute the formation of a cuticular
epithelium much like that described for Phoradendron.
The generally xerophytic features displayed by
Arceuthobium seem inconsistent with known physiology
of the parasite.
P.C. CHENG*, TAN K.H., McGOWAN J.Wm. and FEDER R.
Dept. of Anatomy, Univ. of Illinois, Chicago, IL;
Canadian Synchrotron Radiation Facility(CSRF),
Physical Sci. Lab., Univ. of Wisconsin, WI; Dept.
of Physics, Univ. of Western Ontario, Canada; IBM
T.J. Watson Res. Ctr., NY.-Recent developments in
soft x-ray spectroscopy and contact microscopy.
Feder et al(1981) reported that the x-ray image of
blood platelets is different from the electron image,
which they believe is due to differences in the x-ray
absorption and electron scattering properties of P in
cytoplasmic phosphate compounds. We have also reported
some preliminary attemps on imaging plant tissues by
x-rays. A better understanding of the absorption
spectra of various biological compounds is important
for future interpretation of x-ray microscopic images.
Due to the availbility of a synchrotron source, only
low(20-280 eV) x-ray spectra were used in this study.
Three biological samples, ADP(Na salt), 1-methionine
and crude corn leaf extract(1:1 methanol/chloroform)
and two polyamino acids(homopolymers), poly-l-methio-
nine and poly-cysteine, were used in the study. The
samples were either dissolved in water or EtOH and
coated on a thin Formvar film, or incorporated in the
Formvar film(i.e. leaf extract). Absorption measure-
ment was done on a beam line of Tantalus storage ring
with a Mark IV Grasshopper monochromator(CSRF). The
results show a P L absorption edge in the ADP sample
and a S L edge in the 1-methionine, poly,l-methionine
and poly-cysteine samples. The S L absorption edge of
methionine shows a few eV shift from the atomic state.
Corn leaf extract shows a P edge which could be
contributed by membrane phospholipids.
X-ray contact microscopy of various corn tissues were
conducted with synchrotron radiation and x-rays
generated by a stationary target source(C and V
targets). X-ray contact images were formed on a PMMA
x-ray resist back supported by a Si3N4 window, then
the contact image magnif ied by a TEM.