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Studies in the Gesneriaceae: Development of the Embryo and The

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Studies in the Gesneriaceae: Development of the Embryo and The 71-7393 BAUER, Eleanor Rose, 1930- STUDIES IN THE GESNERIACEAE. DEVELOPMENT OF THE EMBRYO AND THE ENDOSPERM IN AESCHYNANTHUS LOBBIANUS HOOK. The Ohio State University, Ph.D., 1970 Botany University Microfilms, Inc., Ann Arbor, Michigan (£) Copyright by Eleanor Rose Bauer I 1971 I STUDIES IN THE GESNERIACEAE. DEVELOPMENT OF THE EMBRYO AND THE ENDOSPERM IN AESCHYNANTHUS LOBBIANUS HOOK. DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Eleanor Rose Bauer, B.A., M.Sc. ******* The Ohio State University 1970 Approved by Adviser Department of Botany ACKNOWLEDGMENTS I wish to express my appreciation to my adviser, Dr. Glenn W. Blaydes, for his continued encouragement and assistance in the work undertaken. Thanks are extended to Dr. Richard A. Popham and to Mildred Stalder who gave much help in photography and to Dr. Alan S. Heilman for the first two photographs in the paper. Gratitude is also extended to Drs. Bernard S. Meyer, Clarence E. Taft, John A. Schmitt, and Joseph N. Miller for reading this manuscript and giving constructive criticism of the work. ii VITA June 30, 1930 . Born— Cleveland, Ohio 1952 ............ B.A., Case-Western Reserve University, Cleveland, Ohio 1952-1965 ........ Instructor, Science Department, John Marshall High School, Cleveland, Ohio 1958 ........... M.Sc., The Ohio State University, Columbus, Ohio 1965-1966 ..... Muellhaupt Fellowship in Botany, The Ohio State University, Columbus, Ohio 1966-1970 ........ Instructor, Science Department, John Marshall High School, Cleveland, Ohio FIELD OF STUDY Major Field: Botany Studies in Plant Morphology. Professor Glenn W. Blaydes iii CONTENTS Page ACKNOWLEDGMENTS.......................................... ii VITA ............................................................... iii FIGURES ................................................. v INTRODUCTION ............................................ 1 MATERIALS AND METHODS .................................... 5 INVESTIGATION ............................................ 7 Endosperm Formation ........... ....... 7 Embryo Formation 19 Starch Accumulation ........ 42 Anomalous Embryo Development ......................... 46 SUMMARY.................................................. 48 LITERATURE CITED ........................................ 50 iv FIGURES Figure Page 1 Mature fruits with seed dispersal ..... ........ 3 2 Mature seeds .................... 4 3 Polar nuclei and s p e r m ........... 8 4 First endosperm division ......................... 9 5 Bi-nucleate chalazal haustorium, transverse view . 10 6 Chalazal haustorium ................. 11 7 Second endosperm division, in micropylar cell .... 13 8 Second divisions in micropylar region, endosperm . 14 9 Two-celled micropylar haustorium, transverse view . 15 10 Early cellular endosperm ............. ...... 17 11 Fertilization................................. 20 12 Z y g o t e ......................................... 21 13 Proembryo, two-celled stage . .................... 22 14 T-shaped proembryo with two-celled embryo proper . 24 15 Proembryo, quadrant stage ...... .............. 25 16 Proembryo, octant s t a g e ............... 26 17 Globular stage, early .......................... 28 18 Globular stage, later development ..... ........ 30 19 Early cotyledon stage ..... .................... 31 20 Late cotyledon stage, complete embryo .............. 34 21 Late cotyledon stage, shoot apex and cotyledons . 35 22 Mature stage, shoot apex and cotyledons . .......... 36 v FIGURES (continued) Figure Page 23 Late cotyledon stage, hypocotyl and root apex ..... 37 24 Root apex, late cotyledon stage ............38 25 Mature seed .............•••.•.*••40 26 Late cotyledon stage, hypocotyl level, transverse view ................ ......... 4 1 27 Late cotyledon stage, transverse view with three cotyledons ....................47 vi INTRODUCTION Considerable work in embryology has been reported within the Gesneriaceae. Among the earliest workers in the family, Hielscher studied Streptocarpus in 1883 and Balicka-Iwanowska (1889) the endo­ sperm haustoria in Klugia. The earlier work has been reviewed by Schnarf in 1929. Davis (1966) has summarized the more recent work. Studies of cell lineage in early stages of embryo formation have been studied in Klugia notoniana (Arekal, 1961), Rhytidophyllum crenulatum (Cook, 1907), Chirita lavandulacea (Crfetb, 1949), Didymocarpus (Thathachar, 1942), Epithema carnosum (Swamy and Padmanabhan, 1961), and other gesneriads. In the instances reported, the embryo was found to be of the Onagrad type. Papers dealing with endosperm formation within the family note a cellular endosperm from the start, with a micropylar and chalazal haustorium. Detailed accounts of the later stages in the embryo development are lacking in the family. There are a few brief observations on the nature of food reserves in the developing seeds (Cook, 1907; Thathachar, 1942, and Glisifc, 1928). This paper deals with the early stages of embryo formation in Aeschynanthus Lobbianus Hook, as well as the developmental anatomy in the later embryonic stages. The endosperm pattern of development is correlated with the stages in the embryo formation from fertilization to mature embryo stage. Starch reserves in the developing seed and fruit are also considered. 2 The writer was not able to find information concerning the details of embryo or endosperm formation in Aeschynanthus. However, chromosome numbers are available for the genus (Lee, 1962). The writer (1958) reported the embryo sac of Aeschynanthus Lobbianus to be of the monosporic 8-nucleate Polygonum type. The fruit is a linear capsule, two carpels, parietal placentation, with intruded and bifid placentae. The ovulary thus appears quadri-loculate in transverse section. Often fruits may grow to a length of 42 centimeters and contain many small seeds (Fig. 1). Each seed has two long, multi- cellular hairs that develop from the epidermis of the early ovule by cell division. An aril of thin, spherical cells develops from the funiculus during seed formation and is conspicuous as a frothy mass on the mature seed (Fig. 2). Hauss (1927) reported on the seeds of Aeschynanthus lamponqa in a paper dealing with a study of appendages found on seeds. Burtt and Woods (1958) described the curled, hairy, juvenile leaves of the seedling stage of Aeschynanthus. There was some question as to the identity of the species, probably it was Aeschynanthus maculatus. Clarke was the monographer of the genus in 1883. Maheshwari (1963) and others have emphasized the importance of embryology in taxonomic considerations. The Gesneriaceae is a dif­ ficult family to separate from the Bignoniaceae, Scrophulariaceae, and Orobanchaceae (Lawrence, 1951). A close relation of gesneriads to Orobanchaceae is strengthened by the similarity in the early embryo development and endosperm development observed within the two families (Crete, 1955a). This research reinforces the bonds between the two groups. Fig. 1. Mature fruits with seed dispersal in Aeschynanthus Lobbianus Hook. Fig. 2. Mature seeds of Aeschynanthus; seed with both hairs is 22 mm in length; micropyl hair nearest the aril is about 11 mm long. MATERIALS AND METHODS From June 1965 to August 1967 fruits of Aeschynanthus Lob­ bianus were collected as available from plants in the botany green­ houses of The Ohio State University. Samples ranged from those showing syngamy and triple fusion to mature fruit samples 80 days after polli­ nation. Ordinarily, the mature stigma must‘receive pollen from another flower before fruit is set. Sections of the capsule 5 to 10 millimeters long were fixed in Nawaschin's solution. The samples were dehydrated in an alcohol series and embedded in paraffin. The majority of the longitudinal sections were cut at 10 to 20 microns. The trans­ verse sections of fruit were cut at 5 to 12 microns. Older fruits are difficult to section. Safranin-Fast Green was used in staining (Blaydes, 1956; Johansen, 1940). Iodine-Potassium-Iodide solution was used on some preserved sections and fresh material of various ages. This treatment tended to darken the starch grains. The Biuret test was used as an indication of the peptide bond in protein, and Sudan IV stained fat droplets (Meyer, Anderson, and Swanson, 1955). Under greenhouse conditions the interval between the polli­ nation and fertilization varied from one to three days. Approximately 80 days after fertilization, the capsule dehises and mature seeds are released. Since there was a variation in the interval between polli­ nation and fertilization, the age indicated for any morphological 5 stage in this paper is the earliest one. As an example, reference to an early cotyledon stage embryo of 50 days denotes the most advanced stage observed 51 days after pollination and at least 50 days after fertilization. INVESTIGATION Endosperm Formation The writer has found that Aeschynanthus Lobbianus follows the pattern of endosperm formation most often observed in the Gesneriaceae. Polar nuclei fuse shortly before fertilization. Antipodals are ephemeral. Prior to triple fusion a sperm may be observed adjacent to the two polar nuclei (Fig. 3). About one to three days after pollination, an embryo sac contains a zygote, endosperm nucleus, and the remnants of the pollen tube. By four days after fertilization, endosperm development is well underway although the zygote itself does not usually start division until about 25 days later. The first division
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