LEAF AND STEM ANATOMY OF FOUR DIOSCOREA SPECIES D. ROTUNDATA (POIR), D. ALATA (L), D. BULBIFERA (L) AND D. DUMETERUM (KUNTH)

ABSTRACT

The edible tubers from different species of Dioscorea are a major source of food and nutrition for millions of people in the world. The anatomy of the organs (leaves and stems) of Dioscorea rotundata, Dioscorea bulbifera, Dioscorea dumeterum and Dioscorea alata were examined and compared with the aim of identifying or delimiting the existing characters between these species. Anatomical studies were carried out on the leaves and stems of the four species. The result obtained from this investigation showed features of anatomical importance in the leaves and stems of these species. Results from epidermal cells showed differences in the shapes and sizes of the epidermal cell walls. The result from the investigation has proved that the leaf and stem anatomy of the four dioscorea spp exhibits characters like trichomes, spindle, nail, curve-straight appearance in shapes and the presence of stomata on the lower epidermis layer of the leaf, while stomata were absence in the upper epidermis (hypostomatic) in nature. This could be included with other reliable attribute of this species in an attempt to fashion out an authentic classification among the varieties of Dioscoreae. This observation will be useful and contribute to the further classification of Dioscorea species.

TABLE OF CONTENTS

Title page                                                                                                             i

Certification                                                                                                         ii

Declaration                                                                                                         iii

Dedication                                                                                                           iv

Acknowledgments                                                                                                v

Table of contents                                                                                                  vi

List of tables                                                                                                        vii

List of figures                                                                                                       viii

CHAPTER ONE

1.0  INTRODUCTION                                                                                         1

1.2      Justification                                                                                               2

1.3      Aims and Objectives                                                                                  3

CHAPTER TWO

2.0      LITERATURE REVIEW                                                                           4

2.1      D. bulbifera                                                                                               4

2.2      D. alata                                                                                                     6

2.3      Description of one out of the four species of Dioscorea                              8

2.4      Anatomy and Plant Classification                                                               11

CHAPTER THREE

3.0      MATERIALS AND METHOD                                                                13

3.1      Collection and Identification of Plant Materials                                           13

3.2      Anatomical Studies                                                                                   13

3.3      Epidermal Studies                                                                                      14

3.4      Photomicrograph                                                                                       14

CHAPTER FOUR

RESULTS                                                                                                           15

CHAPTER FIVE

5.1      Discussion                                                                                                 17

5.2      Conclusion                                                                                                18

REFERENCES                                                                                                   19

APPENDIX

LIST OF TABLES

2.1      Description of one out of the four species of Dioscorea                   8

LIST OF FIGURES

Plate 4.1: (a) D. bulbifera (stem) showing circular shape wall type arrangement on stem layer cell wall.

              (b) D. bulbifera (stem) showing circular or spherical shaped wall type arrangement on stem layer cell walls.

(c)  D. alata  (stem) showing circular shape wall type arrangement on stem layer cell wall.

(d) D. alata (stem) showing circular or oblong shape wall type arrangement on stem layer cell wall.

Plate 4.2: (a) D. rotundata (stem) showing circular shape wall type arrangement on stem layer cell wall.

              (b) D. rotundata (stem) showing circular or spherical shaped wall type arrangement on stem layer cell walls.

(c)  D. dumeterum   (stem) showing curved or  circular shape wall type arrangement on stem layer cell wall.

(d) D. dumeterum (stem) showing curved - straight wall type arrangement on stem layer cell wall.

Plate 4.3: (a) D. bulbifera (mid rib) showing that parenchyma cells are circular in  nature .

              (b) D. bulbifera (mid rib) showing curved parenchyma cells in shape

(c)  D. dumeterum  (mid rib)  showing curved numerous spindle shape trichomes found on the epidermis cells walls

(d) D. dumeterum (mid rib) showing wavy and needle-like shape cell wall.

Plate 4.4: (a) D. rotundata (mid rib) showing circular shape cell wall

              (b) D. rotundata (mid rib) showing curved-straight shape cell wall

(c)  D. alata   ((mid rib) showing circular shaped cell wall.

(d) D. alata  (mid rib)  showing circular shape cell wall.

Plate 4.5: (a) D. alata (LE) showing Curved shape cell wall.

              (b) D. alata (LE)  showing curved shape cell wall. Presence of stomata

(c)  D. alata   (UE)  showing curved-straight cell wall.

(d) D. alata  (UE)  showing straight epidermal  cell wall. Absence of stomata (hypostamatic)

Plate 4.6: (a) D. rotundata (LE) showing curved epidermal shape cell wall

              (b) D. rotundata (LE) showing curved shape cell wall. Presence of stomata

(c)  D. rotundata (UE) showing curved-straight epidermal cells wall. Absence of stomata (hypostomatic)

 (d) D. rotundata  (UE)  showing curved-straight epidermal cell wall.

Plate 4.7: (a) D. dumeterum (LE) showing spindle shape unicellular trichomes

              (b) D. dumeterum (LE) showing spindle shape unicellular trichomes

(c)  D. dumeterum (UE) showing nail-shaped trichomes

 (d) D. dumeterum (UE)  showing nail-shaped trichomes. Stomata absence.

Plate 4.8: (a) D. bulbifera (LE) showing curved epidermal cell walls.

              (b) D. bulbifera (LE) showing curved-straight epidermal walls. Stomata presence

(c)  D. bulbifera  (UE) showing wavy shaped epidermal walls.

 (d) D. bulbifera  (UE)  showing straight walled epidermal cells.

Plate 4.9: (a) D. bulbifera (L) showing wavy shape epidermal cell wall

              (b) D. bulbifera (L) showing curved epidermal cell wall.

(c)  D. alata  (L) showing curved epidermal cell walls.

 (d) D. alata  (L)  showing curved epidermal cell walls.

Plate 4.10 (a) D. dumeterum (L) showing spindle epidermal cell walls

              (b) D. dumeterum (L) showing spindle or nail epidermal cell walls

(c)  D. rotundata  (L) showing curved epidermal cell walls

 (d) D. rotundata (L)  showing oblong-straight epidermal cell wall.

CHAPTER ONE

1.0                                                    INTRODUCTION

The genus belongs to the family Dioscoreaceae that contains true yams. Dioscoreacea, (yams), is a genus of over 500 species of usually herbaceous (but sometimes woody) herbaceous perennial vines that produce starchy, edible tuberous  roots  that are an important source of food in tropical regions worldwide, including Africa, Asia, Oceania, and Latin America. Yams are herbaceous, climbing, twining, perennial monocots (Wagner et al., 1999). Vines are without tendrils and use dead stems from the previous year’s growth to climb into other vegetation (Morisawa and Tunyalee, 1999).

Yams are dioecious (Wagner, et al., 1999), and produce very small flowers, if any from Flora of North America Association (2009).

For thousand of years, yams have been a staple food for humans. They have been widely cultivated and domesticated throughout the world. Selection and adaptation have occurred in native and nonnative habitats, producing an abundance of ecotypes. Variable yam forms are possible and commonly seen every where, depending on the number of types introduced and escaped. Great variation in the growth and forms of vines, leaves, bulbils and tubers are reported from aerial yams and water yams (Martin and Franklin, 1974), and are also likely in other species. Water yams vines  twine clockwise and may reach 100 feet (30 cm) long (Wunderlin et al., 2003).

Yam vines often have cordate leaves that may be alternate, opposite, or whorled. The flowers, arranged in spikes or racemes, are small and generally unisexual. The fruits are 3-angled or winged capsules (in some species, berries), containing winged seeds. Yam tubers can grow up to 1.5 m (4.9 feet) long and weigh up 70 kg (154 pounds). Yams are versatile vegetables, composed mostly of starches, with significant amount of vitamin C. However, many species of yams must be cooked to be safely eaten, because raw yams contain various natural compound including, phenols, tannins, hydrogen cyanide, oxalate, amylase inhibitor activity and trypsin inhibitor, that can cause illness or lead to nutritional deficiencies if consumed (Edeoga and Okoli, 1991).

Although, the plants are affected by various pathogens pests, the tubers, once harvested, can be stored for four to six months without refrigeration, which makes the valuable resources for the yearly period of  food scarcity at the beginning of the wet season.  Researches revealed that the scientific importance and implications of anatomical features in different groups of plants have been indicated by different authors. This include Dioscoreaceae, where certain anatomical feature were used in the classification of D. alata L.  (Edeoga, 1991).

1.2      Justification

Though information on the anatomy of different groups of plants are available, there is death of information on the anatomy of D. rotundata, D. alata, D. bulbifera and D. dumetorum. This work is to contribute to the information on the anatomy and taxonomy of these four species of yam.

1.3      Aims and Objectives

The objective of this research is to described the anatomical character of four species of the Dioscoreaceae family and to assess the differences and the anatomical features that could be utilized in the biosystematic consideration of the four species in view of their perceived similarities in structural morphology.

-       These is an attempt to fill the gap in our present knowledge in the anatomy of Dioscoreaceae.

-       It was an attempt to identify different characters that exist in the same specie of Dioscorea.

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