الملخص الإنجليزي
This study involves the description of the different developmental stages of Bufo arabicus (in Oman), and the study of the ontogeny of some proteins at different developmental stages. The fertilized eggs were obtained by means of spontaneous and induced fertilization. Human chorionic gonadotrophin hormone (HCGH) was used to induce ovulation and spermatogenesis. The normal development of B. arabicus, at a range of temperature 18 - 24° C is described here. It starts at the zygote (fertilized egg) to the newly metamorphosed toadlet. The ontogeny of B. arabicus is arranged into successive stages numbered 1 - 45. These include the zygote (stage 1), cleavage (stages 2-6), blastula (stages 7 and 8), gastrulation (stages 9-11), the neurulation stages (stages 12-15), embryonic. development (stages 16 - 23), larval period (stages 24 - 41), metamorphosis (stages 42 - 44) and the juvenile / toadlet (stage 45).
The description of the developmental stages is based on the external morphological and physiological characteristics and is accompanied by a sufficient number of photographs. The stages in the present table for the development of B. arabicus are compared with other normal tables of the genus Bufo and other anuran species. The development of B. arabicus resembles very closely that of other Bufo spp. Very minor differences can be seen between the different staging tables of different species because of variations in methods of staging and the criteria on which the table was assigned..
The eggs and tadpoles of different Bufo spp. are compared in some aspects such as; the pigmentation patterns, the mouth parts and duration of the developmental period. It is concluded that B. arabicus has the longest duration of developmental period among the studied toads, which estimated to be about 3 months. Since the current trends are to identify early embryogenesis in molecular terms, so the present staging table for B. arabicus was employed to further analyze the development of this toad in biochemical terms. The expression patterns of lactate dehydrogenase (LDH) isozymes were investigated in B. arabicus adults, embryos and tadpoles using nondenaturing discontinuous polyacrylamide gel electrophoresis. Five LDH isozymes were observed in five different adult tissues. These are; LDH-5(A4), LDH-4(A3B), LDH-3(A2B2), LDH-2(AB3) and LDH-1(B4) in order from the cathode to the anode. The most cathodal isozyme LDH-5 (A4) showed the strongest activity, All embryonic stages tested displayed first the anodic isozymes. Four LDH isozymes are present in the stages 1-16 (fertilized egg - tail bud stage): LDH-1(B4), LDH-2 (ALB), LDH-3(A2B2) and LDH-4(A3B1). The first appearance of the fifth isozyme band LDH-5 (A4) was detected in stage 17 when the muscular response started. This isozyme showed gradual increase in intensity from stage 17 to stage 43.. In order to further correlate morphogenetic events with the protein changes, ontogeny of water-soluble proteins was studied by using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and densitometric analysis. New protein bands were found at early blastula (stage 7), neurulation (stage 12), muscular response (stage 17), heart beat (stage 18), hindlimb bud (stage 25) and well formed tadpole (stage 35). Some protein bands changed in their expression manner (either increased or decreased), some disappeared at particular stages and some showed transitional occurrence. The molecular weight in kda) of these protein bands was determined using Gel Documenter.
