Karyomorphology and isoenzyme variation in certain acacia species

Abstract

study was conducted at the College of Forestry, Vellanikkara, Trichur on karyomorphology and isoenzyme variations of Acacia auriculiformis A. Cunn. ex. Benth. A. mangium Willd., A. ferruginea DC and A. nilotica Willd. ex. Del during 1996 to 1997. For karyomorphological studies, the cytological technique using root tip squash method was standardised employing various pre-treatment chemicals, fixatives and stains. The roots pre-treated in 0.03 per cent 8-hydroxyquinoline for one hour at room temperature were subjected to fixation in Carnoy's B fluid (6:3:1, ethanol: acetic acid : chloroform) for 24 hours. Subsequently, the roots were hydrolysed in , 1 N HCI at 60°C for a duration of three minutes in case of A. nilotica and A. auriculiformis and four minutes in case of A. mangium and A. ferruginea. the roots were then stained in 1.0 per cent aceto orcein for five hours. After that slides were prepared and examined for mitotic chromosomes. From mitotic index prepared, the rate of cell division was found to be at peak between 9.00 am and 10.00 am in all the species. The study has revealed that A. mangium and A. auriculiformis possessed 2n=26 chromosomes, while A. nilotica carried 2n=52 chromosomes. A. ferruginea, the species for which the chromosome studies conducted for the first time also found to carry 2n=26 chromosomes. The chromosome lengths were measured using camera lucida drawings. The chromosome of A. auriculiformis and A. mangium - acacias of Australian origin - are relatively larger compared to that of A. nilotica and A. ferruginea - acacias of Indian subcontinent. The chromosome length of

former two species ranged between 0.75 urn to 1.61 urn and 0 .. 67 urn to 2.60 urn, respectively. The average chromosome length of A. mangium was 1.30 urn while that of A. auriculiformis was 1.16 urn. The chromosome length of A. nilotica ranged between 0.51 urn to 1.25 urn with an average length of 0.79 urn. In case of A. ferruginea, the chromosome length. ranged from 0.56 to 1.44 urn and average length was 0.92 urn. Idiogram have been constructed for all the species based on absolute and relative chromosome length. The two isoenzyme systems, namely, esterase and glutamate oxaloacetate ,transminase (GOT) were analysed using polyacrylamide gel electrophoresis. Both isoenzymes together produced seven bands with three for esterase and four for GOT. The bands Est-3 (Rm = 0.50) and GOT-3 (Rm = 0.26) were present in A. mangium as well as in A. auriculiformis this indicate presence of similar type of monomorphic gene loci for both enzymes systems in this two species, while the rest of the isoenzyme bands showed variation in their mobility. From the cytological and isoenzyme studies, it is suggested that A. auriculiformis and A. mangium are genetically related where as A. ferruginea and A. nilotica are distinctly different.