MFSc

A 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.