3.2. Influence of carbon sources on phenolic secretion in callus culture
Among the different concentrations of carbon sources tested, 3%
maltose was found to be the best carbon source for efficient callus
culture followed by glucose. Maltose showed a minor impact on
tissue browning both at lower and higher concentrations. On the
other hand, MSB5medium supplemented with glucose at both lower
and higher concentrations exhibited increased secretion of phenolic
compounds. In present study, phenolic secretion was comparatively
higher in cotyledons than hypocotyl explants. Moreover secretion of
phenolic compounds was quite increasing both hypocotyl and
cotyledon incorporated with fructose, glucose and sucrose. But
maltose was found to play a significant role in controlling phenolic
secretion from both explants. However, maltose also showed low
amount of phenolic secretion below and above 3%, specifically in
cotyledon inoculated medium. Meanwhile, fructose showed poor
callusing response and increased phenolic secretion at all the
concentrations tested. These results are in accordance with the
earlier reports [8,11]. Hence fructose was found to play no significant
role in callus culture of SVPR-2 cotton cultivar. Sucrose upto 1%
showed optimum growth of callus tissues with considerable amount
of phenolic secretion whereas browning of medium was observed
with 3% sucrose due to high secretion of phenolic compounds
(Figs. 1–3). As a result the callus growth was arrested beyond a
particular stage. In contrary, 3% maltose was found to be efficient in
controlling phenolic secretion and so it was used for further studies.
Extracellular hydrolysis of maltose takes place at a slower rate when
compared to sucrose and it is taken up and hydrolysed more slowly.