2,4-D Hyper Accumulation Induced Cellular Responses of <i>Azolla pinnata</i> R. Br. to Sustain Herbicidal Stress

In the present experiment with ongoing concentration (0 µM, 100 µM, 250 µM, 500 µM and 1000 µM) of 2,4-D, the responses of Azolla pinnata R.Br. was evaluated based on cellular functions. Initially, plants were significantly tolerated up to 1000 µM of 2,4-D with its survival. This was accompanied by a steady decline of indole acetic acid (IAA) concentration in tissues with 78.8% over the control. Membrane bound H⁺ -ATPase activity was over expressed within a range of 1.14 to 1.25 folds with activator (KCl) and decreased within a range of 57.3 to 74.6% in response to inhibitor (Vanadate) application. With regards to IAA metabolism, plants recorded a linear increase with wall bound oxidase activity up to maximum concentration of 2,4-D. The variations were more moderated when wall bound IAA-oxidase recorded a linear increase proportionate to the 2,4-D concentrations. This was more extended with the presence of different isoforms of IAA-oxidase which was much more pronounced with distinct polymorphisms of expressed proteins, however, not independent to the 2,4-D concentrations. Polyamines like spermine, spermidine and putrescine (spm, spd and put) were not consistent in concentration with the dosages of 2,4-D. Besides these, plants were induced to apoplastic NAD(P)H oxidase activity maximally by 1.6 folds under 500 µM 2,4-D over control. Still, putrescine responded more or less consistently and recorded maximally 11.9 folds at 500 µM 2,4-D as compared to the control. NAD(P)H oxidase activity recorded maximally 1.6 folds against control and remain consistent throughout the concentrations of 2,4-D. GPX along with APX were more linear in responses through the concentration of 2,4-D except CAT as compared to control. On enzymatic antioxidative activity, peroxidases (GPX and APX) were overexpresed in a similar manner except for catalase with a non-significant rise. In stabilization of cellular redox, glutathione reductase attended maximum value by 2.45 folds at 1000 µM evidenced with significant variations in protein polymorphism. The sensitivity of 2,4- D also appeared in Azolla with a maximum loss of nucleic acids as documented by the comet assay. Moreover, the Azolla might have some DNA damage protective activity as evident using frond extract with plasmid nick assay. Therefore, Azolla plants with its cellular responses is evident to sustain against the 2,4-D herbicidal stress and may be granted in bio remediation process for the contaminated soil.