Morphological and Physiological Effects of Drought Stress on 6-Benzylaminopurine-Assisted In vitro Shoot Multiplication in Amsonia orientalis

In this study, the morphological and physiological effects of drought stress on Amsonia orientalis Decne. were investigated during 6-benzylaminopurine (BAP) -assisted in vitro shoot multiplication. At the end of the incubation period, mean shoot lengths and numbers, H2O2 (hydrogen peroxide) and MDA (malondialdehyde) levels and the activities of SOD (superoxide dismutase), POD (peroxidase) and CAT (catalase) enzymes were analyzed. The osmotic potentials of -0.15, -0.49, -1.03, and -1.76 MPa obtained using polyethylene glycol (PEG-6000) were tested on shoots, and the results were compared with two control groups, with and without BAP. Although the mean number of shoots declined with decreasing osmotic potential compared to control with BAP, it remained at the statistically same level with control without BAP. The mean shoot length was found to be lower than that of the control without BAP in response to the severe drought application. SOD activity showed a significant reduction compared to control values in response to mild drought. However, the activity increased up to the control values in severe drought. POD and CAT activities also decreased under drought while the decrease in CAT activity was more pronounced. H2O2 and MDA levels were found to be increased similarly with elevated drought stress. However, this increase was found to be limited to low levels. The presence of higher antioxidant enzyme activities in the absence of drought stress but unexpected lower activities in lower osmotic potentials (during drought stress) suggested that the application of BAP in A. orientalis may stimulate the non-enzymatic defense mechanism which employs the cellular osmotic regulators, and it may allow this mechanism to be used more efficiently than enzymatic defense system. For this reason, the molecular and physiological functioning of BAP application in plant drought stress needs to be explained in detail. Also, BAP application may be preferred to alleviate the potential adverse effects of drought stress on shoots of A. orientalis in nature