alpha-Pinene inhibits growth and induces oxidative stress in roots.
OBJECTIVE
Determining the mode of action of allelochemicals is one of the challenging aspects in allelopathic studies. Recently, allelochemicals have been proposed to cause oxidative stress in target tissue and induce an antioxidant mechanism. alpha-Pinene, one of the common monoterpenoids emitted from several aromatic plants including forest trees, is known for its growth-inhibitory activity. However, its mechanism of action remains unexplored. The aim of the present study was to determine the inhibitory effect of alpha-pinene on root growth and generation of reactive oxygen species, as indicators of oxidative stress and changes in activities of antioxidant enzymes.


METHODS
Effects of alpha-pinene on early root growth were studied in five test species, Cassia occidentalis, Amaranthus viridis, Triticum aestivum, Pisum sativum and Cicer arietinum. Electrolyte leakage, lipid peroxidation, hydrogen peroxide generation, proline accumulation, and activities of the enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), catalase (CAT) and glutathione reductase (GR) were studied in roots of C. occidentalis.


RESULTS
alpha-Pinene inhibited the radicle growth of all the test species. Exposure of C. occidentalis roots to alpha-pinene enhanced solute leakage, and increased levels of malondialdehyde, proline and hydrogen peroxide, indicating lipid peroxidation and induction of oxidative stress. Activities of the antioxidant enzymes SOD, CAT, GPX, APX and GR were significantly elevated, thereby indicating the enhanced generation of reactive oxygen species (ROS) upon alpha-pinene exposure. Increased levels of scavenging enzymes indicates their induction as a secondary defence mechanism in response to alpha-pinene.


CONCLUSIONS
It is concluded that alpha-pinene inhibits early root growth and causes oxidative damage in root tissue through enhanced generation of ROS, as indicated by increased lipid peroxidation, disruption of membrane integrity and elevated antioxidant enzyme levels.
Singh
Harminder P
HP
Centre for Environment and Vocational Studies, Panjab University Chandigarh 160014, India.
Batish
Daizy R
DR
Kaur
Shalinder
S
Arora
Komal
K
Kohli
Ravinder K
RK
D027721:Amaranthus / Q000187:drug effects / Q000254:growth & development; D000081008:Bicyclic Monoterpenes; D029863:Cicer / Q000187:drug effects / Q000254:growth & development; D039821:Monoterpenes / Q000494:pharmacology*; D018384:Oxidative Stress; D018532:Pisum sativum / Q000187:drug effects / Q000254:growth & development; D018517:Plant Roots / Q000187:drug effects* / Q000254:growth & development*; D029846:Senna Plant / Q000187:drug effects / Q000254:growth & development; D014908:Triticum / Q000187:drug effects / Q000254:growth & development
D000081008:Bicyclic Monoterpenes; D039821:Monoterpenes; C005451:alpha-pinene