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Title: Differential morphological, cytological and biochemical responses of two rice cultivars to coumarin

item MAHMOOD, KHALID - South China Agricultural University
item KHAN, MUHAMMAD - South China Agricultural University
item SONG, YUAN YUAN - South China Agricultural University
item YE, MAO - South China Agricultural University
item LONG, JU - South China Agricultural University
item LUO, SHI MING - South China Agricultural University
item Baerson, Scott
item ZENG, REN SEN - South China Agricultural University

Submitted to: Allelopathy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2013
Publication Date: 4/1/2013
Citation: Mahmood, K., Khan, M.B., Song, Y., Ye, M., Long, J., Luo, S., Baerson, S.R., Zeng, R. 2013. Differential morphological, cytological and biochemical responses of two rice cultivars to coumarin. Allelopathy Journal. 31:281-296.

Interpretive Summary: This article describes studies performed with the compound coumarin, which possesses herbicidal activity and is also thought to act as an allelochemical in natural ecosystems. Allelochemicals include compounds produced by plants which are released into the soil and inhibit the growth of neighboring plants in a competition for light, nutrients, and other limited resources. The work focuses on two different varieties of rice – one which is highly sensitive and one less sensitive to the effects of coumarin, and explores differences in the effects the compound has on these two varieties. Different aspects of growth were examined in plants exposed to coumarin, and the highly sensitive variety was shown to have severely reduced root length and root system complexity, and a significantly reduced number of root hairs lining its root system. The sensitive variety was also found to express important detoxification enzymes at lower levels than the less sensitive variety. Electron microscopy studies also showed increased degradation of cells within the root system of the sensitive variety compared with the less sensitive one. Collectively, the results provide a basis for understanding the different responses exhibited by the two varieties to coumarin, and also provides clues concerning why specific rice varieties are less affected by this compound than others.

Technical Abstract: Plants are often exposed to allelochemicals in the environment produced by neighboring plants. Coumarin is a common allelochemical produced by many higher plants. Two cultivars (susceptible BS-2000 and less susceptible BR-41) of rice (Oryza sativa L.) were selected to compare their differential root morphological, biochemical and cytological responses to coumarin. For both the BS-2000 and BR-41 cultivars, a similar trend in the relative sensitivities of specific root parameters to coumarin could be observed: total number of root hairs > total number of lateral roots > radical length. Light and electron microscopic observations of seedling root and leaf cells revealed that the two cultivars exhibited differential responses to coumarin exposure. BR-41 exhibited higher ribosomal density (RD), more mitochondria in root cells, larger starch granules in leaves, and more vacuoles which were smaller in size as compared to BS-2000. Coumarin also induced different antioxidant responses in the two cultivars. BR-41 showed 23% higher superoxide dismutase (SOD), 16% higher catalase (CAT) and 17% higher peroxide dismutase (POD) activities than BS-2000 when exposed to 400 µM coumarin. However, malondialdehyde (MDA) contents and electrolyte leakage were significantly higher in BS-2000, which exhibited 8 and 10 % higher MDA levels and 49 and 45% higher electrolyte leakage compared with BR-41 when exposed to 200 and 400 µM coumarin, respectively. Our results suggest that biochemical and cytological responses, along with root morphological characteristics jointly affect rice resistance to coumarin stress.