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ABSTRACT
The present study evaluated the variation in growth and genetic responses of maize seedling (Zea mays L.) to cold shock. Seeds were originally exposed to distilled water at room temperature for 48 h before they were completely submerged in buckets of ice for more 0.5, 1.5, 3, 6 and 12h respectively, before removal and immediate transfer to Petri dishes. The control was never exposed to cold water. The set up was left on the laboratory bench for additional 5 days. Results showed significant growth impairment upon exposure to cold shock. The level of growth impairment by ice correlated with length of time of exposure. Length of prominent root significantly reduced upon exposure to cold shock from 141.8mm to as low as 91.4mm in those plants exposed at 1.5h. Length of prominent leaf also significantly reduced from 100.6mm in the control to between 62.6 to 85.5mm in low temperature-exposed plants, notwithstanding the time of exposure. However, exposure of plants to cold shock did not significantly change the number of roots per plants in the germinant (6 – 9roots per plant, p>0.05).There were significant reductions in final germination percent in the low temperature-exposed germinant (35.8 - 60.5%) when compared to the control (88.5%). Results from RAPD marker (OPA04) revealed variations in germinated maize seeds after treatment with different duration of low temperature. The test plantlets treated for 0mins, 30mins and 1.5 h did not have a recognizable complementary sequence to the primer OPA04. Whereas, the primer amplified regions of the genome of test plantlets treated for 3hrs, 6 h and 12 hrs. On RAPD Primer OPA05 also presented diversity among maize seedlings stressed for various durations of cold shock; a fragment of 1200bp was the only band common to all treatments. Whereas maize seedlings exposed at 1.5h had only the 1200bp band, the others had polymorphic bands. Test plants stressed for 30mins had a unique fragment of 200bp. Those stressed for the longest duration of 12hrs had a band of about 350bp, which was absent in the other treatments. Further studies are therefore suggested into aspects of specific genetic characteristics modified by exposure to cold shock as well as a possible physiological basis for interpreting the results of the present study.
