Analysis Of Freezing Pattern And Mechanism Of Plant Leaves Under Low Temperature

The freezing mode is vital to plants under low temperatures,but direct evidence,especially evidences from thermodynamic experiments,of extracellular freezing is still rare.In this paper,exotherms from differential thermal analysis,as well as microscopic observations,of detached leaves in Ligustrum lucidum and Euonymus japonicus during cooling were presented.Results from the two different investigations showed new evidences of extracellular freezing during cooling.From the beginning to reach the peak peak exothermic freezing time required privet fresh isolated leaves for 186 seconds,only 11 seconds to kill the frozen leaves;for Euonymus japonicus,from the beginning to reach the peak peak exothermic freezing time required isolated fresh leaves for 141 seconds,kill the frozen leaves only 14 seconds.According to the freezing heat release of the integral of the total body water ice frozen half relaxation time,the fresh leaves of Ligustrum lucidum in vitro freezing relaxation time of 189 seconds,frozen ice leaf privet kill relaxation time was 73 seconds;Euonymus japonicus fresh isolated leaves of ice relaxation for the 17 time 9 seconds,frozen ice leaves kill the relaxation time is 87 seconds.Privet leaves fresh isolated undercooling of 5.11 degrees,the frozen leaves kill the undercooling of 5.72 degrees.Fresh leaves of Euonymus japonicus in vitro undercooling is 7.58 DEG C;frozen kill leaves undercooling of 7.36 degrees.These results showed that the leaves of two plants and leaves of frozen killed undercooling are not significantly different.The experiments showed evidence for the extracelluar freezing in the two higher plants under low temperature thermodynamically,as well as the differences in the mode of freezing in the living and freeze-killed leaves during cooling.Similar results on the thermodynamic evidence of extracellular freezing and the difference in the mode of freezing up to now.The experiments presented a new approach and deeper insight into the mechanisms of freezing stress and injury in higher plants.The microscopic observations with extensive colourless extracellular ice crystals verified the results of ectracellular freezing from the thermal analysis.Although differential thermal analysis has been widely used in the analysis of the membrane behaviour in plant frost hardiness,results on the thermodynamic evidence of extracellular freezing and the difference in the mode of freezing were not seen up tonow.The experiments presented a new approach and deeper insight into the mechanisms of freezing stress and injury in higher plants.The photosynthetic and respiratory rate were very different in different plants under varied temperatures.Very complicated freezing mode were observed in plant stems,the related mechanisms in association with freezing resistance are to be investigated.The electrolyte leakage from cells under low temperatures suggests that half lethal temperature in Euonymus was significantly lower than in Rosa,indicating that Euonymus was more hardy than Rosa to freezing stress.