Effects Of Low Temperature On Physiological Characterristics Of Different Genotypes Seedling Of Dendrobium Candidum

The aim of this study was to understand the physiological responses of chilling stress and re-growth treatment on three Dendrobium candidum new varieties (ZD-1, ZD-2and ZD-3). In order to obtain the indices of chilling resistance of three new varieties,the malondialdehyde (MDA),chlorophyll(Chl),Soluble sugar(ss) and proline (Pro)content, superoxide dismutase (SOD),catalase (CAT),peroxide enzyme (POD),ascorbate peroxidase (APX) and glutathione reductase(GR) activity in leaves were determined at a range of different temperatures5,0and-2℃for6,12and18h and in recovery growth for5and10d, respectively. The main results were as follows.1.In the leaves of Dendrobium candidum,the content of MDA increased as the Chl content decreased along with the low temperature increase.The activity of SOD, CAT, APX and GR increased in the cell which could effectively clean the active oxygen produced by the low temperature.And the increase of Pro and ss content was to improve the osmotic regulation ability of the plant, while the abilities of chilling resistance enhanced.2.Along with the increase of low temperature stress,the measured physiological indices of three Dendrobium candidum varieties increased at first and then slowly declined, as all the biggest value turn up at0℃treatment. The response degree varied with different varieties.There was the smallest content of MDA accumulation in ZD-3, and the highest SOD,POD,APX activity and Pro,ss content. After excessive stress, it was observed that the decrease of CAT and GR activity in ZD-3was smaller than the other varieties.There was a converse trend when it came to ZD-1. The response of ZD-2was the medium.3. During the recovery treatment, the SOD.POD,APX, GR activity and MDA, Chl,ss,Pro content significantly decreased with the increase of recovery days.After ten-day recoveries,ZD-3quickly recovered from0℃treatment while the measured indices had no significant differences.But ZD-1could hardly recover from chilling stress after short recovery treatment meanwhile from the values of measured indices it could not recover during10days.ZD-2had a recovery state between the ZD-1and ZD-3.4.The variation of the activity of SOD, CAT, APX, GR and the content of MDA, ss, and Pro in Dendrobium candidum leaves was coincident with low temperature stress. It suggested that those physiological indices could be used as efficient and robust indices of chilling resistance for Dendrobium candidum plant. MDA content may be the easiest index.5. It was obtained that chilling resistance of3new varieties was decreased in the order of ZD-3, ZD-2and ZD-1.In conclusion, the Dendrobium candidum plant has a strong response to low temperature stress which would damage the plant growth and physiological activities. On the study, it was showed that Dendrobium candidum seedling could suffer irreversible physiological damage when exposure to0℃more than2or3days. In practice, it’s essential to establish technique scheme for Dendrobium candidum cultivation based on selecting chilling resistance cultivar and improving temperature environment to avoid chilling damage which can keep high quality production of Dendrobium candidum.