The Study On Cold Resistance In Different Phalaenopsis Cultivars

Phalaenopsis is one kind of tropical flower and its suitable growth temperature is above 18℃. The low temperature of northern area of China in winter and spring, the Phalaenopsis must be cultivated in greenhouse with heaters, so that the expenditure is very high. Now the studies about Cineraria, White michelia and chrysanthemum on cold resistant to stress have been done, and that the changes of MDA content, SOD activity and fluorescence parameter (Fv/Fm) can be as indicators for cold resistance of flowers. Now the researches on Phalaenopsis focus on factory yield, tissue culture and gene engineering etc, but the study on cold resistance of Phalaenopsis hasn't been found.There were ten varieties of Phalaenopsis in this study. The SOD activity, CAT activity, soluble sugar concentration, proline concentration, MDA content and electrolytic leakage under low temperature stresses and recovery(day/night 27℃/22℃) including A treatment (day/night temperatures were respectively (day/night11℃/6℃), B treatment (day/night 14℃/9℃), C treatment(day/night 17℃/12℃), D treatment (day/night 20℃/15℃) , E treatment (day/night 23℃/18℃) were studied. According to the results of the study, JT944, GL14 and Wedding Promenade were low, middle and strong resistance to cold stress respectively. In the further study, the three varieties were used as materials to make clear the Phalaenopsis cold resistance mechanism by investigating chlorophyll content, fluorescence parameters and hormone. The results as below:1 The effects of low temperature stress on osmoregulation substance and MDA content in Phalaenopsis.(1)The change of soluble sugar contents in ten varieties of Phalaenopsis all were sensitive to low temperature. When the temperature declined, most of varieties could produce much soluble sugar to alleviate the cold harm. With the temperature lowering, more contents of soluble sugar were accumulated in stronger cold tolerance varieties. The contents of soluble sugar in all varieties decreased under much more low temperature. The contents of soluble sugar in stronger cold resistance varieties(Wedding Promenade and Red Sky) could be equal and even higher than before treatment but the cold sensitvie varieries(GL11 and JT944) was the contrary in the recovery period.(2)The differences of proline contents in ten varieties of Phalaenopsis were significant. The contnets of proline increased with the temperature decling. This indicated that there were some relationships between the proline and low temperature stress. But it was not clear in this study.(3)The MDA contents in ten varieties of Phalaenopsis increased with the treatment time, but the change trends were not related with varieties resistance to cold stress, therefore, its content couldn't be as an indicator of Phalaenopsis resistance to cold stress.(4)The electrolytic leakages in all varieties of Phalaenopsis increased during A treatment, and the increased extents were lower in the cold resistance varieties, the differences between varieties were significant. The electrolytic leakages under B treatment showed the similar change trend with A treatment, but the differences between ten varieties became small. The electrolytic leakages of all Phalaenopsis slightly increased except JT944, so it showed that most Phalaenopsis couldn't be harmed in 9℃. Because the electrolytic leakages became lower and lower with the temperature increasing and they all could recover under recovery treatments, this indicated that the harm on Phalaenopsis leaves was reversible.2 Effects of low temperatures on SOD and CAT activities of Phalaenopsis.The SOD activities showed different change. With the temperature declining its activities increased , especially in Wedding Promenade. This showed the SOD activity was sensitive to temperature changes. The change of CAT activity was the same as SOD activity. They together alleviate the harm of active oxygen species.The difference of SOD and CAT activities between varieties were larger and larger with the temperature decreasing. It could be concluded that the effects of temperature changes in normal range on Phalaenopsis were little, but they were large in low temperature stress. It implies that it is important to increase the temperature when the outer temperature was low, even the increased extend was small.3 Effects of low temperature stress on chlorophyll content and fluorescence parameters of Phalaenopsis. (1)The chlorophyll content of all Phalaenopsis decreased under low temperature stress. After A treatment, the chlorophyll content of Wedding Promenade could resume to half of the normal situation under recovery treatment, but the cold-sensitive JT944 couldn't resume. This showed that the chlorophyll was very sensitive to low temperature. After B treatment, all varieties could resume to above 80% of normal situation except JT944, so it indicated the photosynthesis organization couldn't been hurt heavily and the threshold low temperature at night endurable by most of Phalaenopsis cultivars was about 9℃.(2)The fluorescence parameters Fv/Fm andΦPSII of JT944 decreased during A treatment and couldn't recover under recovery treatment; F0 firstly increased then decreased and decreased to 0 under recovery treatment; qP showed the same change with Fv/Fm during A treatment but could recover partly under recovery treatment. The fluorescence parameters Fv/Fm andΦPSII of Wedding Promenade also decreased during A treatment but could recover mostly. F0 slightly increased and qP didn't change under B treatment as well as recovery treatment. Fv/Fm andΦPSII of GL14 and wedding promenade decreased lightly, F0 increased and qP didn't change under B treatment. They all could resume fully under recovery treatment. Fv/Fm andΦPSII of JT944 decreased remarkably, but could recover. The F0 increased notably in the fifth day of treatment, but could resume. This showed that the inactivation ofΦPSII was reversible under this temperature.The change of qP was the same asΦPSII and Fv/Fm. F0 of three varieties all decreased during recovery treatment. The change trends of fluorescence parameters under C, D and E treatments were the same as B treatment.4 The changes of hormone in Phalaenopsis under low temperature stressThe ABA content of Wedding Promenade increased rapidly under low temperature stress and kept continuous increasing with the temperature stress time, while JT944 showed contrary trend. The GA content in Wedding Promenade leaves was higher but it didn't change in other varieties. The change of IAA content was not significant in the early treatment. With the treatment going, it rapidly accumulated in Wedding Promenade and was contrary in the JT944.From the above, osmoregulation substance, the antioxidant enzymes and ABA content were sensitive to low temperature and they could enhance the Phalaenopsis resistance to cold stress. However, there were differences between varieties. So the chlorophyll content, Fv/Fm and SOD activity could be as indicators of Phalaenopsis resistance to cold stress.