Effects Of NAA On Physiological Characteristics Of Poinsettia Seedlings Under Water Stress

In order to provide scientific bases for comparing drought-resistance of each variety, choosing the excellent varieties, and improving water-saving cultivation techniques, the physiological characteristics of Poinsettia Seedlings at different NAA concentrations were studied with spectrophotometry and chlorophyⅡfluorescence technique, and the effect of NAA on drought resistance was discussed.Millenium, a poinsettia variety, was adopted to study the growth, the physiological indices and the chlorophyⅡfluorescence parameters of its seedlings leaves under water stress at different concentrations of naphthalene acetic aicd (NAA) applications. The effects of NAA on physiological characteristics of poinsettia were researched under water stress. The main results were as follows:(1)The drought resistance and adaptability of this poinsettia variety is weak, it is sensitive to water deficiency.(2)The concentrations of soluble sugar, proline and the activities of SOD, POD in the leaves of poinsettia showed the variation tendency of falling after rising. Chlorophyll content increased at the beginning of water stress, and then sharply decreased to a low level. MDA content increased along with the process of water stress. As the water stress prolonged, minimal fluorescence (Fo), non-photochemical quenching coefficient (qN) were rised obviously. at the same time, maximum fluorescence (Fm), photochemical maximum efficiency of PSⅡ(Fv/Fm), potential photochemical efficiency (Fv/Fo),actual photochemical efficiency of PSⅡ(Yield), photochemical quenching coefficient (qP) were declined significantly. These changes indicated that the plants have adaptability to maintain the metabolism balance by regulating both osmotic substances and protective enzyme short-term water stress. But serious stress break the balance of active oxygen, weakened osmotic adjust action, decreased membrane permeability, and damaged reaction center of PSⅡ, weakened photosynthesis, lead the plant to wilt and die.(3) The physiological characteristics changed obviously after sprayed NAA on the leaves under water stress. Spraying with 0.05～0.5 mg·L-1 NAA reduced the concentrations of soluble sugar and MDA in the leaf of poinsettia, remained the proline content and enzyme activities and decreased the decomposition of Chl. These treatments also decreased the rising amplitude of Fo and qN, retarded the descent range of chlorophyll fluorescence parameters which are Fm, Fv/Fm, Fv/Fo, yield, and qP. The treatment with 1.0 mg·L-1 NAA have inverse impact to poinsettia seedlings. It can be concluded that low concentration NAA treatments could improve the efficiency radical scavenging system, inhibit the accumulation of active oxygen and lessen membrane damage, alleviate photosynthetic system destruction and strengthen the drought resistance of poinsettia, promoted the growth. Conversely, the damage of water stress to poinsettia could be aggravated under higher NAA condition, higher concentration could weaken the drought resistance, accelerate the plant wilt and die.(4)According to the study results, effect of 0.5 mg·L-1 NAA was better than other disposals. So the optimal treatment concentration of NAA was 0.5 mg·L-1.