Physiological Effects Of Salicylic Acid On Barley Photosystem Ⅱ Under Osmotic Stress Studies On Pollen Morphology And A New Species Of Roscoea (Zingiberaceae) In China

Chapter 1 Physiological Effects of Salicylic Acid on Barley Photosystem II Under Osmotic StressSalicylic acid (SA) is a simple hydroxybenzene in plant. As an endogenesis signal molecule, the effects of SA on many physiological progresses in plant have been paid more and more attentions. In recent years, the ability of SA to improve the endurance of plants in abiotic stress, such as salt, cold, hot and drought has been found. We tried to study the effects of exogenous SA pretreatment on the physiological functions and photosynthesis system II of barley seedlings under osmotic stress, and primarily evaluated the effects of exogenous SA to PSII major proteins D1, D2 and LHC II and the transcripts of corresponding genes psbA, psbD and cab and the interaction of PSII, ROS and SA under osmotic stress.The material for study is barley (Hordeum vulgare L.): the roots of control seedlings (CK) were submerged in half-strength Hoagland's nutrient solution; the roots of SA pretreated seedlings (SA) were submerged in 0.25mmol/L SA+half-strength Hoagland's nutrient solution; the roots of SA+D pretreated seedlings were submerged 0.25mmol/L SA+half-strength Hoagland's nutrient solution+0.5mmol/L DMTU(dimethylthioutea). Osmotic stress was initiated by submerging the roots of the seedlings into PEG solutions with an osmotic potential of - 0.6 MPa in beakers. All samples were treated for 0, 24, 48, and 72 h.Barley seedlings pretreated with different concentrations of SA pretreatment 24h were transferred into PEG solutions with an osmotic potential of - 0.6 MPa (16%) in beakers for 48 h. then the effects of different concentrations (0～1.5 mmol/L) of SA used in pretreatment were examined by the electrolyte leakage of membranes and Malonydialdehyde (MDA) Contents of leaves. It was shown that application of exogenous SA pretreatment at 0.25mmol/L most decreased the electrolyte leakage of membranes and MDA Contents of leaves, indicating that the effects of SA were related closely to concentration of SA used.The decrease in relative water content (RWC), and increase in electrolyte leakage of plasma membranes and MDA in water-stressed leaves were alleviated by SA pretreatment. The protective effects of SA in SA+D barley seedlings disappeared because SA-induced H₂O₂ was eliminated by DMTU, indicating that protective effects of SA was associated with ROS. In SA+D leaves, leaf total H₂O₂ changed differently from plastid H₂O₂, which almost did not increase.SDS-PAGE and Western blotting analysis showed that decrease in the PSII major protein D1, D2, and LHCII were alleviated by SA and SA+D pretreatment under osmotic stress because of lower levels of ROS in plastids of both pretreatments.Northern blotting analysis indicated that the transcripts of nuclear-coded cab and rbcS were different from those of plastid-coded psbA and psbD. The decrease in transcripts of cab and rbcS in SA+D barley seedings was more serious than that in SA and CK, which was in accord with the changes of ROS in cytosol. Compared with CK, the transcripts of psbA and psbD in SA and SA+D decreased slightly, which were in accord with the changes of ROS in plastid. the decrease in transcripts of cab did not lead to decrease of level of LHCII, because sustainability of LHCII content did not need corresponding mRNA and was associated with inner ROS in plastid.After 24h of SA pretreatments, stomatal conductance and CO₂ assimilation rate decreased, which can be regarded as a stress response. As the water stress developed, a less decrease of stomatal conductance and CO₂ assimilation rate was observed in SA plants, indicating that SA pretreatment improved water stress tolerance. and the effects of stomatal closure induced by SA pretreatment disappeared in SA+D pretreated plants because H₂O₂ was eliminated, showing that water stress tolerance promoted by SA pretreatment was relative to ROS. After 1 day pretreatment with SA or with SA+D, higher values of Fv/Fm, Fv'/Fm' andΦ_PSII were observed during subsequent osmotic stress, showing that SA had a protective role of the efficiency of Fv/Fm, Fv'/Fm' andΦ_PSII. These effects were associated with the low level of ROS in plastid.After 24h pretreatment with SA and before osmotic stress, a higher value of Fv'/Fm' revealed the efficiency of excitaion energy capture by open reaction centres (Fv'/Fm') increased in the case of heat dissipation, meanwhile, corresponding value of NPQ was remarkbly lower than that in CK. In other words, pretreatment with SA could reduce the heat dissipation of PS II. After 1 day pretreatment with SA+D and before osmatic stress, the values of Fv'/Fm' and NPQ distributed between that of SA and CK, indicating that the modulating effect of SA for heat dissipation of PSII partly depended on ROS.As a whole, SA pretreatment enhanced water stress tolerance of barley seedlings, and the effects of SA were related closely to concentration of SA pretreatment. Osmotic stress tolerance enhanced by SA pretreatment was associated with ROS. The decrease in PSII major proteins D1, D2 and LHC II and the transcripts of corresponding genes psbA, psbD and cab were alleviated by SA pretreatment under water stress. We found that enhanced osmotic stress tolerance in barley seedings by SA pretreatment was mainly mediated with ROS, rather than the SA itself.Chapter 2 Studies on Pollen Morphology and A New Species of Roscoea (Zingiberaceae) in ChinaPollen morphology of 11 species and 3 varieties of Roscoea (Zingiberaceae) in China was studied under both light microscope and scanning electron microscope, and a new species of Roscoea was also reported in this paper.Roscoea cangshanensis M. H. Luo, X. F. Gao & H. H. Lin, a new species of the Zingiberaceae from Yunnan, China, is described and illustrated. The new species is related to R. forrestii Cowley in habit, but differs in having 2-lobed labellum, each lobe 2-lobulate, base narrowed to a stalk with white lines, and narrower leaf blade, (2-)7-24×1.5-2.5 cm, with base narrowed to petiolelike. The new species is also similar to R. debilis Gagnep. in having leaf base narrowed to petiolike, labellum obovate-cuneate, 2.5-3.5×2.5-3.0 cm, with white lines at throat, but differs in having bracts non-tubular, shorter, 5-15 mm long, concealed in leaf sheaths, corolla tubes longer, 10-12.5 cm long, labellum 2-lobed with each lobe further 2-lobulate.Pollen grains of Roscoea are spherical, subspherical, 47.2—88.5μm in size, nonaperturate. The wall is composed of a very thin exine and a thick intine. The exine is spinate, crapy or smooth between spines, and spinas are about 1.8—3.4μm.According to pollen morphology, the pollen of Roscoea belonged to Group Long-spinate , Subtype Spinate, Type Nonaperturate, and could be considered as a natural group, and was divided into two subgroups: Subgroup crapy-surface and Subgroup smooth-surface. The taxonomic significance of the pollen types in Roscoea was also discussed.