Research On Anatomic Structure Of Drought Resistance And Physiological Characteristic Of Upland Rice

In order to research the drought resistance of upland rice, upland rice varieties, rice varieties withstrong drought resistance and rice varieties with weak drought resistance were used as experimentalmaterials, carring out in experimental plot of Jilin Agricultural University between 2006 and 2007.Anatomic structure,photosynthesis physiological nature,antioxygen system and osmoregulation of rice andupland rice varieties were studied under dry cultivation conditions. The characteristics of drought resistanceof upland rice varieties were systematically studied, which offered theoretical bases to utilize furtheranti-drought resources and develop production of upland rice. The experimental results were as followed:1. Under dry cultivation condition, the average yield of upland rice varieties was the highest(5458kg·hm^-2); the rice varieties with strong drought resistance was the secondary (4400kg·hm^-2), and therice varieties with weak drought resistance was the lowest (3355kg·hm^-2).2. During the tilling-flowering stage, there were many vessels in deutoxylem of roots, the area ofvessels and stelae were large and aerenchyma was undeveloped in upland rice varieties, but aerenchyma ofrice varieties was developed; The amount of vessels in principal vein vascular of leaf in upland rice varietieswas decreasing, but that of small vessels was increasing and the amount of vascular and total median veindiameter of inner vessels in upland rice varieties were larger than in rice varieties. Upland rice varietiesdidn't have a big difference from rice varieties in the amount of gas cavity with small area and obviouslyaugmented cuticle thickness. Big length and width but small density of stomata in leaf in upland ricevarieties contribute to exchange gas and increase transportation of water and decrease transpiration andthus enhance the drought resistance.3. Net photosynthetic rate, stomatal conductance and content of chlorophyl of leaf in upland ricevarieties during different periods of duration were all higher than in rice varieties. Net Pn showedsignificantly positive correlation with Gs and significantly negative correlation with transpiration rate,intercellural CO₂ concentration and significantly positive correlation with water use efficiency. When netPn and Gs were high and Ci was lower, which indicate that it was stronger in assimilation CO₂ in uplandrice varieties and continually increasing Pn could also have limited factors from non-stomata in leaves. Theapparent mesophyll conductance showed significantly positive correlation with the yield and correlationcoefficient was the highest (r=0.8965^**, r=0.9962^**) during maturation period. Transpiration rate showedsignificantly negative correlation with the yield (r=0.-6637^**, r=0.-8284^**) during the flowering andmaturation stage. The water use efficiency at flowering stage and maturation stage also showed verysignificantly positive correlation with the yield(r=0.8904^**, r=0.8986^**) and this correlation illustrate that the flowering stage and maturation stage are important stages for yield formation of upland rice under drycultivation condition. Reduction transpiration of water, enhancement the water use efficiency andmaintenance of higher photosynthetic productivity of upland rice varieties under dry cultivation conditionadapte them to drought and became physiological basis of high yield.Daily variation of net Pn and Gs of upland rice varieties and rice varieties was consistent duringfilling-flowering stage, which all showed change of daily depression and photosynthesis midday depressionunder dry cultivation condition. The maximum value of net Pn were measured at 10 am and 12 am declinedand net Pn a little increased in the afternoon14, soon began to decline. Daily variation of Tr showedunimodal curve and peak value occurred at 12 am. Midday depression of photosynthesis had happened wascaused by the effect of water deficit on stomatal and other factors. Upland rice varieties had slight degree ofphotosynthesis midday depression and net Pn was maintained to be higher value.4. The content of malonaldehyde and membrane permeability of leaf in upland rice varieties was lowerthan rice varieties. The activities of superoxide enzyme,catalase and peroxidase were all higher than ricevarieties. The change trend of activity of SOD was firstly increasing and then decreasing and the trend ofCAT,POD were basically consistent with that of SOD. The band of POD isoenzymes with smallmolecular weight in upland rice varieties was presented in POD isoenzymes electrophoresis pattern at latestage. The leaves senescence of upland rice were slower than rice, because upland rice have highantioxidase activities and more POD isoenzymes of small molecular weight which make photosynthesissmoothly.5. The content of soluble proteins in upland rice varieties was higher than in rice varieties showed thatupland rice varieties maintained normal metabolism and adapted them to drought through synthesizingsoluble proteins under drought stress. The band of many soluble proteins with small molecular weight inupland rice varieties was presented in electrophoresis pattern and these proteins could adjust cell toosmotical absorption of water and make drought resistance increasing. The activity of nitrate reductase inupland rice varieties was higher than in rice varieties. At the seedling stage the activity of enzyme was thehighest but had a big decrease accompanying with the process of growth. The activity of nitrate reductaseshowed positive correlation with the content of soluble proteins at seedling stage and filling stage(r=0.6409^*, r=0.5817^*).6. The content of proline in upland rice varieties were higher than in rice varieties during the wholeperiod of duration, High content of proline contributed to increase drought resistance of varieties, whichthe content of proline reflected the differences in drought resistance among varieties. The solublesaccharides content of leaves was higher than rice varieties from seedling stage to filling stage, but it waslower at maturation stage. Soluble saccharides in leaf might participate in osmoregulation at early periodof duration. The synthesis of opportune abscisic acids adapted upland rice varieties to drought stress and increase drought resistance of plants by which regulated stomata on-off and induced a large amount ofsynthesis of regulatory substances under dry cultivation condition at early period of duration. However,the content of abscisic acid became decreased and slow down insenecence during maturation period. Therice varieties synthesized small amount of abscisic acid had weak drought resistance at early period ofduration, but high content of abscisic acid speeded up insencence at maturation stage.Through analysing anatomic structure,yield and physiological and biochemical indexes, the resultsshow that thick cuticle of upland rice and small stoma density can diminish transpiration, increase WUE,and maintenance higher photosynthesis productivity. Some rice varieties with strong drought resistancecould be suitable for dry cultivation and become germplasm resource for selection of upland rice varieties.In addition, net photosynthetic rate, the activity of nitrate reductase and antioxidase, POD isoenzymes,anti-drought proteins and the content of abscisic acid and proline could be used as physiological andbiochemical indexes for selecting upland rice varieties with high-yield and drought resistance.