| With the aim to elucidate the underlying physiological basis of flue-cured tobacco response to drought stress,comparative analysis was conducted among different drought-resistance tobacco cultivars at the seedling stage in this paper.The results showed that:1.The effect of drought stress on seedling biomass,root morphology,from different flue-cured tobacco cultivars including Y6,Y10,Y12 and ZY100 were investigated by hydroponic experiment using polyethylene glycol(PEG-6000)in this study.The relationship between root growth and water supply conditions was close in this study.Drought stimulated the flue-cured tobacco seedling roots growth,while the growth of shoots was inhibited.Four flue-cured tobacco cultivars root shoot ratio were significantly higher,compared with that in the control.Y6 and Y12 root biomass,total root length,root surface area and root volume were significantly increased,but root average diameter was decreased,while the root tolerance of Y10 and ZY100 were poor in the performance of the moderate drought stress,root morphology index increased very little,or even decline.2.Drought stress have an important influence on leaf stomata characteristics of Y6,Y12,Y10,which has decreased stomatal density and increased the stomatal length and width,but the total pore area of unit area was almost unchanged,while ZY100 seedling was greatly affected by drought stress,its total pore area of leaf area per significantly increased.The chloroplast ultrastructure of Y6 and Y12 changed little under drought stress,while Y10 and ZY100 changed more obviously.The shape of chloroplast in mesophyll cell changed and separated from cell wall,chloroplast envelope broke down,which resulted in the destruction of chloroplast integrity.3.In condition of drought stress,photosynthetic rate(Pn),the transpiration rate(Tr)and stomatal conductance(Gs)of four kinds of tobacco seedlings showed a downward trend decline,and intercellular CO2 concentration(Ci)was increased,indicating that the photosynthetic rate of the four flue-cured tobacco cultivars was inhibited under drought stress and the decline of photosynthesis was considered as a result of no-stomatal restriction under moderate stress.In conditions of 20%concentration PEG,the changes of chlorophyll content to drought stress were differed significantly among four flue-cured tobacco cultivars.The chlorophyll contents of Y6 and Y12 were significantly increased,while Y10 and Z100 seedlings increased little or even decreased.The comprehensive analysis showed that Y6 is drought-resistant cultivar,ZY100 is drought sensitive cultivar,Y12 and Y10 are somewhere in between,drought resistance of the four flue-cured tobacco cultivars was in the order of Y6>Y12>Y10>ZY100 at seedling stage.4.The physiological and biochemical indexes change of two different flue-cured tobacco cultivars were investigated under conditions of light drought(LD),intermediate drought(MD)and severe drought(SD).The results showed that malondialdehyde(MDA)and hydrogen peroxide(H2O2)contents were significantly increased than that of the control,while activities of protective enzymes and chlorophyll contents were obviously increased and then significantly decreased under the intermediate or severe drought treatments.The increase of enzyme activities in drought tolerance Y10 was greater than that in drought sensitive Y12.the increase of MDA contents in Y10 was greater than Y12,which contributing to regulate activity of the protection system during the initial phase of drought stress,and the negative effects of drought during the stress period were observed.Subordinate function of drought-resistance and its relationship with drought-resistance indexes of flue-cured tobacco species were used for a quantitative evaluation of comprehensive drought resistance.The drought resistance capability of two different flue-cured tobacco species was in the order Y12>Y10.The grey correlative degree of drought-resistance with other physiological indexes was in the rank of MDA content,SOD activity,H2O2 content,Chl(a/b),POD activity,CAT activity and Chl(a+b)content.Therefore,the activity of SOD,MDA content and Chl(a/b)can be used as effective indicators for identification of drought resistance,while H2O2,CAT activity,POD activity and Chl(a+b)content can be used for reference indicators at seedling stage in flue-cured tobacco species.5.In the study,the drought-resistance difference of nine flue-cured tobacco seedlings were compared under drought stress that was hydroponic cultured by the mass fraction of 20%PEG-6000.By the methods of principal component analysis,subordinate function,and cluster analysis,a comprehensive evaluation was performed on the drought-resistance of 16 physiologic indices of nine flue-cured tobacco cultivars.16 physiologic indices had different responses under drought stress.Among which,free proline(Pro),H2O2,and ascorbic peroxidase(APX)showed the greatest sensitivity.There existed significant correlations in the drought-resistance coefficients of parts of the physiological indices.Four principal factors presented 88.6%of the information of the 16 indices,and the cultivars ’Y6’,’Y12’,’Yuyan87’,and ’Y8’ had the strongest drought-resistance for the 4 principal factors,respectively.The comprehensive evaluation value of the drought-resistance of the 9 cultivars was in the order of ’Y6’>’Y12’>’Y87’>’Y8’>’QY96’>’Y11’>ZY100>’K326’>’Y10’.All flue-cured tobacco cultivars could be clustered into 3 groups,and ’Y6’,’Y12’,’Y87’ and ’Y8’ belonged to the drought-resistance group. |
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