Shoot Culture And Somatic Embryogenesis In Aspen Clones

Isoprene is emitted from many terrestrial plants at high rates,accounting for an estimated 1/3of annual global volatile organic compound emissions from all anthropogenic and biogenic sources combined.Due to its high abundance and atmospheric reactivity,isoprene plays important roles in the oxidative status of atmosphere at regional and global levels,as well as in plant resistance to stress,especially in the protection mechanism of the photosynthetic system.Isoprene is synthesized in chloroplasts by either methyl erythritol-4-phosphate（MEP）pathways,with glyceraldehyde-3-phosphate（GAP）and pyruvate as the main substrates,consuming ATP and NADPH.In order to study the effects of photosynthetic carbon fixation on isoprene emission and its regulatory mechanism,the leaves of hybrid poplar were treated with photorespiration inhibitor（Na HSO₃）,carbon assimilation inhibitor（DL-glyceraldehyde）and their combined treatment.The results show as:（1）Effects of Na HSO₃ treatment on physiological characteristics of hybrid poplar 895（Populus deltoides×Populus nigra）Compared with the water control for 0min,there were no significant effects on the photosynthetic parameters,isoprene emission rate and pigment content at 5,50 and 110min,the Glycolate oxidase（GO）activity decreased significantly.Under Na HSO₃ treatment,compared with the 0min,the net assimilation rate（Pn）,transpiration rate（Tr）and stomatal conductance（Gs）of the leaves were significantly decreased at 50,110 min（P<0.01）;There was no significant difference in pigment content among different treatments（P<0.01）;The photorespiration rate decreased significantly at 110min（P<0.01）;The isoprene emission rate decreased significantly at 110min（P<0.01）,the carbon lost isoprene was significantly increased at 50,110 min（P<0.01）;NPQ was significantly decreased（P<0.01）.（2）Effects of DL-glyceraldehyde treatment on physiological characteristics of hybrid poplar895（Populus deltoides×Populus nigra）Compared with the water control for 0min,the photosynthetic parameters,isoprene emission rate,pigment content,chlorophyll fluorescence parameters of leaves at 5,50 and 110min were not significantly differences.When treated with DL-glyceraldehyde,compared with the 0min,the net assimilation rate（Pn）decreased significantly at 50,110min（P<0.01）,transpiration rate（Tr）,stomatal conductance（Gs）and intercellular CO₂ concentration（Ci）had no significant differences（P>0.05）;the photorespiration rate decreased significantly at 110min（P<0.01）;carotenoid content was significantly increased at5min（P<0.01）;the isoprene emission rate decreased significantly at 110min（P<0.01）,and the DMADP pool decreased significantly at 50,110 min（P<0.01）,and there was no significant difference in carbon lost isoprene at different time（P>0.05）;Y（I）,Y（II）,NPQ,q L had no significant difference（P>0.05）;the H₂O₂ content was significantly increased at 5,50 and 110min,and the O₂^-content was significantly increased at 110min（P<0.01）.（3）Effects of both treatment with Na HSO₃ and DL-glyceraldehyde on physiological characteristics of hybrid poplar 895（Populus deltoides×Populus nigra）Compared with the water control for 0min,there were no significant effects on the photosynthetic parameters,photorespiration rate,isoprene emission rate and pigment content at 5,50 and 110min,and Glycolate oxidase（GO）activity decreased significantly.When Na HSO₃ and DL-glyceraldehyde were combined,the net assimilation rate（Pn）decreased significantly at 50,110min（P<0.01）;Intercellular CO₂ concentration（Ci）was significantly increased at 50min,110min（P<0.01）;the photorespiration rate increased significantly at 110min（P<0.01）;Isoprene emission rate and DMADP pool size were significantly decreased at50,110 min（P<0.01）;Y（I）,Y（II）,q L and NPQ were significantly decreased at each treatment time（P<0.01）;Glycolate oxidase（GO）activity was significantly decreased at 5,110 min（P<0.01）;The H₂O₂ content decreased significantly under the treatment time（P<0.01）;The O₂^-content increased significantly at 50,110min（P<0.01）.In conclusion,the photorespiration inhibitors significantly inhibited the photosynthetic capacity and photorespiration rate of plants,reduced the DMADP pool size,and inhibited the isoprene emission.Isoprene protected the photosynthetic mechanism by consuming the excess power in plants.Carbon assimilation inhibitor treatment also significantly inhibited net assimilation rate,decreased the DMADP pool size,and inhibited the isoprene emission.Combined treatment had a great effect on the plant,the net assimilation rate,PSI,PSII activity and photorespiration rate were significantly inhibited,the DMADP pool was significantly reduced,and the isoprene emission was significantly inhibited.The correlation between the isoprene emission rate and the net assimilation rate and chlorophyll fluorescence parameters under all treatments also indicated that the photosynthetic carbon fixation capacity of plants was closely related to isoprene emission,and significantly affected the DMADP pool size.