Effects Of Twigs' Carbohydrate And ?-KGDH's Inhibitor On Adventitious Root Growth

Asexual reproduction is an important way to preserve plant materials,and the occurrence of adventitious roots is the key,so it is one of the key research fields to explore the mechanism of regulation of adventitious root(AR)formation and growth.Cutting propagation is considered to be one of the effective means to protect the ancient tree resources,but it is difficult for the cuttings of some tree species,such as Ginkgo biloba,to form ARs.Moreover,the formation of ARs becomes more difficult with the increase of tree ages.Although there are some investigations about the relationship between twigs' ages and rooting of the cuttings,however,the influences of carbohydrates on AR formation in different-age twigs were rarely reported.In addition,?-ketoglutarate is an important metabolic intermediate in the tricarboxylic acid cycle(TCA),which is considered to be the cross-road of the carbon-nitrogen metabolism: to produce succinyl-Co A via ?-ketoglutarate dehydrogenase(?-KGDH)or to produce glutamate via glutamate synthase and then form ?-aminobutyric acid(GABA)-shunt.Inhibition of?-KGDH activity can enhance the carbon flux to GABA-shunt,but whether it is related to the AR formation has not yet been reported.Therefore,the relationship between the carbohydrate contents and the rooting of cuttings in the different-age twigs of G.biloba firstly studied,and then the model plant poplar was used to study the effect of inhibiting ?-KGDH on the AR growth by altering carbon metabolism in this study,which would be beneficial to understand the role of carbohydrate and its key metabolism in the AR formation process of trees.The main results were as follows:1.Aiming to understand the relationship of carbohydrates and the growth of ARs in the different-age twigs,the contents of non-structural carbohydrates(NSC)in the corresponding leaves and stems,and rooting rates of the cutting were analyzed in G.biloba.The results showed that: The process of the AR formation included four stages: callus formation(0-4weeks),callus expansion(4-6 weeks),AR initiation(6-8 weeks)and root elongation(after 8weeks).The contents of polysaccharide and total sugars in the leaves from the lower crownwere higher than the upper one,but all the NSC components were no significant differences between the twigs from these two parts.However,the NSC contents had no significant changes in the corresponding leaves,whereas they decreased significantly in the corresponding stem fragments with the increasing ages of twigs,including glucose,fructose,polysaccharide,total sugars and starch,which showed the similar trends with the rooting changes.This indicated that the contents of carbohydrates in the cuttings of different-age twigs were closely related to the AR formation.2.Aiming to understand the alternation of carbon metabolism on the AR formation,succinyl phosphate(SP),a specific inhibitor of ?-KGDH,was applied to the stem segments of the model plant poplar(84 K;Populus alba × P.glandulosa)for 12 d in the condition of tissue culture.The results showed that: Blocking the ?-KGDH activity significantly inhibited the AR growth,led to the significant changes of soluble sugars,organic acids and amino acids,and increased the activity of GABA-shunt;exogenous GABA could also increase the activity of GABA-shunt,and evidently inhibit the growth of ARs,confirming that GABA-shunt was closely related with the formation of ARs.The further transcriptomic analysis demonstrated that carbon metabolism and hormones(IAA,ABA and ethylene)were considerably influenced by the inhibition of ?-KGDH,which might result from the changes of GABA-shunt activity.In conclusion,the present results indicated that the NSC contents had a positive correlation with the formation of ARs(1 year > 2 years > 3 years)in G.biloba,and the enhancement of GABA-shunt activity induced by the blocking of ?-KGDH was closely associated with the growth of poplar ARs,which might be one of the key factors in regulating the formation of ARs,providing a better basis for the clonal propagation and improvement of resistance in trees.