Drought Resistance Evaluation Of Transgenic Populus.alba × P. Berolinensis With JEFR36 Gene And Its Physiological Mechanism

Populus is one of the widest distribution and largest culivation fast-growing timber species.It is also the most important afforestation tree specises in northern China.Populus genetic improvement has been put on fast growth,but ignored the stress tolerance improvement for a long time.So,it causes that populus improvement is difficult to play its role in arid and semi-arid lands.Breeding and improvement of drought-resistant poplar varieties are undertaken by genetic engineering,and it plays an positive role on the use of arid,semi-arid wasteland.In our study,transgenic P.alba × P.berolinensis?ABJ01?and non-transgenic P.alba × P.berolinensis?9#?were used as test materials.The drought resistance of ABJ01 was studied by measurement the poplar growth,leaf anatomical structure,photosynthetic parameter,physiological and biochemical properties under soil drought stress,and root tip ion flow under hydroponic PEG simulated drought stress conditions.This study will to conduct the evaluation of drought resistance of transgenic P.alba × P.berolinensis and illustrate the drought tolerance mechanism of drought resistance of transgenic poplar ABJ01 from physiological sides initially.In addition,our study will provide a certain research foundation for further study of transgenic poplar drought tolerance mechanism,and provide scientific proofs for the promotion and application of transgenic poplar.The main results were as follows:1.Transgenic P.alba × P.berolinensis had stronger growth advantage and more developed leaf palisade tissue under drought stress,which implying the drought tolerance of transgenic poplar was enhanced.It showed that seedling height and ground diameter of ABJ01 were higher than 9# at 3 different treatment time points?10 d,20 d,30 d?under drought stress.ABJ01 had more ground diameter increment than control under moderate drought stress treatment after 20 d,and the seedling height of transgenic poplar was significantly greater than control when exposure to severe drought stress after 20 d and 30 d.While the specific leaf area and gross dry weight of ABJ01 were higher than that of control at 30 d under moderate and severe drought stress.Meanwhile,compared with control,the leaves of ABJ01 were notably thicker at 20 d under moderate stress,and leaf upper epidermis and lower epidermis of ABJ01 were remarkably thicker at 3 different treatment time points.But the palisade tissues of ABJ01 were significantly thicker than 9# under moderate drought stress when exposure to moderate drought stress for 10 d and 30 d and exposure to severe drought stress for 20 d.And the thickness of spongy parenchyma in ABJ01 was lower than that of 9# at 30 d under both moderate drought and severe drought stress.2.Compared with non-transgenic P.alba × P.berolinensis,transgenic P.alba × P.berolinensis had stronger photosynthetic capacity,gas exchange ability and water retaining capacity when exposure to drought stress,and the differences was more obvious with the increase of drought stress.Both net photosynthetic rate?Pn?and stomatal conductance?Gs?of ABJ01 were remarkable higher than 9# under moderate drought stress condition after 20 d and severe drought stress at three time points under.And the transpiration rate?Tr?of ABJ01 was lower than 9# at 20 d and 30 d after drought treatment.Whilethe chlorophyll a,chlorophyll b and total chlorophyll contents of ABJ01 were more than those in 9# at the same time,but significant level was reached under severe drought stress Fv/Fm value of ABJ01 was higher than 9# at 30 d after drought stress,but the value reached significant level only under moderate drought stress;so that it showed the damage of PSII in ABJ01 was smaller than 9#.3.Compared with non-transgenic P.alba × P.berolinensis,transgenic P.alba × P.berolinensis had stronger osmotic adjustment ability and active-oxygen scavenging ability under drought stress.The proline contents?Pro?of ABJ01 was higher than that of 9# under moderate drought stress and severe drought stress after 20 d and 30 d treatment,and the difference reached significant level in moderate drought stress condition.The SOD activity,POD activity and CAT activity were stronger than 9# at 20 d and 30 d treatment after exposure to moderate drought stress and severe drought stress,and the difference reached significant level.4.The root of transgenic poplar had stronger K⁺ and Ca²⁺ ion absorption capacity under PEG stress treatment.The K⁺ efflux speed of ABJ01 was slower than 9#,the difference reached significant level under 10% PEG treatment.And the influx capacity of Ca²⁺ was notably higher than 9# under 20% PEG stress condition.Potassium content were remarkable higher than 9# in ABJ01 root tips under 20% PEG treatment.While ABJ01 accumulated more elemental calcium under PEG treatment condition under 10% and 20% PEG treatment.In conclusion,the growth advantage of transgenic poplar is notable.Physiological mechanism of drought resistance is mainly reflected in increasing the palisade tissue,reducing the thickness of spongy tissue,improving the osmotic regulation and active oxygen removal capacity,and reducing transpiration response to improve its drought resilience.While the Pn and gas exchange capacity of transgenic poplar was improved effectivly under drought stress.All of that help to maintain its rapid growth.In addition,exogenous gene JERF36 could increase the Ca²⁺ influx and decrease the K⁺ efflux of root tip cytoplasm to maintain relatively higher Ca²⁺,K⁺ level of transgenic poplar,which could enhance abilities of osmotic adjustment and water absorbing of transgenic poplar to improve the drought resistance ability of transgenic poplar.