Functional Study Of Tetraploid Malus Prunifolia In Salt And Drought Stresses

Apple(Malus domestica Borkh.)is one of the four major fruits in the world.The Loess Plateau in northwest China has a semi-arid continental monsoon climate and a large daily temperature differences,which is very suitable for the growth of apples and other crops.However,the annual rainfall in this region is low,and the problems of soil salinization and drought seriously restrict the sustainable development of apples in the northwest region.Malus prunifolia is widely used as a rootstock for apple grafting due to its excellent characteristics,including its high emergence rate,good grafting affinity and fast growth.However,Malus prunifolia is an arborized rootstock.In fact,the seedlings of raw and propagated seeds are not uniform,the fruit yield is very low,and the offspring are seriously separated.Moreover,the current research on dwarf apple rootstock varieties with strong stress resistance is still relatively scarce.At the same time,in recent years,the dwarfing attribute and high stress resistance of apple polyploid rootstocks have been paid attention to.Therefore,the improvement of Malus prunifolia is the main goal to improve its salt tolerance and drought resistance by inducing chromosome doubling of Malus prunifolia.Although many studies have demonstrated that the stress resistance of polyploid plants is generally enhanced,the underlying physiological and molecular mechanisms of stress resistance are complex and require further study.In this context,this study analyzed the salinity and drought resistance of tetraploid and diploid Malus prunifolia.The main findings are as follows:1.Using diploid and polyploid apple rootstock M.prunifolia as test materials,the effect of chromosome doubling on plant growth under salt stress was studied through hydroponic experiments.The results of the study showed that:compared with diploid,polyploid plants are more salt-tolerant,have higher photosynthetic efficiency,thicker leaf epidermis and palisade tissue,and shorter but denser root systems.Under salt stress,polyploid leaves and roots accumulate less Na+,the expression of the three SOS pathway genes is up-regulated,and less ROS is produced.Under salt stress,the ABA and JA levels of polyploid plants are also significantly higher than diploid plants.Under normal growth conditions,the levels of GAs in polyploid leaves were much lower than diploid leaves;however,after salt treatment,polyploid leaves showed up-regulation of essential GAs synthesis genes.These results indicated that the enhancement of salt tolerance of tetraploid M.prunifolia was mainly achieved by changing the morphology of leaves and roots,the accumulation of Na+,the improvement of antioxidant capacity and the change of plant hormone levels.2.Using diploid and tetraploid apple rootstock M.prunifolia as the test material,the drought resistance function of tetraploid M.prunifolia was studied by short-term drought test.The results showed that the effect of drought stress on the growth of tetraploid M.prunifolia was significantly lower than that of diploid M.prunifolia Using paraffin sections to observe under a microscope,it was found that the leaves of tetraploid plants became thicker and wider under drought stress,and the thickness of palisade tissue was also significantly higher than that of diploid plants.Moreover,the net photosynthetic rate of the tetraploid line was significantly higher than that of the diploid line under drought stress,and the tetraploid M.prunifolia leaves could maintain a higher Fv/Fm value under drought stress,which was beneficial to the normal photosynthesis of the plant.effect.In addition,the antioxidant capacity and related enzyme activities of the tetraploid lines were higher than those of the control.Under drought stress,the ABA and ZR levels of tetraploid plants were also significantly higher than those of diploid plants.These results indicated that the enhanced drought resistance of the tetraploid M.prunifolia was mainly achieved by changing plant leaf morphology,enhancing photosynthetic capacity,antioxidant capacity,and changing endogenous hormone content(ZR,ABA,and GAs).