Effect Of Zinc Deficiency On Root Growth And Cell Wall Components Of Malus Hupehensis Rehd.

Zinc is one of necessary trace metal elements for plant growth and development,its absorption,transport and distribution in plants have an important effect.Zinc is the composition of many enzymes and proteins in plants,and is involved in metabolism of plants.Zinc deficiency is a widespread phenomenon of plants,apple trees are zinc-sensitive species,studies have proved that zinc deficiency results in preventing the roots of zinc transport to the upper part become hard,easily accumulating in the roots with the time prolonged,and the abroveground parts give the emergence of zinc deficiency.The root cell wall is the first barrier that the plant absorb zinc ions,consists mainly of many polysaccharide macromolecules,and contains negatively charged functional groups which could combine with positively charged zinc ions.The apple rootstock‘Malus hupehensis Rehd.'was used as material.The effects of root cell wall on zinc adsorption and fixation and The physiological mechanism of zinc accumulation under zinc deficiency was studied.The main results are as following:(1)There were two different zinc levels,zinc-adequate(4?mol·L-1),zinc-free(0?mol·L-1)treatment on Malus hupehensis Rehd in this experiment.The results showed that the zinc-free hydroponic seedlings of Malus hupehensis Rehd.caused the maked zinc deficiency symptoms.The height of zinc deficiency plants was significantly lower than that of normal plants,and the number of leaves was less than that of normal treatment.The internode was shortened and the leaf area was reduced,while these symptoms were not obvious in zinc-adequate.The results of dynamic monitoring of root morphology and root activity were shown: at the intitial stage of zinc deficiency treatment,Root length,root tip number,root surface area and total root volume of the root system were higher under zinc deficiency stress than normal treatment,and the root activity was also improved compared with the normal treatment,which indicated that zinc deficiency was promoted the growth of roots at the early time.With the prolongation of zinc deficiency,the zinc-free treatment root was gradually inhibited,many root morphological indicators decline and root activity decreased,Which indicated a significant inhibition of root growth at this time.The growth of roots were inhibited under zinc deficiency appeared on the 7th day after treatment.In the initial stage the zinc-free treatment promoted root growth,and showed inhibition of growth at late stage,thereby affecting the zinc ion absorption.(2)Zinc deficiency stress affects the antioxidant enzyme activity and malondialdehyde content of plant roots to a certain extent.The results showed that SOD and POD activities were significantly lower than those of normal plants under zinc deficiency,CAT activity is the opposite.The results showed that the plant was mainly caused by increasing of CAT activity to reduce the harmful substances produced by the metabolism of plants and reduce the damage caused by zinc deficiency.MDA content showed that the zinc deficiency treatment was significantly higher than that of normal treatment,indicating that the degree of membrane lipid peroxidation was damaged to a certain extent.(3)Measure the zinc content in roots,stems and leaves,it showed the zinc content wes the highest in root,but the lowest in leaves.With zinc deficiency time prolonged,The zinc content in the initial stage of zinc deficiency decreased rapidly,later become smaller.The accumulation of zinc in the roots has the same trend.The zinc content in the cell wall is also reduced slower in the later stage of zinc deficiency.The content of zinc in the cell wall composition pectin and HC1 was consistent with the change of zinc content in the cell wall.The zinc content in HC2 is basically no change.In summary,the cell wall has a certain adsorption of zinc,hinder the transport of zinc to the ground,and gradually accumulated in the roots.(4)The content of each component in root cells was significantly changed under zinc deficiency,the pectin content under zinc deficiency was higher than that of the normal treated plants.With the prolongation of zinc deficiency time,the content gradually increased.HC1 content of normal plant was higher than zinc deficiency treatment at the initial stage.The changes of normal treatment in the late stage of zinc deficiency were not obvious,and the plant treated with zinc deficiency increased significantly.HC2 content of zinc deficiency was higher than normal treatment,pectin methylesterase(PME)activity in normal plants was higher than that in zinc deficiency stress plants at the initial stage,after this time both PME activity was increased,the PME activity of zinc deficiency treatment was significantly higher than that of normal plants.Therefore,the reason of cell wall involved in root adsorption and fixed zinc is mainly by increasing the pectin,hemicellulose content,and increasing PME activity,which ultimately increase the ability of cell walls to bind to immobilized zinc ions,and zinc accumulates in the roots.