Effects Of Boron And Auxin On Axillary Bud And Root Morphology Of Pea(Pisum Sativum)

Apical Dominance is widely used in production.Topping or controlling lateral branch growth are often used to regulate plant morphogenesis and construct ideal plant type to promote yield.Boron plays an indispensable role in the growth and development of crops.Boron deficiency affects the morphological formation of shoots and roots,leading to yield reduction.The maintenance of Apical Dominance is closely related to the concentration level and concentration gradient of auxin in the stem.We speculate that the effect of boron deficiency on Apical Dominance is related to the transport of auxin in the stem.On the other hand,most of the auxins in roots come from shoots,which means that the effect of boron deficiency on auxins in stems may affect the growth of roots.In this study,the effects of boron deficiency on shoot apical dominance and root growth of pea（Zhongwan No.5）were observed by setting different boron levels,top removal,adding exogenous auxin and auxin transport inhibitor treatments.The effects of boron deficiency on shoot transport of auxin were studied by directly observing plant morphology and axillary bud growth.The effects of aboveground auxin on root system at different boron levels were also studied.The aim of the experiment is to further verify the Auxin Polar Transport Flow Hypothesis of lateral bud growth and explore the relationship between boron deficiency symptoms and auxin level in root system,so as to provide theoretical basis for plant type regulation.The main contents and results are as follows:1)The results showed that pea（Zhongwan No.5）,which was cultivated for 30days under the condition of boron addition,could grow normally and enter reproductive growth at the 7th/8th node,and axillary buds at those node after 7th/8th developed into flower buds.The axillary buds of 1st-6th/7th nodes were dormant and undeveloped.Boron deficiency resulted in less nodes and shorter internodes,inhibited the shoot height and fresh weight significanl.The apical buds of boron deficient plants could not develop into flower bud and then died,this led to the development of lateral buds and the broken of plant Apical Dominance.Compared with roots with boron supply,boron deficient roots became thicker and yellow,and the root fresh weight,total length,total area and total volume of roots decreased significantly,while the average diameter of roots increased significantly.It indicates that boron plays an important role in plant morphogenesis and reproductive growth.2)After removing the apex,exogenous auxin(100mg.L^-1,1000mg.L^-1 and1500mg.L^-1)was supplemented at the top again.Lower part of stem treated with boron was inhibited With the increase of treatment time and concentration,the inhibition increased.But exogenous auxin had no significant effect on the growth of buds and leaves in lower part of stem treated with boron deficiency.The inhibition concentration of auxin on axillary buds of boron treatment was lower than that of boron deficiency(100mg.L^-1 and 100 mg.L^-1,respectively).100mg.L^-1 auxin inhibited 2nd axillary buds treated but promoted 3rd axillary buds in boron treatment.These phenomena indicated that boron deficiency was not conducive to auxin polar transport and auxin concentration gradient in the stem to regulate the growth of axillary buds,which also reflected boron deficiency may promote the growth of axillary buds by inhibiting the output of auxin of apical bud and its transport in stem.3)High concentration of exogenous auxin in shoot inhibited the total length and total surface area of root system with boron,but had no significant effect on root volume and root average diameter;The concentration of auxin in shoot had no significant effect on root system in boron deficiency.Combined with the study of adding auxin directly to root system grow in boron deficiency,which promoting root regrowth,it showed that the inhibition of boron deficiency on root system may be partly through inhibiting auxin transport to roots and reducing the concentration of root auxin.4)Under boron condition,topping and applying 5mmol.L^-1 auxin transport inhibitor（NPA）under apical bud could break the Apical Dominance of plants,indicating that the existence of apical bud auxin and the output of apical bud auxin could maintain the Apical Dominance and maintain the plant type of apical bud preferential growth.Under boron deficiency,auxin accumulated in the upper part of the stem after the third section of the plant was surrounded by the NPA treatment,which could restore the Apical Dominance of the plant.The phenomenon of promoting or inhibiting the growth of axillary bud with NPA treatment on different parts of the stem fits the Auxin Polar Transport Flow Hypothesis.5)When NPA was added to the shoot,the total length,total root area and total root volume of roots decreased under boron condition,which was significantly different from the control.Low level of auxin was not conducive to root growth.Compared with boron deficiency,the average diameter of root decreased significantly after the auxin levels transported to the roots have decreased,which weakened the effect of boron deficiency on root coarsening to a certain extent.It is suggested that the increase of root diameter caused by boron deficiency may be related to the increase and accumulation of auxin in the early stage of root system.The results showed that the changes of root index were related to the concentration of auxin in roots.The results could reflect the changes of auxin level promote the occurrence of boron deficiency symptoms to some extent,but could not explain the order of them.In conclusion,boron deficiency inhibits plant growth.Boron deficiency breaks the plant Apical Dominance probably by inhibiting the output of apical bud auxin and its main stem transportation.At the same time,There is a certain relationship between the level of auxin and the symptom of boron deficiency;Boron synergistic auxin regulates plant architecture.