| Lotus belongs to a perennial aquatic herb of Nelumbo in Nymphaeaceae,and it has been cultivated for more than 3,000 years in China.The enlarged rhizomes(commonly known as lotus root)is edible with rich nutrition,so it is deeply loved by people.In addition,the product organ is usually believed as one kind of off-season vegetable containing various ions and minerals.Therefore,lotus has become an important aquatic vegetable in China.The formation of adventitious roots directly affects the plant development due to its under-development of principle root.Light,as one of necessary environmental factors for plant growth is involved in formation of adventitious roots.In this study,the light including light intensity,photoperiod and light quality was applied to analyze the effect on the adventitious root development of lotus seedlings.Base on these data,primary mechanisim of adventitious root formation was summarized.We obtained the following results:1.The developmental processes of adventitious root were identified using paraffin section technique under dark,5 000 lx and 30 000 lx light intensity conditions.The results showed that primordia of adventitious root in darkness could not break hypocotyl epidermis within investigation days.The development of adventitious root primordia in 5 000 lx light intensity was slower than that of 30 000 lx light intensity,suggesting that the strong of the light intensity is helpful for the development of adventitious roots in lotus seedlings.2.The seedlings of lotus root were treated with various light intensities,photoperiods and light qualities with aim to identify their effect on the growth and development of adventitious roots.It was shown that no adventitious root was formed in lotus hypocotyl in darkness.For light intensity treatment,the developmental process of adventitious root treated with 20 000 lx and 30000 lx light intensity were significantly promoted,although no difference was found above two kinds of light intensity.For light photoperiod analysis,16 h/d and 24 h/d photoperiods dramatically accelerated adventitious roots formation in seedling hypocotyl.For light quality analysis,the red light showed the most negative effect on the development of adventitious root when compared with green light and blue light(no difference of effect between green light and blue light).3.The treatment with 10 ?mol/L IAA,based on application of various light intensities could significantly promoted formation of adventitious root in lotus seedlings,and while 10?mol/L IAA combined with darkness inhibited above process.The development of adventitious root was inhibited after the first leaf was shaded,and no difference was found between first leaf and second leaf after shaded treatment respectively.4.The seedlings were treated with different light intensities(dark,5 000 lx,15 000 lx and 30 000 lx)and photoperiods(0 h/d,4 h/d,8 h/d,12 h/d,16 h/d)to monitor the changes of POD activity.We found that POD and SOD activity was not changed under the darkness condition,and other light intensities(5 000 lx,15 000 lx and 30 000 lx)could enhance POD activity within 10 days.The SOD activity increased firstly and then decreased after 30 000 lx light intensity,8 h/d,12 h/d and 16 h/d photoperiod treatments,and the other treated plants showed an upward trend within 10 days.5.The treatments with darkness,5 000 lx,15 000 lx and 30 000 lx light intensity was carried out to identify the change of IAA content during adventitious root development in lotus.Aside from darkness treatment,the IAA content with others treatments was firstly increased,and then decreased.The number of adventitious root reach the maximum after 4 d treatment with 30000 lx,and while 6 d was needed for 5 000 lx or 15 000 lx treatment.The same phenomenon was found after treatment with 0 h/d,4 h/d,8 h/d,12 h/d and 16 h/d photoperiod.The IAA content was firstly increased,and reach maximum at 4 d,and then decreased under 12 h/d and 16 h/d conditions.However IAA contenet of other treatments(4 h/d and 8 h/d)reached the maximum at 6 d,suggesting that light intensity significantly affect endogenous IAA content during adventitious root formation.6.The lotus seedling hypocotyls treated with various light intensity,and three libraries were constructed and sequenced by RNA-seq technique to analyze metabolism change.We found that a total of 892 genes changed expression including 465 up-regulated genes and 427 down-regulated genes in 5 000 lx/dark libraries;In 30 000 lx/dark libraries,350 differentially expressed genes were found.Among which,192 genes were increased in expression,and 158 genes expression were decreased;In addition,we found that the expression of 867 genes was changed in 30 000 lx/5 000 lx libraries with 502 up-regulated genes and 365 down-regulated genes.The expression of 10 differential genes was analyzed by qRT-PCR method to identify the data accuracy derived from RNA-seq technique.The results showed that the the expression counted by qRT-PCR method was consistent with that of RNA-seq technique. |
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