| Drought stress is an important abiotic stress that seriously inhibits plant growth and consequently decreases productivity.Drought stress can affect the normal physiological metabolism of plants.Drought stress will lead to stomatal closure and inhibit the absorption of water,which will result in osmotic stress.Drought stress also can damage the chloroplast structure and reduce the photosynthetic rate.Moreover,reactive oxygen species(ROS)accumulation are induced by drought stress,which could destroy the structure of biomacromolecule and cytomembrane.Lutein participates in the assembly of antenna pigment protein complexes and stabilizes the structure of light-harvesting pigment protein complexes.Lutein is a supplementary pigment that absorbs light energy.Lutein can also dissipate excess excitation energy and protect plant against photodamage.Lutein has some functions in plants such as clearing free radical and antioxidant.However,its biological function under abiotic stress is not yet clear.Tomato carotenoid ?-hydroxylase is one of the important enzymes that catalyze the synthesis of lutein,which is encoded by the SlLUT1 gene.In this study,we used transgenic tobacco overexpressing SlLUT1 to investigate the effects of SlLUT1 on drought stress in tobacco.The main results of this study are listed as follows:(1)The promoter of the SlLUT1 gene was found on the Sol Genomics Network website and analyzed using the PlantCARE website.It includes some stress response motifs that contain drought stresss response element.We detected the expression of the SlLUT1 gene which was induced by drought stress using Luciferase in Arabidopsis thaliana transformed with the SlLUT1 gene promoter.Real-time fluorescence quantitative PCR(qRT-PCR)also confirmed this result.(2)The expression level of SlLUT1 in transgenic tobacco was determined by qRT-PCR.The results showed that the expression of OE-19 was the highest.The expression of SlLUT1 gene in transgenic plants was increased under drought treatment.At the same time,we also measured the contents of lutein in all line before and after the treatment with drought stress.And the results were consistent with the qRT-PCR results.(3)The growth status of transgenic tobacco was same to WT tobacco under normal condition.However,the transgenic tobacco showed higher seed germination rate,lower leaf wilting,and higher relative water content compared to WT under drought stress.(4)Compared with WT,transgenic plants have more complete chloroplast structure and photosystem II protein complexes under drought stress.And the transgenic lines had higher chlorophyll content and photosynthetic performance than WT under drought stress.The photosynthetic performance was examined in all lines treated with dithiothreitol(DTT)which was used to inhibit the xanthophyll cycle in plants.It was found that the photoinhibition was light and electron transfer was smooth in the transgenic lines.(5)It was found that the ROS content of the transgenic lines was lower than that of WT tobacco.However,activities of the anti-oxidative enzyme are not the reason for this result.In addition,malondialdehyde(MDA)content and relative electrical conductivity(REC)increased with drought condition.Compared with WT,the MDA content and REC levels of the transgenic lines were lower,indicating that the cell membranes suffered less photodamage in the transgenic lines.(6)The contents of proline and soluble sugar increased under drought stress,but,there was no significant difference between WT and transgenic lines.In addition,we detected the transcript levels of stress-related genes such as P5 CS and ERD10 S in tobacco.The results showed that these genes were up-regulated in different degrees under drought stress,and there was no difference between WT and transgenic lines. |
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