Phloem loading and transport of sugar from leaves to sink tissues such as fruits are crucial for yield formation.Camellia oleifera is an evergreen horticultural crop with high value;however,its low production limits t...Phloem loading and transport of sugar from leaves to sink tissues such as fruits are crucial for yield formation.Camellia oleifera is an evergreen horticultural crop with high value;however,its low production limits the development of the C.oleifera industry.In this study,using a combination of ultrastructural observation,fluorescence loss in photobleaching(FLIP)and inhibitor treatment,we revealed that C.oleifera leaves mainly adopt a symplastic loading route from mesophyll cells to the surrounding vascular bundle cells in minor veins.HPLC assays showed that sucrose is the main sugar transported and only a small amount of raffinose or stachyose was detected in petioles,supporting a passive symplastic loading route in C.oleifera leaves.Compared to leaves grown this year(LT),the carbohydrate synthesis capacity in leaves grown last year(LL)was decreased while LL retained more soluble sugar,suggesting a decrease in transport capacity with leaf ageing.TEM and tissue staining showed that a reduction in plasmodesmata density leads to a decline in the degree of cellular coupling and is responsible for the weakening transport capacity in older leaves.RNA-seq revealed several differentially expressed genes(DEGs)including CoPDCB1-1,CoSUT1 and CoSWEET12,which are likely involved in the regulation of phloem loading and sugar transport.An expression correlation network is constructed between PD-callose binding protein genes,sugar transporter genes and senescence-associated genes.Collectively,this study provides the evidence of the passive symplastic phloem loading pathway in C.oleifera leaves and constructs the correlation between sugar transport and leaf ageing.展开更多
Leaves from three_year_old solar greenhouse nectarine trees ( Prunus persica L. var. nectarina Ait. “Zao Hong Yan”) were used as materials in this study. It was the first time that the ultrastructural charact...Leaves from three_year_old solar greenhouse nectarine trees ( Prunus persica L. var. nectarina Ait. “Zao Hong Yan”) were used as materials in this study. It was the first time that the ultrastructural characteristics of phloem tissues of source leaves were observed and compared in normal and weak light intensities using the transmission electron microscopy. Results showed that the average diameters of companion cells (CC) and sieve elements (SE) of all kinds of veins were bigger in normal than that in weak light intensity, indicating that light could influence the cell development and growth. Dense cytoplasm with abundant mitochondria, endoplasmic reticulums, multivesicular bodies, vesicles and plastids were observed in normal light intensity. On the contrary, CC with small vacuolar structures and few mitochondrias, endoplasmic reticulums were shown in weak light. Misalignment of grana thylakoid margins of nectarine leaves also was seen in weak light. The sieve pores of SEs were obstructed in weak light. Chloroplasts with numerous starch grains and few mitochondrias were noticed in the mesophyll cell (MES) surrounding the bundle sheath in weak light. The storage of starch grains appeared to result from an unbalance between photosynthate production and export of photosynthates. This observation provided a strong support to the point that most leaves export the most of assimilates in the light time. Plasmodesmal densities between SE/CC, CC/PP (phloem parenchyma cell), PP/PP and PP/BSC (bundle_sheath cell) decreased in weak light. Plasmodesmata were observed between CC/SE (NS) (nacreous_walled sieve element), PP/BSC in branch veins in normal light intensity, but not in weak light. Thus apoplasmic pathway may be the main mode of transport of assimilates in weak light, however symplasmic pathway may be the main mode of transport of assimilates in normal light intensity. These results demonstrated that the solar greenhouse nectarine trees could be adapted to the weak light via the ultrastructure variation of phloem tissues of the source leaves.展开更多
Sucrose is produced in mesophyll cells and transferred into phloem cells before it is delivered long- distance to sink tissues. However, little is known about how sucrose transport is regulated in plants. Here, we ide...Sucrose is produced in mesophyll cells and transferred into phloem cells before it is delivered long- distance to sink tissues. However, little is known about how sucrose transport is regulated in plants. Here, we identified a T-DNA insertional mutant of Oryza sativa DNA BINDING WITH ONE FINGER 11 （OsDOF11）, which is expressed in the vascular cells of photosynthetic organs and in various sink tissues. The osdofll mutant plants are semi-dwarf and have fewer tillers and smaller panicles as compared with wild-type （WT） plants. Although sucrose enhanced root elongation in young WT seedlings, this enhance- ment did not occur in osdof11 seedlings due to reduced sucrose uptake. Sugar transport rate analyses revealed that less sugar was transported in osdofll plants than in the WT. Expression of four Sucrose Transporter （SUT） genes-OsSUT1, OsSUT3, OsSUT4, and OsSUT5-as well as two Sugars Will Eventually be Exported Transporters （SWEET） genes, OsSWEETll and OsSWEET14, was altered in various organs of the mutant, including the leaves. Chromatin immunoprecipitation assays showed that OsDOFll directly binds the promoter regions of SUT1, OsSWEETll, and OsSWEET14, indicating that the expression of these transporters responsible for sucrose transport via apopiastic loading is coordinately controlled by OsDOFll. We also observed that osdofll mutant plants were less susceptible to infection byXanthomonas oryzae pathovar oryzae, suggesting that OsDOFll participates in sugar distribution during pathogenic in- vasion. Collectively, these results suggest that OsDOFll modulates sugar transport by regulating the expression of both SUT and SWEET genes in rice.展开更多
基金supported by grants from National Natural Science Foundation of China(grant number 32071798 to L.Y.Z)。
文摘Phloem loading and transport of sugar from leaves to sink tissues such as fruits are crucial for yield formation.Camellia oleifera is an evergreen horticultural crop with high value;however,its low production limits the development of the C.oleifera industry.In this study,using a combination of ultrastructural observation,fluorescence loss in photobleaching(FLIP)and inhibitor treatment,we revealed that C.oleifera leaves mainly adopt a symplastic loading route from mesophyll cells to the surrounding vascular bundle cells in minor veins.HPLC assays showed that sucrose is the main sugar transported and only a small amount of raffinose or stachyose was detected in petioles,supporting a passive symplastic loading route in C.oleifera leaves.Compared to leaves grown this year(LT),the carbohydrate synthesis capacity in leaves grown last year(LL)was decreased while LL retained more soluble sugar,suggesting a decrease in transport capacity with leaf ageing.TEM and tissue staining showed that a reduction in plasmodesmata density leads to a decline in the degree of cellular coupling and is responsible for the weakening transport capacity in older leaves.RNA-seq revealed several differentially expressed genes(DEGs)including CoPDCB1-1,CoSUT1 and CoSWEET12,which are likely involved in the regulation of phloem loading and sugar transport.An expression correlation network is constructed between PD-callose binding protein genes,sugar transporter genes and senescence-associated genes.Collectively,this study provides the evidence of the passive symplastic phloem loading pathway in C.oleifera leaves and constructs the correlation between sugar transport and leaf ageing.
文摘Leaves from three_year_old solar greenhouse nectarine trees ( Prunus persica L. var. nectarina Ait. “Zao Hong Yan”) were used as materials in this study. It was the first time that the ultrastructural characteristics of phloem tissues of source leaves were observed and compared in normal and weak light intensities using the transmission electron microscopy. Results showed that the average diameters of companion cells (CC) and sieve elements (SE) of all kinds of veins were bigger in normal than that in weak light intensity, indicating that light could influence the cell development and growth. Dense cytoplasm with abundant mitochondria, endoplasmic reticulums, multivesicular bodies, vesicles and plastids were observed in normal light intensity. On the contrary, CC with small vacuolar structures and few mitochondrias, endoplasmic reticulums were shown in weak light. Misalignment of grana thylakoid margins of nectarine leaves also was seen in weak light. The sieve pores of SEs were obstructed in weak light. Chloroplasts with numerous starch grains and few mitochondrias were noticed in the mesophyll cell (MES) surrounding the bundle sheath in weak light. The storage of starch grains appeared to result from an unbalance between photosynthate production and export of photosynthates. This observation provided a strong support to the point that most leaves export the most of assimilates in the light time. Plasmodesmal densities between SE/CC, CC/PP (phloem parenchyma cell), PP/PP and PP/BSC (bundle_sheath cell) decreased in weak light. Plasmodesmata were observed between CC/SE (NS) (nacreous_walled sieve element), PP/BSC in branch veins in normal light intensity, but not in weak light. Thus apoplasmic pathway may be the main mode of transport of assimilates in weak light, however symplasmic pathway may be the main mode of transport of assimilates in normal light intensity. These results demonstrated that the solar greenhouse nectarine trees could be adapted to the weak light via the ultrastructure variation of phloem tissues of the source leaves.
文摘Sucrose is produced in mesophyll cells and transferred into phloem cells before it is delivered long- distance to sink tissues. However, little is known about how sucrose transport is regulated in plants. Here, we identified a T-DNA insertional mutant of Oryza sativa DNA BINDING WITH ONE FINGER 11 （OsDOF11）, which is expressed in the vascular cells of photosynthetic organs and in various sink tissues. The osdofll mutant plants are semi-dwarf and have fewer tillers and smaller panicles as compared with wild-type （WT） plants. Although sucrose enhanced root elongation in young WT seedlings, this enhance- ment did not occur in osdof11 seedlings due to reduced sucrose uptake. Sugar transport rate analyses revealed that less sugar was transported in osdofll plants than in the WT. Expression of four Sucrose Transporter （SUT） genes-OsSUT1, OsSUT3, OsSUT4, and OsSUT5-as well as two Sugars Will Eventually be Exported Transporters （SWEET） genes, OsSWEETll and OsSWEET14, was altered in various organs of the mutant, including the leaves. Chromatin immunoprecipitation assays showed that OsDOFll directly binds the promoter regions of SUT1, OsSWEETll, and OsSWEET14, indicating that the expression of these transporters responsible for sucrose transport via apopiastic loading is coordinately controlled by OsDOFll. We also observed that osdofll mutant plants were less susceptible to infection byXanthomonas oryzae pathovar oryzae, suggesting that OsDOFll participates in sugar distribution during pathogenic in- vasion. Collectively, these results suggest that OsDOFll modulates sugar transport by regulating the expression of both SUT and SWEET genes in rice.
