During anthesis, there is an increased demand for carbohydrates due to pollen maturation and nectary secretion that warrants a systematic phloem unloading strategy for sugar partitioning. Sugar transporters are key components of the apoplasmic phloem unloading strategy and control the sugar flux needed for plant development. Currently, the phloem unloading strategy during anthesis has not been explored in cucumber, and the question of which sugar transporters are active during flower anthesis is poorly understood. In this study, a study utilizing the phloem-mobile symplasmic tracer carboxyfluorescein (CF) suggested that the phloem unloading was symplasmically isolated in the receptacle and nectary of cucumber flowers at anthesis. We also identified a hexose transporter that is highly expressed in cucumber flower, Sugar Will Eventually be Exported Transporter 7a (SWEET7a). CsSWEET7a was mainly expressed in receptacle and nectary tissues in both male and female flowers, where its expression level increased rapidly right before anthesis. At anthesis, the CsSWEET7a protein was specifically localized to the phloem region of the receptacle and nectary, indicating that CsSWEET7a may function in the apoplasmic phloem unloading during flower anthesis. Although cucumber mainly transports raffinose family oligosaccharides (RFOs) in the phloem, sucrose, glucose, and fructose are the major sugars in the flower receptacle and the nectary as well as in nectar at anthesis. In addition, the transcript levels of genes encoding soluble sugar hydrolases (α-galactosidase, sucrose synthase, cytoplasmic invertase, and cell wall invertase) were correlated with that of CsSWEET7a. These results indicated that CsSWEET7a may be involved in sugar partitioning as an exporter in the phloem of the receptacle and nectary to supply carbohydrates for flower anthesis and nectar secretion in cucumber.
To explore a new way for utilizing heterosis in Setaria italica Beauv., three foxtail millet varieties, namely Wujiuzhuaruangu, Xianggu and Huangjingu, were used in this study. In three different developmental stages, we sprayed plant with three different concentrations of Chemical Hybridizing Agent SQ-1, and control plant with water. Results showed that male sterility rates in Wujiuzhuaruangu and Xianggu reached 95% to 100% under the proper spraying concentration at the specific developmental stage, and that in Huangjingu was lower than 90%. At seven-leaf in Wujiuzhuaruangu and at eight-leaf in Xianggu were the best developmental stages for spraying, two varieties had the same optimal spraying concentrations for the highest rate of male sterility, which was 5 kg ha -1 . In conclusion, the specific genotypes of foxtail millet at the suitable developmental stage can be induced 95-100% male sterility by spraying SQ-1 at an optimum dosage, which provides a theoretical basis of heterosis and new technical support for using CHA SQ-1 to produce foxtail millet hybrid.
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