| Summary: | 碩士 === 國立臺灣大學 === 園藝學研究所 === 103 === Phosphorus (P), one of the essential macronutrients of plant, is not only an important component of genetic materials and cellular structure, but also a key factor involved in many physiological and biochemical reactions. Previous studies showed that phosphorus use efficiencies of lettuce (Lactuca sativa L.) varied depending on morphological types and cultivars. Therefore, this research investigated the physiological responses of semi-heading lettuce under various phosphorus treatments. In addition, gene expression analysis was conducted using microarray and quantitative reverse transcription PCR (qRT-PCR) techniques in semi-heading lettuce under various phosphorus treatments.
Semi-heading lettuce plants cultured under different light intensities displayed different growth rates, and the phosphorus starvation responses were also different. During seedling stage, shoot and root phosphate concentrations were significantly decreased after Pi starvation for 3 days under either high or low light intensities. The shoot fresh weight was significantly decreased after Pi starvation for 3 days under high light intensity condition, and was significantly decreased after Pi starvation for 5 days under low light intensity condition. During growing stage under either high or low light intensities, the shoot fresh weight, shoot and root Pi concentrations were significantly decreased after Pi starvation for 5 days, the water content was significantly decreased after Pi starvation for 10 days, and the hydrogen peroxide concentration was significantly increased after Pi starvation for 10 days. The chlorophyll and carotenoids concentrations were significantly increased after Pi starvation for 5 days under high light intensity condition, but increased after Pi starvation for 10 days under low light intensity condition. During harvesting stage under either high or low light intensities, shoot and root Pi concentrations were significantly decreased after Pi starvation for 5 days. However, during this stage, even after Pi starvation for 10 days, there were no significant difference between Pi treatments in shoot fresh weight, water content, chlorophyll concentration, carotenoids concentration, hydrogen peroxide concentration and nitrate concentration.
In this research, the Pi starvation induced gene- Lsa031437.1 was identified in semi-heading lettuce via microarray analysis. The function of Lsa031437.1 may involves in the reaction of oxidation-reduction in plants. Expression patterns of Lsa031437.1 in responses to Pi starvation treatments were further confirmed by qRT-PCR techniques. Then, the Lsa031437.1 promoter fusion with β-glucuronidase (GUS) construct was transiently expressed in lettuce leaf via agroinfiltration. GUS staining results showed that the expression levels of GUS signal in leaves were similar when plants grown under Pi sufficient and starvation conditions. This result indicated that Lsa031437.1 promoter:GUS construct in combination with agroinfiltration technique may be not suitable for monitoring phosphorus status in lettuce.
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