The Physiological Mechanism Of Leaf Color Change And Nitrogen Regulation On Rice

Nitrogen is the mass element for plant growth, and leaf color diagnose is one of the important method for appropriate fertilize. In order to clarify the mechanism of leaf color change of leaf rice, the experiment performed from 2005 to 2007 with hydroponics solution with yujing6hao and liangyoupeijiu as materials. With four different nitrogen concentrations as followed: without nitrogen added; 40 mg/L and 80mg/L nitrogen concentration sustained and nitrogen concentration changed during growth stage. Studied the law of the leaf color change of rice canopy , and the relation between nitrogen uptake and SPAD, and the relation between the leaf color change and key enzymes of nitrogen metabolism( GS and GOGAT ) and sugar metabolism (SS and SPS). During different growth stage, transfer the rice planted with no nitrogen treatment to 40 mg/L nitrogen concentration treatment studied the dynamic change of leaf color, and the enzymes of carbon and nitrogen metabolism. The results as followed:1. The canopy leaf color had clear change even without nitrogen added; the color depth of leaf of different nitrogen treatments had significant differences one variety. The SPAD of leaf color of canopy rice leaf increased as the nitrogen concentration increased exhibited as followed: no nitrogen added treatment < nitrogen changed treatment≤40 mg/L treatment < 80 mg/L treatment. It indicated: the change of leaf color was a biological procession, which restrained by inherent rhythm. To some extent; nitrogen content had regulative effect on the depth of leaf color, but could not change the inherent rhythm.2. The dynamic change of nitrogen uptake rate of two varieties'40 and 80mg/L nitrogen treatments had the same tendency. From transplant to the former tillering stage, the nitrogen uptake rate increased gradually, then until booting stage, keeps stable relatively. During this period, the nitrogen uptake rate had small rolls. After the spike draw out, and then decreased. The nitrogen uptake rate in the changed nitrogen content solution of the two varieties changes as the nitrogen content change. The SPAD of 40 and 80mg/L nitrogen treatments also exhibited the same tendency as the nitrogen uptakes rate at the former stage of tillering. From the former stage of tillering until booting, the SPAD of canopy leaf keep steady relatively. After the spike draw out, and then decreased. At the former stage of tillering, the SPAD of changed nitrogen content treatment had the same trend as the two other nitrogen treatment. From the middle stage of tillering until booting, the SPAD of canopy leaf had clear change as the nitrogen content changed and the growth stage developed. The canopy leaf color of the two varieties was regulated by nitrogen uptake rate two weeks ago. Under nitrogen-changed condition, the SPAD of uppermost three leaves had significant positive relation with its nitrogen uptake rate two weeks ago. With normal and excessive nitrogen concentration treatments, the SPAD of 3rd and 4th leaf had significant positive relation with its nitrogen uptake rate two weeks ago. Namely, under short nitrogen condition, the upper leaf was more sensitive to nitrogen, when nitrogen was enough or excessive; the lower leaf position was more sensitive to nitrogen.3. The change range of activities of root GS was small during the growth stage, which planted in the solution without nitrogen. The activities of roots GS of yujing6hao were active at the middle stage of tillering, which was nitrogen added treatment, they all had one apex. At the elongating stage, the activities of roots GS keep steady. During booting and heading stage, the three treatments all had an apex of GS activities. Liangyoupeijiu had the same change trend. The activities of root GOGAT of different treatments had the same change tendency in one variety. The apex of enzymes activities appeared at the middle stage of tillering, the end stage of tillering and booting stage, respectively. The second apex of GOGAT activity of liangyoupeijiu was one week earlier than yujing6hao The change trend of activities of GS in leaf was similar in the two varieties, the apex of enzymes activities appeared at the middle stage of tillering (13th, July), the end stage of tillering (27th, July), and booting stage (24th, August), respectively. With the nitrogen added treatments, activities of GS in leaf showed the same trend with same nitrogen content between the two varieties, and the apex of enzymes activities appeared at the middle stage of tillering (13th, July), the end stage of tillering or the former stage of elongating (27th, July or 3th , August), and booting stage (24th, August), respectively. From the correlate analysis, it can conclude, the enzymes of nitrogen metabolism (GS or GOGAT) had significant positive relation with the same enzymes in leaf at the same time. It indicated that the change of the activities of nitrogen metabolism enzymes in leaf and root were unanimously. The activities of nitrogen metabolism enzymes in root of different treatments of the two varieties influenced by root's nitrogen uptake rate one week before, and the SPAD of leaf had close relation with its nitrogen metabolism enzymes. It means, the nitrogen absorbed by root transformed into chlorophyll and be reflected on leaf color need about two weeks; the result was accord with the other people's conclusion. The SPAD had significant positive relation with the enzymes on Indica variety, but the Japonica variety exhibited negative relation.4. The SS activities of different treatments of yujing6hao had the same change trend, and theirs apex appeared the same time as their SPAD the same nitrogen treatment in leaf. The SS activities of different treatments of liangyoupeijiu had three apexes during the growth stage, and the time that appeared had some difference with their SPAD in leaf. The SPS activities of 40 mg/L nitrogen treatment of yujing6hao had three apexes during the growth stage, and the time that they appeared at the same time with its SPAD apexes, the three other nitrogen treatments only had two enzymes activities apexes,there was no obvious SPS activity apex appeared at tillering stage, and the follow two SPS activity apexes appeared the same time as the SPAD. In conclusion, the activities of SS and SPS had obvious influence on SPAD in leaf. The SPAD of different treatments of yujing6hao had significant positive relation with their activities of SS and SPS the same week. The SPAD of different treatments of liangyoupeijiu had significant negative relation with their activities of SS one week after, and exhibited significant positive relation with their activities of SPS in leaf.5. The two varieties rice planted in solution without nitrogen, the SPAD of leaf change had the same tendency after added nitrogen during different growth stage, their leaf SPAD increased as the treatment time prolongs. The difference between the activities of nitrogen metabolism enzymes of the two varieties was during booting stage. At the former and middle stage of tillering, the activities of GS of yujing6hao exhibited as single apex curve, but liangyoupeijiu exhibited as increased as the treat time prolongs at the former stage of tillering, and then at the middle stage of tillering decreased. At the booting stage, the activities of GS of two varieties showed as increased as the nitrogen treatment time prolongs. At the former stage of tillering, the activities of GOGAT of yujing6hao showed as letter"V"as the nitrogen treatment time prolongs, and liangyoupeijiu GOGAT activities sustaining increased .From middle stage of tillering until the former stage of elongating , the activities of the two nitrogen metabolism enzymes of the two varieties had the same change tendency. During the booting stage, the activities of the two enzymes all exhibited as single apex curves, but the appearance of the max number of the activities of yujing6hao was three days earlier. The change of the activities of SS and SPS of two varieties were similar during tillering stage and elongating stage. At the booting stage, both the activities of SPS of yujing6hao and the activities of SS of liangyoupeijiu increased as the nitrogen treat time prolongs. Both the activities of SPS of liangyoupeijiu and the activities of SS of yujing6hao attained their max at the 12th day after nitrogen treat.