Later growth period;nitrogen loss in plant;nitrogen redistribution;nitrogen-use efficiency;oilseed rape
To determine the relationship between nitrogen (N) redistribution of oilseed rape (Brassica napus L.) varieties and N-use efficiency during later growth stages, the differences in N-use efficiency between two varieties (X-36 and X-50) were studied using the (15)N labeling method with sand culture under complete nutrient solution conditions. Results showed that X-36 had greater grain yield not because of greater N uptake but because of greater grain yield per unit N in the plant and N-harvesting index. The average proportion of N in the two varieties that was redistributed from the vegetative organs to the grain was 65.1%. The redistribution amount and the proportion of N absorbed at the stem elongation stage and redistributed into the grain of two varieties were the greatest; the least were amounts absorbed at the siliquing stage. The high- N-use-efficiency variety (X-36), when compared with the low-N-use-efficiency variety (X-50), had slower redistribution speed of N before the siliquing stage, which then became faster after the siliquing stage. The amount of N redistributed to the grains and its proportion were larger, whereas those toward the silique husk were smaller. The amount of N loss from the plant and its proportion were smaller, and the velocity of N loss was also slower. This explains why varieties with high N efficiency have high N-harvesting index. At the later growth stages, N redistribution in the vegetative organs will significantly affect N-use efficiency.
The relationship between nitrogen efficiency (NE), defined as seed yield per unit nitrogen (N) application, and seed quality was examined in two oilseed rape (Brassica napus L.) varieties at 5 N application levels, 0.6, 3, 6, 12, 15 mmol L-1, N-1, N-2, N-3, N-4 and N-5, respectively. Seed yield, oil yield and protein content were increased with the increase in N application level, but NE and oil content were decreased, and the fatty acid composition in seed was hardly changed. Analysis of seven fatty acids revealed a slight decrease in the contents of erucic acid and arachidonic acid with the increase in N application level, but no obvious change in the contents of palmitic acid, stearic acid, oleic acid, linoleic acid and linolenic acid. Compared with the low NE variety H29, the seed yield and contents of erucic acid and arachidonic acid in the high NE variety bin270 were more markedly increased with the increase in N application level, and the oil content was hardly changed. The seed yield, oil content and oil yield were higher in the high NE variety than in the low NE variety at all 5 N application levels. There were no significant differences in protein, palmitic acid, stearic acid and oleic acid contents between the varieties at any of the 5 N application levels, but there were slight differences in the linoleic acid and linolenic acid contents between the two varieties. In brief, N application improved oil yield more greatly in the high NE variety than in the low NE variety, but hardly affected the fatty acid composition. Therefore, the seed quality and oil content of oilseed rape may not be decreased by breeding of a high NE variety with a high N absorption efficiency and high N use efficiency.
N use efficiency;Proton pumps in the tonoplast;N reutilization;Oilseed rape (Brassica napus)
Nitrate (NO3-) can accumulate in high concentrations in plant cell vacuoles if it is not reduced, reutilized or transported into the cytoplasm. Such accumulation of NO3- in the vacuole occurs when mechanisms for NO3- assimilation in the cytoplasm are saturated. Moreover, other processes such as efflux across the plasma membrane might affect NO3- accumulation in the vacuole. These are the main reasons limiting nitrogen use efficiency (NUE) in plants. This study elucidates mechanisms for NO3- transport from the cytoplasm to vacuoles by the V-proton pump (V-ATPase and V-PPase) and their relationship with different NUE in four Brassica napus genotypes. Pot experiments were conducted in a greenhouse under normal (15.0 mmol L-1) and limited N (7.5 mmol L-1) concentrations of nitrate using B. napus genotypes that demonstrated either high (742 and Xiangyou 15) or low (814 and H8) NUE (g g(-1)). Specific inhibitors of V-ATPase and V-PPase increased nitrate reductase (NR) activity, resulting in greatly decreased NO3- in plant tissues. Nitrate reductase activity and NO3- content correlated more highly to V-PPase activity than they did to V-ATPase activity, and correlation between V-PPase activity and NO3- content was significantly higher than it was to V-ATPase. Genotypes with high NUE had significantly lower activities of V-ATPase and V-PPase than those with low NUE. In the high-NUE plants, lower activities of V-proton pump underlie mechanisms that result in significantly lower NO3- content in plant tissues of the high-NUE genotypes than those found in plant tissues of the low-NUE genotypes. Our results show that the tonoplast proton pumps V-PPase and V-ATPase strongly negatively affect NR activity and positively affect NO3- content. V-PPase contributed more to this regulatory mechanism than did V-ATPase.
ZHANG Zhen-hua;LIU Qiang;SONG Hai-xing;RONG Xiang-min;Abdelbagi M Ismail
Agricultural Sciences in China,2011年10(2):195-206 ISSN：1671-2927
[Abdelbagi M Ismail] Crops and Environment Science Division,International Rice Research Institute,Metro Manila Philippines;[ZHANG Zhen-hua; LIU Qiang; SONG Hai-xing; RONG Xiang-min] College of Resources and Environmental Sciences,Hunan Agricultural University
[Ismail, AM] Int Rice Res Inst, Crops & Environm Sci Div, Metro Manila DAPO Box 7777, Manila, Philippines.
The study was conducted to investigate the effects of applying different concentrations of the macronutrients K(+), Ca(2+), and Mg(2+) on the responses of contrasting rice (Oryza sativa L.) genotypes under salt stress. A solution culture experiment was conducted in a phytotron at the International Rice Research Institute (IRRI), under controlled temperature and humidity and natural sunlight. When subjected to salt stress of 100 mmol L(-1) using NaCl, the salt tolerant genotypes FL478 and IR1651, accumulated less Na(+) and maintained lower ratios of Na(+)/K(+), Na(+)/Ca(2+), and Na(+)/Mg(2+) than the sensitive genotypes IR29 and Azucena. These tolerant genotypes also had higher concentrations of K(+) in their shoots and greater root and shoot biomass and green leaf area. Tolerant genotypes also maintained much lower concentration of Na(+) and lower and more favorable ratios of Na(+)/K(+), Na(+)/Ca(2+), and Na(+)/Mg(2+) in their active and developing tissues. Salt tolerance and shoot and root growth of both tolerant and sensitive genotypes were enhanced considerably when higher concentrations of Ca(2+) and Mg(2+) were applied in culture solution. The concentration of Na(+) and the ratios of Na(+)/K(+), Na(+)/Ca(2+), and Na(+)/Mg(2+) in shoots also declined significantly. The beneficial effects of higher calcium were greater than that of magnesium and application of higher concentration of K(+) seems to have minor effects. Responses to salinity in rice can therefore be considerably enhanced through proper nutrient management, by increasing the concentrations of nutrient elements that have favorable effects such as Ca(2+) and Mg(2+). Calcium is particularly more effective than both magnesium and potassium, and can be applied at relatively larger quantities in salt affected soils.
Two winter oilseed rape varieties grown in sand culture were labeled with (15)Nitrogen (N-15) at different growth stages to show the route of nitrogen (N) absorption, distribution, and transfer in oilseed rape (Brassica napus L.). Averaged over the two varieties, 84% of the N absorbed at the seedling stage, and 67% of the N absorbed at the stem elongation stage were distributed into the leaves. Of the N absorbed at flowering stage, 43% was distributed into the leaves and 36% into stems. However, 42.4% of the N absorbed at siliquing stage was directly found into the silique. The proportion of the N redistributed from vegetative organs into reproductive organs was 34%, 44%, 41%, and 32%, at seedling, stem elongation, flowering, and siliquing stages, respectively. The amounts of N transferred were 203, 326, 218, and 82 mg per plant, respectively. This corresponded to 65% of the total in the grain. The proportions of N lost after absorption were 24%, 11%, 12%, and 7% at the four growth stages, respectively. The amounts lost were 142, 79, 43, and 16 mg per plant, respectively. N absorbed at early growth stages in oilseed rape was mainly distributed to the leaves first, and then redistributed to the reproductive organs later. This route provided most of the N for the reproductive organs.
N-use efficiency;Nitrate;Proton pumps in the tonoplast;Nitrate reductase;Vacuole;Brassica napus
Nitrate, once taken up by plants, can either be stored in vacuoles or reduced by nitrate reductase in the cytoplasm. High accumulation of NO3 (-) in the vacuole occurs when assimilation into the cytoplasm is saturated. This study elucidates how proton pumps at the tonoplast (V-ATPase and V-PPase) affect the NO3 (-) content of Brassica napus by controlling the distribution of NO3 (-) between the cytoplasm and vacuole. Pot experiments were conducted in a greenhouse under normal N (15.0 mM nitrate) conditions using B. napus genotypes that demonstrated either high (Xiangyou15) or low (814) nitrogen use efficiency (NUE). The NO3 (-) content of the high NUE genotype was significantly lower than that of the low NUE genotype, whereas the total N per plant of the two genotypes was almost the same, suggesting that the different NUE between the two genotypes is not due to the difference of NO3 (-) uptake. The relative expression levels of V-ATPase (vha-a3) and V-PPase (avp1) genes in the high NUE genotype were significantly lower than in the low NUE genotype, resulting in lower V-ATPase and V-PPase activities in the high NUE genotype. The transport of NO3 (-) and protons from the cytoplasm to the vacuole is powered by V-ATPase and V-PPase, so their lower activities increase H+ efflux from and reduce NO3 (-) influx into the vacuoles of the high NUE genotype. We conclude that the lower activity of proton pumps at the tonoplast is the main reason the high NUE genotype possesses lower NO3 (-) content and higher N-use efficiency.
hi order to investigate the mechanisms of nitrogen (N) re-distribution in response to proteolytic enzyme (PE), glutamine synthetase (GS) and glutamate synthetase (GOGAT) activities and the effects on N use efficiency (NUB). Two oilseed rape genotypes were grown in sand culture in a greenhouse under normal (15.0 mmol L-1 NO3-) and limited-N (7.5 mmol L-1 NO3-) levels. Isotope (N-15) labeling and enzyme inhibitors against the PE, GS and GOGAT enzymes were used. We found that, when the two genotypes were subjected to specific inhibitors of PE, GS, and GOGAT, the activities of these enzymes were significantly decreased, resulting in reduced N re-distributed from leaf to grain, as well as reduced NUB. L- glutamine and free amino acid contents in the phloem sap were primarily influenced by PE and GS activities, whereas grain yield was primary regulated by GOGAT activity during the later growth stages. These findings suggest that PE, GS, and GOGAT are key enzymes for the regulation of N re-distribution in plant tissues during later growth stages, with grain yield and NUB of oilseed rape being positively regulated by PE, GS and GOGAT activities.