The critical nitrogen concentration of a plant can be de®ned as the minimum nitrogen concentratio... more The critical nitrogen concentration of a plant can be de®ned as the minimum nitrogen concentration required for maximum growth rate at any time. It has been suggested that the relationship between the critical N concentration and dry matter per unit ground area for a wide range of crops is the same and is independent of climatic zone. Results presented in this paper support the concept of a critical N-dilution curve for yield of rice (Oryza sativa L.), which may be independent of climatic zone. The similarity between the nitrogen dilution curves for temperate and tropical environments indicates that there is no intrinsic difference in the ratio of carbon-to-nitrogen capture in those environments even though the ®nal aboveground biomasses differed. Both the rate and duration of resource capture are probably limiting yields in tropical environments. In order to break through the current ceiling-yield barrier of approximately 10 t grain ha À1 in the tropics, superior germplasm must be lodging resistant and capable of acquiring 144 kg N ha À1 (N 0.5 ) in the ®rst 35 days following transplanting. An examination of the rates of nitrogen acquisition indicated that more emphasis must be placed on providing suf®cient nitrogen during the early stage of crop growth if higher yields are to be obtained. The time course of nitrogen accumulation by the aboveground biomass was calculated for weights greater than 1 t ha À1 ; at weights less than this there were insuf®cient data to make calculations. At weights of aboveground biomass greater than 1 t ha À1 , the rate of nitrogen acquisition per unit ground area declined. The decline probably re¯ected a lowering in crop demand for soil nitrogen caused by the internal cycling of nitrogen from aging to young developing tissues; roots' age may also play a part in the decline. The estimated rate of demand for nitrogen by the panicle exceeded the rate at which the aboveground biomass acquired it, emphasizing the importance of having a large`reservoir' of nitrogen in vegetative tissues. Such a reservoir would ensure that the nitrogen demand of the panicle could be met without causing the photosynthetic capacity of the crop to prematurely lose its ability to meet the carbohydrate demand of the panicle. #
<p>(A)The photosynthesis rate per internal CO<sub>2</sub> concentration respons... more <p>(A)The photosynthesis rate per internal CO<sub>2</sub> concentration response curves (ACi) for the low δ<sup>13</sup>CBC<sub>1</sub>F<sub>2</sub> (green square), normal δ<sup>13</sup>CBC<sub>1</sub>F<sub>2</sub> (blue square) and wildtype (WT) (red square). The maximum rate of photosynthesis (P<sub>max</sub>), carboxylation efficiency (CE) and CO<sub>2</sub> compensation points (CP) are shown in the table. However, the CO<sub>2</sub> compensation point is high for low δ<sup>13</sup>C mutants. The squares show data of 3<sup>rd</sup> leaf and circles for the 4<sup>th</sup> leaf. The green, blue, and red colors represent low δ<sup>13</sup>C BC<sub>1</sub>F<sub>2</sub>, normal δ<sup>13</sup>C BC<sub>1</sub>F<sub>2</sub>, and WT, respectively. (B)The light response curve (LRC) for the low δ<sup>13</sup>C BC<sub>1</sub>F<sub>2</sub> (green square) normal δ<sup>13</sup>CBC<sub>1</sub>F<sub>2</sub> (blue square) and wildtype (red square). The maximum rate of photosynthesis (J<sub>max</sub>), quantum efficiency (QE) and light compensation point (RD) are shown in the table. The squares show data of 3<sup>rd</sup> leaf and circles of the 4<sup>th</sup> leaf. The green, blue and red marks represent low δ<sup>13</sup>C BC<sub>1</sub>F<sub>2</sub>, normal δ<sup>13</sup>C BC<sub>1</sub>F<sub>2</sub>, and WT, respectively.</p
<p>The red dots show the presence of chlorophyll in the leaf section. (D,E, and F) The stom... more <p>The red dots show the presence of chlorophyll in the leaf section. (D,E, and F) The stomatal densities of the seedlings are in the same order as above. The low δ<sup>13</sup>C BC<sub>1</sub>F<sub>2</sub> mutants had more stomata per mm<sup>2</sup> than the WT/normal. Scale: in A, B, and C the magnification is 20x and the scale shown is 20 μm; in D, E and F magnification is 10x and the scale shown is 100 μm.</p
<p>The percentage of green, pale and albino were 92, 4, and 4, respectively in the M<sub... more <p>The percentage of green, pale and albino were 92, 4, and 4, respectively in the M<sub>1</sub> population.</p
<p>The SNPs, from the locus of the genome associated with the mutant phenotype, causing ami... more <p>The SNPs, from the locus of the genome associated with the mutant phenotype, causing amino acid changes.</p
<p>The focused image of q arm of chromosome 10 where the alternate allele frequency was hig... more <p>The focused image of q arm of chromosome 10 where the alternate allele frequency was high (≈1) in SbPool 1 and SbPool 2, the pools with low δ<sup>13</sup>C and fatal samples about 0.5 in SbPool 3, the pool with normal δ<sup>13</sup>C but slow growing samples and about 0.33 in SbPool 4, the pool with normal δ<sup>13</sup>C and phenotype.</p
Potentially, the most consistent and damaging consequences of climate change for rice could come ... more Potentially, the most consistent and damaging consequences of climate change for rice could come through the yield-depress-ing effects of high temperature (Sheehy et al 2006). Anthesis is very susceptible to damage in the 35–40 °C temperature range and exposure for a matter of a few hours during flowering can reduce floral reproduction
The specification of vascular patterning in plants has interested plant biologists for many years... more The specification of vascular patterning in plants has interested plant biologists for many years, but in the last decade a new context for this interest has emerged. Specifically, recent proposals to engineer C4 traits into C3 plants such as rice demand an understanding of how the distinctive venation pattern in the leaves of C4 plants is elaborated. High vein density with Kranz anatomy, where photosynthetic cells are arranged in encircling layers around vascular bundles, is one of the major traits that differentiate C4 from C3 species. To identify genetic factors that specify C4 leaf anatomy we generated ethyl-methanesulfonate and gamma-ray mutagenized populations of the C4 species sorghum (Sorghum bicolor), and screened for lines with reduced vein density. Two mutations were identified that conferred low vein density. Both mutations segregated in backcrossed F2 populations as homozygous recessive alleles. Bulk segregant analysis using next generation sequencing revealed that in both cases, the mutant phenotype was associated with mutations in the Cytochrome P450 90D2 gene that encodes an enzyme in the brassinosteroid biosynthesis pathway. Lack of complementation in allelism tests confirmed this result. These data indicate that the brassinosteroid pathway promotes high vein density in the sorghum leaf, and suggest that differences between C4 and C3 leaf anatomy may arise in part through differential activity of this pathway in the two leaf types. This article is protected by copyright. All rights reserved.
Rice is the most important crop in the world for human food. Over the past 40 years, its producti... more Rice is the most important crop in the world for human food. Over the past 40 years, its production has kept pace with the increase in population. However, it is clear that the gains of the first Green Revolution are largely exhausted. Rice with C 4 photosynthesis could make a major contribution to a second Green Revolution. To assess how that change could affect rice, it is necessary to understand how the rice crop works. In this paper, we examine the properties of individual rice plants both as single individuals and as members of dense crop communities. To estimate the potential of C 4 rice, we compare the yields and radiation-use efficiencies of maize, rice, and a C 4 weed. In that context, the properties of rice canopies with respect to the interception of solar radiation and its effect on leaf temperature are examined. The influence of sink size with respect to source strength is also discussed. It is possible that wild rice types have some of the anatomical features peculiar to C 4 plants and that the wild types may contain C 3 -C 4 intermediates. Consequently, we report results obtained from an examination of C 4 characteristics in the 22 species of wild rice.
The critical nitrogen concentration of a plant can be de®ned as the minimum nitrogen concentratio... more The critical nitrogen concentration of a plant can be de®ned as the minimum nitrogen concentration required for maximum growth rate at any time. It has been suggested that the relationship between the critical N concentration and dry matter per unit ground area for a wide range of crops is the same and is independent of climatic zone. Results presented in this paper support the concept of a critical N-dilution curve for yield of rice (Oryza sativa L.), which may be independent of climatic zone. The similarity between the nitrogen dilution curves for temperate and tropical environments indicates that there is no intrinsic difference in the ratio of carbon-to-nitrogen capture in those environments even though the ®nal aboveground biomasses differed. Both the rate and duration of resource capture are probably limiting yields in tropical environments. In order to break through the current ceiling-yield barrier of approximately 10 t grain ha À1 in the tropics, superior germplasm must be lodging resistant and capable of acquiring 144 kg N ha À1 (N 0.5) in the ®rst 35 days following transplanting. An examination of the rates of nitrogen acquisition indicated that more emphasis must be placed on providing suf®cient nitrogen during the early stage of crop growth if higher yields are to be obtained. The time course of nitrogen accumulation by the aboveground biomass was calculated for weights greater than 1 t ha À1 ; at weights less than this there were insuf®cient data to make calculations. At weights of aboveground biomass greater than 1 t ha À1 , the rate of nitrogen acquisition per unit ground area declined. The decline probably re¯ected a lowering in crop demand for soil nitrogen caused by the internal cycling of nitrogen from aging to young developing tissues; roots' age may also play a part in the decline. The estimated rate of demand for nitrogen by the panicle exceeded the rate at which the aboveground biomass acquired it, emphasizing the importance of having a large`reservoir' of nitrogen in vegetative tissues. Such a reservoir would ensure that the nitrogen demand of the panicle could be met without causing the photosynthetic capacity of the crop to prematurely lose its ability to meet the carbohydrate demand of the panicle.
Every day almost one billion people suffer from chronic hunger, and the situation is expected to ... more Every day almost one billion people suffer from chronic hunger, and the situation is expected to deteriorate with a projected population growth to 9 billion worldwide by 2050. In order to provide adequate nutrition into the future, rice yields in Asia need to increase by 60%, a change that may be achieved by introduction of the C 4 photosynthetic cycle into rice. The international C 4 Rice Consortium was founded in order to test the feasibility of installing the C 4 engine into rice. This review provides an update on two of the many approaches employed by the C 4 Rice Consortium: namely, metabolic C 4 engineering and identification of determinants of leaf anatomy by mutant screens. The aim of the metabolic C 4 engineering approach is to generate a two-celled C 4 shuttle in rice by expressing the classical enzymes of the NADP-ME C 4 cycle in a cell-appropriate manner. The aim is also to restrict RuBisCO and glycine decarboxylase expression to the bundle sheath (BS) cells of rice in a C 4-like fashion by specifically down-regulating their expression in rice mesophyll (M) cells. In addition to the changes in biochemistry, two-celled C 4 species show a convergence in leaf anatomy that include increased vein density and reduced numbers of M cells between veins. By screening rice activation-tagged lines and loss-of-function sorghum mutants we endeavour to identify genes controlling these key traits.
Failure to meet the increasing demand for food from Asia's rising population will result in ... more Failure to meet the increasing demand for food from Asia's rising population will result in misery for hundreds of millions. A 40% increase in rice production by 2020 is required and this must come from increased yield per hectare, because the total area of suitable land ...
The specification of vascular patterning in plants has interested plant biologists for many years... more The specification of vascular patterning in plants has interested plant biologists for many years. In the last decade a new context has emerged for this interest. Specifically, recent proposals to engineer C4 traits into C3 plants such as rice require an understanding of how the distinctive venation pattern in the leaves of C4 plants is determined. High vein density with Kranz anatomy, whereby photosynthetic cells are arranged in encircling layers around vascular bundles, is one of the major traits that differentiate C4 species from C3 species. To identify genetic factors that specify C4 leaf anatomy, we generated ethyl methanesulfonate- and cray- mutagenized populations of the C4 species sorghum (Sorghum bicolor), and screened for lines with reduced vein density. Two mutations were identified that conferred low vein density. Both mutations segregated in backcrossed F2 populations as homozygous recessive alleles. Bulk segregant analysis using nextgeneration sequencing revealed that,...
The critical nitrogen concentration of a plant can be de®ned as the minimum nitrogen concentratio... more The critical nitrogen concentration of a plant can be de®ned as the minimum nitrogen concentration required for maximum growth rate at any time. It has been suggested that the relationship between the critical N concentration and dry matter per unit ground area for a wide range of crops is the same and is independent of climatic zone. Results presented in this paper support the concept of a critical N-dilution curve for yield of rice (Oryza sativa L.), which may be independent of climatic zone. The similarity between the nitrogen dilution curves for temperate and tropical environments indicates that there is no intrinsic difference in the ratio of carbon-to-nitrogen capture in those environments even though the ®nal aboveground biomasses differed. Both the rate and duration of resource capture are probably limiting yields in tropical environments. In order to break through the current ceiling-yield barrier of approximately 10 t grain ha À1 in the tropics, superior germplasm must be lodging resistant and capable of acquiring 144 kg N ha À1 (N 0.5 ) in the ®rst 35 days following transplanting. An examination of the rates of nitrogen acquisition indicated that more emphasis must be placed on providing suf®cient nitrogen during the early stage of crop growth if higher yields are to be obtained. The time course of nitrogen accumulation by the aboveground biomass was calculated for weights greater than 1 t ha À1 ; at weights less than this there were insuf®cient data to make calculations. At weights of aboveground biomass greater than 1 t ha À1 , the rate of nitrogen acquisition per unit ground area declined. The decline probably re¯ected a lowering in crop demand for soil nitrogen caused by the internal cycling of nitrogen from aging to young developing tissues; roots' age may also play a part in the decline. The estimated rate of demand for nitrogen by the panicle exceeded the rate at which the aboveground biomass acquired it, emphasizing the importance of having a large`reservoir' of nitrogen in vegetative tissues. Such a reservoir would ensure that the nitrogen demand of the panicle could be met without causing the photosynthetic capacity of the crop to prematurely lose its ability to meet the carbohydrate demand of the panicle. #
<p>(A)The photosynthesis rate per internal CO<sub>2</sub> concentration respons... more <p>(A)The photosynthesis rate per internal CO<sub>2</sub> concentration response curves (ACi) for the low δ<sup>13</sup>CBC<sub>1</sub>F<sub>2</sub> (green square), normal δ<sup>13</sup>CBC<sub>1</sub>F<sub>2</sub> (blue square) and wildtype (WT) (red square). The maximum rate of photosynthesis (P<sub>max</sub>), carboxylation efficiency (CE) and CO<sub>2</sub> compensation points (CP) are shown in the table. However, the CO<sub>2</sub> compensation point is high for low δ<sup>13</sup>C mutants. The squares show data of 3<sup>rd</sup> leaf and circles for the 4<sup>th</sup> leaf. The green, blue, and red colors represent low δ<sup>13</sup>C BC<sub>1</sub>F<sub>2</sub>, normal δ<sup>13</sup>C BC<sub>1</sub>F<sub>2</sub>, and WT, respectively. (B)The light response curve (LRC) for the low δ<sup>13</sup>C BC<sub>1</sub>F<sub>2</sub> (green square) normal δ<sup>13</sup>CBC<sub>1</sub>F<sub>2</sub> (blue square) and wildtype (red square). The maximum rate of photosynthesis (J<sub>max</sub>), quantum efficiency (QE) and light compensation point (RD) are shown in the table. The squares show data of 3<sup>rd</sup> leaf and circles of the 4<sup>th</sup> leaf. The green, blue and red marks represent low δ<sup>13</sup>C BC<sub>1</sub>F<sub>2</sub>, normal δ<sup>13</sup>C BC<sub>1</sub>F<sub>2</sub>, and WT, respectively.</p
<p>The red dots show the presence of chlorophyll in the leaf section. (D,E, and F) The stom... more <p>The red dots show the presence of chlorophyll in the leaf section. (D,E, and F) The stomatal densities of the seedlings are in the same order as above. The low δ<sup>13</sup>C BC<sub>1</sub>F<sub>2</sub> mutants had more stomata per mm<sup>2</sup> than the WT/normal. Scale: in A, B, and C the magnification is 20x and the scale shown is 20 μm; in D, E and F magnification is 10x and the scale shown is 100 μm.</p
<p>The percentage of green, pale and albino were 92, 4, and 4, respectively in the M<sub... more <p>The percentage of green, pale and albino were 92, 4, and 4, respectively in the M<sub>1</sub> population.</p
<p>The SNPs, from the locus of the genome associated with the mutant phenotype, causing ami... more <p>The SNPs, from the locus of the genome associated with the mutant phenotype, causing amino acid changes.</p
<p>The focused image of q arm of chromosome 10 where the alternate allele frequency was hig... more <p>The focused image of q arm of chromosome 10 where the alternate allele frequency was high (≈1) in SbPool 1 and SbPool 2, the pools with low δ<sup>13</sup>C and fatal samples about 0.5 in SbPool 3, the pool with normal δ<sup>13</sup>C but slow growing samples and about 0.33 in SbPool 4, the pool with normal δ<sup>13</sup>C and phenotype.</p
Potentially, the most consistent and damaging consequences of climate change for rice could come ... more Potentially, the most consistent and damaging consequences of climate change for rice could come through the yield-depress-ing effects of high temperature (Sheehy et al 2006). Anthesis is very susceptible to damage in the 35–40 °C temperature range and exposure for a matter of a few hours during flowering can reduce floral reproduction
The specification of vascular patterning in plants has interested plant biologists for many years... more The specification of vascular patterning in plants has interested plant biologists for many years, but in the last decade a new context for this interest has emerged. Specifically, recent proposals to engineer C4 traits into C3 plants such as rice demand an understanding of how the distinctive venation pattern in the leaves of C4 plants is elaborated. High vein density with Kranz anatomy, where photosynthetic cells are arranged in encircling layers around vascular bundles, is one of the major traits that differentiate C4 from C3 species. To identify genetic factors that specify C4 leaf anatomy we generated ethyl-methanesulfonate and gamma-ray mutagenized populations of the C4 species sorghum (Sorghum bicolor), and screened for lines with reduced vein density. Two mutations were identified that conferred low vein density. Both mutations segregated in backcrossed F2 populations as homozygous recessive alleles. Bulk segregant analysis using next generation sequencing revealed that in both cases, the mutant phenotype was associated with mutations in the Cytochrome P450 90D2 gene that encodes an enzyme in the brassinosteroid biosynthesis pathway. Lack of complementation in allelism tests confirmed this result. These data indicate that the brassinosteroid pathway promotes high vein density in the sorghum leaf, and suggest that differences between C4 and C3 leaf anatomy may arise in part through differential activity of this pathway in the two leaf types. This article is protected by copyright. All rights reserved.
Rice is the most important crop in the world for human food. Over the past 40 years, its producti... more Rice is the most important crop in the world for human food. Over the past 40 years, its production has kept pace with the increase in population. However, it is clear that the gains of the first Green Revolution are largely exhausted. Rice with C 4 photosynthesis could make a major contribution to a second Green Revolution. To assess how that change could affect rice, it is necessary to understand how the rice crop works. In this paper, we examine the properties of individual rice plants both as single individuals and as members of dense crop communities. To estimate the potential of C 4 rice, we compare the yields and radiation-use efficiencies of maize, rice, and a C 4 weed. In that context, the properties of rice canopies with respect to the interception of solar radiation and its effect on leaf temperature are examined. The influence of sink size with respect to source strength is also discussed. It is possible that wild rice types have some of the anatomical features peculiar to C 4 plants and that the wild types may contain C 3 -C 4 intermediates. Consequently, we report results obtained from an examination of C 4 characteristics in the 22 species of wild rice.
The critical nitrogen concentration of a plant can be de®ned as the minimum nitrogen concentratio... more The critical nitrogen concentration of a plant can be de®ned as the minimum nitrogen concentration required for maximum growth rate at any time. It has been suggested that the relationship between the critical N concentration and dry matter per unit ground area for a wide range of crops is the same and is independent of climatic zone. Results presented in this paper support the concept of a critical N-dilution curve for yield of rice (Oryza sativa L.), which may be independent of climatic zone. The similarity between the nitrogen dilution curves for temperate and tropical environments indicates that there is no intrinsic difference in the ratio of carbon-to-nitrogen capture in those environments even though the ®nal aboveground biomasses differed. Both the rate and duration of resource capture are probably limiting yields in tropical environments. In order to break through the current ceiling-yield barrier of approximately 10 t grain ha À1 in the tropics, superior germplasm must be lodging resistant and capable of acquiring 144 kg N ha À1 (N 0.5) in the ®rst 35 days following transplanting. An examination of the rates of nitrogen acquisition indicated that more emphasis must be placed on providing suf®cient nitrogen during the early stage of crop growth if higher yields are to be obtained. The time course of nitrogen accumulation by the aboveground biomass was calculated for weights greater than 1 t ha À1 ; at weights less than this there were insuf®cient data to make calculations. At weights of aboveground biomass greater than 1 t ha À1 , the rate of nitrogen acquisition per unit ground area declined. The decline probably re¯ected a lowering in crop demand for soil nitrogen caused by the internal cycling of nitrogen from aging to young developing tissues; roots' age may also play a part in the decline. The estimated rate of demand for nitrogen by the panicle exceeded the rate at which the aboveground biomass acquired it, emphasizing the importance of having a large`reservoir' of nitrogen in vegetative tissues. Such a reservoir would ensure that the nitrogen demand of the panicle could be met without causing the photosynthetic capacity of the crop to prematurely lose its ability to meet the carbohydrate demand of the panicle.
Every day almost one billion people suffer from chronic hunger, and the situation is expected to ... more Every day almost one billion people suffer from chronic hunger, and the situation is expected to deteriorate with a projected population growth to 9 billion worldwide by 2050. In order to provide adequate nutrition into the future, rice yields in Asia need to increase by 60%, a change that may be achieved by introduction of the C 4 photosynthetic cycle into rice. The international C 4 Rice Consortium was founded in order to test the feasibility of installing the C 4 engine into rice. This review provides an update on two of the many approaches employed by the C 4 Rice Consortium: namely, metabolic C 4 engineering and identification of determinants of leaf anatomy by mutant screens. The aim of the metabolic C 4 engineering approach is to generate a two-celled C 4 shuttle in rice by expressing the classical enzymes of the NADP-ME C 4 cycle in a cell-appropriate manner. The aim is also to restrict RuBisCO and glycine decarboxylase expression to the bundle sheath (BS) cells of rice in a C 4-like fashion by specifically down-regulating their expression in rice mesophyll (M) cells. In addition to the changes in biochemistry, two-celled C 4 species show a convergence in leaf anatomy that include increased vein density and reduced numbers of M cells between veins. By screening rice activation-tagged lines and loss-of-function sorghum mutants we endeavour to identify genes controlling these key traits.
Failure to meet the increasing demand for food from Asia's rising population will result in ... more Failure to meet the increasing demand for food from Asia's rising population will result in misery for hundreds of millions. A 40% increase in rice production by 2020 is required and this must come from increased yield per hectare, because the total area of suitable land ...
The specification of vascular patterning in plants has interested plant biologists for many years... more The specification of vascular patterning in plants has interested plant biologists for many years. In the last decade a new context has emerged for this interest. Specifically, recent proposals to engineer C4 traits into C3 plants such as rice require an understanding of how the distinctive venation pattern in the leaves of C4 plants is determined. High vein density with Kranz anatomy, whereby photosynthetic cells are arranged in encircling layers around vascular bundles, is one of the major traits that differentiate C4 species from C3 species. To identify genetic factors that specify C4 leaf anatomy, we generated ethyl methanesulfonate- and cray- mutagenized populations of the C4 species sorghum (Sorghum bicolor), and screened for lines with reduced vein density. Two mutations were identified that conferred low vein density. Both mutations segregated in backcrossed F2 populations as homozygous recessive alleles. Bulk segregant analysis using nextgeneration sequencing revealed that,...
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