Publicação
The phytohormone mediated affair of Triticum durum and Azospirillum brasilense: a case study on plant-bacteria interaction
| Resumo: | One of the greatest challenges that mankind faces is being able to feed a growing population while trying to minimize its environmental impact. To achieve this, we need to combine an increase in crop yield with a more eco-friendly approach in agriculture. A possible solution is through the utilization of plant growth promoting rhizobacteria (PGPR). Among those PGPR, Azospirillum is considered as one of the most important rhizobacterial genus. Since it was discovered, more than 40 years ago, the genus Azospirillum became the most studied plant growth-promoting bacteria, being used worldwide for improving plant growth and crop yield. It has been reported that inoculation with Azospirillum leads to changes in the plant root system, with increased root proliferation. Which in turn, leads to an increase in root density, enhancing plants capacity to access water and nutrients, as it extends the area explored by the root system, the so-called sponge effect. This work shows that nitric oxide (NO) and indole-3-acetic acid (IAA) mediate the A. brasilense-induced increase in the number of second order roots (SORs) in wheat, without affecting the first order root (FORs) structure. Those effects combine, lead to an increase in root density. Application of a NO scavenger – 2-(4- carboxyphenyl)-4,4,5,5, -tetramethylimidazoline-1-oxyl- 3-oxide (cPTIO) and an auxin scavenger – α-(p-Chlorophenoxy) isobutyric acid (PCIB), either together or separated, completely block the A. brasilense effect on the root system. While the application of a NO donor - sodium nitroprusside (SNP) and a synthetic auxin – Naphthaleneacetic acid (NAA), either together or separated, mimic the effects of inoculation. It was also showed that NO and IAA mediate the A. brasilense direct increase of the wheat biomass production, through the stimulation of the plant photosynthetic activity. Application of cPTIO completely blocked the A. brasilense effects, while application of PCIB only partially blocked the effects of the inoculation. The application of SNP and NAA, together or separated, mimic the effects of the bacterial inoculation. The IAA production by A. brasilense is very dependent on the availability of tryptophan and increases with a higher initial inoculum concentration. Whereas denitrification might be actual a positive feature for bacterial inoculants, as it produced NO which is fundamental for the A. brasilense plant growth promoting (PGP) effects. Although these phytohormones are not just produced as part of the symbiotic relationship between plants and the bacteria, as a novel of possible other roles for the pathways involved in the production of IAA and NO, have been discovered and proposed in the last few years. The PGP effects of A. brasilense seem to be broad and not limited to some varieties, as from the 2 varieties of Triticum durum tested (Marialva and Preto Amarelo), inoculation resulted in positive effects on the number of SORs and in the biomass production of both varieties, despite the differences between them. With the more ancestral variety (Preto Amarelo) being more responsive to A. brasilense inoculation. These effects are positive for plant growth and development as well as for the environment. Since increasing root density leads to increased nutrient use efficiency and therefore decreased agricultural environmental impacts. While the direct increase in the biomass production due to the inoculation of A. brasilense, leads to an increased crop yield. |
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| Autores principais: | Ferreira, Rodolfo Filipe Nunes |
| Assunto: | Ácido indolacético Azospirillum brasilense Fitohormonas Óxido nítrico Trigo Teses de mestrado - 2018 |
| Ano: | 2018 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Lisboa |
| Idioma: | inglês |
| Origem: | Repositório da Universidade de Lisboa |
| Resumo: | One of the greatest challenges that mankind faces is being able to feed a growing population while trying to minimize its environmental impact. To achieve this, we need to combine an increase in crop yield with a more eco-friendly approach in agriculture. A possible solution is through the utilization of plant growth promoting rhizobacteria (PGPR). Among those PGPR, Azospirillum is considered as one of the most important rhizobacterial genus. Since it was discovered, more than 40 years ago, the genus Azospirillum became the most studied plant growth-promoting bacteria, being used worldwide for improving plant growth and crop yield. It has been reported that inoculation with Azospirillum leads to changes in the plant root system, with increased root proliferation. Which in turn, leads to an increase in root density, enhancing plants capacity to access water and nutrients, as it extends the area explored by the root system, the so-called sponge effect. This work shows that nitric oxide (NO) and indole-3-acetic acid (IAA) mediate the A. brasilense-induced increase in the number of second order roots (SORs) in wheat, without affecting the first order root (FORs) structure. Those effects combine, lead to an increase in root density. Application of a NO scavenger – 2-(4- carboxyphenyl)-4,4,5,5, -tetramethylimidazoline-1-oxyl- 3-oxide (cPTIO) and an auxin scavenger – α-(p-Chlorophenoxy) isobutyric acid (PCIB), either together or separated, completely block the A. brasilense effect on the root system. While the application of a NO donor - sodium nitroprusside (SNP) and a synthetic auxin – Naphthaleneacetic acid (NAA), either together or separated, mimic the effects of inoculation. It was also showed that NO and IAA mediate the A. brasilense direct increase of the wheat biomass production, through the stimulation of the plant photosynthetic activity. Application of cPTIO completely blocked the A. brasilense effects, while application of PCIB only partially blocked the effects of the inoculation. The application of SNP and NAA, together or separated, mimic the effects of the bacterial inoculation. The IAA production by A. brasilense is very dependent on the availability of tryptophan and increases with a higher initial inoculum concentration. Whereas denitrification might be actual a positive feature for bacterial inoculants, as it produced NO which is fundamental for the A. brasilense plant growth promoting (PGP) effects. Although these phytohormones are not just produced as part of the symbiotic relationship between plants and the bacteria, as a novel of possible other roles for the pathways involved in the production of IAA and NO, have been discovered and proposed in the last few years. The PGP effects of A. brasilense seem to be broad and not limited to some varieties, as from the 2 varieties of Triticum durum tested (Marialva and Preto Amarelo), inoculation resulted in positive effects on the number of SORs and in the biomass production of both varieties, despite the differences between them. With the more ancestral variety (Preto Amarelo) being more responsive to A. brasilense inoculation. These effects are positive for plant growth and development as well as for the environment. Since increasing root density leads to increased nutrient use efficiency and therefore decreased agricultural environmental impacts. While the direct increase in the biomass production due to the inoculation of A. brasilense, leads to an increased crop yield. |
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