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Rapid Crown Root Development Confers Tolerance to Zinc Deficiency in Rice.

Nanda AK, Wissuwa M - Front Plant Sci (2016)

Bottom Line: Zinc (Zn) deficiency is one of the leading nutrient disorders in rice (Oryza sativa).We therefore conclude that the rate of crown root initiation was differentially affected by Zn deficiency between genotypes.Rapid crown root development, following transplanting, was identified as a main causative trait for tolerance to Zn deficiency and better Zn retranslocation from shoot to root was a key attribute of Zn-efficient genotypes.

View Article: PubMed Central - PubMed

Affiliation: Crop, Livestock and Environment Division, Japan International Research Center for Agricultural Sciences Tsukuba, Japan.

ABSTRACT
Zinc (Zn) deficiency is one of the leading nutrient disorders in rice (Oryza sativa). Many studies have identified Zn-efficient rice genotypes, but causal mechanisms for Zn deficiency tolerance remain poorly understood. Here, we report a detailed study of the impact of Zn deficiency on crown root development of rice genotypes, differing in their tolerance to this stress. Zn deficiency delayed crown root development and plant biomass accumulation in both Zn-efficient and inefficient genotypes, with the effects being much stronger in the latter. Zn-efficient genotypes had developed new crown roots as early as 3 days after transplanting (DAT) to a Zn deficient field and that was followed by a significant increase in total biomass by 7 DAT. Zn-inefficient genotypes developed few new crown roots and did not increase biomass during the first 7 days following transplanting. This correlated with Zn-efficient genotypes retranslocating a higher proportion of shoot-Zn to their roots, compared to Zn-inefficient genotypes. These latter genotypes were furthermore not efficient in utilizing the limited Zn for root development. Histological analyses indicated no anomalies in crown tissue of Zn-efficient or inefficient genotypes that would have suggested crown root emergence was impeded. We therefore conclude that the rate of crown root initiation was differentially affected by Zn deficiency between genotypes. Rapid crown root development, following transplanting, was identified as a main causative trait for tolerance to Zn deficiency and better Zn retranslocation from shoot to root was a key attribute of Zn-efficient genotypes.

No MeSH data available.


Related in: MedlinePlus

Crown root development in IR74 (Zn-inefficient) and RIL46 (Zn-efficient), grown in nutrient solution with and without Zn. Cross-sections of crowns showing crown root developmental stages from differentiation of the epidermis and endodermis, Cr3, to emergence, Cr7 (A–E). Scale bar: 50 μm. Average number of crown roots at different developmental stages, from Cr3 to Cr7, in RIL46 and IR74, grown in nutrient solutions containing no (-zinc) or 1.5 μM Zn (+zinc) (F). Statistical significant data (p < 0.05) between crown root developmental stages (Cr) are indicated by different letters. Error bars represent SEM (n = 5).
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Figure 4: Crown root development in IR74 (Zn-inefficient) and RIL46 (Zn-efficient), grown in nutrient solution with and without Zn. Cross-sections of crowns showing crown root developmental stages from differentiation of the epidermis and endodermis, Cr3, to emergence, Cr7 (A–E). Scale bar: 50 μm. Average number of crown roots at different developmental stages, from Cr3 to Cr7, in RIL46 and IR74, grown in nutrient solutions containing no (-zinc) or 1.5 μM Zn (+zinc) (F). Statistical significant data (p < 0.05) between crown root developmental stages (Cr) are indicated by different letters. Error bars represent SEM (n = 5).

Mentions: To investigate in more details the effects of Zn deficiency on root development, crowns were harvested 2 WAT, cross-sectioned and crown root developmental stages were observed microscopically. Seven stages of crown root development have been described, from the establishment of the initial cells that form the crown root primordia (Cr1), to the emergence of the crown root (Cr7; Itoh et al., 2005). Our technique allowed us to easily and reproducibly identify developing crown roots from stages Cr3 (differentiation of endodermis and epidermis) up to Cr7 (crown root emergence; Figures 4A–E). Although absolute crown root number per developmental stage varied between replicates of the same genotypes, the same trend was always observed: in the absence of Zn, crown roots from stages Cr3 to Cr6 were few and similar in both RIL46 and IR74 (Figure 4F). However, the total sum of developing roots (t) from stages Cr3 to Cr6 was 25% higher in the Zn-efficient RIL46 (t = 15.6), compared to the inefficient IR74 (t = 11.6). The number of emerged crown roots (stage Cr7) was higher than root number counts obtained from whole plants from the same experiment (Figure 2A), which was most likely due to roots that had emerged, but were still too short to be observed with the naked eye. Nevertheless, RIL46 had 30% more emerged roots (t = 31.8), compared to IR74 (t = 22.4). A similar trend was found when grown in the presence of Zn, only at a higher rate (Figure 4F).


Rapid Crown Root Development Confers Tolerance to Zinc Deficiency in Rice.

Nanda AK, Wissuwa M - Front Plant Sci (2016)

Crown root development in IR74 (Zn-inefficient) and RIL46 (Zn-efficient), grown in nutrient solution with and without Zn. Cross-sections of crowns showing crown root developmental stages from differentiation of the epidermis and endodermis, Cr3, to emergence, Cr7 (A–E). Scale bar: 50 μm. Average number of crown roots at different developmental stages, from Cr3 to Cr7, in RIL46 and IR74, grown in nutrient solutions containing no (-zinc) or 1.5 μM Zn (+zinc) (F). Statistical significant data (p < 0.05) between crown root developmental stages (Cr) are indicated by different letters. Error bars represent SEM (n = 5).
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Figure 4: Crown root development in IR74 (Zn-inefficient) and RIL46 (Zn-efficient), grown in nutrient solution with and without Zn. Cross-sections of crowns showing crown root developmental stages from differentiation of the epidermis and endodermis, Cr3, to emergence, Cr7 (A–E). Scale bar: 50 μm. Average number of crown roots at different developmental stages, from Cr3 to Cr7, in RIL46 and IR74, grown in nutrient solutions containing no (-zinc) or 1.5 μM Zn (+zinc) (F). Statistical significant data (p < 0.05) between crown root developmental stages (Cr) are indicated by different letters. Error bars represent SEM (n = 5).
Mentions: To investigate in more details the effects of Zn deficiency on root development, crowns were harvested 2 WAT, cross-sectioned and crown root developmental stages were observed microscopically. Seven stages of crown root development have been described, from the establishment of the initial cells that form the crown root primordia (Cr1), to the emergence of the crown root (Cr7; Itoh et al., 2005). Our technique allowed us to easily and reproducibly identify developing crown roots from stages Cr3 (differentiation of endodermis and epidermis) up to Cr7 (crown root emergence; Figures 4A–E). Although absolute crown root number per developmental stage varied between replicates of the same genotypes, the same trend was always observed: in the absence of Zn, crown roots from stages Cr3 to Cr6 were few and similar in both RIL46 and IR74 (Figure 4F). However, the total sum of developing roots (t) from stages Cr3 to Cr6 was 25% higher in the Zn-efficient RIL46 (t = 15.6), compared to the inefficient IR74 (t = 11.6). The number of emerged crown roots (stage Cr7) was higher than root number counts obtained from whole plants from the same experiment (Figure 2A), which was most likely due to roots that had emerged, but were still too short to be observed with the naked eye. Nevertheless, RIL46 had 30% more emerged roots (t = 31.8), compared to IR74 (t = 22.4). A similar trend was found when grown in the presence of Zn, only at a higher rate (Figure 4F).

Bottom Line: Zinc (Zn) deficiency is one of the leading nutrient disorders in rice (Oryza sativa).We therefore conclude that the rate of crown root initiation was differentially affected by Zn deficiency between genotypes.Rapid crown root development, following transplanting, was identified as a main causative trait for tolerance to Zn deficiency and better Zn retranslocation from shoot to root was a key attribute of Zn-efficient genotypes.

View Article: PubMed Central - PubMed

Affiliation: Crop, Livestock and Environment Division, Japan International Research Center for Agricultural Sciences Tsukuba, Japan.

ABSTRACT
Zinc (Zn) deficiency is one of the leading nutrient disorders in rice (Oryza sativa). Many studies have identified Zn-efficient rice genotypes, but causal mechanisms for Zn deficiency tolerance remain poorly understood. Here, we report a detailed study of the impact of Zn deficiency on crown root development of rice genotypes, differing in their tolerance to this stress. Zn deficiency delayed crown root development and plant biomass accumulation in both Zn-efficient and inefficient genotypes, with the effects being much stronger in the latter. Zn-efficient genotypes had developed new crown roots as early as 3 days after transplanting (DAT) to a Zn deficient field and that was followed by a significant increase in total biomass by 7 DAT. Zn-inefficient genotypes developed few new crown roots and did not increase biomass during the first 7 days following transplanting. This correlated with Zn-efficient genotypes retranslocating a higher proportion of shoot-Zn to their roots, compared to Zn-inefficient genotypes. These latter genotypes were furthermore not efficient in utilizing the limited Zn for root development. Histological analyses indicated no anomalies in crown tissue of Zn-efficient or inefficient genotypes that would have suggested crown root emergence was impeded. We therefore conclude that the rate of crown root initiation was differentially affected by Zn deficiency between genotypes. Rapid crown root development, following transplanting, was identified as a main causative trait for tolerance to Zn deficiency and better Zn retranslocation from shoot to root was a key attribute of Zn-efficient genotypes.

No MeSH data available.


Related in: MedlinePlus