Ethylene works as a possible regulator for the rootlet elongation and transcription of genes for phosphorus acquisition in cluster roots of Lupinus albus L.

Figures & data

Figure 1. Cluster root (CR) developmental stages in white lupin and relative gene expression for LaACC oxidase1 and LaACC synthase1 in 3 developmental stages.

(a) Photograph of white lupin CRs formed under P deficiency. CRs were divided into four developmental stages, including the tip of CR (TCR), immature CR (ICR), mature CR (MCR), whose rootlets were the longest of the four, and senescence CR (SCR). Sampling was conducted based on appearance. Scale bar indicates 1 cm. (b) Transcription level of Lalb_Chr20g0119141 (ACC oxidase1) and Lalb_Chr05g0224501 (ACC synthase1), which were selected on the basis of RNA-Seq data (Secco et al. 2014) in different CR stages and TR (tip of root) under P sufficiency (n = 5). Expression of TCR under -P is standard (= 1.0). The housekeeping gene was selected gene encoding 40S ribosomal protein S8. Different letters indicate a statistically significant difference (p < 0.05; Tukey-Kramer) among treatments. Error bars indicate standard error.

Table 1. Plant biomass and P concentration in shoot and root after Co²⁺ and 1-aminocyclopropane-1-carboxylic acid (ACC) treatments. Different letters indicate statistically significant differences (p < 0.05; Tukey-Kramer) among treatments (n = 5).

Treatment	Plant-DW (mg)	Shoot-P (mg/g-DW)	Root-P (mg/g-DW)
+P	1614.7 ± 89.4 ^a	10.71 ± 0.37 ^a	16.48 ± 0.29 ^a
-P	872.0 ± 34.1 ^b	1.57 ± 0.15 ^b	1.78 ± 0.04 ^b
-P with CoCl2	780.6 ± 100.3 ^b	1.32 ± 0.03 ^b	1.82 ± 0.04 ^b
-P with ACC	782.9 ± 171.6 ^b	1.27 ± 0.05 ^b	1.76 ± 0.07 ^b

Figure 2. Cluster roots (CRs) influenced by reagent related to ethylene.

(a) Length of MCR (mature CR) rootlets under different Co²⁺ concentration (n = 3). (b) Photograph of representative MCR each treatment with a scale bar of 1 cm. All photos are of same fold. (c) Length of MCR rootlets (n = 5). (d) Number of ICR (immature CR), MCR and SCR (senescence CR) (n = 5). -P, -P + Co²⁺, and -P + ACC show plants under P deficiency, plants after application of CoCl₂ for 9 days, and plants after the application of 1-aminocyclopropane-1-carboxylic acid (ACC) for 9 days, respectively. Different letters show a statistically significant difference (p < 0.05; Tukey-Kramer) among treatments. Error bars indicate standard error.

Figure 3. Relative gene expression for a)LaERF, b)LaS8H, c)LaMYB72, d)LabHLH39, e)LaSAP2, f)LaSAP1, g)LaPT1, h)LaCS1, i)LaCS2, and j)LaMATE6 in roots.

Relative gene expression in root grown in full nutrient solution (+P) or solutions without P (-P) and additional application of CoCl₂ for 9 days (-P+ Co²⁺) or 1-aminocyclopropane-1-carboxylic acid (-P+ ACC), in different cluster root (CR) stages (TCR; the tip of CR under -P, ICR; immature CR, MCR; mature CR) under P deficiency and TR (tip of root) under P sufficiency (n = 5). Expression of TCR under -P is standard (= 1.0). The housekeeping gene was selected gene encoding 40S ribosomal protein S8. Different letters indicate a statistically significant difference (p < 0.05; Tukey-Kramer) among treatments. Error bars indicate standard error.

Figure 4. Effects of Co²⁺ and 1-aminocyclopropane-1-carboxylic acid (ACC) on citrate concentration in roots.

Citrate concentration in root grown in full nutrient solution (+P) or solutions without P (-P) and additional application of CoCl₂ for 9 days (-P+ Co²⁺) or ACC (-P+ ACC), in different cluster root (CR) stages (TCR; the tip of root under +P or tip of CR under -P, ICR; immature CR, MCR; mature CR) under P deficiency and TR (tip of root) under P sufficiency (n = 5). Different letters show a statistically significant difference (p < 0.05; Tukey-Kramer) among treatments. Error bars indicate standard error.

Figure 5. Schematic diagram to represent for the role of ethylene in cluster root (CR). ACC, 1-aminocyclopropane-1-carboxylic acid.

Secco, D., H. X. Shou, J. Whelan, and O. Berkowitz. 2014. “RNA-Seq Analysis Identifies an Intricate Regulatory Network Controlling Cluster Root Development in White Lupin.” BMC Genomics 15: 230. doi:10.1186/1471-2164-15-230.

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