ABA mediates PEG-mediated premature differentiation of root apical meristem in plants

Abstract

Root apical meristem (RAM) is central for indeterminate growth of plant roots and in sensing environmental stimuli, such as water status. Recently, we reported that PEG8000-simulated mild and moderate osmotic stress induces premature differentiation of RAM, which is a conserved adaptive mechanism in higher plants to cope with water stress. Microarray data analysis revealed that the ABA signaling pathway may be involved in water stress-induced RAM premature differentiation. Here we showed that in wheat, ABA contents increased under water stress with the highest level of ABA in the RAM. Exogenous ABA also induces RAM premature differentiation in both wheat and Arabidopsis plants. Further genetic analysis revealed that loss of function mutations in ABA2 and ABA receptors significantly reduced the level of root tip swelling and RAM premature differentiation in response to PEG-simulated water stress. Together, the results suggest that ABA participates in regulation of PEG-mediated premature differentiation of RAM.

Keywords: ABA; ABA, abscisic acid; PEG8000, polyethylene glycol; RAM, root apical meristem; premature differentiation; root apical meristem; water stress.

Figure 1.

ABA promotes root meristem premature differentiation. (A) ABA contents in root RAM region (RAM, 2 mm in length) and the region above the RAM (ARAM, 2 mm in length) were measured. Six-day-old K199 variety of wheat root tips were collected at 0, 8 and 72 h after 5% PEG8000 treatment. (B) Six-day-old K199 variety of wheat seedlings were treated with 20 μM ABA solution at 0 and 72 h and stained with 0.005% Tetrazolium Violet (reddish color). Bar = 0.5 mm. (C) Quantification of length of stained root tips (reddish color) shown in (B). (D) Six-day-old Arabidopsis seedlings (Col-0) were treated with 2 μM ABA solution at 0 and 72 h. The red arrowheads show the transition zone. Bar = 100 μm. (E) Quantification of meristem size shown in (D). The meristem sizes of root tips are defined by measuring the length from the initial cortical cell adjacent to the quiescence center to the first enlarged cortex cell. Data are presented as means ± SD, and columns marked with asterisks indicate significant differences in each treatment using Student's t-test analysis (P < 0.05).

Figure 2.

ABA involves in root swollen and premature differentiation under water stress. (A) Six-day-old seedlings of Col-0, aba2–1 and pyr1/pyl1pyl4 mutants were treated with (PEG8000) or without (CK) 5% PEG8000 solution for 3 d Bar = 0.2 mm. (B) Quantification of root width shown in (A). (C) Quantification of root meristem size shown in (A). Data are presented as means ± SD, and columns marked with asterisks indicate significant differences in each treatment using Student's t-test analysis (P < 0.05).