Differential Responses of Water Uptake Pathways and Expression of Two Aquaporin Genes to Water-Deficit in Rice Seedlings of Two Genotypes

doi:10.1016/j.rsci.2017.03.001

Abstract

Abstract:

Water-deficit (WD) is a major abiotic stress constraining crop productivity worldwide. Zhenshan 97 is a drought-susceptible rice genotype, while IRAT109 is a drought-resistant one. However, the physiological basis of the difference remains unclear. These two genotypes had similar total water uptake rates under both WD and well-watered (WW) conditions, and their water uptake rates under WD were significantly decreased compared with those under WW. However, the water uptake rate via the cell-to-cell pathway was significantly increased in Zhenshan 97 but decreased in IRAT109 under WD, whereas the opposite trends were observed through the apoplastic pathway. These results indicated that the stress responses and relative contributions of these two water uptake pathways were associated with rice genotype under WD. The expression levels of OsPIP2;4 and OsPIP2;5 genes were significantly higher in roots of Zhenshan 97 than in IRAT109 under the two conditions. OsPIP2;4 expression in roots was significantly up-regulated under WD, while OsPIP2;5 expression showed no significant change. These results suggest that the expression levels of OsPIP2;4 and OsPIP2;5 in rice are dependent on genotype and water availability. Compared with Zhenshan 97, IRAT109 had a higher root dry weight, water uptake rate and xylem sap flow rate, and lower leaf water potential and root porosity under WD, which might be responsible for the drought resistance in IRAT109.

Key words: aquaporin expression, OsPIP2;4, OsPIP2;5, rice, root porosity, water-deficit, water uptake pathway

Ai-hua Xu, Ke-hui Cui, Wen-cheng Wang, Zhen-mei Wang, Jian-liang Huang, Li-xiao Nie, Yong Li, Shao-bing Peng. Differential Responses of Water Uptake Pathways and Expression of Two Aquaporin Genes to Water-Deficit in Rice Seedlings of Two Genotypes[J]. Rice Science, 2017, 24(4): 187-197.

Figures/Tables 6

Fig. 1. Dry weights of two genotypes under well-watered and water-deficit treatments.Data are Mean ± SE (n = 4). Significant differences were observed between the two treatments and between the two genotypes at the 0.05 level, except between Zhenshan 97 and IRAT109 under well-watered condition for root dry weight.

Table 1 Water-related traits in two genotypes under well-watered (WW) and water-deficit (WD) conditions.

Genotype	Treatment	LWP (MPa)	RWC (%)	Total water uptake [g/(h∙plant)]	WURt	WURa	WUR_AQP
Genotype	Treatment	LWP (MPa)	RWC (%)	Total water uptake [g/(h∙plant)]	[g/(g∙h)]	[g/(g∙h)]	[g/(g∙h)]
Zhenshan 97	WW	-0.84 ± 0.02 aA	96.3 ± 0.7 aA	21.5 ± 0.9 aB	15.2 ± 0.6 aA	11.0 ± 0.4 aA	4.3 ± 0.3 aB
	WD	-0.99 ± 0.02 bA	91.3 ± 0.9 bA	7.2 ± 0.1 bB	7.7 ± 0.3 bA	4.5 ± 0.3 bB	3.2 ± 0.1 bA
IRAT109	WW	-0.99 ± 0.04 aB	91.4 ± 1.7 aB	24.4 ± 0.7 aA	15.5 ± 0.7 aA	9.0 ± 0.6 aB	6.5 ± 0.5 aA
	WD	-1.41 ± 0.03 bB	89.7 ± 1.1 bA	9.4 ± 0.6 bA	8.4 ± 0.8 bA	6.5 ± 0.5 bA	1.9 ± 0.4 bB
Two-way ANOVA	Genotype (G)	100.3**	8.1*	15.4**	0.6	0	1.9
	Treatment (T)	102.1**	8.8*	517.1**	141.7**	110.7**	63.7**
	G × T	24.9**	1.9	0.3	0.2	22.4**	24.8**

Fig. 2. Xylem sap flow rate and root porosity in two genotypes under well-watered and water-deficit treatments.Data are Mean ± SE (n = 4). Significant differences were observed between the two genotypes under water deficit condition and between the two treatments at the 0.05 level for the two traits, whereas no significant difference was observed between the two genotypes under well-watered condition for the two traits.

Fig. 3. Relationships between root porosity and xylem sap flow rate and water uptake rate.

Table 2 Relative expression of root aquaporins (%) at mRNA level under well-watered (WW) and water-deficit (WD) conditions.

Genotype	Treatment	OsPIP2;4	OsPIP2;5
Zhenshan 97	WW	61.0 ± 4.3 bA	100.0 ± 9.5 aA *
	WD	126.9 ± 4.9 aA	104.2 ± 5.2 aA
IRAT109	WW	22.4 ± 1.8 bB	60.4 ± 2.4 aB **
	WD	37.9 ± 1.4 aB	52.3 ± 2.3 aB **
Two-way ANOVA	Genotype (G)	427.9**	103.9**
	Treatment (T)	418.8**	4
	G × T	117.7**	49.6**

Fig. 4. Thickening and lignification of parenchyma cell walls of roots (bar = 10 μm). A and B, Zhenshan 97 and IRAT109 under well-watered treatment, respectively; C and D, Zhenshan 97 and IRAT109 under water-deficit treatment, respectively.

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