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. 2022 Nov 8:13:1007145.
doi: 10.3389/fpls.2022.1007145. eCollection 2022.

Response of root and root hair phenotypes of cotton seedlings under high temperature revealed with RhizoPot

Cong Fan  1 , Mingyu Hou  2 , Peng Si  1 , Hongchun Sun  1 , Ke Zhang  1 , Zhiying Bai  2 , Guiyan Wang  1 , Cundong Li  1 , Liantao Liu  1 , Yongjiang Zhang  1
Affiliations

Response of root and root hair phenotypes of cotton seedlings under high temperature revealed with RhizoPot

Cong Fan et al. Front Plant Sci. .

Abstract

Driven by the increase in its frequency and duration, high temperature weather is increasingly seriously affecting crop development. High temperature inhibits the leaf development, flowering, and pollination of cotton, but its effects on the roots and root hair phenotypes and lifespans remain unclear. Thus, this study selected the two cotton varieties Nongda 601 (ND) and Guoxin 9 (GX) as materials and adopted the RhizoPot, an in situ root observation system, to investigate the effects of high temperature (38°C day and 32°C night) on the growth dynamics of the aboveground parts and root phenotypes of cotton at the seedling stage. The results showed that high temperature reduced the net photosynthetic rate and chlorophyll content, decreased the dry matter accumulation and transfer to the root, and lowered the root-shoot ratio (R/S ratio). The root phenotypes changed significantly under high temperature. After 7 d of high temperature stress, the root lengths of ND and GX decreased by 78.14 mm and 59.64 mm, respectively. Their specific root lengths increased by 79.60% and 66.11%, respectively. Their specific root surface areas increased by 418.70 cm2·g-1 and 433.42 cm2·g-1, respectively. Their proportions of very fine roots increased to 99.26% and 97.16%, respectively. After the removal of high temperature (RHT), their root lengths tended to increase, and their proportions of very fine roots continued to increase. The root hairs of ND and GX were also significantly affected by high temperature. In particular, the root hair densities of ND and GX decreased by 52.53% and 56.25%, respectively. Their average root hair lengths decreased by 96.62% and 74.29%, respectively. Their root hair lifespans decreased by 7 d and 10 d, respectively. After the RHT, their average root hair lengths failed to recover. A principal component analysis indicated that the root architectures were significantly affected by root hair density, average root hair length, specific root length, and specific root surface area under high temperatures. In summary, cotton adapts to high temperature environments by increasing the specific root length, specific root surface area, and the proportions of very fine roots, and reducing the lifespan of root hairs.

Keywords: RhizoPot; cotton; high temperature; in situ root; root dynamics; root hair.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Schematic diagram of the in situ root observation system RhizoPot (A), RhizoPot growth imaging device (B), In situ root system image (C), rendering of the segmented in situ root image (D).
Figure 2
Figure 2
Changes in plant height (A), stem diameter (B), leaf area (C), and relative chlorophyll content (D) of two cotton varieties under normal conditions and high temperature and after 7 d of recovery. The means of three replicates ± standard error are depicted. For each trait, bars with the same letter are not significantly different according to Duncan’s test at a p<0.05 threshold. ns, not significant (p>0.05).
Figure 3
Figure 3
Changes in net photosynthetic rate (Pn) (A), maximum photochemical efficiency (Fv/Fm) (B), and actual photochemical quantum yield (ΦPSII) (C) of two cotton varieties under normal conditions and high temperature and after 7 d of recovery. The means of three replicates ± standard error are depicted. For each trait, bars with the same letter are not significantly different according to Duncan’s test at a p<0.05 threshold. ns, not significant (p>0.05).
Figure 4
Figure 4
Changes in the root length (A), root surface area (B), root volume (C), and average root diameter (D) of two cotton varieties under normal conditions and high temperature and after 7 d recovery.
Figure 5
Figure 5
Changes in the root growth rate (A) and root length density (B) of two cotton varieties under normal conditions and high temperature and after 7 d recovery.
Figure 6
Figure 6
Changes in the proportions of fine roots and very fine roots of two cotton varieties under normal conditions and high temperature and after 7 d recovery (A: CKND; B: CKGX; C: HTND; D: HTGX).
Figure 7
Figure 7
Changes in the root hair density (A), average root hair length (B), and root hair survival (C) of two cotton varieties under normal conditions and high temperature and after 7 d recovery. (A) values are the means of three replicates ± standard error, (B) values are the means of four replicates ± standard error, n, the number of root hairs used to draw the survival curve; The p -values indicate the statistical significance of the effect of high temperature stress on the root hair lifespan of cotton. For each trait, bars with the same letter are not significantly different according to Duncan’s test at a p<0.05 threshold. ns, not significant.
Figure 8
Figure 8
Images of the same root region of cotton root hairs under high temperature stress. Scale bar, 500 μm. Images shown are taken on 1d (A), 3d (B), 5d (C), 7d (D).
Figure 9
Figure 9
Pearson correlation matrix between the cotton traits. The level of significance of the correlations is indicated as follows: *p< 0.05; **p< 0.01. PH, plant height; SD, stem diameter; LA, leaf area; SPAD, spad value; Pn, net photosynthetic rate; Fv/Fm, maximum photochemical efficiency; ΦPsII, actual photochemical quantum yield; RFW, root fresh weight; RDW, root dry weight; R/S, root-shoot ratio; RL, root length; RA, root surface area; RV, root volume; RD, average root diameter; SRL, specific root length; SRSA, specific root surface area; SRV, specific root volume; RGR, root growth rate; RLD, root length density; VFR, proportion of very fine roots; FR, proportion of fine roots; RHD, root hair density; ARHL, average root hair length; RHL, root hair lifespan.
Figure 10
Figure 10
Principal component analysis of 17 root system indicators (abbreviated as in Figure 9 ).
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