3.5 RCS is closely related to root and aboveground growth
To
clarify the physiological role of RCS in regulating the development of
the whole root system and aboveground parts, we measured several traits,
such as root architecture and shoots, at different time points (Figures
7-8). There were genotypic differences in the response of cotton roots
to drought stress
(Figure
7A). Specifically, compared to ”Ji 228”, the total root length, root dry
weight, specific root surface area, root volume, root tissue density,
average length - lateral roots, average length - all roots, and convex
hull area of the ”Guoxin 02” were increased by 45.92%, 90.00%,
98.70%, 37.56%, 84.00%, 28.04%, 30.63%, 16.97%, and 15.65%,
respectively, under drought stress (Figures 7BCDEGIJM). However, the
lateral root angle was significantly reduced by 23.34% (Figure 7K).
The
impact of drought stress on aboveground traits of cotton plants was the
highest at 15 days after treatment (Figure S2 and Figure S3). Under
drought stress, the F v/F m, leaf area, leaf water
potential, plant height, relative leaf water content, stomatal length,
stomatal width, and stomatal opening of ”Guoxin 02” increased by
80.21%, 40.05%, 15.56%, 18.42 %, 29.91%, 15.09%, 23.68%, and
18.75%, respectively, (Figures 8ABCFGIJK) compared to ”Ji 228”.
However, the leaf water saturation deficit and stomatal density showed a
significant reduction of 9.79% and 5.91%, respectively (Figures 8EL).
Pearson correlation analysis showed that the
cortical senescence percentage at
the 6 cm, 9 cm and 12 cm segments from the root tip were positively
correlated with root total length, root dry weight, root tissue density,
leaf water potential, leaf relative water content, andF v/F m (p < 0.05, Figures 3ABCGHI).
3.6
Structural equation model of RCS and drought tolerance
To further investigate the direct and indirect effects of RCS on cotton
drought tolerance, we generated a structural equation model to examine
the relationship between RCS and cotton drought tolerance and determine
the path coefficients between the two (Figure 9). The structural
equation model showed a significant correlation between RCS and drought
tolerance, with a P -value of 0.033*. This indicated that the
pathway was valid, with an effect coefficient of 0.986. Overall, the
model demonstrated a good fit (Table S2).