Drought is associated with inhibition of pollen tube directional growth via enhancing nitric oxide signaling in Gossypium hirsutum ovules

Résumé fourni par la source

Drought disrupts pollen tube guidance via nitric oxide accumulation at the ovular micropyle, leading to fertilization failure Drought stress increased the relative expression of GhNIAD and NR activity in the ovules of both cotton cultivars, promoting the conversion of NO2- to NO. The reduction in GSNOR activity under drought conditions inhibited the breakdown of GSNO, maintaining higher NO levels in the ovules. Drought stress has been reported to impair chemotropism of pollen tube growth in the pistil, yet the physiological mechanisms underlying this phenomenon remain unexplored in G . hirsutum . This study hypothesized that drought-induced nitric oxide (NO) changes in ovules may inhibit pollen tube directional growth. To test the above hypothesis, pools experiments were conducted using two cotton ( Gossypium hirsutum L.) cultivars Yuzaomian 9110 (drought-sensitive) and Dexiamian 1 (drought-tolerant) under water stress. Results demonstrated that drought stress inhibited the directional growth of pollen tube to the embryo sac and simultaneously reduced fertilization rate, the number of cotton seeds per boll as well as the single boll weight. Moreover, correlation analyses showed that NO content in the ovules had significantly negative correlation with the fertilization rate, implying that NO changes in ovules might inhibit pollen tube directional growth and subsequent yield component formation. Further analyses showed that drought stress elevated nitrate reductase (NR) activity in the ovules of both cultivars, facilitating the conversion of nitrite (NO 2 - ) to NO. This process was accompanied by the up-regulation of NR gene ( GhNIAD ) expressions in the drought-affected ovules of both cultivars, further promoting NO synthesis. The reduction in S-nitrosoglutathione reductase (GSNOR) activity under drought conditions was correlated with an accumulation of S-nitrosoglutathione (GSNO), suggesting that the compromised removal of NO contributed to the higher NO levels in the ovules. Additionally, elevated NO levels may, as part of a regulatory mechanism, further inhibit the activity of GSNOR in the ovules of both cultivars under drought stress. Thus, these findings revealed that drought leads to the accumulation of NO in the cotton ovules, which may be a factor inhibiting pollen tube growth. Of course, this causal relationship requires more evidence to be confirmed in future research. These results provide novel insights into the molecular-physiological mechanisms by which water deficit triggers reproductive failure in cotton.

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