Coronatine‐induced lateral‐root formation in cotton (Gossypium hirsutum) seedlings under potassium‐sufficient and ‐deficient conditions in relation to auxin

Abstract

AbstractA large root system plays a decisive role in potassium (K)‐acquisition efficiency of cotton. Coronatine (COR), a non‐host‐specific phytotoxin, may affect the auxin level in plants and might therefore be useful in regulating lateral‐root (LR) development. Our objectives were (1) to examine the effects of COR on root development, especially the LR formation in hydroponically grown cotton seedlings, and (2) to explore possible mechanisms involved. The results showed that K deficiency (0.05 mM) significantly reduced LR formation in cotton seedlings, possibly due to the decrease of endogenous indole acetic acid (IAA) in roots by more than half. Following the application of 10 nM COR, the LRs significantly increased by 26% in K‐sufficient (0.5 mM) solution and by 95% in K‐deficient solution. Although COR did not increase the free IAA level in the primary root, the polar auxin‐transport inhibitor N‐1‐naphthylphthalamic acid (NPA) decreased its stimulating effects on LR formation by 25%–30%, suggesting that the COR‐induced LR formation was independent of increased auxin level but likely associated with auxin transport. Treatment of plants with 1‐naphthalene acetic acid (NAA) increased LR formation at NAA concentrations of 100 nM, but had no effect at 10 nM. In the presence of 1 nM COR, however, NAA increased LR formation at 10 nM concentrations. This indicates that LR formation due to COR possibly involves changes in auxin sensitivity. In addition, the shorter LRs of COR‐treated seedlings were clearly restored when COR was removed from solutions for 12 d, and the total root length, total root surface area as well as K uptake increased significantly, suggesting that COR may be potentially useful for enhancing the K‐acquisition efficiency of cotton seedlings.