Low pH stress activates several genes for lateral root formation and detoxification of aluminum ions in Cotton plants

Abstract

In low pH condition of soils (pH<5), Al is solubilized into a phytotoxic form Al(H2O)63+ and inhibits the plant root growth and development. Precisely, during low pH stress (e.g., pH 4.75), aluminum compound converts into its ionic form and becomes higher in level which is a limiting factor for plant root growth and seedling formation. Under aluminum (Al) toxic conditions, the organic acid transporters for example citrate and malate transporters in plasma membrane are involved in organic acid release and form non phytotoxic stable complexes with Al3+ in the rhizosphere. The study showed that, the cotton seedlings exhibited very sensitive phenotypes to low pH stress conditions due to high accumulation of ionic Al stress, the seedlings displayed retarded primary, secondary root growth and small cotyledons. These results indicated that cotton plants are susceptible to low pH condition.. As a whole without fine divisions the root system becomes corraloid in structure which will be having squat secondary roots. Plant has developed a natural defense mechanism in order to combat this unfavorable environment. Expression profile and Al complexation with organic acid exudates studies clearly revealed that both GhALMT1 and GhALS3 genes are involved in Al3+detoxification mechanisms. The remarkable expression was detected for GhALS3 under both low pH and aluminum stress condition in comparison to wild type untreated control whereas GhALMT1 expression was only activated under Al3+ stress condition. Our study, displayed enhanced citrate and malate excretion values in the wild type plants which are treated with Al and H+ stress. Thus, it can be clearly mentioned that GhALMT1 and GhALS3 is playing a significant role in low pHstress tolerance of cotton plant.