Physiological, biochemical and molecular responses to low pH stress in citrus junos seedlings

Excessive soil acidity negatively affects citrus growth and development worldwide. However, less information has been presented on its tolerance to low pH stress (LPS). Here, the way in which citrus plants respond to LPS was investigated at morphological, physiological and molecular levels. Under LPS, the root length and diameter were significantly decreased. The malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents and catalase (CAT) activity were significantly enhanced. LPS increased the root indole-3-acetic acid (IAA) and gibberellins (GAs) contents, and leaf chlorophyll content. Additionally, nutrient uptake was significantly affected by LPS. RNA-seq data revealed that a total of 1319 genes responded to LPS, of which 573 and 746 genes were up- and down-regulated, respectively. These differentially expressed genes (DEGs) were mainly linked to carbon metabolism, reactive oxygen species scavenging, nutrient uptake and transport, and hormone synthesis/signalling. Taken together, our data provided an essential foundation for future elucidation of the LPS tolerance of citrus plants.