Synchronisation of changes in maize growth and hormone levels (abscisic acid and ethylene) during soil drying

X Li1,2, S Wilkinson1, B Forde1 and W Davies1

  1. Lancaster Environment Centre, Lancaster University, UK, LA1 4YQ
  2. Present address: CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia

Improved understanding of plant physiological responses to drought stress in both shoot and root is important for enhancing plant drought resistance. In this study, a 6-day progressive soil drying pot experiment was conducted to investigate the synchronisation of physiological responses in maize (Zea mays L.) leaves and roots. During Days 2-3, when the drought was mild (23-32% soil water content in the drying pots vs. ca. 41% in the well-watered pots), root growth was stimulated. After Day 4, when the drought became severe (<18% soil water content), both root growth and leaf elongation were inhibited. The root ABA level increased gradually with the decrease in root water potential after 2-day of drying. The leaf ABA level significantly increased from Day 4, which was one day before the leaf water potential significantly decreased. The ethylene production from leaves and roots were inhibited by soil drying, which occurred later than the increase in ABA levels in leaves and roots respectively. In addition, the stomatal conductance of the younger leaves decreased from Day 3 of soil drying, which was earlier than the response of the older leaves and synchronous with the early root changes in growth rate, water potential and ABA level. Therefore, with the exception of the stomatal conductance response of the younger leaves, roots showed earlier physiological responses to soil drying than leaves. Root ABA accumulation started synchronously with the changes in root growth rate and root water potential, which suggests that ABA may be involved in regulating the stimulation of root growth under mild drought.