ObjectivesThe objective of this study was to reveal effects of zinc (Zn) deficiency stress on plant root growth, endogenous IAA content and key auxin transport genes expressions in roots of maize. It would provide some molecular biological evidences of maize plants subjected to Zn deficiency stress.

MethodsThe maize cultivar Zhengdan958 was chosen as the test crop. Hydroponic culture experiment was conducted with Zn 0 and 1.0 μmol/L treatments. The plant shoot and root biomass were weighted. Dry plant samples were digested with HNO₃-H₂O₂ for Zn determination by atomic absorption spectrophotometer. Root samples were stored in FAA solution (70% alcohol︰38% formaldehyde︰acetic acid = 90︰5︰5 by volume ratio) prior to measurements. The root systems were digitized for image analysis with WinRHIZO sofware. Root length, diameter, volume and surface area were obtained. The endogenous indole-3-acetic acid of fresh root samples was determined by gas chromatography-mass spectrometer. Real-time quantitative PCR technique was used to quantify the expression levels of ZmAUX1 and ZmPIN1c in the roots.

ResultsThe results showed that Zn content of maize shoots without Zn application was below the critical level of 20 μg/g. Zn deficiency stress significantly decreased shoot dry weight, root surface, root volume, root diameter, total root length, total lateral root length, and average lateral root length, but increased lateral root density. The concentrations of indole-3-acetic acid (IAA) within the regions of 2 cm from root tips were lower by about 30% under Zn deficient condition than normal Zn treatment. Moreover, there was no significant difference for IAA content between the two regions under no Zn added. The expressions of ZmAUX1 and ZmPIN1c were significantly declined by limited Zn supply.

ConclusionsZn deficiency might change IAA distribution in roots through inhibiting expressions of ZmAUX1 and ZmPIN1c, which would have a negative influence on root growth and development.