Abstract: We explored the relationship between root depth and compensatory growth of corn seedlings during post-drought re-watering from April 20 to June 3, on the basis of leaf cytokinin induced by roots. Four treatments including wetness, wetness with root cutting, re-watering, and re-watering with root cutting were set up. At the end of drought stress period (28 days after seedling emergence), root cutting was conducted to remove deep roots as cutting root system into two halves by horizontal cross in the middle position of pot longitudinal section with a thin knife. Compared with wetness treatment, drought stress inhibited corn growth by decreasing biomass of the whole plant. Rewatering induced roots to produce cytokinin in the absence of root cutting, which was then transported to leaves through the xylem sap. The enhanced cytokinin in leaves increasednet photosynthetic rate and biomass of the whole plant. As a result, faster growth occurred in corns during post-drought re-watering without root cutting. Under root cutting, although stimulated by re-watering, the shallow roots could not induce high-level production of cytokinin. We found no changes of cytokinin content and net photosynthetic rate in leaves under root cutting treatments. The biomass of whole plant did not increase rapidly, and no rapid growth occurred in corn with root cutting. In summary, rootinduced cytokinin is a key factor in corn compensatory growth during postdrought rewatering. Root cutting leads to the loss of deep roots, and shallow roots of corn hardly produce cytokinin, which cannot result in compensatory growth. Our results showed that deep roots play a key role in the compensatory growth of corn during post-drought re-watering.

Key words: drought stress, photosynthetic pigment, chlorophyll fluorescence parameter, Cyclobalanopsis glauca