The Growth Zone of Maize Leaves is an Ideal Model System for Systems Biology Approaches to Investigate the Effects of Drought Stress on Organ Growth Regulation

AbstractDrought is the most important yield-limiting factor under natural and agricultural conditions and therefore detailed knowledge of its impact on plant growth regulation is crucial. The maize leaf represents an attractive system for growth studies, because of its spatial gradient, allowing sampling of dividing, expanding and mature cells at the same time, and its big size, providing enough material for molecular analyses: a big advantage over the model plant Arabidopsis thaliana.By means of a kinematic analysis we showed that drought inhibits leaf growth by reducing cell division rates in the meristem and cell expansion rates in the elongation zone. A transcriptome analysis provided a molecular basis for the observed inhibition of cell division rates, but also pointed at distinct effects on the development of the photosynthetic machinery, and antioxidant and redox systems. The effects on these pathways were subsequently confirmed by detailed biochemical analysis of the activity of key enzymes and quantification of metabolites.We demonstrated the functional significance of the identified transcriptional and physiological changes, showing that 1. Increasing the antioxidant capacity in the growth zone, by overexpression of iron superoxide dismutase, increases leaf growth under control and drought conditions. 2. Increased expression of photosynthesis genes under stress facilitates faster growth upon re-watering compared to unstressed controls