Kinematic analysis of leaf growth in grasses: a comment on Spatial and temporal quantitative analysis of cell division and elongation rate in growing wheat leaves under saline conditions.

Hu and Schmidhalter (2008) conducted a study with wheat seedlings growing in saline and non-stressed (control) conditions with the aim of identifying and quantifying the cellular basis for the reduction in leaf growth. We applaud their goals as salinity is an important issue for plant ecology and food production; however, we have concerns about the methodology used and the subsequent conclusions that are drawn. Hu and Schmidhalter measured independently the leaf elongation rate and the epidermal cell length distribution in the growth zone of leaf 4, and used these data to investigate the spatial distribution of cell division rates and the kinetics of cell elongation in the abaxial epidermis. They reported that the saline treatment significantly reduced leaf elongation rate by about 18% and final epidermal cell length by about 12%. Based on these data, and using established methods, we calculate a 6% reduction in the cell production rate due to salinity (see below). In contrast, they reported that the saline treatment significantly reduced the cell division rate by approximately 30% in the zone of most active meristematic activity and that overall cell production (the integral of cell division rate throughout the meristem) was reduced by approximately 24% (see maximum cell flux in their figure 6). This implied that cell production was impaired more by saline conditions than cell elongation. We have looked carefully at the methodology used and the data pre-