The epidermis of the wheat leaf is a single cell layer organized as longitudinally oriented parallel rows of cells that are elongated in the direction from base to leaf tip. Some of the epidermal cells differentiate into trichomes, the unicellular unbranched epidermal outgrowths. Trichomes form a specific spacing and size pattern on leaf blade surface; their size ranges from several mkm to millimeters. Different wheat cultivars characterized by different pubescence density and the trichome length distribution. Notably, trichomes in wheat arranged in rows at a similar distance from each other. We put forward a simple phenomenological model to account for this pattern formation on growing linear leaf blade.

We assume a simple mechanical cell-based model for symplastic growth of linear leaf containing the following steps: (1) in the direction of the leaf width generation of an initial cell layer from one cell due to cell growth and division, (2) in the direction base to leaf tip generation of parallel cell rows from every cell of the initial layer without either movement of the cells or new contacts between them and accompanied by mutual adjustment between all the cells. Also we assume that on the second step cells of initial layer produce some substances which diffuse along the cell rows and mark zones of stemness, amplification and elongation characterizing by its growth function and division rate.

In the work hypotheses are tested that the trichome spacing pattern is established in amplification cell zone by the following mechanism selecting single trichome cell from otherwise equivalent epidermal cells. We propose that trichome produce a substance which diffuses along the cell row and inhibits the formation of other trichomes. We assume that the postulated inhibitor is destroyed by epidermal cells, so that a gradient is set up around a trichome cell, and that there is a threshold level of inhibitor below which development of the trichome cell begins (the above-threshold region defining an inhibitory zone). It is supposed that an epidermal cell embarks upon an irrevocable course of differentiation into trichome as soon as the concentration of inhibitor falls below threshold.

This model was used to fit experimental data on quantitative characteristics describing wheat leaf pubescence obtained by the method LHDetect2 (http://wheatdb.org/lhdetect2). We have optimized parameters of the model by fitting different patterns of trichomes distribution on the leaf blade for different wheat cultivars.

wheat leaf; trichome patterning; symplastic growth; computational model