Biomechanical and Morphometric Differences in Triticum aestivum Seedlings Differing in Rht Gene-Dosage

Biomechanical and morphometric comparisons among coleoptiles from wheat seedlings differing in Rht gene-dosage (Rht = 0, 2, 4 doses) are presented in an effort to evaluate the influence of Rht on the mechanics of soil penetration by this organ. Rht is known to reduce seedling establishment compared to the wild type. Data from 3–7-day-old seedlings indicate that Rht reduces tissue elastic modulus E, increases the second moment of area I, and decreases the slenderness ratio (l/r) of coleoptiles.Rht-related changes in E and I are such that the flexural stiffness of coleoptiles from Rht plants does not differ significantly from the wild type-hence the growing coleoptiles of all three genotypes have equivalent biomechanical capacity to penetrate the soil. Rht reduction of coleoptile slenderness ratios confers a capacity to safely sustain higher axial compressive loads compared to coleoptiles with equivalent flexural stiffness but higher ratios. However, wild type seedlings produce longer coleoptiles and longer subcrown internodes than Rht seedlings. Longer coleoptiles deliver the crown node closer to the top of the soil before the crown node extends beyond the lateral confinement of the coleoptile. This reduces the potential for buckling of the subcrown internode and leaves due to the compressive loading of soil. Rht affects a variety of mechanical features whose influence is dependent upon the stage of seedling growth and the degree of soil compaction. However, at equivalent depths of burial which exceed the maximum length of coleoptiles and moderate soil compaction, Rht is biomechanically disadvantageous to seedling establishment.