Comparing root porosity of sunflower adventitious root segments using cross-sectioning and buoyancy method under hypoxic condition

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Two well-known methods of root porosity measurement (i.e. buoyancy and cross-sectional) were used to evaluate the porosity of adventitious roots of 3-day hypoxia treated sunflower (<I>Helianthus annus</I> L.) cultivars to address the effect of hypoxia on root porosity as well as advantages and disadvantages of each method. In the first experiment, length of adventitious roots of two sunflower cultivars (CMS14 × R-864 and Hysun-33) was divided to three segments as apical, middle, and basal portions and porosity was measured via both methods. In buoyancy method, root porosities of Hysun-33 and CMS14 × R-864 cultivars were 5.12% and 6.47% in aerated and 11.58% and 15.71% in hypoxic condition, respectively. There is no statistically significant difference between cultivars in aerated condition. In contrast, more than twice additional aerenchyma formation was observed due to hypoxic condition in comparison to aerated condition. Results of cross-sectional method showed that middle portion of adventitious roots is the place that aerenchyma initiates to form, but well-developed aerenchyma was seen at about 80-90 mm behind the root apex (basal portion) under hypoxia. The results of root porosity of basal portion of adventitious roots of four sunflower cultivars (CMS14 × R-864, CMS51 × R-14, CMS19 × R-N1-118 and Hysun-33) showed higher amounts of root porosity in buoyancy method in comparison to cross-sectional method.