Translocation of Carbon in Powdery Mildewed Barley

This paper compares translocation in healthy and powdery mildew (Erysiphe graminis f. sp. hordei, race CR3) infected barley (Hordeum vulgare, variety Manchuria). The sink-like properties of the powdery mildew infection were used to determine what effect imposing a sink in the midst of normal source tissue (mature primary leaf) had on the translocation process. The pattern of translocation was determined by monitoring the movement of (14)C which was photosynthetically incorporated from (14)C either by the primary or second leaf. In the healthy primary leaf of barley, (14)C fixed in the tip section of the blade was preferentially translocated to the root, whereas (14)C fixed in the basal section was primarily translocated to the shoot. When a sporulating powdery mildew infection was present in the mid-section of the primary leaf, (14)C fixed in that section or in the acropetal healthy tip section readily accumulated in the infection area. Labeled carbon fixed in the healthy basal section was translocated into the other parts of the plant with only a small fraction moving acropetally into the infected mid-section. The (14)C fixed by the second leaf was translocated to the root and younger shoot with very little entering the primary leaf. The presence of the mildew infection did not alter this pattern.