STUDIES OF NECROTIC LESIONS IN CORN STALKS

Littlefield , Larry J., and Roy D. Wilcoxson . (U. Minnesota, St. Paul.) Studies of necrotic lesions in corn stalks . Amer. Jour. Bot. 49(10): 1072–1078. Illus. 1962.—In 3-day-old necrotic lesions in corn stalks caused by Fusarium graminearum, ground parenchyma cells were discolored and small amounts of a dark substance were present in the cells. The walls of phloem cells were also slightly discolored and a small amount of dark substance was present in the xylem cells. In older lesions the discoloration of parenchyma and phloem cells was more intense; many of the cells contained occluding substances; many phloem protoplasts collapsed, and xylem cells were partially to completely occluded. The occluding substance filling the cells appeared to be translocated from the lesion into the vessel elements extending beyond the lesion so that the bundles appeared as long, dark streaks in the stalk. The occluding substance in xylem, but not in phloem or parenchyma, stained with ruthenium red, a result indicating presence of pectin. Pectinase, however, did not remove the occluding substance. The pectinase dissolved the parenchyma cells in healthy tissues but not in the necrotic lesions. Necrosis in naturally infected plants began as small lesions, but the parenchyma cells quickly dissolved leaving the vascular bundles free of ground parenchyma. No occlusions were found in the central vascular system; a few xylem cells in the peripheral vascular system were occluded with the same substance observed in artificially inoculated plants. Phloem was entirely destroyed by the pathogen. The necrosis prevented upward movement of dye solution in the stalk, but did not measurably affect transpiration, probably because the lesions were not large. Yield was reduced in plants when lesions involved more than 50% of the tissue in inoculated internodes. Smaller lesions had no effect on yield.     

Tubular Transport Maxima of PAH and Diodrast Measured Individually in the Aglomerular Kidney of Lophius, and Simultaneously as Competitors Under Conditions of Equimolar Loading

The maximal tubular transfer rates (Tm) of both p-aminohippurate (PAH) and diodrast (3,5-diiodo-4-pyridone-N-acetic acid or iodopyracet) were found to be fixed and reproducible when measured separately in Lophius (goosefish) under standard laboratory conditions. Expressed on a molar basis Tm_PAH was four times Tm_D. However, when these transport competitors were presented simultaneously in equimolar concentrations with the plasma levels of each sufficiently high enough to saturate the carrier system, the relative rates of excretion were reversed with the diodrast transfer rate then four times that of PAH. The combined rate of excretion was far below Tm_PAH alone, and roughly equal to Tm_D. Interaction with a common carrier was indicated by the gradations in degree of inhibition which resulted when plasma concentration ratios of diodrast to PAH were extended from 0.1 to 3.2, and PAH transfer rates expressed as percentage of Tm_PAH were correspondingly depressed from 17 to 1.0 per cent respectively. These observations again point up the inverse relationship between transfer rate and competitive effectiveness which exists for members of a series of substances actively transported by a common mechanism. It appears that carrier affinity and dissociation characteristics may be quite different for various compounds in a series, and also that these parameters may vary significantly from species to species.