Effects of Endophytic Infection by Fusarium moniliforme on Corn Growth and Cellular Morphology

Kernels of corn, Zea mays, were inoculated with Fusarium moniliforme to analyze seedling growth and development during endophytic, symptomless infection. In planta F. moniliforme distribution and seedling growth, expressed as shoot diameter, plant height, leaf length, and dry weight, were examined weekly for 28 days after planting. Even though no visible disease symptoms developed, F. moniliforme was isolated from most segments taken from seedlings grown from inoculated, but not noninoculated, kernels from the earliest to the latest sampling. F. moniliforme did not alter the rate or percentage of kernel germination, but seedlings grown from inoculated kernels had suppressed shoot diameter, plant height, leaf length, and plant weight 7 days after planting. However, seedling growth from inoculated kernels was similar to or greater than that from noninoculated kernels at 28 days. Histological modifications in seedlings grown from inoculated kernels included accelerated lignin deposition in shoots and modified chloroplast orientation in leaves. In summary, gross morphology and histology were altered in corn seedlings during symptomless, endophytic infection by F. moniliforme.

Evidence that circularly dichroic chlorophyll forms a-682 and a-710 are oriented at right angles to the thylakoid membranes of whole chloroplasts, and that the circular dichroism is light-dependent

Chloroplasts from the pea (Pisum sativum L.) suspended in iso-osmotic buffered medium were oriented by flow in specially constructed cuvettes and examined for circular dichroism (c.d.). In one cuvette the flow was transverse to the direction of the light-path, but the other cuvette was designed so that flow and the light-path were coaxial. The induced orientation is such that the chloroplasts appear to move edgewise. C.d. was maximum when the light-path lay in the plane of the chloroplast disc. The intense c.d. of intact chloroplasts ascribed by Gregory & Raps [Biochem. J. (1974) 142, 193-201] to bulk chlorophyll a was found to contain two components, one the split-exciton type centred at 682nm and the other a simple maximum at 700-710 nm. The chlorophyll a-710 form was distinguished by its greater dependence on chloroplast orientation. The preferred direction of the transition moment in both chlorophyll forms was at right angles to the plane of the chloroplast, that is, at right angles to the plane of the thylakoids. This is in conflict with several reports based on polarization of fluorescence. It is suggested that the present effect is due to thylakoid-thylakoid interaction. Evidence for this is the reversible diminution in the c.d. signal caused by illumination in the presence of electron-transport reagents. It is argued that the c.d. is an indicator of chlorophyll movement, or changes in the thylakoid-thylakoid distance, possibly related to ion movement, affecting energy transfer between photosynthetic units.