OCCURRENCE OF A STELAR LESION DURING IMBIBITIONAL CHILLING OF ZEA MAYS L.

Radicle growth of the corn inbred Oh5lA was reduced by imbibitional chilling at 5 C. The effect was mediated by the initial moisture of the kernel prior to hydration. Five percent initial moisture kernels were injured while 13% initial moisture kernels were not. The formation of a structural lesion in the radicle during the first 24 hr of hydration at 5 C of 5% initial moisture kernels was correlated with subsequent radicle growth reduction at 25 C. The lesion did not form during hydration of 13% initial moisture kernels at 5 C, in kernels hydrated at 25 C, in unimbibed kernels, or in heat-killed, coldimbibed kernels. The lesion also did not appear during the imbibitional chilling of the corn inbred B8 which did not exhibit radicle growth reduction. Two sources of Oh5lA with similar lesion frequencies were different in the severity of growth reduction. While the lesion became sealed at 25 C subsequent to cold hydration, growth reduction differences were not fully explained by this phenomenon. In one source more seedlings exhibited reduced growth than expected from the frequency of observable lesions. Therefore, other types of damage contributed to the reduction of radicle growth. AFTER COLD stress (2 to 15 C) during imbibition, various seeds exhibit injury as a loss of viability or reduced growth during subsequent germination at favorable temperatures (20-30 C). Injury is dependent upon the initial seed moisture content prior to imbibitional chilling in cotton (Gossypium hirsutum L.) (Christiansen, 1969), lima bean (Phaseolus lunatus L.) (Pollock, 1969), garden bean (Phaseolus vulgaris L.) (Pollock, Roos, and Manalo, 1969), soybean (Glycine max (L.) Merr.) (Obendorf and Hobbs, 1970; Hobbs and Obendorf, 1972), sorghum (Sorghum bicolor Moench.) (Phillips and Youngman, 1971), and corn (Zea mays L.) (Cal and Obendorf, 1972). Seed at low initial moisture content (5 to 8% on a fresh weight basis) is injured while seed at 13-20%o initial moisture is not. In corn the injury was independent of energy metabolism when measured by 02 uptake of intact kernels, ATP content of embryos and embryonic axes, adenylate energy charge of embryos, and mitochondrial activity of embryos (Cohn and Obendorf, 1976). From this study it was concluded that the mechanism of imbibitional chilling injury of seeds was, therefore, probably different from the l Received for publication 28 March 1977; revision accepted 2 August 1977. Contribution from the Department of Agronomy, New York State College of Agriculture and Life Sciences. Agronomy Series paper 1202. This study was part of a dissertation filed in partial fulfillment of the requirements of the degree of Doctor of Philosophy in Plant Physiology, Cornell University, Ithaca, New York. The authors thank Dr. D. J. Paolillo, Jr. for his generous assistance and consultation. 2 Department of Biology, University of Virginia, Charlottesville 22901. mechanism of injury observed in fully hydrated plant tissues as described by Lyons (1973). Cal and Obendorf (1972) observed that imbibitional chilling of corn primarily affected root rather than shoot growth. In many cases radicle tip abortion occurred (Obendorf, Cal, and Hobbs, 1971). A similar observation was made by Christiansen (1963) in his studies of cotton. Cold hydration of cacao (Theobroma cacao L.) resulted in the destruction of cotyledonary tannin cells (Ibanez, Casas, and Redshaw, 1965). In yeast (Saccharomyces cereviseae) cell lysis and loss of cell contents were observed after cold hydration (Van Steveninck and Ledeboer, 1974). Based upon these reports of structural injury during hydration, an anatomical study of Oh5lA inbred corn was initiated to determine if gross structural damage could be observed as a result of imbibitional chilling. A stelar lesion was observed following the imbibitional chilling of low initial moisture corn kernels. The objectives of this study were to characterize the conditions necessary for lesion formation and to estimate the contribution of the lesion to the radicle growth reduction observed after imbibitional chilling. MATERIALS AND METHODs-Seed stocksOh51A inbred corn was chosen for study based upon its sensitivity to imbibitional chilling (Cal and Obendorf, 1972). Texas male sterile kernels (Oh51A-PA(T)) were obtained from Pennsylvania Foundation Seed (1969 harvest). Normal cytoplasm kernels (Oh51A-IN(N)) were originally obtained from C. 0. Grogan, Dept. of Plant Breeding and Biometry, Cornell University,