Light and temperature-related behavior of coleoptiles and epicotyls

Several lines of corn we have been examining for sensitivity to light and temperature show remarkable differences which may have some use in corn breeding. Since the coleoptile and epicotyl (first internode) are responsible for getting the shoot through the soil, these two tissues and their responsiveness could be selected for in simple seedling tests which take less than a week to run. The behavior of these two tissues has been quite spectacular among certain lines and has been used routinely in freshman classes to demonstrate light sensitivity in plant tissues. Table 1 gives some of the preliminary data we have collected on several commercially available lines--mostly sweet corns.

Seeds were germinated on 9" x 9" x 2" glass-covered stainless steel pans lined with toweling and facial tissue moistened with 70 cc of tap water. Plants were grown 60 cm from a light source supplied by fourteen 200 W cool white fluorescent lamps supplemented by twelve 50 W incandescent bulbs. Continuous light conditions were maintained for the seven-day test period. 20 coleoptiles and epicotyls were measured and recorded as average values in Table 1. Since different wavelengths have been reported to be effective in the control of seedling growth, plants were grown under plastic filters of blue, green, yellow, red and far-red along with controls under white light and complete darkness for the seven-day period. Duplicate experiments were run in growth chambers set for 21 C and 27 C.

Different levels of temperature sensitivity can be seen for dark-grown seedlings for both coleoptiles and epicotyls. Under filters, Silver Queen showed the greatest temperature differences for coleoptile elongation while, except for far-red, little temperature-related variation was noted for its epicotyls. Far-red filters permitted the greatest amount of elongation though generally less than that of dark-grown seedlings. Most coleoptiles show elongation in the dark; Silver Queen is exceptional since elongation appeared to be inhibited under dark conditions. In yellow light most epicotyls show reduced elongation. MM 475, a local field-corn hybrid, shows quite vigorous coleoptile elongation under all filters while the epicotyls show considerable inhibition for the same filters. In this hybrid it would seem from seedling performance that the coleoptile is responsible for getting the shoot above ground under reduced light conditions.

Table 1.

Bernard C. Mikula and Amy Smith


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