Light dosage for 50% inhibition of epicotyl growth

In the previous section it was pointed out that epicotyl growth can be inhibited by light. Seedlings were germinated as outlined in MGCNL 56. White light from a 15OW incandescent source (with internal reflector) was administered to seedlings 48 hours old. No light treatments exceeded 30 minutes; intensity was controlled by a rheostat. Table 1 shows the dosage-response relationship for Sprite, a yellow sweet corn variety. As light dosage is increased to nearly 100x, the length of epicotyls is reduced to less than 1/2 those developed in continuous darkness. It is interesting to note that over this range little or no difference is produced in coleoptile length. It may be concluded that the energy for stimulating coleoptile elongation is of the order of 100x less than the energy required for 50% reduction in epicotyl lengths.

Table 1. Effect of light dosage on epicotyl and coleoptile lengths of seven-day-old seedlings incubated in the dark except for the above light treatment. Light administered to 48-hour-old seedlings; no light treatments exceeded 30 min.

Bernard C. Mikula and Amy Smith


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