Ethylene, Nitrate and Nitrite Interactions in the Promotion of Dark Germination of Common Purslane Seeds

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Abstract
Ethylene (10 μ1−1) caused about one-third of highly dark-dormant seeds of common purslane (Portulaca oleracea L.) to germinate in the dark. Attempts were made to increase germination in the dark with nitrate and ethylene combinations. When applied directly to the seeds, KNO3 did not stimulate germination and KNO3 plus ethylene did not increase germination above that of ethylene alone. Pre-incubation of seeds in KNO3 for 4 to 7 d before the ethylene applications significantly increased germination. The effects of the KNO3 pre-incubation were additive at each of four ethylene concentrations (0.1–100 μ11−1). Potassium nitrate was effective only when ethylene followed the KNO3 pre-incubation period. Potassium nitrite stimulated about 25 per cent of the seeds to germinate without a pre-incubation period and without ethylene. Also, ethylene plus KNO2 enhanced germination above that achieved by either stimulus alone. Silver nitrate did not block the ethylene promotion of germination, but reversed the typical ethylene inhibition of seedling growth following germination. The results support the views that nitrate exerted its effect via conversion to nitrite within the seed and that the rate of nitrate conversion may be a limiting factor in the dark germination of common purslane seeds. Ethylene may facilitate nitrite activity by increasing seed sensitivity to the stimulus.

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