SEED DORMANCY IN AVENA-FATUA - INTERACTING EFFECTS OF NITRATE, WATER AND SEED COAT INJURY

In experiments conducted under controlled conditions, KNO3 (50 or 100 mM) promoted germination of a dormant strain (AN 474) of Avena fatua w hen either one or two holes were pierced in the lower (adaxial) surfac e of the caryopsis in contact with the nitrate solution. Germination w as increased by increasing either the KNO3 concentration or the number of holes in the seed coat. The germination response induced by the ap plication of water to a hole pierced in the upper surface of the caryo psis was increased by pre-treatment of the intact caryopsis with KNO3. Treatment with either 50 or 100 mM KNO3 caused a transient reduction in embryo water content of intact caryopses, but increased the nitrate and amino-N content of pierced caryopses prior to germination. Supply ing a 100 mM solution of KNO3 to pierced caryopses reduced the total w ater potential and osmotic potential of the embryo, and increased its pressure potential by the same amount as an equimolar solution of KCl; however, while both treatments promoted germination, the KNO3 induced more rapid germination than the KCl. Both treatments also increased t he K+ content of the embryo, the KNO3 again having the greater effect. These results are consistent with the hypothesis, based on our previo us investigations, that KNO3 promotes germination of dormant caryopses by accumulating in the embryo where it acts osmotically to increase w ater uptake. It is also postulated that, in contrast to KCl, KNO3 may combine an osmotic effect on water uptake with a nutritional effect on protein synthesis.