Seed dormancy in Avena fatua: Interacting effects of nitrate, water and seed coat injury

In experiments conducted under controlled conditions. KNO₃ (50 or 100 m M ) promoted germination of a dormant strain (AN 474) of Avena fatua when either one or two holes were pierced in the lower (adaxial) surface of the caryopsis in contact with the nitrate solution. Germination was increased by increasing either the KNO₃ concentration or the number of holes in the seed coat. The germination response induced by the application of water to a hole pierced in the upper surface of the caryopsis was. increased by pre-treatment of the intact caryopsis with KNO₃. Treatment with either 50 or 100 m M KNO₃ caused a transient reduction in embryo water content of intact cary-opses, but increased the nitrate and amino- N content of pierced caryopses prior to germination. Supplying a 100 m M solution of KNO₃ to pierced caryopses reduced the total water potential and osmotic potential of the embryo, and increased its pressure potential by the same amount as an equimolar solution of KC1; however, while both treatments promoted germination, the KNO₃ induced more rapid germination than the KCI. Both treatments also increased the K⁺ content of the embryo, the KNO₃ again having the greater effect. These results are consistent with the hypothesis, based on our previous investigations, that KNO₃ promotes germination of dormant caryopses by accumulating in the embryo where it acts osmotically to increase water uptake. It is also postulated, that, in contrast to KCI, KNG₃ may combine an osmotic effect on water uptake with a nutritional effect on protein synthesis.