Water uptake during germination of barley

Abstract

The amount of water taken up by germinating barley seeds was determined 2–10 h after sowing. The increase in fresh weight was the same in seeds sown on plates containing 9 to 25 ml of water or immersed in tanks of aerated water; but it was significantly lower in seeds sown on 6 ml. Barley grains transferred from 6 to 25 ml of water increase their rate of uptake and within 2 h they have taken up a similar amount of water as seeds sown on 25 ml. Water uptake is also influenced by seed weight; heavy seed take up more water than light seed but their percentage increase in fresh weight is lower. Variation in seed weight and water uptake cannot be ignored in attempts to relate water uptake to germination. Seed germination begins with the uptake of water. Water in excess of the volume needed for germination to begin may, however, prevent or delay germination [1–3] and subsequently, at least in barley [4, 5] it inhibits coleoptile growth. These effects may result from a reduced supply of oxygen to the embryo [2,3, 6–8]. Seeds whose germination is delayed, or inhibited, by excess water are said to be water-sensitive [1, 2, 6–8]. A study of water uptake by germinating barley grains showed: ( 1) as the amount of water available to the barley increased so did the amount taken up, ( 2) as the amount of water taken up increased, percentage germination decreased; these results led to the suggestion that “a process initiating germination is inhibited by an excess of water within the corn” [1]. The response of barley seeds to differences in the ambient volume of water is seen as early as 6–12 h after sowing [9]; at 6 h, percent germination is higher on 20 ml than on 9 ml of water but by 12 h, germination on 20 ml is inhibited and barley seeds are showing the typical response to increases in the ambient volume of water. In view of this response, we have determined the amount of water taken up by barley seeds in the first 10 h after sowing. We show that inhibition of germination is not due entirely to an increased uptake of water.