Gibberellin‐like Substances in Developing Barley Grain and Their Relation to Dry Weight Increase

Gibberellin‐like activity of two varieties of barley ( Hordeum vulgare L.) at different stages of grain development was determined by barley endosperm bioassay (acid phosphatase bioassay). Activity of the acidic ethyl‐acetate fraction (“free” GAs) in both varieties displayed two maxima, a first maximum at the 9th day and a second one 20 to 21 days after pollination. Activity of the n ‐butanol fraction (“bound” GAs) first dropped to a minimum level at the 9th day, then increased to reach a maximum 32 days after pollination, and finally decreased again towards maturity. From the 9th day after pollination, a conversion of “free” GAs to “bound” GAs has probably occurred. From the 12th day after pollination, the curves of rate of dry weight increase and of “free” GAs run nearly parallel, but the latter reached its maximum about 2–4 days earlier than the former. The results indicate that gibberellins may participate in the regulation of the accumulation processes into the barley grain.