Grain filling Pattern by Measurement of Indolyl-3-Acetic acid and Gibberellin and Cytokinin content in the Grains

Grain filling patterns and their relationships with indole-3-acetic acid (IAA) and gibberellin (GA contents in the grains and roots during grain development were examined inGrain growth rate (GGR), gibberellins,cytokinin and indolyl-3-acetic acid (IAA) levels were studied at different grain type and position within developing grains of wheat (Triticumaestivum L. var. Bahar). Main spikes were divided into three grain positions included proximal, middle, and distal regions, and further into two grain types included basal and apical grains. Three grain filling patterns based on the filling rate of superior and inferior spikelets were observed. All spikelets started filling early and fast at the early filling stage. All spikelets filled slowly at the early filling stage and reached the maximum filling rate late and superior spikelets started filling and reached the maximum filling rate much earlier than the inferior ones.Grain dry matter accumulation, gibberellins including GA1, GA3 and GA4,and IAA levels were determined in ten labeled spikes which sampled five times, seven days interval startedfrom seventh day after anthesis (DAA) up to 30th DAA, and also in maturity. Gibberellins and IAA contentsincreased until 16th and23stDAA, respectively.Changes in Z + ZR contents in the superior and inferior spikelets were associated with the grain filling patterns. The maximum level of grain growth rate (GGR) was observedat 16th DAA. Furthermore, the differences in both gibberellins and IAA contents, among spikelets in differentregions of the spike, and also among grains within a spikelet were correlated with the differences in dry matteraccumulation. Grain filling percentage was significantly correlated with Z + ZR contents in the grains and roots at the early and middle grain filling stages. IAA and GA (GAl + GA3 + GA4) contents in the grains and roots were not significantly correlated with grain filling percentage. The results suggest that cytokinins in the grains and roots during the early phase of grain development play an important role in regulating grain filling pattern and consequently influence grain filling percentage.