Determination of Indole-3-acetic Acid at Different Positions and Types of Grains in Wheat by Fluoressence Spectroscopy

Dry matter accumulation and indole-3-acetic acid (IAA) level of grains in various positions within the wheat (Triticum aestivum L. Var. PBW-343) spike and spikelet were investigated during the grain filling period. Mother shoots were partitioning into proximal, middle and distal regions and further into bold and small grains. Ten labeled spikes were sampled every 4 days from 3 days after anthesis (DAA) to 23 DAA, and every 7 days from 23 DAA to maturity. Results have shown that the IAA level increased rapidly from about 7 until 19 days after anthesis and then decreased depends upon the position of grains in spike and spikelet. The differences in IAA levels, both among spikelets in different regions of the spike and also among grains within a spikelet, were positively correlated with the differences in dry matter accumulation. The close spatial and developmental correlation between IAA concentration and dry matter accumulation indicates a causal relationship between endosperm cell division and/or enlargement and IAA levels. The results suggest that IAA in the grains during the early phase of grain development play an important role in regulating grain filling pattern and consequently influence grain filling percentage.