Relationship between cytokinin content and dry matter accumulation in different position and types of grains within spike and spikelet of wheat

Dry matter accumulation and cytokinin (zeatin and zeatin riboside) levels of grains in various positions within the wheat (Triticum aestivum L. Var. Pishtaz) spike and spikelet were investigated during the grain filling duration. This experiment was conducted in greenhouse of Islamic Azad University¡ Saveh Branch¡ in 2010-11 farming year. Main shoot of wheat were partitioned into proximal¡ middle and distal regions and further into bold (basal) and small (apical) 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 indicate that the cytokinin level increased rapidly from about 7 until 15 days after anthesis and then decreased depending upon the position of grains in spike and spikelet. The differences in cytokinin 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. Higher zeatin and zeatin riboside contents in the grains at the early grain filling stage¡ may promote the division of endosperm cells¡ thus constitute a powerful sink¡ and enhance assimilate migration and its accumulation in the developing grains. The results suggest that cytokinins 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.