Effect of exogenous application of ABA and CK at different stages of grain development on some physiological aspects of source and sink relationship in two bread wheat cultivars

Plant growth regulators are the most important internal regulatory agents that adjust plant growth and development in relationship to gentic and environmental conditions. Among the plant growth regulators, cytokinins (CK) and abscisic acid (ABA) not only regulating the process of senescence and remobilization, but also have major roles on formation of sink and source strength and capacity. This study carried out to determine effect of exogenous application of CK and ABA (50 µM) on some physiological aspects of source and sink strength of two wheat cultivars (Marvdasht, Zagros), using a split plot arrangment based on Randomized Complete Block Design (RCBD) with three replications, in experimental field of the univereisty of Tehran, in 2005-2006 growing season. Results showed that when these plant growth regulators applied at different stages of grain growth including cell division (CD) and grain filling (GF), grain yield, biomass, harvest index (HI), 1000 grain weight and grain no. spike-1, significantly changed. Application of CK at CD stage, led to higher grain yield, biomass and grain no. spike-1. However, ABA at GF stage and CK at CD stage increased HI and significantly affected soluble proteins, chlorophyll content, photosynthesis rate, stomatal conductance and ABA and CK concentrations in flag leaves. In contrary, exogenous application of ABA increased ABA concentration of developing grains, while had inverse effect on IAA of the same grains. It can be coneluded that exogenous application of CK at cell division stage in grain growth phase may significantly improve biomass and grain yield.