PHOTOSYNTHETIC PARAMETERS WERE MODIFIED IN WHEAT (TRITICUM AESTIVUM L.) FLAG LEAVES BY TWO PHENYLUREA CYTOKININS

The effects of two cytokinin-like substances, 3-CP-2PU and 3-CP-4MPU (100 mu mol L-1), on such photosynthetic parameters as stomatal conductance (G(s)), net photosynthetic rate (P-n), enzyme activities of carbonic anhydrase (CA) and phosphoenolpyruvate carboxylase (PEPC), and chlorophyll and protein contents in wheat flag leaves were investigated. The studied parameters were measured on the seventh and fourteenth days after the chemical treatment, as both time periods involve the early grain-filling stage. The 3-CP-2PU-treated leaves showed an increase in P-n and CA and PEPC activities on the seventh day. In contrast, the treatment with 3-CP-4MPU decreased G(s) and P-n but induced both enzyme activities in a higher degree. On the fourteenth day, both compounds opened the stomata approximately equally (similar to 50%), but their stimulating effect on P-n was different. Flag leaf chlorophyll and soluble protein also increased, especially in the 3-CP-4MPU-treated leaves. Higher P-n of the treated flag leaves at the early filling stage was positively associated with grain yield, a higher number of grains per plant, and 1000-grain weights. This study demonstrates for the first time the ability of two phenylurea compounds to increase the photosynthetic capacity of wheat flag leaves.