Impact of Growth Retardants on Corn Leaf Morphology and Gas Exchange Traits

Abstract

Growth retardant (GR) application often produces compact plants with dark green foliage and reduced leaf size. These morphological alterations can affect leaf gas exchange and biochemical traits associated wiith photosynthesis. We conducted greenhouse experiments by growing corn (Zea mays L.) plants under optimum water and nutrient conditions to evaluate the impact of two GR treatments a seed‐applied treatment of BAS110.. W[1‐(2,4‐dichlorophenyl)‐2methoxy‐1‐methyl‐2(1H‐1,2,4‐triazol‐1‐yl) ethanol] at 250 mg kg‐1 of seed and an ethephon (2‐chloroethyl phosphonic acid) treatment (a foliar‐applied solution containing 100 μg a.i ehephon L−1 of water applied at three‐leaf stage), on leaf gas exchange characteristics [leaf stomatal conductance to H2O vapor (g5), leaf intercellular CO2 concentration (Ci) and leaf CO2 exchange rate (CER)] and water use efficiency, and other plant morphological traits. A CER vs. Ci response curve was also determined to assess the carboxylation efficiency for control and treated plants. Both GR reduced total plant leaf area and dry weight by about 21 to 31% relative to the control but increased specific leaf weight and weighted stomatal density by 7 to 19%. Leaf protein and chlorophyll contents were nearly doubled in GR‐treated plants. Leaf g3 Ci and CER were significantly higher in GR‐treated vs. control plants while CER/gs was significantly lower in GR‐treated plants. The CER vs. Ci response curve exhibited higher initial slope in GR‐treated plants compared to control plants, indicating a higher carboxylation efficiency. Our data indicate that GR application reduced leaf sie, concentrated photosynthetic pigments and enzymes, and enhanced CER of corn.