Effects of the growth retardant ancymidol on sunflower morphology, pigments, and leaf anatomy

Abstract

Ancymidol, (α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidine methanol) at 66 and 132 mg/l, caused significant decreases in height, number of nodes, leaf area, fresh weight, and dry weight of four varieties of Helianthus annuus L. (sunflower). Treatment with ancymidol resulted in a darker green appearance of the foliage and significantly increased chlorophyll per unit area, as measured spectrophotometrically, in all varieties compared to the control. However, significant increases in chlorophyll a, chlorophyll b, and total chlorophyll were found in only two varieties when measured on a weight basis using high performance liquid chromatography (HPLC). Ancymidol application significantly increased the levels of three xanthophylls including neoxanthin, violaxanthin, and lutein in the four varieties, but had no effect on β-carotene measured on a weight basis by HPLC. Treatment with ancymidol at 132 mg/l active ingredient significantly increased leaf thickness, palisade cell height, and number of cells per unit area, and significantly decreased percentage of intercellular space in developing cv. Mammoth Russian leaves. Significant increases in stomatal density and total stomata per adaxial leaf surface area were also attributed to ancymidol application. Treatment with gibberellic acid (GA₃) reversed the effects of ancymidol on leaf anatomy. The modification in leaf anatomy due to ancymidol treatment in developing cv. Mammoth Russian sunflower leaves did not occur in mature leaves. However, application of ancymidol to mature cv. Mammoth Russian sunflower leaves did significantly increase chlorophyll levels on a unit area and unit weight basis measured spectrophotometrically. Total chlorophyll per leaf was also significantly increased. Thus, an uncoupling of darker green foliage and modified leaf anatomy was found. Application of GA₃ also reversed the effects of ancymidol on developing leaf chlorophyll levels. Significant increases in specific leaf weight due to ancymidol treatment occurred in developing and mature leaves of cv. Mammoth Russian sunflower.