Note on relationship between leaf soluble carbohydrate and chlorophyll concentrations in maize during leaf senescence

Abstract

Leaf senescence is typically associated with loss of chlorophyll and decline in photosynthetic capacity. The objectives of this study were: (i) to quantify the relationship between chlorophyll (SPAD) and soluble-carbohydrate concentrations in maize ( Zea mays L.) leaves during leaf senescence and (ii) to examine whether this relationship differed between an old and a recent maize hybrid. Field experiments were conducted in 1995 at two locations. A range of leaf soluble-carbohydrate concentrations and SPAD values was obtained through various source-manipulation of source activity by defoliation and thinning. Defoliation treatments were imposed at 3, 4, and 5 weeks after silking. The thinning treatment was imposed at 3 weeks after silking. Two maize hybrids were composed: Pride 5 (old) and Pioneer 3902 (recent). Leaves at three leaf positions, near the topmost ear and the ear internode were sampled at weekly intervals, from 3 weeks after silking until visual completion of leaf senescence. Leaf and internode soluble-carbohydrate concentration declined following defoliation, although the response in leaves was delayed compared to that in the stem. SPAD readings and soluble-carbohydrate concentrations were positively correlated below a plateau value of 55 mg glucose equivalents g −1 leaf. The correlation between SPAD and soluble-carbohydrate concentration was similar for the old and recent maize hybrid.