Stress-mediated enhancement of β-amylase activity in pearl millet and maize leaves is dependent on light

Abstract

Exposure to light stimulates β-amylase activity in leaves of etiolated seedlings of pearl millet (Pennisetum americanum) and maize (Zea mays). Intercellular fractionation showed that nearly all of the β-amylase activity in the leaf is confined to the mesophyll cells. Subcellular fractionation revealed that in the mesophyll cells, most of the β-amylase activity is localized in the vacuole. Water and salt stress stimulated β-amylase activity by several fold in light-grown seedlings, but caused only a slight stimulation in etiolated seedlings. Photooxidative loss of chloroplasts by Norflurazon (NF)-treatment in light-grown seedlings also stimulated β-amylase activity by several fold. Similarly, in the zebra and yellow stripe mutants of pearl millet, chloroplast deficient yellow stripes of the leaf had a higher β-amylase level compared with the green portions. Transfer of NF-treated and water-stressed etiolated seedlings to light also significantly stimulated β-amylase activity. Western blot analysis demonstrated that the stimulation of β-amylase activity is associated with an increase in its protein level. The results indicate that in maize and pearl millet leaves, light is needed for stress-mediated enhancement of β-amylase activity.