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

Exposure to light stimulates beta-amylase activity in leaves of etiolated s eedlings of pearl miller (Pennisetum americanum) and maize (Zea mays). Inte rcellular fractionation showed that nearly all of the beta-amylase activity in the leaf is confined to the mesophyll cells. Subcellular fractionation revealed that in the mesophyll cells, most of the beta-amylase activity is localized in the vacuole. Water and salt stress stimulated beta-amylase act ivity by several fold in light-grown seedlings, but caused only a slight st imulation in etiolated seedlings. Photooxidative loss of chloroplasts by No rflurazon (NF)-treatment in light-grown seedlings also stimulated beta-amyl ase activity by several fold. Similarly, in the zebra and yellow stripe mut ants of pearl millet, chloroplast deficient yellow stripes of the leaf had a higher beta-amylase level compared with the green portions. Transfer of N F-treated and water-stressed etiolated seedlings to light also significantl y stimulated beta-amylase activity Western blot analysis demonstrated that the stimulation of beta-amylase activity is associated with an increase in its protein level. The results indicate that in maize and pearl miller leav es, light is needed for stress-mediated enhancement of beta-amylase activit y.