LIGHT-DEPENDENT AND STRESS-DEPENDENT ENHANCEMENT OF AMYLOLYTIC ACTIVITIES IN WHITE AND GREEN BARLEY LEAVES - BETA-AMYLASES ARE STRESS-INDUCED PROTEINS

Amylolytic activity was extracted from green and white primary leaves of the barley (Hordeum vulgare L.) mutant line albostrians (variety Haisa) and from normally green and Norflurazon-bleached leaves of the non-mutant variety Maresi. In each case it could be resolved into three fractions (I, II, III) by anion-exchange chromatography on DEAE-Fractogel, each of which represented exe- or beta-amylases (EC 3.2.1.2). In green leaves of light-grown plants, the activities of enzymes I and II increased to maximum values at 9 to 10 days, whereby that of enzyme III attained a maximum Value at 4 to 5 days and decreased thereafter to a value amounting to 20%. White leaves exhibited 3- to 5-fold higher activities respective in all three fractions than did the green leaves upon growth in light. In dark-grown white leaves the amylolytic activity was slightly lower than that of the green leaves upon growth in light, but was distributed in a similar manner among the three fractions. Illumination (10 W m(-2)) of 8 day old dark-grown green mutant leaves resulted in a 1.5-fold activity enhancement over the dark control while the activity in white mutant tissue increased 4-fold. High light intensity (100 W m(-2)), an increase in growth temperature from 25 degrees C to 35 degrees C, or growth in the presence of 300 mM sorbitol or 200 mM NaCl all stimulated the amylolytic activity of both white and green leaf tissues, due in particular to selective increase of the fraction III activity. It is proposed that the activity stimulations due to strong illumination, elevated temperatures and decreased water potential are general responses to stress, and that the stress response of white mutant and bleached non-mutant tissues to light is considerably higher than that of green leaf tissue due to the lack of light-absorbing pigments.