Soluble-starch-synthesizing and sucrose-degrading enzymes in Onoclea spores

Abstract

Sucrose degradation and starch accumulation in imbibed spores of Onoclea sensibilis occur slowly in the dark and are accelerated two- to four-fold when irradiated with low fluence of red light. The accelerated rates of starch accumulation and sucrose degradation begin 4–6 hr after irradiation and precede the completion of germination. The effect of 5 min of red irradiation on the extractable activities of the enzymes involved in starch and sucrose metabolism was investigated as a possible means by which light accelerates the flux of metabolites through these pathways. The accumulation of starch from exogenous sucrose in unirradiated spores and the specific radioactivity of newly synthesized starch in irradiated and unirradiated spores were determined to see if the lack of sucrose degradation and starch synthesis in unirradiated spores is due to limited availability of substrates. Irradiation did not increase the maximum catalytic activities of the soluble starch synthesizing or soluble sucrose degrading enzymes during the 24 hr period following irradiation when compared with those in the unirradiated spores. Incubation of unirradiated spores on exogenous sucrose increased starch accumulation to a level comparable to that in irradiated spores incubated on distilled water suggesting that enzymes for sucrose catabolism and starch anabolism are active in situ in unirradiated spores. Irradiation caused a decrease in the specific radioactivity of starch without decreasing the incorporation of label. Therefore, light regulation of starch synthesis and sucrose degradation in Onoclea spores is not a result of enhanced activity of the soluble enzymes investigated. With respect to starch synthesis, irradiation causes an increase in availability of substrates that can be utilized for starch synthesis.