Proietti S, Moscatello S, Scartazza A, Brugnoli E, Battistelli A
Abstract: Although living wood accumulates large quantities of storage carbohydrates, our knowledge of the physiological and biochemical control of wood reserve accumulation is quite scarce. In this report we describe seasonal variations of the amount and type of wood storage carbohydrate of two year old walnut (Juglans regia L. cv Lozeronne) plants during an annual cycle and we evaluate the effect of late summer drought on the wood content of storage carbohydrate of the same plants. Furthermore, we report our first results on the analysis of the biochemical control of starch synthesis in walnut wood. Starch was the most abundant sugar in wood, its content reached about 40 % of the dry weight in the tap root. The content of storage compounds decreased consistently in spring showing that a large proportion of carbohydrate reserves was mobilised to sustain spring flush. During summer the amount of storage carbohydrate increased in wood of well irrigated plants. Drought caused a severe inhibition of both growth and storage carbohydrate accumulation so that the amount of reserves per plant at the end of the growing season was strongly reduced by drought. In order to study the biochemical control of starch accumulation in walnut wood, we purified from this tissue, the ADPglucose pyrophosphorylase (AGP) (E.C. 22.214.171.124) a key enzyme of the starch synthesis pathway, to a sufficient degree to evaluate its sensitivity to allosteric control. The enzyme showed allosteric activation by 3PGA and inhibition by inorganic phosphate. The activity of AGP per unit of storage tissue was in excess to the physiological rate of starch accumulation, this indicates that allosteric control of AGP can play a relevant role in the control of starch accumulation also in wood of J. regia.
Citazione: Proietti S, Moscatello S, Scartazza A, Brugnoli E, Battistelli A (1999). Physiological and biochemical control of carbohydrate accumulation in wood of Juglans regia L. . 2° Congresso Nazionale SISEF, Bologna, 20 – 22 Ott 1999, Contributo no. #c2.6.32