Search

The goal of our work was a role of phosphorylase (EC. 2.4.1.1) in starch accumulation in plastids of storage parenchyma cells in potato minitubers forming under clinorotation. An increased enzyme activity under the influence of simulated microgravity has been revealed by using the biochemical and electron cytochemical methods. The obtained results suggest the correlation between an increase in phosphorylase activity and acceleration growth rate and senescence of plant storage organs in microgravity.

The major purpose of these experiments were to investigate growth of potato storage organs and starch synthesis in minitubers at slow horizontal clinorotation (2 rpm), which partly mimics microgravity, and a secondary goal was to study the activity and localization of phosphorylase (EC 2.4.1.1) in storage parenchyma under these conditions. Miniplants of Solanum tuberosum L. (cv Adreta) were grown in culture for 30 days for both the vertical control and the horizontal clinorotation. During long-term clinorotation, an acceleration of minituber formation, and an increase of amyloplast number and size in storage parenchyma cells, as well as increased starch content, was observed in the minitubers. The differences among cytochemical reaction intensity, activity of phosphorylase, and carbohydrate content in storage parenchyma cells of minitubers grown in a horizontal clinostat were established by electron-cytochemical and biochemical methods. It is shown that high phosphorylase activity is correlated with increased starch content during extended clinorotation. The results demonstrate the increase in carbohydrate metabolism and possible accelerated growth of storage organs under the influence of microgravity, as mimicked by clinorotation; therefore, clinorotation can be used as a basis for future studies on mechanisms of starch synthesis under microgravity., (c2003 COSPAR. Published by Elsevier Ltd. All rights reserved.)

It is established that high plant growth and development in microgravity occurred normal. However, the change of plant growth rate is accompanied by the change of carbohydrate metabolism in photosynthesized cells (Kordyum, 1997). The decrease of starch grain size in chloroplasts and the decrease of content cellulose in cell wall were revealed (Sytnik et al., 1984; Nedukha, 1996). The change carbohydrate metabolism in photosynthesized organs could influence on the growth of underground organs and content of storage carbohydrates in these organs. Therefore, the aim of our study was to investigate the long-term clinorotation influence on the formation, structure of potato minitubers and content of starch and sugars in minitubers.

Formation and structure of potato minitubers grown aseptically for 30 days on a horizontal clinostat and in stationary control have been studied by light and electron microscopy. It was demonstrated that the number of plants that formed minitubers, their size and fresh weight, was higher when clino-rotated than in the stationary control. It was revealed that the amount of amyloplasts in parenchyma cell sections was doubled in minitubers formed under clino-rotation. Other factors (shape of minitubers and size of reserve parenchyma cells) did not differ from the stationary control. The changes in amyloplast ultrastructure suggest accelerated cell maturity of potato reserve parenchyma in extended clino-rotation., (c 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved.)