Hiroto Yoshioka

Seasonal changes of carbohydrates metabolism in apple trees

Abstract Apple tree ( Malus pumila Mill. var. domestica ‘Jonagold’) accumulated starch in roots and branches as a reserve carbohydrate. This accumulation of starch was observed to occur from July to November, while the amount of soluble carbohydrates in the roots and branches was relatively small and showed little variation. After November, accompanying the fall of temperature, the starch changed to soluble carbohydrates and accumulated, especially as sucrose, in these organs. In summer, when starch accumulated in the wood and bark tissues of 2-year-old branch sections, starch synthase activities decreased to half of those in winter, while the amylase activity decreased to one quarter. Consequently, the metabolism of starch appears to have been changed from degradation to synthesis, and starch may be accumulated in these tissues. In winter, the amylase, sucrose-6P synthase and sucrose synthase activities in the wood and bark tissues increased, changing the starch to glucose, fructose and sucrose. These soluble carbohydrates may play an important role in the cold- and frost-resistance of a tree in winter, as well as providing a supply of energy and substrates for the early growth of shoots in spring. When trees were grown in water culture with non-nitrogen fertilizer, the amylase, sucrose-6P synthase and sucrose synthase activities of the wood and bark tissues in branches were suppressed in comparison to control trees supplied with nitrogen fertilizer. Starch synthase activity in the bark tissue was also suppressed, but the wood tissue showed the same level as the control trees. Consequently, abundant starch accumulated in the wood tissue of trees grown in non-nitrogen fertilizer. This may indicate that wood tissues, by depositing starch, may play a role in keeping the balance of demand and supply in carbohydrates.

Changes in the levels of mRNAs for putative cell wall-related genes during peach fruit development☆

Cell wall changes are important factors for understanding fruit development. Four cDNA clones putatively encoding xyloglucan endotransglycosylase (pfPpXet1), expansin (pfPpExp2), sucrose synthase (pfPpSS1), and cellulose synthase (pfPpCesA1), which are all assumed to relate to cell wall modification, were isolated from developing fruit of peach (Prunus persica cv. Akatsuki), and the relationships between their mRNA accumulations and fruit development were investigated. Each of these four clones showed a different and characteristic pattern of mRNA expression. For example, the accumulation pattern of pfPpExp2 mRNA was in accordance with peach fruit development; i.e., it is abundant in the fruit when the fruit is growing and hardly detectable in the fruit when the fruit growth slows. The pfPpXet1 mRNA was detected in fruit in the earlier stages of development only. The result suggests that cell wall-related genes are differentially regulated during fruit development in peach.

The effect of shoot-bending on the amount of diffusible indole-3-acetic acid and its transport in shoots of Japanese pear

The amount of diffusible indole-3-acetic acid (IAA) in shoots ofJapanese pear (Pyrus pyrifolia) decreased when vertical shootswere bent at an angle of 45°. A significant decrease of diffusibleIAA was observed one day after shoot bending (DAB), and the degree ofthis decrease was larger in the apical region of the shoot than in thebasal region. The decrease caused by the shoot bending increased withthe duration of the treatment. The IAA amounts in the bent shoot in theapical, central, and basal segments on 1 DAB were58.2±6.4%, 92.6±7.6%, and79.1±7.1% of the control, while 43.7±4.1%,30.8±2.9%, and 39.4±2.5% on 14 DAB.Radiolabelled IAA transport velocity was also examined, but it was notinfluenced by the shoot angle in the apical region of the shoot.However, the IAA transport velocity in the basal region decreased. Itdropped first on 1 DAB, but it recovered to the control level 3 DAB,then it decreased again on 14 DAB. A large increase in ethyleneproduction was observed in the bent shoot, but it seemed transient anddid not continue for 14 days. These results suggest that the decrease ofdiffusible IAA amounts may be induced not by the decrease of IAAtransport velocity but by the production/supply of IAA in the apicalregion.