The kinetics of the movement of statoliths in gravity-perceiving root cap cells of Lens culinaris L. and the force responsible for it have been analysed under 1 g and under microgravity conditions (S/MM-03 mission of Spacehab 1996). At the beginning of the experiment in space, the amyloplasts were grouped at the distal pole of the statocytes by a root-tip-directed 1-g centrifugal acceleration. The seedlings were then placed in microgravity for increasing periods of time (13, 29, 46 or 122 min) and chemically fixed. During the first 29 min of microgravity there were local displacements (mean velocity: 0.154 microm min(-1)) of some amyloplasts (first at the front of the group and then at the rear). Nevertheless, the group of amyloplasts tended to reconstitute. After 122 min in microgravity the bulk of amyloplasts had almost reached the proximal pole where further movement was blocked by the nucleus. After a longer period in microgravity (4 h; experiment carried out 1994 during the IML 2 mission) the statoliths reached a stable position due to the fact that they were stopped by the nucleus. The position was similar to that observed in roots grown continuously in microgravity. Treatment with cytochalasin D (CD) did not stop the movement of the amyloplasts but slowed down the velocity of their displacement (0.019 microm min(-1)). Initial movement patterns were the same as in control roots in water. Comparisons of mean velocities of amyloplast movements in roots in space and in inverted roots on earth showed that the force responsible for the movement in microgravity (Fc) was about 86% less (Fc = 0.016 pN) than the gravity force (Fg = 0.11 pN). Treatment with CD reduced Fc by two-thirds. The apparent viscosity of the statocyte cytoplasm was found to be 1 Pa s or 3.3 Pa s for control roots or CD treated roots, respectively. Brownian motion or elastic forces due to endoplasmic reticulum membranes do not cause the movement of the amyloplasts in microgravity. It is concluded that the force transporting the statoliths is caused by the actomyosin system.

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--Introduction. A recent laboratory study demonstrated a negative correlation between the ethylene production of fruit during ripening and the length of their commercial life. The aim of our work was to determine whether there is a putative relationship between ethylene production of fruit during ripening and the length of the growth period before ripening. A positive answer would make this an important parameter for early selection in breeding programs. Materials and Methods. Four banana varieties representing a broad range of growth period lengths were studied. Ethylene biosynthesis was examined through ethylene production and content in free 1-aminocyclopropane-1-carboxylic acid (ACC)-the immediate precursor of the hormone-during fruit development and ripening. Fruit ripening was totally achieved on the plant. Results. Ethylene production started to be detected at the breaker stage. It peaked at the "fully dark-yellow-extremities included" stage for all varieties. Two varieties, i.e., Sowmuk and IDN 110, presented the highest production levels [(26 and 19) µL ethylene·h -1 ·kg -1 of fresh weight at peak, respectively). Galéo and Grande Naine had lower ethylene yields. The two most productive varieties also presented a drastic increase in free ACC at ripening onset. Conclusion. There is no relationship between ethylene production of bananas ripened on the plant and the length of the fruit growth period prior to ripening onset.France / Musa (bananas) / fruits / developmental stages / ripening / ethylene production Y a-t'il une relation entre la production d'éthylène de bananes mûrissant sur le bananier et la longueur de la phase de croissance du fruit avant le début de sa maturation ?Résumé --Introduction. Une étude récente menée en laboratoire a mis en évidence une corrélation négative entre la production d'éthylène des bananes pendant leur maturation et leur durée de vie commerciale. L'objectif de notre travail a été de savoir s'il existait une relation entre la production d'éthylène du fruit pendant la maturation et la durée de la période de croissance en vert, avant que la maturation ne commence. Une réponse positive serait importante pour une sélection précoce lors de programmes de création variétale. Matériel et méthodes. Quatre variétés présentant différentes durées de phase de croissance ont été étudiées. La biosynthèse d'éthylène a été suivie par la production d'éthylène et la teneur en acide 1-aminocyclopropane-1-carboxylique (ACC), le précurseur immédiat de cette hormone, pendant le développement et la maturation du fruit. Les fruits ont totalement mûri sur le bananier. Résultats. La production d'éthylène a commencé à être détectée au stade de coloration tournant du fruit. Pour les quatre variétés étudiées, elle a été maximale au stade « complètement jaune soutenu, y compris les extrémités ». Deux variétés, Sowmuk et IDN 110, ont eu les niveaux de production d'éthylène les plus élevés [respectivement, des maxima de (26 et 19) µL d'éthylène·h -1 ·kg -1 de poids frais]. Les variétés Galéo et ...

Biochemical characterization of pulp of banana fruit: measurement of soluble sugars, organic acids, free ACC and in vitro ACC oxidase. Abstract-Introduction. We present some protocols aiming at partially characterizing banana fruit quality through measurement of some key biochemical parameters. The principle, key advantages, starting plant material, time required and expected results are presented. Materials and methods. This part describes the required laboratory materials and the steps necessary for achieving four protocols making it possible to measure sugar, organic acids and free ACC contents, and in vitro ACC oxidase activity. Results. Standard results obtained by using the protocols described are presented in the figures. France / Musa sp. / methods / fruits / measurement / quality Caractérisation biochimique de la pulpe de banane : mesure des sucres solubles, des acides organiques, de l'ACC libre et de l'ACC oxydase in vitro. Résumé-Introduction. Nous présentons quelques protocoles visant à caractériser partiellement la qualité de la banane par la mesure de quelques paramètres biochimiques importants. Le principe, les principaux avantages, le matériel végétal requis, le temps nécessaire aux mesures et les résultats escomptés sont présentés. Matériel et méthodes. Cette partie décrit le matériel de laboratoire requis et les étapes nécessaires pour réaliser quatre protocoles permettant de mesurer les teneurs en sucre, acides organiques et ACC libre, ainsi que l'activité de l'ACC oxydase in vitro. Résultats. Les résultats standard obtenus en utilisant les protocoles décrits sont illustrés par des figures.

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