Translocation of Organic Substances in Trees. III. The Removal of Sugars from the Sieve Tubes in the White Ash (Fraxinus Americana L.).
نویسنده
چکیده
It has been shown by various investigators that the substances in the sieve tubes are qualitatively the same throughout the plant. This, together with a number of physiological observations, seems to suggest that substances move through the sieve tubes without their being metabolized (2, 8, 23). There is good evidence, however, that the movement over the short distance from the leaf parenchyma to the sieve tubes is an active process. It has been shown by Phillis and AMason (13) that the sugar concentration of sap expressed from leaf tissue containing mainly mesophyll is much lower than that of sap expressed from the inner part of the bark or of leaf tissue containing mainly veins. This was later confirmed by a number of other workers using a wide variety of plants and different methods. Most important-since concentrations of expressed saps are not directly comparable-is the fact that leaf parenchyma cells have been plasmolyzed by the sieve tube exudate of the same plant (7, 14). Transfer of substances into the sieve tubes must therefore occur metabolically. This process has been called "loading" by Barrier and Loomis (1). Huber and Bauer refer to it as ";secretion" (9) because of the striking physiological similarity to the secretion of sugars in nectaries (10, 20, 21). There are a few reports on this movement dealing with both the chemistry of the transferred material and the physiology of the tissues involved (2, 18, 21), but the details are far from known. A parallel problem to that of the introduction of assimilates into the sieve tubes is that of how the assimilates are removed from these translocation channels. The mere fact that they do leave the sieve tubes has led some investigators to believe that the sieve tubes are "leaking." That this is not the case is indicated by the fact that they are, even at great distance from the leaves, under a high turgor pressutre most of the time (see (5)). It will be shown in this paper that the turgor remains high for many days after the leaves have formed abscission layers in the fall, and also after artificial defoliation. The presence of large amounts of stachyose, raffinose and sucrose make white ash a very interesting object for phloem translocation studies. It is significant that these sugars contain the sucrose unit within their molecules. In order to explain our previous observations it was proposed that there is an enzymatic removal of D-galactose units which results in a gradual break-down of the higher oligosaccharides, stachvose and raffinose, as they move down the tree (24). In the present investigation three ash trees have been defoliated, thus cutting off the supply of
منابع مشابه
Translocation of Organic Substances in Trees. V. Experimental Double Interruption of Phloem in White Ash (Fraxinus americana L.).
The student of phloem quickly learns that he is dealing with a tissue that functions normally only in the intact plant. Injury, such as an incision into the phloem, causes a disturbance that extends over great lengths up and down from the point of injury. The disturbance consists of several phases. First of all, there is an immediate and far-reaching turgor release which results in an accelerat...
متن کاملReducing industrial dust pollution by Ash tree Fraxinus excelsior in urban green belt
Heavy metal pollutionis one of the largest problems in the Environment and human being. In industrial and urban areas trees can give better quantifications for pollutant concentrations and atmospheric deposition than non-biological samples. In order to know ability of Fraxinus excelsior (Ash tree) to reduce the concentrations of heavy metals and compared with the concentration of thes...
متن کاملFigure 1. Kriged Surfaces of Percent Basal Area (top) and Percent Canopy Dieback (lower) within the Anf. Title: Landscape Patterns of White Ash (fraxinus Americana) Health in the Allegheny Plateau Region
To assess white ash (Fraxinus americana) health status in the Allegheny Plateau region via 1) examination and refinement of existing FHM/FIA plot data and 2) establishment and sampling of additional ash health plots to enhance existing FHM/FIA data. This enhanced sampling will allow us to explore, in detail, how topographic position and site characteristics (e.g., soil pH and nutrition) are rel...
متن کاملEstimating Height and Diameter Growth of Some Street Trees in Urban Green Spaces
Estimating urban trees growth, especially tree height is very important in urban landscape management. The aim of the study was to predict of tree height base on tree diameter. To achieve this goal, 921 trees from five species were measured in five areas of Mashhad city in 2014. The evaluated trees were ash tree (Fraxinus species), plane tree (Platanus hybrida), white mulberry (Morus alba), ail...
متن کاملHost selection and feeding preference of Agrilus planipennis (Coleoptera: Buprestidae) on ash (Fraxinus spp.).
We studied the host selection behavior and feeding preference of the emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae). A. planipennis is an exotic forest insect pest native to Asia that was discovered in North America in 2002 and is causing widespread mortality of ash trees (Fraxinus spp.) in southeast Michigan and surrounding states. We compared host selection and fee...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید
ثبت ناماگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید
ورودعنوان ژورنال:
- Plant physiology
دوره 33 3 شماره
صفحات -
تاریخ انتشار 1958