Plant physiology translocation

It has long been recognized that boron is required by higher plants [61, 62], and recent research indicates the involvement of boron in three main aspects of plant physiology cell wall structure, membrane function, and reproduction. In vascular plants, boron in solution moves in the transpiration stream from the roots and accumulates in the stems and leaves. Once in the leaves, the translocation of boron is limited and requires a phloem transport mechanism. The nature of this mechanism was only recently elucidated with the isolation of a number of borate polyol compounds from various plants [63-65]. These include sorbitol-borate ester complexes isolated from the floral nectar of peaches and mannitol-borate ester complexes from the phloem sap of celery. The implication is that the movement of boron in plants depends on borate-polyol ester formation with the particular sugar polyol compounds used as transport molecules in specific plants. 

Bago, B., Zipfel, W., Williams, R. M. et al. (2002). Translocation and utilization of fungal storage lipid in the arbuscular mycorrhizal symbiosis. Plant Physiology, 128, 108-24. 

From this outline of the factors that determine availability, we see that the soil controls elemental availability to the extent that it limits mobility (steps 1-3). The soil may also influence absorption by roots (step 4) because it has some control over the chemical forms (speciation) that elements take in solution. The important effect of speciation is discussed in more detail in the next section. The soil may even affect translocation of elements within the plant, since there is evidence that mobility in plants is sensitive to the specific chemical form absorbed from soil solution. For example, it appears that iron absorbed from soil solution as a bicarbonate salt is immobile within the plant root and not translocated to the top. Another example is the immobility of zinc and lead in plant roots that are well supplied with phosphate. It may be that chemical precipitation reactions within (or possibly on) roots are limiting translocation. The questions raised here about the chemical forms of elements within plants fall into the realm of plant physiology and will not be pursued further. 

Calcium plays multiple roles in plant physiology and a deficiency of calcium shows up early and in dramatic ways in plant appearance. Calcium is a constituent of cell walls in the form of calcium pectate. The middle lamella is composed mainly of calcium and magnesium pectates (56). Calcium also plays a role in the formation of cell membranes and lipid structures (57)- Calcium in small amounts is pecessary for normal mitosis and it also plays a role as an activator for numerous enzymes (58). Calcium is thought to play a role in carbohydrate translocation and somehow in the development of mitochondria (59). 

STEWART I. 1963. Chelation in the absorption and translocation of mineral elements. Annual Review of Plant Physiology, 14, 295-310. STRICKLAND R.C., CHANEY W.R. and LAMOREAUX R.J. 1979. Organic matter influences phytotoxicity of cadmium to soybeans. Plant and Soil, 5, 393-402. 

C. P. Swanson. Translocation of organic solutes, in Plant Physiology, vol. II, pp. 481-551, edited by F. C. Steward. Academic Press, New York, 1969. 

Kronzucker HJ, Schjoerring JK, Emer Y, Kirk GJD, Siddiqi MY, Glass ADM. 1998b. Dynamic interactions between root NH4+ influx and long-distance N translocation in rice insights into feedback processes. Plant and Cell Physiology 39 1287-1293. 

D. The most widely used herbicide at present is 2,4-D. As far as the selective use of 2,4-D on cereal crops is concerned, the amine formulations seem perfectly satisfactory. As a translocated herbicide, results are not too good. In some localities, 2,4-D has been effective in treating perennial weeds, but in other places results have been disappointing. The differences seem related to the movement of the material after it gets into the plant, and here the physiology of the plant, as well as the nature of the chemical, is concerned. 

Hopf and Kandler92 conducted a detailed investigation of the physiological importance of umbelliferose in plants, and showed that it serves as a temporary reserve-carbohydrate, similar to the role of sucrose. In the ripe fruits of some species of Umbellifereae, the concentration of this oligosaccharide is higher than that of sucrose. On the other hand, during photosynthesis, it is less effectively translocated from the leaves than sucrose the turnover is also slower. 

Professor Filhr discussed penetration, translocation and distribution of fungicides in plants. These aspects of fungicide performance are often critical in determining the success of a systemic fungicide in a particular type of application. The ability to penetrate into plant tissue and move while retaining activity therein is the primary basis for the superiority of the newer systemic fungicides over the older surface protectants. Internal therapeu-tants may also influence the host physiology and as a consequence, be assisted by the natural defense system of the host. 

Lepka, P., Stitt, M., Moll, E. and Seemuller, E. (1999). Effect of phytoplasmal infection on concentration and translocation of carbohydrates and aminoacids in periwinkle and tobacco. Physiology and Molecular Plant Pathology, 55 59-68. 

On the basis of these differences it is reasonable to expect differences in physiological and biological action. Indeed, the members of the group show a wide variability in the mode of uptake (root, stem, leaf), the measure and rate of absorption and translocation, and their distribution and metabolism within the plant. All of these differences indicate that in spite of their chemical relationship, the biological mode of action of the individual active substances is different, as well as the detoxication mechanism of the herbicides in the plants of different sensitivity, the latter phenomenon being responsible for their selectivity. 

In addition to the detoxification processes described, other factors play important parts in determining the physiological selectivity. For example, the translocation rate of the. r-triazine taken up by a plant varies considerably, depending on the plant species. When translocation is rapid, the quantity of triazine ne ed to cause wilting more easily reaches the chloroplasts. 

Although the exact role of boron in plants is unknown, several physiological and biochemical activities associated with tissue boron content have been supported experimentally. This review covers some recent work on the role of boron in (1) organic translocation in plants, (2) enzymatic reactions, (3) plant growth regulator response, (4) cell division, (5) cell maturation, (6) nucleic acid metabolism, (7) phenolic acid biosynthesis, and (8) cell wall metabolism. 

The uptake of Pb by plant roots and its translocation to the shoots varies seasonally. In broad terms, there is a positive relationship between the concentration in the soil and that in the plant (Davies, 1995). A review of the evolutionary and physiological responses of plants to heavy elements, such as lead, was given by Turner (1994). 

Antibody-based immunoassays may become widely accessible and might turn into routine procedures in physiological, biochemical and molecular biological studies on plant secondary metabolites. Future development in this field will provide a detailed knowledge of tissue and organ distribution, intracellular localization and translocation of secondary products. 

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