Pressure and Flow Relations in Vascular Bundles of the Tomato Plant

Abstract

.Sumtnary. In the tomato plant water flows through primary xylenm in accordanice with Poiseuille's law. This relation and the analogy between Poiseuille's and Ohm's law were employed to calctulate rates of flow and differences in pressure within vascular bunidles when transpiration rates from individual leaves were known. The resistance of vascular bundles to flow was calculated from a modificationl of Poiseuille's law and from neasurements of vessels in all bundles. The rates of flow in all bundles were derived from a set of simultaneous linear equations of flow, written to correspond with the nature of the vascular network. XValues of the (lifference in pressure associated with flow in bundles were derived from resistances and flow rates in individual bundles. These agreed substantially with values observed in a comparable plant.In large bundles, vessels occur in a frequency distribution that is approximately normal with respect either to the logarithms of their radii or to the fourth power of their radii. 'I'lle largest vessels in a bundle transport most of the water when they are functioning. The tomato plant containis 2 types of vascular bundle. The large bundles of the stem formii a network by joining above each node in combinations of 2 at a time. The small bundles of the stem and petiolar bundles are independent of other bundles from their origins at junctions to their termini. The small bundles offer high resistance to flow, whereas the resistance of large bundles is low. The average conductance of large bundles decreases from the base to the apex of the stem. That of small vascular bundles remains low and more or less constant throughout the plant.Only a small difference in pressure is required to maintain flow in large bundles. For lower leaves, the driving pressure required to move water to the base of a petiole is considerably less than that which moves water through petioles. The difference in pressure that maintains flow increases steadily for successively higher nodes. However, the pressure that drives flow to leaves is not always greater for higher leaves than for intermiediate ones. For the plant examined, the highest leaves required a smaller amount of energy to inove water from the ground than intermediate leaves did. This was also true of thc power expended in moving water to individual leaves.In the large network bundles, significant cross transfer of flowv occurs at junction points from one bundic to another. Because of the interconnections between large bundles. pressure and flow relations are apparently not greatly altered when localized dysfunction occurs in the vessels of larg,e bundles. In small, independent bundles, a localized dysfunction in vessels produces; a signiificant effect on pressure alnd flow relations.WAater moves from one point to another at a rate that is proportional to the difference in potential an(d inversely proportional to the resistance to flow between these points. Gradmann (4). van den Honert (7), and Bonner (2) have each contributed to this concept, alnd rece...

Relationship Between Plant Vascular Architecture and Within-Plant Distribution of ‘Candidatus Liberibacter solanacearum’ in Potato

“…The dye always accumulated uniformly in each of the three leaflets of leaf 5. Our results suggest that patterns in vascular connectivity of potato are similar to those reported in tomato (Dimond 1966;Orians et al 2000): the right half of leaf 2, left half of leaf 3, and all of leaf 5 share direct vascular connections with the export leaf, whereas leaves −1, 1, and 4 have minimal vascular connections with the export leaf (Fig. 2B).…”

“…Vascular connectivity among leaves is based on their phyllotactive arrangement. In general, leaves that are vertically aligned in their phyllotactive arrangement share direct vascular connections and transport the greatest amounts of vascular contents, leaves with adjacent alignment share partial vascular connections and transport less, and leaves with an opposite alignment lack vascular connections and transport the least (Dimond 1966;Orians et al 2000;Orians 2005). Vascular architecture can also refer to the arrangement of vascular bundles in plant stems.…”

Water Potential Gradients in Field Tobacco

“…However, since only the basal half of a leaf was placed in the pressure chamber, it appears more likely in the present case that the major resistance occurred within the petiole or at the nodal junction between the stem and leaf. Dimond (5) in an anatomical study of the water-conducting tissues of a tomato plant showed a marked change in resistance to flow between the stem and petiole in all leaves except the small upper ones. The change in resistance was the result of a decrease in the radius of the xylem vessels and a reduction in the number of vascular bundles.…”

Changes in axial hydraulic conductivity along elongating leaf blades in relation to xylem maturation in tall fescue

“…The Poiseuille equation has been widely used to predict conductivity in the xylem. Results, however, have been variable, with measured conductivity and flows ranging from 20-100% of theoretical values (Dimond, 1966 ;Calkin et al, 1986 ;Hargrave et al, 1994).…”