Role of Cytokinin in Vessel Regeneration in Wounded Coleus Internodes

Cytokinin was found to be a controlling or limiting factor invessel regeneration around a wound in internodes of Coleus blumeiBenth. in which the endogenous cytokinin level was minimized.The cytokinin was applied in aqueous solution to the base ofexcised, mature internodes that had an active vascular cambium.Each internode also received IAA in lanolin at its apical end.Under low (0.1 %, w/w) or high (10%, w/w) auxin concentrations,the control internodes (without exogenous cytokinin) exhibitedsmall amounts of vessel regeneration. At appropriate concentrationszeatin, kinetin and 6-benzylamino-purine (BAP) induced a significantincrease in vessel regeneration around the wound. The threecytokinins also induced novel patterns of supplementary regenerationfurther from the wound surface. Kinetin and BAP showed the strongestpromoting effect at 5 and 10 µg ml^–1, while zeatinwas most effective at 20 µg ml^–1. At a low (0.1%) auxin level zeatin was the most effective cytokinin, whereaskinetin was the most effective one at high (1 %) auxin. An inhibitoryeffect on vessel regeneration was observed at the highest kinetinconcentration tested (50 µg ml^–1). The regenerationof vessels induced by cytokinin was very polar. Many more regeneratedvessel members differentiated below the wound than above it,and the regeneration process proceeded acropetally from thebase of the internode to its upper parts. Our results implya basipetal polar increase in cambium responsiveness along thestem axis from internode 5 to 7. The possible significance ofsuch a basipetal increase in cambium sensitivity in wood formationin trees is discussed. Auxin, Coleus blumei, cytokinin, vascular differentiation, vessel regeneration, wound xylem     

Effect of the Gall-forming Aphid Slavum wertheimae on the Differentiation of Xylem in Branches of Pistacia atlantica

The gall-forming aphid Slavum wertheimae H.R.L., which formscoral-like galls on branches of Pistacia atlantica Desf. trees,induces both qualitative and quantiative changes in xylem differentiationin the branch below the gall. More xylem is formed than in ungalledbranches, and the aphid-induced xylem is characterized by numerouswide vessels in the latewood. In control branches that werenot carrying galls, only a few narrow vessels differentiatedin the latewood. The differentiation of numerous wide vesselsat the end of the growing season, when the population of aphidsin the gall reaches its maximum size, makes possible a substantialincrease of sap movement into the gall tissues Gall-forming aphids, Slavum wertheimae, Pistacia atlantica, vessel size, xylem differentiation (latewood)     

Role of auxin and gibberellin in regenerative differentiation of tracheids in Pinus pinea seedlings

A new experimental system was developed for studying the hormonal mechanisms which control tracheid differentiation. In this system the tracheids redifferentiated from parenchyma cells in the hypocotyl of young Pinus pinea L. seedlings. The experimentally induced tracheids have unique shapes and patterns, and are therefore easily distinguished from the primary and secondary tracheids formed before the experiments. Auxin (0·1–1% NAA) alone sufficed to cause the redifferentiation of short tracheids, usually in discontinuous patterns across the hypocotyl. Gibberellin by itself did not induce redifferentiated tracheids. Combinations of auxin with gibberellin (0·1% NAA+0·1–1% GA₃) promoted the differentiation of long tracheids (up to threefold greater than those induced by auxin) in continuous patterns along the stem axis. Gibberellin in the presence of auxin promoted tracheid elongation by stimulating intrusive growth of both the upper and lower ends of the differentiating tracheids. The role of auxin and gibberellin in controlling the evolution of tracheary elements, from tracheids to vessels and fibres, is discussed.     

Experimental Induction of Dilatation Meristems in Melia azedarach L.

Dilatation meristems were induced experimentally in the barkof Melia azedarach L. by mechanical bark blocking, wounding,and by application of 1.0% of either naphthaleneacetic acid(NAA) or of ethrel. The treatments induced the formation ofdilatation meristems in the rays, in the axial phloem parenchyma,and in the primary cortex. Dilatation was the result of bothcell divisions and cell enlargement. The dilatation meristemswere sometimes several cells wide, and were formed in all possibleorientations; some were even branched. In many cases, whirlswere formed as the result of dilatation activity in many directionsover a small bark area. The possible hormonal regulation ofdilatation activity is discussed. Auxin, bark, cortex, dilatation, ethylene     

Spicule Formation in the Invertebrates with Special Reference to the Gorgonian Leptogorgia virgulata

Many of the invertebrates possess calcium carbonate spicules.This paper is a review of the formation of these structuresin the Porifera, Coelenterata, Platyhelminthes, Mollusca, Echinodermataand Ascidiacea. Mature spicules appear to be extracellular structures.Sponge spicules initiate intercellularly then become extracellular.Alcyonarian, turbellarian, echinoid and ascidian spicule depositionbegins intracellularly and then becomes extracellular. The continuationof growth in the extracellular environment has not been documentedexcept for the echinoids. Placophoran spicules initiate andremain as extracellular structures. Early spicule growth seemsto occur from or within a single cell. However, cell aggregationand/or neighboring cells appear to be important to the processof spicule formation. The spicule forming cells, in general,are found in a collagenous medium which may be associated withspicule growth. The organic matrix from the spicules of the gorgonian Leptogorgiavirgulata is a glycoprotein. Autoradiography reveals that thismatrix is apparently synthesized in the rough endoplasmic reticulumand Golgi complexes and then transported to the spicule formingvacuole via Golgi vesicles. To gain information about the entryand transport of calcium ions, the effects of ouabain and vanadateon calcium uptake were examined. Ouabain had no effect on calciumuptake. Vanadate treatment increased the uptake of calcium inscleroblasts and epithelial tissue and decreased its uptakein spicules. This may suggest that vanadate sensitive ATPasesare involved in the pumping of calcium out of scleroblasts,out of epithelial cells into the mesoglea, and into scleroblastorganelles. Autoradiography using ⁴⁵Ca indicates that the majorityof these ions initially accumulate in the branch axis. The labelmoves through the axial epithelium to the mesoglea and reachesthe spiculeforming vacuoles in the scleroblasts via dense bodies     

Role of ethylene and auxin in regenerative differentiation and orientation of tracheids in Pinus pinea seedlings

A low auxin concentration (0.1% naphthalene acetic acid) induced tracheids with longitudinal polarity parallel to the hypocotyl axis in young Pinus pinea seedlings. Application of 0.1% ethrel laterally and 0.1% naphthalene acetic acid apically disturbed axial tracheid polarity and promoted the differentiation of tracheids with a lateral orientation. Ethrel by itself, with no auxin background, did not affect tracheid differentiation. Apical application of 1% gibberellic acid with the low auxin, reversed the polarity disorder induced by ethrel. Disturbance of axial tracheid polarity was observed under a high auxin concentration (0.5% naphthalene acetic acid) which was similar to the combined effect of ethrel and auxin. The high auxin concentration increased tracheid number significantly. This effect was curtailed following treatment with inhibitors of ethylene formation (Co²⁺; 1-aminoethoxy- vinylglycine) and action (Ag²⁺). The role of ethylene in controlling the differentiation of radial tracheids, which characterize the vascular rays of pines, is discussed.     

Variant secondary growth in old stems of Ephedra campylopoda G. A. Mey

LEV-YADUN, S. & ALONI, R., 1993. Variant secondary growth in old stems of Ephedra campylopoda C. A. Mey. Ephedra campylopoda C. A. Mey is a woody climber of the Ephedraceae. The vascular rays of old, thick stems of E. campylopoda differ greatly from the known ray structure found in young stems of the same species, and from the common ray structure of other woody species. The large rays in thick stems include xylem in various orientations, and they intermingle with the axial system. We suggest that this is a variant secondary growth, a common characteristic of climbers.     

Naturally Occurring Regenerative Differentiation of Xylem Around Adventitious Roots in Luffa cylindrica Seedlings

Regeneration of xylem induced by adventitious root formationin the hypocotyl of Luff a cylindrica Roem. seedlings is described.This naturally occurring form of xylem regeneration involvesthe formation of a bypass of regenerated tracheary elementsaround a root without external severance of the vascular strands.The regeneration of xylem around an adventitious root is polarand is very similar in its developmental pattern to the well-knownxylem regeneration induced by wounding vascular strands. Adventitious root formation, Luffa cylindrica Roem, regenerated tracheary elements, vascular differentiation, xylem regeneration.     

An Experimental Method for Studying the Differentiation of Vessel Endings

A simple experimental method for studying the differentiationof vessel endings is described. Vessel endings are induced andtheir location is determined experimentally along an internodeby a complete horizontal cut. The frequency of vessel endingsis very high in the first 5 mm immediately below the cut andtheir number declined sharply in the basipetal direction. Patternsof the secondary wall of complete and partly dissolved vesselendings are demonstrated. Hydraulic safety zone, Luffa cylindrica, vessel differentiation, vessel endings, xylem anatomy