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     

ADENOSINE TRIPHOSPHATASE ACTIVITY IN GERMINATING LETTUCE SEEDS

Mitochondria isolated from lettuce seeds and seedlings are capableof hydrolyzing ATP. On basis of pH optima, there are at leasttwo and probably three enzymes possessing ATPase activity. Oneof them is inhibited by EDTA and all of them are inhibited byNaF. The ATP ase activity of the mitochondria is very slight in imbibedseeds but increases considerably with seedling growth. Othercomponents of the cell also contain ATP hydrolyzing enzymes;however, most of these phosphatases in the seedling seem tobe soluble enzymes. (Received December 12, 1961; )     

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)     

Source of Induction and Sites of Primary Phloem Fibre Differentiation in Coleus blumei

The fact that fibre induction is strictly basipetal is usedhere to study the long distance effect of young growing leaveson acropetal primary phloem fibre differentiation. Excisionexperiments are used to show that young leaves induce fibredifferentiation around a wound a few internodes below them.No fibers appeared in the younger internodes between the youngleaves and the mature internode. Young leaves yield shorterfibres than those which differentiate under mature leaves, indicatingthat more than one stimulus is involved in the induction process.Fibre differentiation in nodes is faster than in subtendinginternodes. Wounding causes rapid differentiation of phloemfibres above and beside the wound. The rapid differentiationin the node as well as around the wound can be understood asan effect of a high local concentration of inductive stimulus.It is proved that the ability of the cells to respond to inductiondetermines the pattern of their differentiation which in thiscase is counter-directional to the induction. Coleus blumei, phloem fibres, differentiation     

Partitioning of [14C]sucrose and Acid Invertase Activity in Reproductive Organs of Pepper Plants in Relation to Their Abscission Under Heat Stress

The effect of heat stress on processes related to carbohydratepartitioning was investigated in young bell pepper (Capsicumannum L. cv. Maor) plants in relation to abscission of theirreproductive organs at different stages of development. None of the reproductive organs abscised after 5 d in a normalday/night temperature regime (25/18°C). With a temperatureregime of 35°C day, 25°C night, abscission occurredin only a small portion of the flower buds and none of the flowersand fruitlets. However, when temperatures in the day and nightwere reversed (25/35°C, day/night) all the buds and someof the flowers abscised during that time period. The young fruitat the first node did not abscise under any temperature regime.The abscission rate of the flower buds was reduced under heatstress if the developing fruit at the first node had been removed. High temperature during either the light or dark periods reducedthe export of [¹⁴C]sucrose from the source leaf (fed for 48h with [¹⁴C]sucrose). Both heat stress and fruit presence reduced the relative amountof [¹⁴C]sucrose which was exported to the flower buds, flowersand roots. Likewise, these treatments reduced the concentrationof reducing sugars in the reproductive organs. Concomitantly,the heat stress and fruit presence on the first node reducedthe activity of soluble acid invertase in the flower buds andthe roots, but not in young leaves. Overall, the results show that heat stress causes alternationin sucrose distribution in the plant, but may also have specificeffects on metabolic activities related to sucrose import andutilization in flower buds and flowers which in turn may enhancetheir abscission. Bell pepper, (Capsicum annuum L. cv. Maor), abscission, acidinvertase, heat stress, reproductive organs, sink leaves. Bell pepper, (Capsicum annuum L. cv. Maor), abscission, acid invertase, heat stress, reproductive organs, sink leaves.     

Petiole Pithiness in Celery Leaves: Induction by Environmental Stresses and the Involvement of Abscisic Acid

Petiole pithiness in celery, Apium graveolens L., was found to be stimulated by several types of root stress. Flooding of the root zone as well as nutrition deficiency required a prolonged period (25–30 days), but water deprivation had a rapid (2–3 days) effect on pithiness development. Pithiness development induced by water deprivation is not reversible upon rehydration of whole plants but is reversible upon rehydration of affected petiole slices. The stimulation of water stress-related pithiness was found to be associated with an increased level of endogenous free abscisic acid (ABA). Exogenously applied ABA stimulated petiole pithiness of detached leaves in a concentration-dependent fashion. It is suggested that in celery, ABA is an agent which mediates stimulation of petiole pithiness by water stress.     

The Effect of Fruit Load, Defoliation and Night Temperature on the Morphology of Pepper Flowers and on Fruit Shape

The shape and regularity of bell pepper (Capsicum annuumL.)fruit are known to be determined at a very early stage of flowerdevelopment. Small, flattened fruit which are commonly parthenocarpicdevelop under low-temperatures (below 16 °C) from flowerswith enlarged ovaries. In such flowers self-pollination is notefficient because of the large distance between the stigma andstamens. Flower deformation of this kind is common during thewinter season. In the present study it was found that deformationsof flowers, similar to those found under low temperatures, wereinduced in 15 d by complete removal of fruit from plants growingunder night-time temperatures of 18 °C. Only flowers whichwere at the pre-anthesis stage at the time of fruit removalwere deformed by this treatment. Removal of leaves from thelower part of the plant (source leaves) partially reduced theeffect of fruit removal on the shape of the flowers and on subsequentfruit morphology. Fruit removal induced significant increasesin the concentrations of starch and reducing sugars, but notsucrose, in the flower buds. Likewise, flower buds of plantswhich grew under a night-time temperature of 12 °C containedmore carbohydrate than those which grew at 18 °C. Theseresults suggest that flower morphology in pepper is at leastpartly controlled by source-sink relationships. Assimilateswhich are normally transferred to developing fruit may be transported,upon fruit removal, to the flower buds which subsequently swell.A similar increase in assimilate translocation to flower budsmay occur under low temperatures, subsequently causing deformationof fruit.Copyright 1999 Annals of Botany Company Pepper, (Capsicum annuumL), flower shape, low temperatures, source-sink relationship, fruit shape, seeds, reducing sugars, sucrose, starch.     

Changes of Carbohydrates in Pepper (Capsicum annuum L.) Flowers in Relation to Their Abscission Under Different Shading Regimes

Abscission of pepper flowers is enhanced under conditions oflow light and high temperature. Our study shows that pepperflowers accumulate assimilates, particularly in the ovary, duringthe day time, and accumulate starch, which is then metabolizedin the subsequent dark period. With the exception of the petals,the ovary contains the highest total amounts of sugars and starch,compared with other flower parts and contains the highest totalactivity, as well as activity calculated on fresh mass basis,of sucrose synthase, in accordance with the role of this enzymein starch biosynthesis. Low light intensity or leaf removaldecreased sugar accumulation in the flower and subsequentlycaused flower abscission. The threshold of light intensity fordaily sugar accumulation in the sink leaves was much lower thanin flowers, resulting in higher daytime accumulation of sugarsin the sink leaves than in the adjacent flower buds under anylight intensity, suggesting a competition for assimilates betweenthese organs. Flowers of bell pepper cv. ‘Maor’and ‘899’ (sensitive to abscission) accumulatedless soluble sugars and starch under shade than the flowersof bell pepper cv. ‘Mazurka’ and of paprika cv.‘Lehava’ (less sensitive). The results suggest thatthe flower capacity to accumulate sugars and starch during theday is an important factor in determining flower retention andfruit set. Pepper; Capsicum annuum L.; abscission; shading; pepper flowers; ovary; leaves; sugars; starch; acid invertase; sucrose synthase     

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