Effect of Gibberellin on Mature Euonymus europaeus L. Seeds

The release from dormancy of Euonvmus europaeus L embryos bya brief treatment with GA₃ has been studied During 48 h incubationof dormant embryos in GA-free medium, phospholipid levels increasedat first, then declined sharply over the last 6 h When the embryoswere placed in GA₃ medium during this 6 h period levels of totalphospholipids as well as of phosphatidylethanolamine increasedwhilst phosphatidylinositol and phosphatidylcholine declinedslightly Fine structural changes stimulated by a brief GA₃ treatmentwere of different character depending on tissue region (1) ‘destructive’changes occurred in the superficial procortical parenchyma onthe hypocotyl/radicle boundary, involving autolysis and decompartmentationof organelles, (2) ‘positive’ changes occurred inregions close to root and shoot apical meristems, involvingdegradation of protein bodies and their conversion into vacuoles,and the proliferation of various organelles A number of differenceswere noted when the changes in GA₃-treated embryos were comparedwith those induced by low temperature, which also overcomesdormancy The results suggest that germination is accompaniedby different cytological events depending on whether it is inducedby cold or GA₃ The growth of embryos in which dormancy was overcomeby GA3 was due to the activation of the apical root meristemclose to the quiescent centre, whilst in embryos in which germinationwas induced by low temperature, the periphery of hypotocotyl/radicleboundary was the site of activation Euonymus europaeus L, dormant embryo, fine structure, phospholipids, GA₃ and cold treatments     

Positive and Negative Messages from Roots Induce Foliar Desiccation and Stomatal Closure in Flooded Pea Plants

Flooding the soil for 5–7 d caused partial desiccationin leaves of pea plants (Pisum sativum. L. cv. ‘Sprite’).The injury was associated with anaerobiosis in the soil, a largeincrease in the permeability of leaf tissue to electrolytesand other substances, a low leaf water content and an increasedwater saturation deficit (WSD). Desiccating leaves also lackedthe capacity to rehydrate in humid atmospheres, a disabilityexpressed as a water resaturation deficit (WRSD). This irreversibleinjury was preceded during the first 4–5 d of floodingby closure of stomata within 24 h, decreased transpiration,an unusually large leaf water content and small WSD. Leaf waterpotentials were higher than those in well-drained controls.Also, there was no appreciable WRSD. Leaflets detached fromflooded plants during this early phase retained their watermore effectively than those from controls when left exposedto the atmosphere for 5 min. Stomatal closure and the associated increase in leaf hydrationcould be simulated by excising leaves and incubating them withtheir petioles in open vials of water. Thus, such changes inflooded plants possibly represented a response to a deficiencyin the supply of substances that would usually be transportedfrom roots to leaves in healthy plants (negative message). Ionleakage and the associated loss of leaf hydration that occurswhen flooding is extended for more than 5 d could not be simulatedby isolating the leaves from the roots. Appearance of this symptomdepended on leaves remaining attached to flooded root systems,implying that the damage is caused by injurious substances passingupwards (positive message). Both ethylene and ethanol have beeneliminated as likely causes, but flooding increased phosphorusin the leaves to concentrations that may be toxic. Key words: Pisum sativum, Flooding, Foliar desiccation, Stomata, Ethylene     

Endopeptidase Activity of Phage λ-Endolysin

JACOB and Fuerst^1,2 demonstrated the presence of a bacteriolytic enzyme (λ-endolysin) in the induced cultures of lysogenic Escherichia coli K12 (λ). The enzyme was later identified as the product of gene R; of phage λ³ which is involved in bacterial lysis at the end of a latent period. The enzyme is apt to form spheroplast-like structures in E. coli² and one would therefore expect its substrate to be murein.     

Phospholipid Involvement in Frost Tolerance

Changes in frost tolerance and in phospholipid content were studied in the leaves of winter rape plants (Brassica napus L. var. oleifera L. cv. Górczański) grown under natural or artificially controlled conditions. Frost hardening was found to be a three-stage process. During the first stage, occurring at low but above freezing environmental temperatures, phospholipid changes do not seem to be directly related to the leaf frost tolerance. This stage of hardening is possibly related to a metabolic shift caused by the cessation of growth. The achievement of the second level of frost tolerance in the fully turgid leaves depends on the occurrence of sub-freezing temperature and is related to increase in phospholipid level. It was shown that freezing brought about phospholipid degradation which was reversible only in slightly injured leaves with a relatively high phospholipid content. The third stage of hardening is related to frost-induced dehydration of the cells and may overlap the second one.     

Age-related Changes in the Ultrastructure and Membrane Properties of Brassica napus L. Seeds

The ultrastructure was studied of imbibed non-aged winter rape(Brassica napus L.) seeds in comparison with that of artificiallyaged seeds in which viability was partially or completely impaired.In parallel, measurements were made of lipid-phosphorus content,the leakage of phosphate from the seeds and their vigour andgerminability. Decreases in lipid-phosphorus which accompaniedthe loss of viability corresponded to an increase in phosphateleakage, suggesting damage to cellular membranes. Three ultrastructuralsymptoms possibly related to age-induced membrane deteriorationwere observed: (i) the lowering of electron contrast in allcellular membranes excluding plasmalemma; (ii) coalescence ofsmall storage lipid bodies to larger units presumably as a resultof the degradation of enclosing half-unit membranes; and (iii)the appearance of protoplasmic inclusions inside the storageprotein bodies, possibly resulting from rupture of the enclosingunit membranes. It is suggested that the presence of enlarged fibrillar centresin nucleoli of low viability seeds observed here for the firsttime in aged seed material may be the morphological manifestationof age-induced damage to nucleic acids. Brassica napus L, seeds, accelerated ageing, ultrastructure, leakage     

Ultrastructural Studies on Development in Mature Seeds; Embryos of Euonymus europaea L. Dormant or Cultured at +25 ?C

Ultrastructural observations on naturally dispersed and dehydratedseeds of Euonymus europaea L. were performed. It was shown thatduring the culture of isolated embryos at 25 ?C for 7 d thematuration of protein bodies continued; the initial juvenileform (single protein body per cell with dispersed contents)was developing into a more advanced form (single body splitto form several sub-units with condensed contents). Parallelbiochemical determinations pointed to an increase in insolubleprotein levels. There were no changes in other storage organelles,lipid bodies, either in the fine structure or in the level oftriacylglycerols. Deterioration of cellular membranes (in mitochondria,proplastids and protein bodies) similar to that described forageing was observed in cells at the periphery of the embryonicaxis. It is concluded that during the culture of E. europaeaembryos the maturation programme of development in protein bodiesis being continued. Key words: Embryonic axis, storage protein and lipid body, maturation     

Seasonal abscisic acid accumulation in stem cambial region of Pinus silvestris, and its contribution to the hypothesis of a late-wood control system in conifers

Gradual accumulation of natural inhibitor in tissues comprising the cambial zone and about 1 mm of the youngest phloem of the basal region of the Pinus silvestris stem during the season was detected by both extraction and diffusion methods followed by bioassays. The purified inhibitor was chromatographically identified as similar to abscisic acid. Taking into account earlier numerous results, the hypothesis is formulated that the seasonal accumulation of abscisic acid affects phenomena associated with auxin polar transport, so that autolytic breakdown of protoplasts, which terminates differentiation of tracheids in stem secondary xylem is delayed. This effect extends the maturation phase and results in formation of thick-walled tracheids, characteristic for the late-wood in conifers.     

Reassessing the role of phospholipase D in the Arabidopsis wounding response

Plants respond to wounding by means of a multitude of reactions, with the purpose of stifling herbivore assault. Phospholipase D (PLD) has previously been implicated in the wounding response. Arabidopsis ( Arabidopsis thaliana ) AtPLD α 1 has been proposed to be activated in intact cells, and the phosphatidic acid (PA) it produces to serve as a precursor for jasmonic acid (JA) synthesis and to be required for wounding-induced gene expression. Independently, PLD activity has been reported to have a bearing on wounding-induced MAPK activation. However, which PLD isoforms are activated, where this activity takes place (in the wounded or non-wounded cells) and what exactly the consequences are is a question that has not been comprehensively addressed. Here, we show that PLD activity during the wounding response is restricted to the ruptured cells using ³²P_i-labelled phospholipid analyses of Arabidopsis pld knock-out mutants and PLD -silenced tomato cell-suspension cultures. pldα1 knock-out lines have reduced wounding-induced PA production, and the remainder is completely eliminated in a pldα1 / δ double knock-out line. Surprisingly, wounding-induced protein kinase activation, AtLOX2 gene expression and JA biosynthesis were not affected in these knock-out lines. Moreover, larvae of the Cabbage White butterfly ( Pieris rapae ) grew equally well on wild-type and the pld knock-out mutants.     

Hormonal Modulation of the Oscillatory System Involved in Polar Transport of Auxin

The amount of natural auxin collected in agar as a result of basipetal efflux from the cambial region of successive short sections of pine stem varies so that a wave-like pattern is formed. The wave-length is several times longer than the cell length in the cambial region, suggesting the existence of a supracellular oscillatory system, which forms a morphogenic field in the stem tissues, The amplitude of the auxin wave is amplified by apical application of IAA to the longer stem sections, particularly at she time of spring initiation of cambial activity. The wave of auxin disappears after simultaneous apical application of IAA and ABA. The modulatory effects of IAA and ABA are translocated along the investigated stem sections faster than known transport velocities of IAA molecules. This fact is considered as evidence of apical control of the morphogenic field by way of influence upon a supracellular system of conjugated oscillators in the tissue.     

Modification of stress tolerance by dehydration pretreatment in winter rape hypocotyls

Dehydration of isolated rape hypocotyls (Brassica napus L. var. oleifera L. cv. Górczański) to a water saturation deficít of about 60% resulted in increased tolerance to subsequent desiccation and to prolonged immersion in water. Dehydration pretreatment followed by restoration of tissue turgidity, caused a decrease in leakage of electrolytes, ultraviolet-absorbing materials and ninhydrin-reactive substances from the desiccated or water immersed hypocotyl tissue. A hardening effect of tissue dehydration is supposed to be related to an improved stability of cell membranes.