Death of mitochondria during programmed cell death of leaf mesophyll cells

The role of plant mitochondria in the programmed cell death (PCD) is widely discussed. However, spectrum and sequence of mitochondrial structural changes during different types of PCD in leaves are poorly described. Pea, cucumber and rye plants were grown under controlled growing conditions. A part of them were sprinkled with ethylene releaser to accelerate cell death. During yellowing the palisade parenchyma mitochondria were attracted to nuclear envelope. Mitochondrial matrix became electron translucent. Mitochondria entered vacuole by invagination of tonoplast and formed multivesicular bodies. Ethephon treatment increased the frequency of sticking of mitochondria to the nuclear envelope or chloroplasts and peroxisomes. Mitochondria divided by different mechanisms and became enclosed in Golgi and ER derived authopagic vacuoles or in the central vacuole. Several fold increase of the diameter of cristae became typical. In all cases mitochondria were attached to nuclear envelope. It can be considered as structural mechanism of promoting of PCD.     

Regulation of α-amylase activity in Amaranthus caudatus seeds by methyl jasmonate, gibberellin A3, benzyladenine and ethylene

Methyl jasmonate (JA-Me) at 10^–3 Minhibited Amaranthus caudatus seed germination anddecreased -amylase activity. Exogenous gibberellin A₃(GA₃) and ethylene, but not benzyladenine (BA), increased activity ofthe enzyme in the presence of JA-Me, with ethylene being the most effective. Theinhibitor of ethylene action, 2,5-norbornadiene (NBD) inhibited seed germinationand decreased -amylase activity. The inhibitory action of JA-Me onAmaranthus caudatus seed germination is associated with theinhibition of -amylase activity. Exogenous GA₃ and ethylenecontrol both -amylase activity and seed germination in the presence of JA-Me.     

Influence of ethylene on adventitious root formation in mung bean hypocotyl cuttings

The relationship between ethylene and adventitious root formation in mung bean hypocotyl cuttings was studied.Ethephon, an ethylene-releasing compound, at 5 x 10 -5 M increased root number and root dry weight on hypo-cotyl cuttings. When ethephon was applied to hypocotyl at different times after excision, there were two effectivetimes for root production i.e. between 06 h and 18-24 h. These two time periods correspond to the induction phase and the late initiation phase of root development, respectively. After excision, three peaks of ethylene productionwere observed. The first peak commencing at 6 h started the sequence of reactions leading root formation, the second peak appearing at 12 h coincided with the beginning of the increase of the IAA level during primordia initiation, and the third peak showing at 48 h played a role in root differentiation and growth. Ethylene stimulated rooting by enhancing the increase in auxins. Thus it appears that the IAA-induced ethylene production may be a factor involved in the stimulation of adventitious root formation.     

Dormancy and germination responses of halophyte seeds to the application of ethylene

Ethylene is invariably produced during seed germination but its role in regulating seed dormancy and germination is poorly understood. Seeds of 22 halophytic species having different life forms – salt secreting dicots, salt secreting monocots, stem succulents and leaf succulents were germinated in Petri dishes kept in a growth chamber set at 20/30 °C (night/day) temperature and a 12 hr light period. Sodium chloride and ethephon were added to the medium from the beginning of the experiment. Seed germination was recorded every other day for twenty days. Application of ethylene did not have any significant effect on releasing seeds from innate dormancy. However, it appeared to have a role in alleviation of salinity effects which varied from negative in certain species to almost complete alleviation of high salinity effects in others.Our data indicates that ethylene appears to have little role in breaking innate seed dormancy however, in most halophyte seeds studied, application of ethylene alleviate the salinity effect to various degrees. Halophyte seeds which could germinate under saline conditions approaching twice the salinity of seawater may offer clues to understand management of seed germination under highly saline conditions. To cite this article: M.A. Khan et al., C. R. Biologies 332 (2009).     

Influence of exogenous ethylene on cambial activity,xylogenesis and ray initiation in young shoots of Leucaena leucocephala (lam.) de Wit

The effect of exogenous ethephon on cambial activity, xylem production and ray population in young shoots of Leucaena leucocephala was investigated anatomically. The application of ethephon showed a diphasic effect on cambial activity and xylogenesis in a dose dependent manner. Lower concentration of ethephon enhanced cambial activity while high concentrations reduced cambial cell divisions and daughter-cell differentiation. High ethephon concentration also resulted in shorter vessel elements, thick walled fibers and phenolic accumulation in ray cells and vessel elements, whereas low concentration allowed elongation of fibers and vessel elements. The density of rays increased significantly with increase in ethylene concentration. The evaluation of longitudinal sections of cambial zone in ethephon treated plants showed high frequency of transformation of fusiform initials into ray initials through divisions and segmentation, resulting in high ray frequency in both xylem and phloem. The present study demonstrates that ethylene plays an important role in regulating secondary vascular tissue composition by reducing the population of fusiform initials in the cambium.     

ETHEPHON (2-CHLOROETHYLPHOSPHONIC ACID) EFFECTS ON SCENEDESMUS QUADRICAUDA (CHLOROPHYCEAE)1,2

Growth of Scenedesmus quadricauda (Turp.) Bréb. was significantly increased when the cultures were grown in Ethephon 68–241 (2-chloroethylphosphonic acid) at concentrations of 0.001–1.0 μg · ml^?1. At 0.1 μg · ml^?1, Ethephon caused a significant increase in RNA levels on a dry weight basis. Total protein and DNA levels increased but not significantly. These data indicate that ethylene, the decomposition product of Ethephon at physiological pH, has some effect on the metabolism of algae.     

Ultrastructural changes and diosgenin content in cell suspensions of <Emphasis Type="Italic">Trigonella foenum-graecum</Emphasis> L. by ethylene treatment

This paper studies the effect of different concentrations of ethephon (an ethylene releasing compound) on the level of the steroidal sapogenin diosgenin in cell suspensions of Trigonella foenum-graecum L. The results reveal that diosgenin synthesis and/or accumulation was stimulated by 5 ppm ethephon treatment, an increase of 126% being observed, while concentrations of 25 ppm and 50 ppm reduced the levels of this secondary compound. Changes in the isopentenyl diphosphate isomerase activity, increased cell diameter, decreased cell packing (with all the ethephon concentrations assayed), increased cytoplasmic density (5 ppm ethephon treatment) and alterations in the membrane structures (25 and 50 ppm ethephon treatments) were also observed.