Edgardo R. Montaldi

Drought Stress Syndrome in Wheat Is Provoked by Ethylene Evolution Imbalance and Reversed by Rewatering, Aminoethoxyvinylglycine, or Sodium Benzoate

Abstract. In this work we present evidence that the drought stress syndrome in the flag leaves and ears of wheat plants, provoked by the production of ethylene (shortening the grain filling period and lowering the grain weight) is reversed by the application of a free radical scavenger, sodium benzoate or the ethylene synthesis inhibitor, aminoethoxyvinylglycine. Rehydration by watering also attenuated the detrimental effect of the water deficit. Consequently, the grain filling period was longer, the grain weight increased, and the total protein content was higher than that in plants watered regularly.

Ethylene as promoter of wheat grain maturation and ear senescence

This work was aimed at testing the involvement of ethylene in the maturation of grain and senescence of the foliar structures of the wheat inflorescence. Whole wheat ears emitted ethylene to the atmosphere. From pre-anthesis, ethylene emission progressively increased from 0.76 nl g−1FW h−1 to a peak 1.53 nl g−1FW h−1 at the hard dough stage of the grains, to fall to a minimum of 0.10 nl g−1FW h−1 at the dormant seed stage. Ethephon increased the ethylene release, hastened the process of grain maturation and senescence of the ears. Aminoethoxyvinylglycine and silver thiosulfate produced the opposite effects. It is concluded that ethylene plays a role in grain maturation and in the senescence of the green bracts of the inflorescence.

Antioxidant enzymes and lipid peroxidation during aging of Chrysanthemum morifolium RAM petals

Abstract To characterize the physiological status of petals over the senescence period, the rate of leakage of electrolytes and weight were measured in Chrysanthemum morifolium RAM petals. Both a significant increase in electrolyte leakage to the external medium and a concomitant decrease of flower weight were observed. Lipid peroxidation was evaluated by measurements of thiobarbituric acid reactive substance (TBARS) in Chrysanthemum morifolium RAM petals during senescence, that was arbitrarily divided into five stages. TBARS content was higher in petals from stage 5 (complete wilting) than in stage 1 (blooming). Non-significant differences were detected in ethylene production between petals classified in stages 1–3 (50 ± 4 pmol/g fresh weight/h). The activity of the enzymes involved in hydroperoxide metabolism was determined. The activities of superoxide dismutase (SOD), catalase, peroxidases and ascorbate peroxidase (AP) were measured. SOD activity showed a maximum value at stage 3 (245 ± 30 U/mg protein), followed by a decline. A progressive increase in peroxidase (5-fold increase) and AP (6-fold increase) activities was measured as a function of time. Petals in stage 1 showed lower catalase activity (20.8 ± 0.5 μmol/min/mg protein) than petals in stages 2–5 (43 ± 3 μmol/min/mg protein). The data presented here suggest that lipid peroxidation and membrane damage are involved in deterioration of Chrysanthemum morifolium RAM petals. The significant increase in the activity of SOD, catalase, peroxidases and AP in the initial stages of senescence, indicates that antioxidant defenses are triggered by coordinated mechanisms to control damage by aging in petals.

Senescence of flag leaves and ears of wheat hastened by methyl jasmonate

Abstract. Treatment of flag leaves and ears of wheat plants with MJ (jasmonic acid methylester) (10−5 and 10−4m) did not increase ethylene production, but it did accelerate senescence as indicated by the loss of chlorophyll. MJ also caused the closure of stomata, and consequently the rates of transpiration and photosynthesis decreased. Early maturity shortened the grain filling period, so the thousand grain weight was lower. Although ethylene elicited the same physiologic effects, the syndrome of senescence by MJ is independent of the former. We conclude that senescence and death in wheat are far from being elucidated; however, MJ and ethylene seem to participate in the phenomenon.

Modulation of Progressive Leaf Senescence by the Red:Far-Red Ratio of Incident Light

Unifoliate soybean leaves were irradiated with different red:far-red ratios (R:FR) while the shoot above the leaves was kept under a constant R:FR. The R:FR was changed by lowering the red photon fluence rate. An R:FR of 0.07 accelerated chlorophyll and protein loss and enhanced the rate of exudation of amino acids from the detached irradiated leaves. Different photon fluence rates of far-red were added to a background of cool white fluorescent light, to lower R:FR without significantly changing photosynthetically active radiation. R:FR of 0.09-0.18 accelerated chlorophyll loss. These results are consistent with the view that the R:FR may modulate progressive senescence and that low R:FR occurring in shadelight may promote senescence.

Emission of water stress ethylene in wheat (Triticum aestivum L.) ears: effects of rewatering

In this work it has been found that ethylene production increased only slightly under conditions of a moderate or severe water stress. However, the rehydration of the plants at full turgor after desiccation caused a high emission of ethylene. The desiccation would not irreversibly inactivate the enzymes of the ethylene pathway, since rehydration made the synthesis recommence almost immediately. Water deficit also increased the free radical levels and the antioxidant scavengers, such as superoxide dismutase. Free radicals promote the conversion of 1-amino-cyclopropane-1-carboxylic acid to ethylene, then it is logical to think that both chemical species are involved in the phenomenon of the acceleration of the grain maturity before the plant collapses.

Ethylene production and responses to exogenous ethylene in senescing petals of Chrysanthemum morifolium RAM cv. Unsei

Abstract Senescence of chrysanthemum (Chrysanthemum morifolium RAM cv. Unsei) petals was associated with a marked deterioration of the plasma membrane and loss of water. The rates of ethylene synthesis declined after full bloom, and became non-detectable by the time the first symptoms of senescence were apparent. The drop in ethylene production correlated with a reciprocal increase in 1-aminocyclopropane-1-carboxylic acid (ACC) content. At full bloom, pre-treatment of petals with 1 mM ACC increased their rates of ethylene production several fold, but the capacity to convert exogenous ACC into ethylene decline thereafter. Inhibitors of ethylene synthesis (i.e. aminoxyacetic acid) or ethylene action (i.e. silver thiosulfate) had no effect on senescence, implying that the minute amounts of ethylene synthesized by petals are below the threshold to cause any acceleration of this process. However, petal senescence was significantly accelerated by a 24 h treatment with 3 ppm of ethylene at full bloom, or by continuous treatment with ethephon and ACC at concentrations that produce a significant increase of ethylene synthesis. Thus, our results show that petal senescence in some varieties of chrysanthemum is sensitive to exogenous ethylene, and that the extended vase life that is characteristic of these flowers may be due to their low rates of ethylene synthesis.

Stolon differentiation in Cynodon dactylon (L.) pers. mediated by phytochrome

Abstract Bermudagrass (Cynodon dactylon (L.) Pers.) stolons irradiated with R light showed an upward curvature, an increase in leaf and internode lengths, and sugar contents notably lower than those from stolons grown in darkness or under R + FR. Stolons under R + FR were like those in darkness for their horizontally straight growth, short internodes, and scale-like leaves. These observations indicate that the phytochrome system is involved in the differentiation of rhizomes. It is suggested that its mechanism of action is through affecting changes in the distribution of photoassimilates.

Plant architecture of Paspalum vaginatum schwartz modified by nitrate and ammonium nutrition

Paspalum vaginatum Schwartz plants were grown under greenhouse conditions in a continuous-flow hydroponic culture, containing - NO or + NH or NH 4 NO 3 as nitrogen source. After 30 days, the size of aerial biomass and root system decreased significantly when plants were supplied with + NH as exclusive nitrogen source. Compared to - 3 NO treatment, reducing and non-reducing sugars were decreasing together with a significant increase in amino acids content. + NH -nutrition caused tillers to grow toward an orthogravitropic position (average angle of 68∞ with respect to the horizontal), and with -nutrition, tillers tended to become diagravitropic (average angle of 23∞). With NH 4 NO 3 all the parameters measured had values in between those of the other two sources. Thus, the morphologic differences among plants growing in - NO or + NH nutrition confirm the hypothesis

PHOTOASSIMILATE PARTITIONING MODULATED BY PHYTOCHROME IN BERMUDA GRASS (CYNODON DACTYLON (L) PERS.)

Abstract Cynodon dactylon stolons grown under R + FR are similar to those in complete darkness and show diagravitropic growth, short internodes and scale-like leaves. It has been established that stem diagravitropism is due to high sucrose content. Regardless of the R:FR ratio, with both a relatively large leaf area and high photon flux density (PFD), stolons grow diagravitropically. Whereas with a small leaf area and low PFD, stems tend to grow orthotropically. As to intermediate situations, namely high PFD with a small leaf area or low PFD with large leaf area, photoassimilate distribution is modulated by phytochrome. Under the said conditions, stolons grown under low R:FR values keep their diagravitropic growth, while they switch their growth habits and become orthotrops when the R:FR ratio reaches 0.65 or 0.76. The present work proves the hypothesis that photoassimilate distribution is controlled by R:FR ratio when sucrose content is kept within a certain range, with the strongest sinks being Far Red irradiated and darkness-grown stolons.