Changes in 1-aminocyclopropane-1-carboxylic-acid content of cut carnation flowers in relation to their senescence

The rise in ethylene production accompanying the respiration climacteric and senescence of cut carnation flowers (Dianthus caryophyllus L. cv. White Sim) was associated with a 30-fold increase in the concentration of 1-aminocyclopropane-1-carboxylic acid (ACC) in the petals (initial content 0.3 nmol/g fresh weight). Pretreatment of the flowers with silver thiosulfate (STS) retarded flower senescence and prevented the increase in ACC concentration in the petals. An increase in ACC in the remaining flower parts, which appeared to precede the increase in the petals, was only partially prevented by the STS pretreatment. Addition of aminoxyacetic acid (2 mM) to the solution in which the flowers were kept completely inhibited accumulation of ACC in all flower parts.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AOA -aminoxyacetic acid - STS silver thiosulfate complex     

Protease activity during rice leaf senescence

A protease activity was detected in rice (Oryza sativa L. cv. Ratna) leaves that hydrolysed hemoglobin more efficiently than bovine serum albumin. The activity was high when the enzyme was extracted and assayed with tris-maleate buffer [tris (hydroxymethyl) methyl amino-maleate] pH 7.0 rather than with water or with citrate-phosphate buffer pH 7.0. The enzyme had a strong dependence on sulfhydryl groups for its activity without which it was inaotive. The pH optimum was 7.0 and the temperature optimum was 40 °C. Protease activity expressed per unit leaf fresh weight (absolute activity) increased only little during senescence of detached rice leaves while the same activity expressed per unit soluble protein content (specific activity) increased by a greater factor (about 5 times) than absolute activity. Total and soluble protein content decreased during the senescence of detached leaves. Benzimidazole (10-3M) and kinetin (0.5xl0-5M) treatment arrested the increase of the protease activity and the deorease in the protein content during detached leaf senescence. It was indicative that protease protein was more stable than the bulk of other proteins in senescing leaves.     

Increased oxidative stress,lipid peroxidation and protein degradation trigger senescence in <Emphasis Type="Italic">Iris versicolor</Emphasis> L. flowers

Dynamics in various physiological and biochemical aspects were studied during various stages (I—tight bud stage to VI—senescent stage) of flower development in Iris versicolor. Floral diameter, fresh & dry mass and water content increased during flower opening and decreased towards senescence. Senescence was found to be related to the increased lipid peroxidation which was reflected in the decreased membrane stability index towards senescence. This increase in the lipid peroxidation was probably initiated by increased lipoxygenase activity which shot up just prior to the increase in lipid peroxidation. Soluble protein content showed a marginal decrease towards senescence with a corresponding increase in specific protease activity. Sugar fractions and α-amino acids showed a significant decrease towards senescence. Superoxide dismutase and ascorbate peroxidase activity increased as the flowers opened and thereafter a significant decrease was registered towards senescence. Catalase activity improved as the flower matures, but decreased prior to flower opening through senescence. The protein patterns from the tepal tissues resolved through electrophoresis showed a consistency in proteins upto the flower opening but a marginal decrease was registered in both high and low molecular weight proteins towards senescence. However, a protein of molecular weight 76.5 kDa showed up during senescent stages which may have a role in flower senescence.     

Effect of cycloheximide on some physiological changes associated with senescence of detached flowers of Iris germanica L.

Silverthiosulphate which is a potent inhibitor of ethylene action was found to be ineffective in delaying senescence of detached flowers of Iris germanica whereas cycloheximide, a protein synthesis inhibitor, effectively delayed the senescence of these flowers and extended the longevity to 6 days. However, this treatment resulted in suppression of bud opening. When cycloheximide treatment was given at progressive intervals it became less effective in inhibiting bud opening and delaying senescence. Cycloheximide treatment maintained a higher protein content in the perianth tissue of flowers compared to untreated flowers.     

Enhanced expression of serine proteases during floral senescence in Gladiolus

Programmed cell death during senescence in plants is associated with proteolysis that helps in remobilization of nitrogen to other growing tissues. In this paper, we provide one of the few reports for the expression of specific serine proteases during senescence associated proteolysis in Gladiolus grandiflorus flowers. Senescence in tepals, stamens and carpels results in an increase in total protease activity and a decrease in total protein content. Of the total protease activity, serine proteases account for about 67-70% while cysteine proteases account for only 23-25%. In-gel assays using gelatin as a substrate and specific protease inhibitors reveal the enhanced activity of two trypsin-type serine proteases of sizes 75 kDa and 125 kDa during the course of senescence. The activity of the 125 kDa protease increases not only during tepal senescence but also during stamen and carpel senescence indicating that it is responsive to general senescence signals.     

Post-pollination changes in the floral organs of two <Emphasis Type="Italic">Cymbidium</Emphasis> species

It was observed that the unpollinated flowers of Cymbidium pendulum (Roxb.) Sw. and C. aloifolium (L.) Sw. stayed fresh for 20 and 18 d, respectively, but attained senescence in 8 and 7 d, respectively, after pollination. The higher content of total soluble sugars, reducing sugars and free amino acids was observed in all the floral organs of pollinated flowers than in unpollinated ones. Pollination also up-regulated the activity of hydrolytic (α-amylase, β-amylase, invertase) and proteolytic enzymes (proteases) in floral organs. Amongst floral organs, the lip and perianth possessed highest contents of metabolites. Application of auxin inhibitor (0.25 μM triiodobenzoic acid) and ethylene inhibitor (0.25 μM AgNO₃) to the pollinated flowers partially prevented the process of senescence.     

冷藏唐菖蒲切花瓶插过程中水分平衡及若干生理指标的变化

测定唐菖蒲新鲜切花和冷藏切花瓶插过程中的水分平衡、鲜重与某些生理指标的变化。结果表明,瓶插过程中,冷藏切花吸水和失水初时受阻,鲜重增加值大大低于新鲜切花;与瓶插同期的新鲜切花相比,冷藏切花各部位小花花瓣和苞片可溶性蛋白质明显降低,丙二醛(MDA)含量明显较高,过氧化物酶(POD)活性和过氧化氢酶(CAT)活性均明显下降。对唐菖蒲切花冷藏后品质变劣的原因作了讨论。     

Effect of water deficit on photosynthetic and other physiological responses in grapevine (Vitis vinifera L. cv. Riesling) plants

The grapevine (Vitis vinifera L. cv. Riesling) plants subjected to water deficit were studied for changes in relative water content (RWC), leaf dry mass, contents of chlorophyll (Chl), total leaf proteins, free amino acids, and proline, and activities of ribulose-1,5-bisphosphate carboxylase (RuBPC), nitrate reductase (NR), and protease. In water-stressed plants RWC, leaf dry matter, Chl content, net photosynthetic rate (P _N), and RuBPC and NR activities were significantly decreased. The total leaf protein content also declined with increase in the accumulation of free amino acids. Concurrently, the protease activity in the tissues was also increased. A significant two-fold increase in proline content was recorded.     

黄土区不同林龄刺槐人工林细根的衰老生理特征

以黄土高原刺槐人工林为研究对象,采用手工挖掘法,配合完整土块法获取根系样品,分析幼龄(11a),中龄(22a),成熟(34a)刺槐人工林细根活力、可溶性糖含量、可溶性蛋白含量和细胞膜透性等细根衰老生理指标的差异,为深入了解刺槐细根的生长和衰老机制提供参考。结果表明:(1)在生长季节,刺槐细根活力表现为,幼龄林成熟林中龄林,可溶性糖含量、可溶性蛋白含量随着林龄增大而增加,而细胞膜透性则随林龄的增加而减小。(2)随着根序增加,根活力和可溶性糖含量增加,而可溶性蛋白含量和细胞膜透性则呈波动式降低。这表明,在生长季节幼龄林细根较中龄林和成熟林更容易出现衰老,刺槐不同根序衰老具有顺序性,衰老先从1级根开始,然后是2级根和3级根。     

Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Content and Activity in Wheat, Rye and Triticale

Photosynthetic parameters were measured in triticale and its parents wheat and rye. Soluble protein content in leaves, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) content per fresh mass, total chlorophyll content, biomass yield, leaf area, leaf mass and specific leaf mass were higher but Rubisco content expressed as percentage of soluble protein, carboxylase activity, photosynthetic rate and stomatal conductance were significantly lower in rye than in wheat. Native-PAGE of Rubisco revealed that rye carboxylase was different from that of wheat. The difference was not related to either the small or large subunit of Rubisco but, may be, to the ionic and/or other properties of the Rubisco protein moiety. Triticale Rubisco was similar to wheat. For most of the studied physiological parameters, triticale showed much more similarity with wheat than with rye.     

Biochemical Changes in Excised Leaves of Oryza sativa Subjected to Water Stress

Excised rice (Oryza sativa L. cv. Ratna) leaves were used to compare the changes in the levels of various biochemical intermediates and enzyme activities during senescence in turgid and water-stressed conditions. Chlorophyll, total protein and soluble protein content decreased but α-amino nitrogen content increased during the senescence of turgid leaves. In the leaves subjected to water stress, these changes were accelerated, the acceleration being greater with higher degree of water stress. Starch, soluble sugars, total carbohydrates and non-reducing sugar content decreased during senescence of turgid leaves. Water stress accelerated the changes in the levels of starch and non-reducing sugar, but the changes in the levels of soluble sugars and total carbohydrates were retarded. Reducing sugar content increased at first and then decreased in the turgid leaves, and water stress accelerated the change. The decline in the catalase activity and the increase in the peroxidase activity with time was faster in the water-stressed leaves than in the turgid leaves. Acid inorganic pyrophosphatase activity increased, but alkaline inorganic pyrophosphatase activity decreased during the senescence of turgid leaves, and such changes were accelerated by water stress. The results suggest that water stress does not accelerate all the processes connected with leaf senescence.     

Solute leakage, lipid peroxidation, and protein degradation during the senecence of Iris tepals

A colour change and inrolling of the tepal edges are the first symptoms of senescence of Iris flowers ( Iris x hollandica Tub., cv. Blue Magic). Tepals showed an increase in leakage of both ions and anthocyanins, prior to the visible senescence symptoms. Increased leakage occurred irrespective of the time at which the tepals were severed and placed in water, indicating that the senescence process is inherent in the tepal cells. Net loss of proteins in the tepal edges started after flower opening, and after two more days, when the first symptoms of senescence were observed, the protein level was only 20% of that at harvest. Cycloheximide delayed senescence and resulted in a lower rate of protein loss. Phenylmethylsulfony fluoride (PMSF), a protease inhibitor, had a similar effect on protein levels but did not affect the time to visible senescence, and also several other protease inhibitors did not affect the time to senescence.
During senescence the rate of respiration of the tepals remained unchanged and their rate of ethylene production decreaased. The rate of ethane production, an indicator of lipid peroxidation, was very low and remained unaltered. Antioxidants ( l ascorbic acid, benzoic acid, butylated hydroxytoluene, diphenylamine, propyl gallate, propyl- p -hydroxybenzoate and sodium benzoate) had no effect on the time to tepal senescence. It is concluded that tepal wilting is due to transfer of solutes from the symplast to the apoplast. Although net protein degradation occurs early during the senescence process, its inhibition is not correlated with a delay in the time to senescence. Furthermore, the results do not support the hypothesis that the increase in solute leakage is due to (free radical-mediated) peroxidation of membrane lipids. The present results are in contrast with the ethylene-regulated petal senescence of carnation, which is accompanied by lipid peroxidation.     

郁金香衰老过程中几种保护酶活性的变化

两个郁金香品种在开花后随着可溶性蛋白含下降,细胞内超氧化物歧化酶、过氧化氢酶和过氧化物酶３种保护酶活性也随之下降,同时发生过氧化产物丙二醛的迅速累积;     

Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Specific Proteolysis in Barley Chloroplasts During Dark Induced Senescence

Intact chloroplasts were isolated from dark-senescing primary barley (Hordeum vulgare L.) leaves in order to study selective ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) degradation by the stromal and membrane fractions. RuBPCO specific degradation was estimated and characterised applying sensitive avidin-biotin ELISA method with non-modified or oxidatively modified biotinylated RuBPCO (BR) as substrates. Distinct proteolytic activities were detected. They differed in ATP and divalent metal ion dependence, protease inhibitory profile, and dynamics in the time-course of dark-induced senescence. The results supported involvement of ATP- and metal ion-dependent serine type proteolytic activity against non-modified BR early in induced senescence and appearance of ATP-independent activity at later stage. Active oxygen-modified BR was degraded by ATP-independent serine-type protease probably containing essential SH-groups and requiring divalent metal ions.     

Development and senescence of <Emphasis Type="Italic">Grevillea</Emphasis> ‘Sylvia’ inflorescences,flowers and flower parts

To characterise the physiology of development and senescence for Grevillea Sylvia floral organs, respiration, ethylene production and ACC concentrations in harvested flowers and flower parts were measured. The respiration rate of harvested inflorescences decreased over time during senescence. In contrast, both ethylene production and ACC concentration increased. Individual flowers, either detached from cut inflorescences held in vases at 20 °C or detached from in planta inflorescences at various stages of development, had similar patterns of change in ACC concentration and rates of respiration and ethylene production as whole inflorescences. The correlation between ACC concentration and ethylene production by individual flowers detached from cut inflorescences held in vases was poor (r² = 0.03). The isolated complete gynoecium (inclusive of the pedicel) produced increasing amounts of ethylene during development. Further sub-division of flower parts and measurement of their ethylene production at various stages of development revealed that the distal part of the gynoecium (inclusive of the stigma) had the highest rate of ethylene production. In turn, anthers had higher rates of ethylene production and also higher ACC concentrations than the proximal part of the gynoecium (inclusive of the ovary). Rates of ethylene production and ACC concentrations for tepal abscission zone tissue and adjacent central tepal zone tissue were similar. ACC concentration in pollen was similar to that in senescing perianth tissue. Overall, respiration, ethylene and ACC content measurements suggest that senescence of G. Sylvia is non-climacteric in character. Nonetheless, the phytohormone ethylene is produced and evidently mediates normal flower development and non-climacteric senescence processes.     

Correlative changes in sucrose uptake, ATPase activity and membrane fluidity in carnation petals during senescence

Apparent sucrose uptake. ATPase activity and membrane fluidity changes were studied during the development and senescence of carnation flowers ( Dianthus caryophyllus L., cv. Cerise Royallette). Typical changes associated with senescence of a cut flower, such as respiration, ethylene production and fresh weight, were measured. Concomitant with a rise in respiration and ethylene production and a decline in fresh weight, a sharp decrease in apparent sucrose uptake was observed. Sucrose uptake was pH dependent (pH optimum, 5.5) and influenced by membrane integrity. Apparently, the activity of ATPase is related to sucrose uptake, because similar changes occurred during flower development. In addition, the activity of ATPase was well correlated with membrane fluidity.
It is suggested that sucrose uptake is controlled by ATPase activity, which in turn is modulated by membrane lipid fluidity. The decline in membrane fluidity associated with senescence leads to a corresponding reduction in ATPase activity and sucrose uptake. Further evidence supporting this view comes from experiments in which senescence was enhanced by 1-aminocyclopropane-l-carboxylic acid. It shortened the time to decline in fresh weight, rise in respiration and ethylene production. In parallel, reduction in membrane fluidity, ATPase activity and sucrose uptake were observed.     

Physiological changes accompanying senescence in the ephemeral daylily flower

The daylily flower, Hemerocallis hybrid cv Cradle Song, develops from the opening bud to full senescence in 36 hours. Unlike other ephemeral flowers studied to date, it does not respond to ethylene, but other senescence phenomena are similar. There was a small respiration climacteric coinciding with early flower senescence, and it was also observed in isolated petals and petal slices. Cycloheximide abolished the climacteric and delayed senescence in all three systems. Petal apparent free space increased from 30% at bud opening to 38% at the onset of senescence, and sugar efflux increased from 0.2 to 2.8 milligrams per gram of fresh weight per hour during the same period. A sharp increase in ion efflux from 0.8 to 4.0 micromoles of NaCl equivalents per gram of fresh weight per hour, coinciding with the climacteric, was abolished by cycloheximide. Uptake of radiolabeled inorganic phosphate by petal slices from 100 micromolar solution increased during onset of senescence from 6 to 10 nmoles per gram of fresh weight per hour. Half was esterified; of this, 14% went into ATP, and the cellular energy charge remained high at 0.86 during senescence. The proportion incorporated into phospholipid (2.2%) did not change during senescence, but the proportion in phosphatidyl choline increased and in phosphatidyl glycerol decreased during senescence. The general phosphate ester pattern in presenescent slices closely resembled that in other plant tissues except that phospholipid precursors were more prominent (approximately 20% of total organic ³²P versus 5%). In senescent slices, the proportion of hexose phosphates decreased from 40 to 15% of total organic ³²P and that of phospholipid precursors increased to approximately 50%, suggesting that phospholipid synthesis was blocked early in senescence.