Symptoms Of Senescence Research Articles

A role for GLABRA1 in dark-induced senescence.

The GLABRA (GL1) gene, belonging to the transcription factor-encoding myb gene family, is responsible for trichome formation in Arabidopsis thaliana (L.) Heynh. The leaves and stems of glabra1 mutant plants are devoid of trichomes. Having an easily observable phenotype, the gl1 mutation was one of the first markers established for genetic mapping of Arabidopsis thaliana. Since then, the GL1 gene has been assigned roles in other processes, also related to leaf structure. In this study we present some previously undescribed effects of the gl1 mutation on dark-induced senescence. This process was induced by covering selected mature leaves of Columbia wild-type and gl1 Arabidopsis with black paper for 4 days, while the plants remained growing in a normal photoperiod. While no visible differences in the external symptoms of senescence could be observed in the darkened leaves, the expression of senescence-associated genes was significantly lower in gl1 plants as compared to the wild type. The darkening of leaves led to a decrease in photosynthetic activity and the expression of photosynthesis-associated genes, in comparison to the control leaves. This effect was much less pronounced in gl1 than in the wild type plants. Therefore, gl1 plants seem to be less susceptible to dark-induced aging, suggesting a possible role for the GL1 gene in controlling the onset and progress of senescence. This result is also of practical importance, since gl1 is the genetic background of many other mutants. It may therefore be advisable to revise some of the results obtained with such mutants in light of findings presented here.

Chloroplast Protein Degradation in Senescing Leaves: Proteases and Lytic Compartments.

Leaf senescence is characterized by massive degradation of chloroplast proteins, yet the protease(s) involved is(are) not completely known. Increased expression and/or activities of serine, cysteine, aspartic, and metalloproteases were detected in senescing leaves, but these studies have not provided information on the identities of the proteases responsible for chloroplast protein breakdown. Silencing some senescence-associated proteases has delayed progression of senescence symptoms, yet it is still unclear if these proteases are directly involved in chloroplast protein breakdown. At least four cellular pathways involved in the traffic of chloroplast proteins for degradation outside the chloroplast have been described (i.e., “Rubisco-containing bodies,” “senescence-associated vacuoles,” “ATI1-plastid associated bodies,” and “CV-containing vesicles”), which differ in their dependence on the autophagic machinery, and the identity of the proteins transported and/or degraded. Finding out the proteases involved in, for example, the degradation of Rubisco, may require piling up mutations in several senescence-associated proteases. Alternatively, targeting a proteinaceous protein inhibitor to chloroplasts may allow the inhibitor to reach “Rubisco-containing bodies,” “senescence-associated vacuoles,” “ATI1-plastid associated bodies,” and “CV-containing vesicles” in essentially the way as chloroplast-targeted fluorescent proteins re-localize to these vesicular structures. This might help to reduce proteolytic activity, thereby reducing or slowing down plastid protein degradation during senescence.

Complete genome sequence of a previously undescribed badnavirus occurring in Polyscias fruticosa L. (Ming aralia).

A previously undescribed badnavirus was identified in plants of Polyscias fruticosa (Ming aralia) showing symptoms of mild mosaic and leaf senescence. Characteristic bacilliform virions of the Polyscias badnavirus averaging 30 × 120nm in size were observed by transmission electron microscopy in partially purified leaf tissue extracts from symptomatic but not asymptomatic plants collected in the USA and Nigeria. The isolate from the USA was complete sequenced. The genome is 7592bp in length and contains three open reading frames with an arrangement similar to that of other members of the genus Badnavirus. The largest open reading frame (ORF3) encodes a putative polyprotein, with predicted domains including zinc finger, aspartic protease, reverse transcriptase (RT) and RNase H, in that order. The USA and Nigeria isolates of the virus had a high level (98%) of nucleotide sequence identity in the RT+RNase H region. Within the genus Badnavirus, these viruses were most closely related to schefflera ringspot virus (SRV), sharing 63% identity at the nucleotide level. Based on the ICTV species demarcation criteria for the genus Badnavirus (more than 20% nucleotide sequence divergence in the RT+RNase H region), the Polyscias virus is proposed to be a new member of the genus, and the name polyscias mosaic virus (PoMV) is proposed. The complete genome sequence was deposited in the NCBI GenBank database under accession no. MH475918.

Técnicas para controle químico de palmeiras invasoras em Unidade de Conservação na região metropolitana de São Paulo

Espécies invasoras prejudicam as comunidades vegetais autóctones por eliminar diretamente as espécies nativas ou por inibir a sua regeneração. Há evidências de que as palmeiras exóticas Livistona chinensis e Archontophoenix cunninghamiana, que colonizam remanescentes de Floresta Atlântica, ameaçam os processos sucessionais da vegetação natural e, portanto, devem ser controladas. Neste estudo, avaliamos a eficácia do controle químico dessas palmeiras exóticas com o herbicida glifosato. Efetuamos o controle químico por meio da injeção de glifosato (ROUNDUP TRANSORB R 30%) no estipe de 30 indivíduos de cada espécie, em dosagens variáveis de acordo com o porte das palmeiras. Os sinais de senescência foram ilustrados, descritos e acompanhados semanalmente até a morte de todas as palmeiras, que demorou 18 semanas para L. chinensis e 29 semanas para A. cunninghamiana. O glifosato mostrou-se eficaz para ambas as espécies e recomendado para o controle de palmeiras adultas de grande porte, as quais devem ser priorizadas no manejo, a fim de eliminar as matrizes responsáveis pela oferta de propágulos.

Extra-plastidial degradation of chlorophyll and photosystem I in tobacco leaves involving 'senescence-associated vacuoles'.

Chlorophyll (Chl) loss is the main visible symptom of senescence in leaves. The initial steps of Chl degradation operate within the chloroplast, but the observation that 'senescence-associated vacuoles' (SAVs) contain Chl raises the question of whether SAVs might also contribute to Chl breakdown. Previous confocal microscope observations (Martínez etal., 2008) showed many SAVs containing Chl. Isolated SAVs contained Chla and b (with a Chla/b ratio close to 5) and lower levels of chlorophyllidea. Pheophytina and pheophorbidea were formed after the incubation of SAVs at 30°C in darkness, suggesting the presence of Chl-degrading activities in SAVs. Chl in SAVs was bound to a number of 'green bands'. In the most abundant green band of SAVs, Western blot analysis showed the presence of photosystem I (PSI) Chl-binding proteins, including the PsaA protein of the PSI reaction center and the apoproteins of the light-harvesting complexes (Lhca1-4). This was confirmed by: (i) measurements of 77-K fluorescence emission spectra showing a single emission peak at around 730nm in SAVs; (ii) mass spectrometry of the most prominent green band with the slowest electrophoretic mobility; and (iii) immunofluorescence detection of PsaA in SAVs observed through confocal microscopy. Incubation of SAVs at 30°C in darkness caused a steady decrease in PsaA levels. Overall, these results indicate that SAVs may be involved in the degradation of PSI proteins and their associated chlorophylls during the senescence of leaves.

Jasmonate production through chlorophyll a degradation by Stay-Green in Arabidopsis thaliana

Leaf color change through chlorophyll degradation is a characteristic symptom of senescence. Magnesium removal from chlorophyll a is the initial step in chlorophyll a degradation, in a reaction catalyzed by Stay-Green (SGR). Arabidopsis thaliana has three SGR homologs, SGR1, SGR2, and SGR-like. When SGR1 is overexpressed, both chlorophyll a and b are degraded and leaves turn yellow. This process is visually identical to senescence, suggesting that SGR1 overexpression affects various physiological processes in plants. To examine this possibility, gene expression associated with chlorophyll metabolism and senescence was analyzed following dexamethasone-inducible SGR1 introduction into Arabidopsis. When SGR1 was overexpressed following 18 h of dexamethasone treatment, genes involved in chlorophyll degradation were upregulated, as were senescence-associated genes. These observations suggested that chlorophyll a degradation promotes senescence. As jasmonate is the plant hormone responsible for senescence and was expected to be involved in the regulation of gene expression after dexamethasone treatment, the level of jasmonoyl-isoleucine, the active form of jasmonate, was measured. The jasmonoyl-isoleucine level increased slightly after 10 h of SGR1 overexpression, and this increase became significant after 18 h. These observations suggest that jasmonate is produced through chlorophyll a degradation and affects the promotion of senescence.

Arbuscular Mycorrhiza in Highly Fertilized Maize Cultures Alleviates Short-Term Drought Effects but Does Not Improve Fodder Yield and Quality.

Under fertilization levels specific to intensive farming, the impact of compensation of soil nutritional value by arbuscular mycorrhiza (AM) might be limited. Therefore, the question arises whether modern crop varieties, selected for high NPK assimilation rate, are able to gain symbiotic benefits under other challenging field conditions, such as drought. Accordingly, in this study we aimed to evaluate the contribution of Rhizophagus irregularis to the drought response of a stay-green corn hybrid in pot cultures equally fertilized until silking, compared to non-mycorrhizal (NM) counterparts. The highest tested fertilization regime not detrimental to the long-term vitality of intraradical hyphae reached the levels recommended for field cultivation of silage corn, except phosphorus application restricted to 60%. Under normal watering, mycorrhiza increased leaf nitrogen and phosphorus acquisition but only in cultures supplied with low NPK levels. At high fertilization levels, only the older leaves retained AM dependency, whereas for other leaf positions the AM-NM differences were leveled out. The similar size and nutritional status of highly fertilized AM and NM cultures, used in this study, eliminated fungal benefits before and during the 2-week drought progression. Nevertheless, mycorrhizal contribution became evident at the time of renewed watering, when AM plants showed much faster reversal of drought-induced leaf senescence symptoms: impaired photosynthesis and nitrogen management. Our results suggest that mycorrhiza can alter drought-induced senescence even in stay-green mutants. Moreover, this effect was apparently not mediated by AM-improved growth but triggered by activation of fungal transport at the time of recovery. Interestingly, the fungal protective potential was shown to be preserved at the expense of lowering AM vesicle number. It can be interpreted as engagement of hyphal nutritional resources targeted to maintain the symbiotic relationship despite the reduced vitality of the host. Finally, we compared the productivity of AM and NM cultures subjected to short-term drought at silking time and further fertilized with moderate or high NPK doses until the grain-filling stage. The yield and nutritive value of green forage showed that alleviation of drought-induced senescence by AM was not sufficient to have a significant positive effect on the final productivity compared to NM plants.

Expression of maize calcium-dependent protein kinase (ZmCPK11) improves salt tolerance in transgenic Arabidopsis plants by regulating sodium and potassium homeostasis and stabilizing photosystem II.

In plants, CALCIUM-DEPENDENT PROTEIN KINASES (CDPKs/CPKs) are involved in calcium signaling in response to endogenous and environmental stimuli. Here, we report that ZmCPK11, one of maize CDPKs, participates in salt stress response and tolerance. Salt stress induced expression and upregulated the activity of ZmCPK11 in maize roots and leaves. Activation of ZmCPK11 upon salt stress was also observed in roots and leaves of transgenic Arabidopsis plants expressing ZmCPK11. The transgenic plants showed a long-root phenotype under control conditions and a short-root phenotype under NaCl, abscisic acid (ABA) or jasmonic acid (JA) treatment. Analysis of ABA and JA content in roots indicated that ZmCPK11 can mediate root growth by regulating the levels of these phytohormones. Moreover, 4-week-old transgenic plants were more tolerant to salinity than the wild-type plants. Their leaves were less chlorotic and showed weaker symptoms of senescence accompanied by higher chlorophyll content and higher quantum efficiency of photosystem II. The expression of Na+ /K+ transporters (HKT1, SOS1 and NHX1) and transcription factors (CBF1, CBF2, CBF3, ZAT6 and ZAT10) with known links to salinity tolerance was upregulated in roots of the transgenic plants upon salt stress. Furthermore, the transgenic plants accumulated less Na+ in roots and leaves under salinity, and showed a higher K+ /Na+ ratio in leaves. These results show that the improved salt tolerance in ZmCPK11-transgenic plants could be due to an upregulation of genes involved in the maintenance of intracellular Na+ and K+ homeostasis and a protection of photosystem II against damage.

Long Term Exposure to Low Ethylene and Storage Temperatures Delays Calyx Senescence and Maintains ‘Afourer’ Mandarins and Navel Oranges Quality

Calyx browning and internal quality loss are major physiological causes for the loss of quality in citrus fruit during storage. While the symptoms of calyx senescence are only superficial, it can affect the appearance and consumer acceptability of citrus fruit. In this study, continuous ethylene exposure at different storage temperatures was investigated to assess their effect on calyx senescence and internal qualities in ‘Afourer’ mandarin and Navel orange fruit during storage. ‘Afourer’ mandarin fruit were stored at ≤0.001 (equivalent to ethylene-free air), 0.01, 0.1 and 1 µL L−1 of ethylene at either 5, 10 or 20 °C, whilst in a parallel experiment, Navel oranges were exposed to ≤0.001, 0.1 and 1 µL L−1 ethylene at either 1 or 10 °C. Changes in external and internal postharvest quality parameters were assessed for up to 8 weeks for ‘Afourer’ mandarins and 10 weeks for Navel oranges. At all storage temperatures, high levels of ethylene were found to increase the level of calyx senescence, weight loss, loss of fruit firmness and respiration rates. Also, there were significant effects of ethylene and storage temperatures on total soluble solids (TSS) content, titratable acidity (TA), and ethanol accumulation in both citrus species. Continuous exposure to high ethylene also significantly reduced vitamin C and ferric reducing antioxidant power (FRAP) in ‘Afourer’ mandarins after 8 weeks of storage. Overall, ethylene treatments had a significant effect on both the external and internal qualities of the fruit during storage. The relationship between ethylene concentrations and storage temperatures demonstrate that lowering atmospheric ethylene levels at reduced storage temperatures maintain fruit quality during long term storage.

Class XI Myosins Contribute to Auxin Response and Senescence-Induced Cell Death in Arabidopsis.

The integrity and dynamics of actin cytoskeleton is necessary not only for plant cell architecture but also for membrane trafficking-mediated processes such as polar auxin transport, senescence, and cell death. In Arabidopsis, the inactivation of actin-based molecular motors, class XI myosins, affects the membrane trafficking and integrity of actin cytoskeleton, and thus causes defective plant growth and morphology, altered lifespan and reduced fertility. To evaluate the potential contribution of class XI myosins to the auxin response, senescence and cell death, we followed the flower and leaf development in the triple gene knockout mutant xi1 xi2 xik (3KO) and in rescued line stably expressing myosin XI-K:YFP (3KOR). Assessing the development of primary inflorescence shoots we found that the 3KO plants produced more axillary branches. Exploiting the auxin-dependent reporters DR5::GUS and IAA2::GUS, a significant reduction in auxin responsiveness was found throughout the development of the 3KO plants. Examination of the flower development of the plants stably expressing the auxin transporter PIN1::PIN1-GFP revealed partial loss of PIN1 polarization in developing 3KO pistils. Surprisingly, the stable expression of PIN1::PIN1-GFP significantly enhanced the semi-sterile phenotype of the 3KO plants. Further we investigated the localization of myosin XI-K:YFP in the 3KOR floral organs and revealed its expression pattern in floral primordia, developing pistils, and anther filaments. Interestingly, the XI-K:YFP and PIN1::PIN1-GFP shared partially overlapping but distinct expression patterns throughout floral development. Assessing the foliar development of the 3KO plants revealed increased rosette leaf production with signs of premature yellowing. Symptoms of the premature senescence correlated with massive loss of chlorophyll, increased cell death, early plasmolysis of epidermal cells, and strong up-regulation of the stress-inducible senescence-associated gene SAG13 in 3KO plants. Simultaneously, the reduced auxin responsiveness and premature leaf senescence were accompanied by significant anthocyanin accumulation in 3KO tissues. Collectively, our results provide genetic evidences that Arabidopsis class XI myosins arrange the flower morphogenesis and leaf longevity via contributing to auxin responses, leaf senescence, and cell death.

Phenotypic variation and biomass partitioning during post-flowering in two common bean cultivars (Phaseolus vulgaris L.) under water restriction

Common bean (Phaseolus vulgaris L.) is a major source of dietary protein and minerals in Latin America and Africa. Drought causes severe losses in the yields of many common bean cultivars. In this study, to obtain phenotypic variation over time on common bean under water restriction, we used a phenotyping platform with a sensor for visible (RGB). We hypothesized that greenness identification or “stay green” by high-throughput images is an efficient indicator for identifying differences among the common bean phenotypes. Plants of cultivars V8025 and Canario-60 under greenhouse conditions were irrigated to field capacity until the beginning of the seed-filling stage. Under well-watered conditions, whole plant senescence differed between the cultivars. V8025 seemed to maintain a constant green color throughout the evaluation, whereas the Canario-60 began to show yellowing at 24 d into the evaluation. Images showed early strong symptoms of senescence in the V8025 plants under water restriction; even significant necrosis was observed. In contrast, Canario-60 showed fewer symptoms of senescence than V8025 for half of the evaluations. Although both cultivars showed low yield under water restriction, the Canario-60 seed weight increased significantly. We suggest a non-invasive framework for using an image-based phenotyping platform for common bean screening under stress conditions.

Complementation studies of the Arabidopsis fc1 mutant substantiate essential functions of ferrochelatase 1 during embryogenesis and salt stress.

Ferrochelatase (FC) is the final enzyme for haem formation in the tetrapyrrole biosynthesis pathway and encoded by two genes in higher plants. FC2 exists predominantly in green tissue, whereas FC1 is constitutively expressed. We intended to substantiate the specific roles of FC1. The embryo-lethal fc1-2 mutant was used to express the two genomic FC-encoding sequences under the FC1 and FC2 promoter and explore the complementation of the FC1 deficiency. Apart from the successful complementation with FC1, expression of FC2 under control of the FC1 promoter (pFC1::FC2) compensates for missing FC1 but not by FC2 promoter expression. The complementing lines pFC1FC2(fc1/fc1) succeeded under standard growth condition but failed under salt stress. The pFC1FC2(fc1/fc1) line exhibited symptoms of leaf senescence, including accelerated loss of haem and chlorophyll and elevated gene expression for chlorophyll catabolism. In contrast, ectopic FC1 expression (p35S::FC1) resulted in increased chlorophyll accumulation. The limited ability of FC2 to complement fc1 is explained by a faster turnover of FC2 mRNA during stress. It is suggested that FC1-produced haem is essential for embryogenesis and stress response. The pFC1::FC2 expression readily complements the fc1-2 embryo lethality, whereas higher FC1 transcript content contributes essentially to stress tolerance.

Early Senescence in Older Leaves of Low Nitrate-Grown Atxdh1 Uncovers a Role for Purine Catabolism in N Supply.

The nitrogen (N)-rich ureides allantoin and allantoate, which are products of purine catabolism, play a role in N delivery in Leguminosae. Here, we examined their role as an N source in nonlegume plants using Arabidopsis (Arabidopsis thaliana) plants mutated in XANTHINE DEHYDROGENASE1 (AtXDH1), a catalytic bottleneck in purine catabolism. Older leaves of the Atxdh1 mutant exhibited early senescence, lower soluble protein, and lower organic N levels as compared with wild-type older leaves when grown with 1 mm nitrate but were comparable to the wild type under 5 mm nitrate. Similar nitrate-dependent senescence phenotypes were evident in the older leaves of allantoinase (Ataln) and allantoate amidohydrolase (Ataah) mutants, which also are impaired in purine catabolism. Under low-nitrate conditions, xanthine accumulated in older leaves of Atxdh1, whereas allantoin accumulated in both older and younger leaves of Ataln but not in wild-type leaves, indicating the remobilization of xanthine-degraded products from older to younger leaves. Supporting this notion, ureide transporter expression was enhanced in older leaves of the wild type in low-nitrate as compared with high-nitrate conditions. Elevated transcripts and proteins of AtXDH and AtAAH were detected in low-nitrate-grown wild-type plants, indicating regulation at protein and transcript levels. The higher nitrate reductase activity in Atxdh1 leaves compared with wild-type leaves indicated a need for nitrate assimilation products. Together, these results indicate that the absence of remobilized purine-degraded N from older leaves of Atxdh1 caused senescence symptoms, a result of higher chloroplastic protein degradation in older leaves of low-nitrate-grown plants.

Pre-treatment with 1-methylcyclopropene alleviates methyl bromide-induced internal breakdown, softening and wall degradation in blueberry

Methyl bromide (MeBr) fumigation is the most common quarantine treatment used to control fruit flies in blueberry. Recent studies suggest that the treatments may increase decay and softening during transport, distribution and retail. We evaluated whether the ethylene action inhibitor 1-methylcyclopropene (1-MCP) could counteract the detrimental effects caused by MeBr. ‘Jewel’ and ‘Emerald’ blueberries with 100% surface blue color were harvested and treated with 1-MCP (1 μL L−1 12 h, 4 °C), MeBr (32 g m−3, 3 h, 21 °C), or 1-MCP followed by MeBr. Untreated berries were used as a control. Fruit was stored for 0, 7 or 14 d at 2 °C and internal breakdown, firmness, respiration, weight loss, color, soluble solids, acidity and the total ascorbic acid (AsA), anthocyanin and glutathione (GSH) concentrations were determined. We also assessed pectin solubility by sequential cell wall extraction and neutral sugar composition. MeBr exposure exacerbated internal breakdown and respiration after long-term storage. These effects were significantly reduced by pre-treatment with 1-MCP, indicating that MeBr-induced damage requires ethylene action. 1-MCP application prior to MeBr fumigation also prevented berry softening by delaying solubilization of cell wall uronic acids and galactose. The combination of 1-MCP followed by MeBr caused no detrimental effects on fruit surface color, anthocyanin, weight loss, soluble solids or acidity. MeBr fumigation reduced total GSH concentrations regardless of 1-MCP, indicating that the improved quality retention could not be attributed to the detoxification of the xenobiotic by this compound and was more likely due to inhibition of ethylene-dependent over-ripening and senescence symptoms. Pre-treatment with 1-MCP may be useful to alleviate MeBr-induced deterioration in blueberry.

Expression of a Plastid-Targeted Flavodoxin Decreases Chloroplast Reactive Oxygen Species Accumulation and Delays Senescence in Aging Tobacco Leaves.

Leaf senescence is a concerted physiological process involving controlled degradation of cellular structures and reallocation of breakdown products to other plant organs. It is accompanied by increased production of reactive oxygen species (ROS) that are proposed to signal cell death, although both the origin and the precise role of ROS in the execution of this developmental program are still poorly understood. To investigate the contribution of chloroplast-associated ROS to natural leaf senescence, we used tobacco plants expressing a plastid-targeted flavodoxin, an electron shuttle flavoprotein present in prokaryotes and algae. When expressed in plants, flavodoxin specifically prevents ROS formation in chloroplasts during stress situations. Senescence symptoms were significantly mitigated in these transformants, with decreased accumulation of chloroplastic ROS and differential preservation of chlorophylls, carotenoids, protein contents, cell and chloroplast structures, membrane integrity and cell viability. Flavodoxin also improved maintenance of chlorophyll-protein complexes, photosynthetic electron flow, CO2 assimilation, central metabolic routes and levels of bioactive cytokinins and auxins in aging leaves. Delayed induction of senescence-associated genes indicates that the entire genetic program of senescence was affected by flavodoxin. The results suggest that ROS generated in chloroplasts are involved in the regulation of natural leaf senescence.

Characterization of the pheophorbide a oxygenase/phyllobilin pathway of chlorophyll breakdown in grasses.

Although the PAO/phyllobilin pathway of chlorophyll breakdown is active in grass leaf senescence, the abundance of phyllobilins is far below the amount of degraded chlorophyll. The yellowing of fully developed leaves is the most prominent visual symptom of plant senescence. Thereby, chlorophyll is degraded via the so-called pheophorbide a oxygenase (PAO)/phyllobilin pathway to a species-specific set of phyllobilins, linear tetrapyrrolic products of chlorophyll breakdown. Here, we investigated the diversity and abundance of phyllobilins in cereal and forage crops, i.e. barley, rice, ryegrass, sorghum and wheat, using liquid chromatography-mass spectrometry. A total of thirteen phyllobilins were identified, among them four novel, not yet described ones, pointing to a rather high diversity of phyllobilin-modifying activities present in the Gramineae. Along with these phyllobilins, barley orthologs of known Arabidopsis thaliana chlorophyll catabolic enzymes were demonstrated to localize in the chloroplast, and two of them, i.e. PAO and pheophytin pheophorbide hydrolase, complemented respective Arabidopsis mutants. These data confirm functionality of the PAO/phyllobilin pathway in grasses. Interestingly, when comparing phyllobilin abundance with amounts of degraded chlorophyll in senescent leaves, in most analyzed grass species only minor fractions of chlorophyll were recovered as phyllobilins, opposite to A. thaliana where phyllobilin quantities match degraded chlorophyll rather well. These data show that, despite the presence and activity of the PAO/phyllobilin pathway in barley (and other cereals), phyllobilins do not accumulate stoichiometrically, implying possible degradation of chlorophyll beyond the phyllobilin level.

Capitulum and floret phenology in Baccharis aliena (Asteraceae, Astereae)

Abstract Inflorescence and floral phenological studies are a source of valuable knowledge to interpret reproductive mechanisms and phylogenetic hypothesis in plants. We analyzed the morphology and functionality floret stages that are present in pistillate homogamous and functionally staminate heterogamous capitula of the dioecious species Baccharis aliena. Phenological monitoring of both types of capitula was carried out in cultivated plants of B. aliena. Floret phenological stages were defined in homogamous and heterogamous capitula by morphometric analyses, from pre-anthesis until senescence symptoms first appeared. Florets of homogamous and heterogamous capitula presented visual anthesis before functional anthesis was achieved and this feature was transferred to the phenology of capitulum. Anthesis of successive series occurs centripetally during a period of 21 days in the homogamous capitula and 20 days in the heterogamous capitula. The timing and length of heterogamous and homogamous capitula is tightly coordinated and almost identical, a feature that ensures floret interaction between plants and pollinator activities. Understanding of breeding systems in the Astereae subtribe Baccharidinae will most assuredly provide helpful insights towards a better understanding of the evolution of this highly successful group.

Postharvest responses of sweet cherry fruit and stem tissues revealed by metabolomic profiling

Sweet cherry, a non-climacteric and highly perishable fruit, is usually cold-stored during post-harvest period to prevent senescence; therefore, metabolic profiling in response to cold storage in sweet cherry is of economic and scientific interest. In the present work, metabolic analysis was performed in fruit and stem tissues to determine the metabolic dynamics associated with cold storage in response to 1-methylcyclopropene (1-MCP), an ethylene-action inhibitor, and modified atmosphere packaging (MAP). Fruit (cv. Regina) following harvest were treated with 1-MCP and then cold-stored (0 °C, relative humidity 95%) for 1 month in the presence or in the absence of MAP and subsequently maintained at 20 °C for up to 2 days. Physiological analysis suggested that cold storage stimulated anthocyanin production, respiration rate and stem browning. Cherry stem exposed to 1-MCP displayed senescence symptoms as demonstrated by the higher stem browning and the lower stem traction force while MAP treatment considerably altered these features. The metabolic profile of fruits and stems just following cold storage was distinctly different from those analyzed at harvest. Marked tissue-specific differences were also detected among sweet cherries exposed to individual and to combined 1-MCP and MAP treatments, notably for amino acid biosynthesis. The significance of some of these metabolites as cold storage hallmarks is discussed in the context of the limited knowledge on the 1-MCP and MAP response mechanisms at the level of cherry fruit and stem tissues. Overall, this study provides the first steps toward understanding tissue-specific postharvest behavior in sweet cherry under various conditions.

The efficacy of alternate sugars, trehalose and lactulose, as a postharvest treatment inProtea‘Sylvia’, to alleviate leaf blackening

Most commercially important Protea species and cultivars are susceptible to leaf blackening, a postharvest disorder, in which the foliage develops a brown to black discolouration. Not only does leaf blackening have a significant effect on the quality, it also results in consignment rejection in the case where these flowers are transported to export markets. Currently, the only commercially viable and effective way to delay leaf blackening in some cultivars is to pulse the stems with a glucose solution for a recommended period and/or volume, as soon as possible after harvest. Glucose pulsing deters the inflorescence from drawing carbohydrates from the leaves. In addition, it also acts as an osmolyte by promoting the solution uptake by the flower following cold storage or shipping of dry stems, thereby assisting in maintaining quality and extending vase life. However, glucose pulsing may be difficult to execute when applied on a commercial scale, especially when different species, each with their own glucose concentration and exposure time preferences, are harvested at the same time. Also, some cultivars do not respond to glucose pulsing or they may suffer readily from glucose toxicity. The aim of this study was therefore to assess the efficacy of alternate sugars, trehalose and lactulose, in alleviating leaf blackening. Both sugars have previously been reported to suppress water loss, delay programmed cell death events and delay symptoms of senescence in other cut flowers, but its efficacy to control leaf blackening in Protea has not been established. We tested the effect of these sugars with Protea cultivar 'Sylvia', over a period of 12 days. We found that trehalose has the potential to reduce leaf blackening and maintain flower quality. The effect of glucose is however still more significant than lactulose.

Age dependent variations in the deep brain photoreceptors (DBPs), GnRH-GnIH system and testicular steroidogenesis in Japanese quail, Coturnix coturnix japonica

The complex physiology of aging involves a number of molecular and biochemical events, manifested as signs of senescence. Japanese quail is a very unique and advantageous model to study the signs and symptoms of senescence in the central and peripheral modules of HPG axis. In the present study, we have investigated the age dependent variations in hypothalamic deep brain photoreceptors (DBPs), central GnRH-I/II-GnIH-Mel1cR system, testicular GnRH-GnIH system, testicular steroidogenic genes and proteins, androgen receptor (AR) and serum testosterone level in quail of different age groups [3-wk (sexually immature), 6-wk (sexually mature and crossed the puberty), 16-wk (adult, sexually active and showing full breeding phase) and 144-wk (aged)]. Findings of our present study showed the differential expression of these genes/proteins in quail of different age groups. The low levels of the DBPs, GnRH-I, GnIH, Mel1cR in hypothalamus and GnRH-II in midbrain, significantly decreased testicular GnRH/GnRH-R-GnIH, steroidogenic genes/proteins and serum testosterone were observed in immature quail. The significantly increased expression of opsins in the DBPs, GnRH-I, GnIH, Mel1cR in hypothalamus and GnRH-II in midbrain influences the testicular GnRH-GnIH and stimulate the testicular steroidogenesis in mature and adult quail. In aged quail, the significantly decreased levels of hypothalamic DBPs, GnRH-I, GnIH, Mel1cR and midbrain GnRH-II modulates the testicular GnRH-GnIH and further suppresses the genes/proteins involved in steroidogenesis and results in reduced serum testosterone. Hence, it can be concluded from our findings that the testicular steroidogenesis and its neuroendocrine regulation varies with age, in Japanese quail.