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reduced ability to retain water in the floral organ as senescence begins ( Solomos and Gross, 1997 ). As such, genotypic variation in vase life may be driven by water supply or by the senescence response in the bloom. It is currently unclear whether

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studies conducted in our laboratory have shown that both pre- and postharvest application of LPE is able to reduce senescence and promote shelf life of fruits, cut flowers, and leaf tissue ( Farag and Palta, 1991a , 1991b ; Farag and Palta, 1993a ; Kaur

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Traditional overhead lighting of dense crop stands in controlled environments favors development of upper leaf layers to maximize interception of light incident at the top of the foliar canopy. The resultant mutual shading of lower leaves in the understory of the canopy can severely limit productivity and yield of planophile crops. Intracanopy lighting alleviated the effects of mutual shading in dense, vegetative stands of cowpea [Vigna unguiculata (L.) Walp ssp. unguiculata] growing in a controlled environment by sustaining irradiance within the understory throughout development of this edible-foliage crop. For an overhead lighting system, photosynthetic photon flux (PPF) in the understory was reduced to 1% of its initial value by 35 days of growth. PPF in an intracanopy-lighted stand remained within 30 μmol·m-2·s-1 of initial values throughout the 50-day cropping period. Spectral distribution of radiation within the intracanopy-lighted stand also remained relatively constant throughout canopy development. In the overhead-lighted stand, violet and blue radiation in the understory decreased as much as 60% from initial values. Stability of the radiation environment within the intracanopy-lighted stand delayed leaf senescence 27 days beyond when interior leaves of the overhead-lighted canopy began to turn yellow on day 16. The intracanopy-lighted stand produced twice as much edible biomass per unit electrical energy consumed by lamps as for the overhead-lighted system. The treatment differences were due to the continuous presence of understory irradiation when using intracanopy lighting but not when using overhead lighting, and they underscore the importance of the entire foliar canopy in realizing the full productivity potential of dense crop stands in controlled environments.

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Fungi can colonize senescent sweet corn (Zea mays var. rugosa Bonaf.) tissue. Senescence levels of tissues can be rated. Effects of four planting dates on senescence of standard (su, cv. Merit), and supersweet (sh2, cv. Florida Staysweet) corn at fresh market and seed harvest were determined. Stalk senescence was affected by cultivar (sh2 < su) and planting date (earliest was lowest). Shank senescence was affected by cultivar (fresh market < seed harvest) and planting date (lowest for plants of the earliest and latest plantings). Cob senescence was not affected by cultivar, slightly lower at fresh market than seed harvest, and lower for plants of the later than earlier planting dates. In a second experiment senescence was rated during development of sh2 cultivars. Formation of reproductive structures increased senescence rate. Cultivar had little effect on stalk and cob senescence at fresh market harvest. The cv. `Honey'n Pearl' had the lowest shank senescence rating. Delayed senescence should be incorporated in to corn genotypes.

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reproductive structures surrounded by immature petals and enclosed with chlorophyll-containing sepals ( Chen et al., 2008 ). Postharvest broccoli florets experience senescence similar to those seen in developmental leaf senescence at biochemical and

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Abstract

Before undertaking this survey of senescence in stored leafy vegetables, I thought that there would be a wealth of information available from which I could draw. I was in for a surprise. Even though there exists ample literature on some symptoms of senescence among leafy vegetables, amazingly little research has been published regarding fundamental changes in their physiology as senescence progresses. Among the roughly 100 papers I checked for this presentation, only a few dealt with any basic aspect of hormonal influences on senescence in leafy vegetables (2, 15, 40, 47, 57). I was amazed by this relative neglect of studies of senescence in a group of crops that are of major economic importance. If this symposium does little more than point to where the gaps in knowledge are, it can be considered a success.

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organogenesis, abiotic stress tolerance, photosynthesis, guard cell movement, and postharvest senescence, suggesting that H 2 S acts as an important gaseous regulator in plants, as do NO and CO ( Chen et al., 2011 ; García-Mata and Lamattina, 2010 ; Zhang et

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pathogen-induced cell death in young tissues, it negatively regulates senescence in older tissues. The atmc1 mutants exhibit premature leaf senescence, which is accompanied by earlier expression of the senescence marker AtSAG12 ( Coll et al., 2014

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Abstract

It is difficult, perhaps impossible, to make a clear distinction between the terms “ripening” and “senescence”. Therefore, in this paper I shall accept the view expressed by Huber (16) that ripening is a “....functionally modified, protracted form of senescence”. There are many changes that occur during ripening of fleshy fruits that affect their quality and storage life. In general, these involve alterations in color, flavor, texture, aroma, etc. For any given fruit, these changes can be defined precisely in physiological and biochemical terms and, at least for some processes, specific modifications can be shown to be due to alterations in the activity of particular enzymes. No detailed biochemical description of ripening that applies to all fruits can be given, however, because some do not change color and, in others, different pathways are involved in pigment production. Similarly, mechanisms of softening vary in different fruits, as do the accumulation and metabolism of storage components and the production of compounds contributing to flavor and aroma. I believe that ripening is a programmed event that involves the regulated expression of specific genes. Variations in ripening patterns in different fruits are explicable if one assumes that the genes involved in ripening vary according to the biochemical changes that have been recruited to the ripening program during the course of evolution. It is an essential feature of the gene expression hypothesis that ripening cannot occur without changes in the gene expression, but the nature of the genes involved would be expected to vary from species to species. In the first part of this paper, I shall summarize the evidence that changes in gene expression are required for ripening of tomatoes and then discuss the wider implications for our understanding of the mechanism and regulation of ripening in other fruits and for senescence in general.

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Continuous treatment with 8% ethanol doubled the vase life of `White Sim' carnation (Dianthus caryophyllus L.) flowers. Other alcohols, other concentrations of ethanol, or pulse treatments with up to 8% ethanol had little or no effect. Butanol and longer-chain alcohols shortened vase life and caused the flower stem to fold. During their eventual senescence, the petals of ethanol-treated flowers did not inroll; instead, individual petals dried slowly from their tips. Very little ethylene was produced by ethanol-treated flowers, and the normal increase in ACC content and EFE activity was also suppressed. Ethanol treatment also decreased the flowers' sensitivity to exogenous ethylene.

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