Leaf Senescence

Thomas, Howard; Stoddart, J. L.

doi:10.1146/annurev.pp.31.060180.000503

Cited by 699 publications

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“…For instance, it has been demonstrated that exposing forage species to the ruminal conditions of heat and anoxia in the absence of a microbial inoculum is sufficient to promote rapid degradation of plant protein by the plant's own proteases (61)(62)(63) . Stress-induced proteolysis in plants is a phenomenon that has been widely reported for biotic and abiotic stresses (64)(65)(66)(67) . Finding a way to inhibit this stress-induced proteolysis would therefore produce immediate benefits in terms of decreasing the relative availability of protein breakdown products in recently ingested forage (68) .…”

Section: Plant-based Solutionsmentioning

confidence: 99%

Plant-based strategies towards minimising ‘livestock's long shadow’

et al. 2010

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Ruminant farming is an important component of the human food chain. Ruminants can use offtake from land unsuitable for cereal crop cultivation via interaction with the diverse microbial population in their rumens. The rumen is a continuous flow fermenter for the digestion of ligno-cellulose, with microbial protein and fermentation end-products incorporated by the animal directly or during post-ruminal digestion. However, ruminal fermentation is inefficient in capturing the nutrient resource presented, resulting in environmental pollution and generation of greenhouse gases. Methane is generated as a consequence of ruminal fermentation and poor retention of ingested forage nitrogen causes nitrogenous pollution of water and land and contributes to the generation of nitrous oxide. One possible cause is the imbalanced provision of dietary substrates to the rumen micro-organisms. Deamination of amino acids by ammonia-producing bacteria liberates ammonia which can be assimilated by the rumen bacteria and used for microbial protein synthesis. However, when carbohydrate is limiting, microbial growth is slow, meaning low demand for ammonia for microbial protein synthesis and excretion of the excess. Protein utilisation can therefore be improved by increasing the availability of readily fermentable sugars in forage or by making protein unavailable for proteolysis through complexing with plant secondary products. Alternatively, realisation that grazing cattle ingest living cells has led to the discovery that plant cells undergo endogenous, stress-mediated protein degradation due to the exposure to rumen conditions. This presents the opportunity to decrease the environmental impact of livestock farming by using decreased proteolysis as a selection tool for the development of improved pasture grass varieties. Ruminant: Protein: Nitrogen: Methane: Grass: Clover: Forage Making assessments of the impact and value of livestock farming is complex. The rearing of domestic livestock is important in food production, although there are conflicts between the use of land for production of animal feed as opposed to producing grain for human consumption (1) . The livestock sector is economically valuable. Livestock contributes 1 . 4 % of global gross domestic product providing employment for 20% of the global population in both developed and developing countries (1) . Livestock products can provide an important addition to diet especially in the developing world, providing key vitamins and nutrients. Indeed, the consumption of meat has been linked to both physical and mental development in children (2) , but in the developed world over-consumption of meat has been linked to development of serious health problems (3) . Current projections estimate that the global demand for meat and milk will have doubled by 2050 compared with that at the onset of the 21st century (4) . This is being driven by demographic changes, (the emergence of a larger, but older population) and economic growth (1) . Increased demand for livestock products comes mostl...

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Section: Plant-based Solutionsmentioning

confidence: 99%

Plant-based strategies towards minimising ‘livestock's long shadow’

et al. 2010

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“…The predominance of dinitrogen amino-acids, such as asparagine and glutamine, in autumn leaves (Thomas & Stoddart, 1980) suggests that the breakdown of proteins involves the synthesis of transport units with a minimum C : N ratio (Chapin & Kedrowski, 1983). Nutrient resorption efficiency (R EFF ) may be determined by the distribution of N into mobile and insoluble chemical fractions, leaf chemical composition, carbohydrate flux (source-sink relationships) and climatic conditions (Thomas & Stoddart, 1980 ;Chapin & Kedrowski, 1983 ;Chapin & Moilanen, 1991 ;Nordell & Karlsson, 1995 ;Aerts, 1996). In general, plants resorb about half of their maximum leaf N pool before abscission (Table 2 ; Ericson, 1994).…”

Section:  mentioning

confidence: 99%

Leaf life span and nutrient resorption as determinants of plant nutrient conservation in temperate‐arctic regions

1999

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Nutrient conservation plays an important role in plants adapted to infertile environments. Nutrients can be conserved mainly by extending the life span of plant parts and\or by minimizing the nutrient content of those parts that are abscissed. Together these two parameters (life span and resorption) define the mean residence time (MRT ) of a nutrient. In this review we summarize available information on nitrogen resorption and life span, and evaluate their relationship to the MRT of nitrogen, both between and within species. Abundant information with respect to nitrogen resorption efficiency and life span is available at the leaf level. By definition, woody evergreen plants have a much longer leaf life span than species of other life-forms. Conversely, differences in resorption efficiency among life-forms or among plants in habitats differing in soil fertility appear to be small. Inter-specific variation in leaf life span is much larger than intra-specific variation (factor of 200 compared with 2, respectively), while resorption efficiency varies by about the same magnitude at both levels (factor of 3.8 compared with 2.7, respectively). The importance of resorption efficiency in determining leaf-level MRT increases exponentially towards and above the maximum resorption efficiency observed in nature. This effect is independent of leaf life span, which may explain the lack of life-form related differences in resorption efficiency. When scaling up from the leaf to the whole-plant level, fundamental differences in turnover rate among different plant organs must be considered. Woody species invest c. 50% of their net productivity into their low-turnover stems, while in herbaceous species the life span of stems is only slightly longer than that of leaves. As a result, nutrient turnover of woody (evergreen and deciduous) plants is generally lower than that of herbaceous species (herbs and graminoids) on a whole-plant basis. At the intra-specific level empirical data show that both biomass life span (i.e. the inverse of biomass loss rate) and resorption efficiency are important sources of variation in MRT. However, we argue that the relative importance of resorption efficiency in explaining variation in MRT is lower at the interspecific level, whereas the reverse is true for life span. This is because variation in MRT and life span is much larger at the inter-specific level compared with variation in resorption efficiency. Plant traits related to nutrient conservation are discussed with respect to their implications for leaf structure, plant growth, competition, succession and ecosystem nutrient cycling.

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“…Induced senescence often proceeds faster than natural senescence, although there is a large variation in the progression of senescence between different plant species and even cultivars (Thomas & Stoddart, 1980 ;Thomas, 1987 ;Hensel et al, 1993 ;Morris et al, 1996 ;Thomas & Howarth, 2000). Induction of natural senescence by nutrient starvation or water deficit has been reported, and coincides with molecular evidence for sugarmediated regulation of senescence processes.…”

Section: Senescence In the Rumen ?mentioning

confidence: 84%

Tansley Review No. 118

Kingston‐Smith

Theodorou

2000

New Phytologist

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It is generally assumed that breakdown of plant material in the rumen is a process mediated by gut microorganisms. This view arose because of the identification of a pre-gastric fermentation in the rumen, brought about by a large and diverse microbial population. The extensive use of dried and ground feed particles in forage evaluation might have helped to promote this assumption. However, although the assumption might be correct in animals feeding on conserved forage (hay and silage) where the cells of ingested forage are dead, it is possible that with grazed (living) forage, the role played by plant enzymes in the rumen has been overlooked. In a grazing situation, plant cells that remain intact on entering the rumen are not inert, but will respond to the perceived stresses of the rumen environment for as long as they are metabolically viable. Metabolic adjustments could include anaerobic and heat-shock responses that could promote premature senescence, leading to remobilization of cell components, especially proteins. Moreover, contact of plant cells with colonizing microorganisms in the rumen might promote a type of hypersensitive response, in much the same way as it does outside the rumen. After fresh plant material enters the rumen and prior to extensive plant cell-wall degradation, there is often a phase of rapid proteolysis providing N in excess of that required to maintain the rumen microbial population. The inefficient use of this ingested N results in generation of ammonia and urea in exhaled breath and urine, which promotes welfare and environmental pollution concerns. Therefore an important research goal in livestock agriculture is to find ways of decreasing this initial rate of proteolysis in the rumen. This will benefit the farmer financially (through decreased use of feed supplements), but will also benefit the environment, as N pollution can adversely affect pasture diversity and ecology. This review considers the possible responses of plant metabolism to the rumen environment, and how such considerations could alter current thinking in ruminant agriculture.

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Leaf Senescence

Cited by 699 publications

References 0 publications

Plant-based strategies towards minimising ‘livestock's long shadow’

Plant-based strategies towards minimising ‘livestock's long shadow’

Leaf life span and nutrient resorption as determinants of plant nutrient conservation in temperate‐arctic regions

Tansley Review No. 118

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