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The role of plant cell death in rumen function

Reference	BBS/E/G/00003105
Principal Investigator / Supervisor	Professor Michael Theodorou
Co-Investigators / Co-Supervisors
Institution	Inst of Grassland and Environmental Res
Department	Inst of Grassland and Environmental Res Department
Funding type	Research
Value (£)	721,512
Status	Completed
Type	Institute Project
Start date	01/04/1999
End date	31/03/2003
Duration	48 months

Abstract

The imbalance between protein and energy supply in grazing ruminants is a major factor limiting feed conversion efficiency in the rumen. This necessitates the use of high protein concentrates which, whilst enhancing production, ultimately results in increased environmental pollution associated with intensive ruminant agriculture. We contend that the proteolytic enzymes contained within the living plant cells ingested by grazing ruminants are not instantaneously destroyed by rumen conditions and that their subsequent activity in the rumen contributes significantly to rumen function. The sudden exposure of plant tissue to the extreme stress of the rumen (anaerobic, 39oC) may initiate a specific sequence of cell death events which, lead to changes in protein turnover and the activation of lytic enzymes. These rapid responses to the imposed stress could account for the observed rapid loss of foliar protein in ingested plant biomass in ruminants grazing at pasture - an event previously thought to be caused by the rumen microbial population. IGER studies have shown rapid degradation of plant protein in forage grasses and legumes incubated under rumen-like conditions in vitro in the absence of a rumen microbial population. This is analogous to events occurring in the silo where plant enzymes are known to make a significant contribution to the degradation of foliar proteins. The work of this programme will investigate some of the consequences of plant cell death in ruminants. (A) The onset and progression of plant cell death in the rumen. This work aims to establish the extent to which programmed cell death occurs in plant cells in the rumen environment. Four key areas will be studied: 1) The requirements for and consumption of oxygen by respiring foliar cells entering the rumen, leading to a switch between aerobic and anaerobic metabolism. 2) Cytoplasmic acidosis could occur in plant cells as a result of the accumulation of anaerobic metabolic end products. 3) The induction and extent of DNA damage is critical in cell death processes. 4) It is well documented that antioxidants have a pivotal role in stress responses in intact and excised plants. Thus they may also be important in ameliorating the stress responses of freshly grazed foliage in the rumen. (B) Plant protease activity in the rumen; From our in vitro studies, we can conclude that the rate and extent of protein degradation in the rumen is determined by the plant enzymes contained within ingested forage. We will investigate the determinants of inherent plant protease activity and the susceptibility of proteins to attack by plant proteases. Biochemical assays for protease activity will be used to determine the protease profiles and requirements for new protein synthesis in respect to species- specific, seasonal and developmental effects. The potentially protective role of secondary metabolites in plants in amending these plant enzyme interactions will also be investigated. Three key areas will be studied: 1) Identification of key factors underlying the release of vacuolar proteases and permit their access to cytoplasmic substrates. 2) Loss of adhesion between cells occurs during natural plant death processes, such as dehiscence and abscission. 3) Plant cell degradation in the rumen involves proteolysis, cell death and cellulolysis but it is unclear at present in which order these events take place. Experiments will be carried out to determine the sequence of events and relative involvement of plant and microbial processes. We propose to use genetic algorithms to search for the optimal combination of forage(s) and forage inoculant(s) for ensilage.

Summary

unavailable

Committee	Closed Committee - Agri-food (AF)
Research Topics	X – not assigned to a current Research Topic
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

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