Grass cells ingested by ruminants undergo autolysis which differs from senescence: implications for grass breeding targets and livestock production

• Published in: Plant, cell and environment cell and environment, 2002-10, Vol.25 (10), p.1299-1312
• Main Authors: Beha, E. M., Theodorou, M. K., Thomas, B. J., Kingston‐Smith, A. H.
• Format: Article
• Language: English
• Subjects: agriculture; Agronomy. Soil science and plant productions; Biological and medical sciences; cell death; chloroplasts; Fundamental and applied biological sciences. Psychology; Genetics and breeding of economic plants; Lolium perenne; Metabolism; Nitrogen metabolism; Plant physiology and development; proteolysis; Rubisco; ruminant; Varietal selection. Specialized plant breeding, plant breeding aims; Yield, quality, earliness, varia
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1046/j.1365-3040.2002.00908.x

It is widely believed that the initial degradation of proteins contained in grazed forage is mediated by rumen micro‐organisms, but the authors’ recent work suggests that the plant cells themselves contribute to their own demise. In the present study the responses of Lolium perenne leaves to the rumen environment were investigated by using an in vitro system which simulates the main stresses of the rumen but from which rumen micro‐organisms were excluded. Degradation of leaf protein and the accumulation of amino acids in tissue and bathing medium occurred over a time‐scale that is relevant to rumen function, and in a near 1 : 1 ratio. Significant loss of nuclear material was observed after 6 h incubation and chloroplasts became morphologically more spherical as the incubation progressed. In situ localization suggested that ribulose 1,5 bisphosphate carboxylase/oxygenase was broken down within chloroplasts which from cytology were judged to be intact. We conclude from these data that plant metabolism may play a significant role in breaking down plant proteins within relatively intact organelles in the rumen. The determinations of chlorophyll content and cell viability revealed that the plant processes occurring in the simulated rumen were similar but not identical to those of natural senescence.