Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2001
Publication Date: N/A
Citation: Interpretive Summary: Respiration is the use of energy by living cells to do work. Both growth and reproduction are affected by respiration. As a result, respiration must be carefully controlled or wasted energy would decrease crop yields and reduce agricultural productivity. The control of respiration in plant cells is a subject of ongoing study. A protein complex that is important in the regulation of respiration was studied throughout the life cycle of garden peas. Each of the components of the complex was quantified at well-defined stages of plant development. With a single exception, levels of all of the components changed in concert. This means that the rate of respiration changes as a function of plant age. The exceptional component is shared among three other protein complexes. Thus, the results obtained for this component are the sum of four patterns rather than the single pattern seen for the other components. This information will be important to researchers sin their attempts to increase agricultural productivity by altering controls of plant cell respiration, and to other plant scientists who will try to design more efficient crop plants through either classic breeding or biotechnology.
Technical Abstract: To better understand control of the mitochondrial pyruvate dehydrogenase complex (PDC), total catalytic activity was determined during development of the primary leaves of pea (Pisum sativum L.) seedlings, as well as in each leaf pair of 21-day-old plants. Activity of PDC in clarified homogenates was highest in the youngest organs, then dropped dramatically as the leaves matured and became photosynthetically competent. As leaves began to senesce, total PDC activity dropped to zero. Steady-state mRNA levels were determined using E1 and E3 cDNA probes. The overall pattern of transcript abundance matched the pattern observed for total PDC activity; transcript levels for E1alpha and E1beta approached zero during senescence. Levels of the E1alpha, E1beta, E2, and E3 subunits of the PDC were analyzed in the same samples by using specific antibodies. Quantitation of the immunoblotting results throughout this developmental series showed a pattern in parallel with that of catalytic activity and mRNA levels, although the relative changes in subunit protein levels were not as extreme as the changes in activity. The exception to the global pattern was that of the E3 subunit; lipoamide dehydrogenase. Expression of this enzyme was highest in mature, fully expanded leaves which were active in photosynthesis and photorespiration, reflecting the additional role of E3 as a component of glycine decarboxylase.