Biochemistry of Senescence

205

118

(5,12,13,14) and Perilla (10) leaves. Fraction I protein as usually isolated can probably be considered to be crude RuDPCase' since it often contains several other enzymatic activities in addition to that of RuDPCase (15,18,36). We recently reported that intact barley seedlings placed in extended darkness lost soluble protein, almost all of which was accounted for by the enzyme RuDPCase (9,25). The results of these investigations are not surprising, since this enzyme is considered to be the major storage protein of many plant leaves (18,26). Since RuDPCase is also principally responsible for net fixation of CO2 in plants, its fate during senescence is important. This study is a further extension to show the effects of some chemicals and light on the loss of RuDPCase and to correlate the concurrent development of proteases and esterases during senescence. Evidence is also presented for the turnover of RuDPCase under these conditions. The process of senescence has been studied in intact plants, detached leaves, and leaf discs in both light and dark (31, 37). In general, senescence is speeded by detaching the leaves and/or imposing darkness. Perhaps the most striking changes in senescence are losses of Chl, nucleic acids, and protein (39), accompanied by a general increase in proteolytic activity as measured in vitro. Cytokinins (32,33,37) or light (7)

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Loss of Ribulose 1,5-Diphosphate Carboxylase and Increase in Proteolytic Activity during Senescence of Detached Primary Barley Leaves

Peterson¹,

Huffaker²

1975

205

118

“…The complete protein-synthesizing system is capable, therefore, of being resolved into 2 Table VI 5) This resiult is significanIt in view of the fact thlat thle level of a-mllalase is still rapidly increasin,g in cotvledonls of this age ( see Fig. 1 32) aind have been suggested as a uiseful biological system for studying celluilar seniescence processes (27). AltlhouIgh cell-free protein synthesis has been observed in pea seedling extracts by otlher Nworkers ( 18,29,30), the systems, previously described used cell fractions from those ))Mrts of the plant that remained after excision of the cotyledons; unfortunately, results obtained wvith these systems have not been repro(lucible (8,9,31 3A), does not increacse inidefinitel bhut reaches a finite level after at period of tinme.…”

Section: Resultsmentioning

confidence: 98%

Seed Germination Studies. III. Properties of a Cell-free Amino Acid Incorporating System From Pea Cotyledons; Possible Origin of Cotyledonary α-Amylase

Swain

Dekker

1969

Abstract. Pea cotyledonary a-amylase increases dramaticallv both in specific activity and total activity between days 7 to 10 when germination occurs in the dark. This enzymatic activity does not seem to appear as a consequence of release or formation of an activator, removal of an inhibitor, dissociation of an inactive amylase complex, or proteolytic decomposition of a zymogen precursor. The possibility remains that the a-amylase is newly synthesized during germination. The preparation and properties of a cell-free protein-synthesizing system from germinating pea cotyledons is described; polyuridylic acid must be added for L-phenylalanine incorporation. Active microsomal preparations can be obtained from cotyledons germinated 10 days.Seed germination is frequently accompanied bv marked increases in the level of activity of certain enzymes (3,4,12,17, 23,32). It has been noted that these often dramatic increases in biocatalytic activity are not necessarily associated only with those parts of the seedling that are actively growing. Rather. the same phenomenon is also observed in the storage tissues of the endosperm or cotyledon (4, 17, 32).We showed in previous reports '(25, 26) that a number of enzvmes required for the degradation of seed carbohydrate reserves are present in the cotvledon of the germinating pea, and at least 2 of these enzymes, an a-amylase and a phosphorylase. increase manyfold in total activity during the time period of germination. Since, in many instances, the cells of plant storage organs neither grow nor divide, the question arises as to what the origin of such new enzymatic activities mlay be. Other workers dernonstrated that activation of latent enzyme occurs in the case of the ,-amylase of wheat (21,22), zymogen activation causes an increase in acid phosphatase and isocitritase activiti-es of a variety of seeds (17), whereas isocitritase (6,10). malate synthetase (10), tyramine methylpherase (12), and barley a-amvlase (5, 28) increase in activity as a result of de novo enzyme synthesis.We report here studies which show that cotvledonary a-amylase of peas most likely does not appear during germination as a consequence of the formation or release of a specific activator, the removal of an inhibitor, or the activation of a latent form (or zymogen precursor) of the enzyme. The possibility that the enzyme is newly synthesized is not eliminated.A cell-free protein-synthesizing system from the cotyledons of germinating peas has been prepared and its properties determined. A catalytically-active microsomal fraction can be prepared from cotyledons at a time during germination when the level of oa-amvlase activity is rapidlv increasilng.

“…A number of explanations of this phenomenon which have been proposed but not fully sutbstantiated, have been reviewed by Biale (2), Varner (16), Spencer (15) and by Rowan (12). Millerd et al (9) advanced the idea that at the induction of the climacteric an endogenous un-coupler of oxidative phosphorylation was formed which released a restraint on oxygen utilization.…”

mentioning

confidence: 99%

Phosphorylation in Avocado Fruit Slices in Relation to the Respiratory Climacteric

Young¹,

Biale²

1967

Sumiiiary. The rate of uptake of inorganic phosphate by tissue discs from both preclimacteric and climacteric peak avocados is linear for at least 60 minutes. The loss cf 32p upon excessive washing was much greater from peak than from preclimacteric tissue. Short inctubation periods and, most important, rapid washing procedures are essential for meaningful comparisons.Phosphate esterification proceed,ed at a much greater rate in climacteric than in preclimacteric tissue. The phosphorylation was sensitive to 2,4-dinitrophenol (DNP). The A-DP to ATP ratio decreased materially with the advance of ripening. It was concluded that neither uncoupling nor acceptor control can account for the onset of the respiratory rise. Changes in permeability appear to play an important role in fruit metabol,ism during the climacteric.Many fruit exhibit a marked increase in respiratory activity shortly after picking which has been referred to as the climacteric rise in respiration. A number of explanations of this phenomenon which have been proposed but not fully sutbstantiated, have been reviewed by Biale (2), Varner (16), Spencer (15) and by Rowan (12). Millerd et al. (9) advanced the idea that at the induction of the climacteric an endogenous un-coupler of oxidative phosphorylation was formed which released a restraint on oxygen utilization. Pearson and Robertson (10) and Hulme (7) proposed a different mechanism which could also account for the rise in resipiration. They suggested that oxidation was limited by the amount of ADP available to the phosphorylative sites in the preclimacteric tissue. With the induction of the clifmacteric increased protein synthesis would tendi to increase the ADP/ATP ratio and release respiration from the restraint imposed by limiting levels of ADP.The uncoupl,ing hypothesis was supported by experiments with tissue slices which showed the addition of the uncoupler 2,4-dinitrophenol i(DNP) caused an increase in oxygen uptake in tissue slices of preclimacteric but not of clinacteric fruit (9). On the other hand, experiments with isolated mitochondria could not be explained by thiis hypothesis. Romani and Biale (11)