Glucose Metabolism of Various Tissues of Pear Buds

Abstract

Various tissues in flower buds of Pyrus calleryana Decne. differ in their metabolic activity. Brown outer scales utilized more exogenously supplied glucose, particularly through the pentose phosphate pathway, than did the central axes and the green inner scales. They also contained more endogenous reducing sugars, and glucose leaked out more readily from the brown scales than from the other tissues. In contrast, respiration of the central axes was nine times as great as that of the brown scales, and two to four times as much glucose was metabolized through glycolysis. Membranes of the central axes were less permeable to glucose. Because the brown scales are 75% of the dry weight of the bud, they domiinate its pattern of glucose metabolism.The resting flower bud of a tree is a complex organ composed of at least three different tissues: the brown outer scales; the green inner scales; and the central axis. In studying metabolism of buds, most investigators have used the entire structure and found that the metabolism resembled that of old rather than of young tissues. Thom's work (17), which included a comparison of bud parts, is a notable exception.In developing a procedure for extracting RNA from pear buds, we found that unknown substances in the brown scales interfered with the extraction of nucleic acids from the central (3,5,9,12,16,18). Buds also contain a substantial amount of fatty material (6). In the bud cells the deposition of a lipoid layer on the surface of the protoplasm is associated with the separation of the protoplasm from the cell walls (7). As the plants leave the rest period the protoplasm absorbs water and swells (6, 19). Glucose metabolism changes during swelling. The contribution of the pentose-P pathway to respiration decreases and the role of the Embden-Meyerhof-Parnas glycolytic pathway increases during this time (19). The change in water content of buds during swelling indicates that resting buds are relatively dry. Dehydrated tissues have been shown to respire more through the pentose-P pathway (11), and this can be accepted as an explanation for the relatively high pentose-P pathway activity in resting buds. The state of dehydration may mimic the effect of the age of the tissues with respect to their respiratory pattern.Another measure of cell age is the permeability of cell membranes. Increases in permeability of cell membranes with age were observed in apples (4), avocados (15), bananas (2), and bean endocarp (10) and are considered normal for senescing tissues (13). MATERIAS AND METHODSPlant Material. Terminal flower buds from two 7-year-old trees of Pyrus calleryana Decne. were collected between midJanuary and mid-March 1970. The upper portion of both trees had flowered at least four times before the start of the experiment. We cut shoot tips from the tree 5 to 8 feet above ground and brought them into the laboratory. There we excised the terminal buds and stripped away all the bud scales. The outermost two or three scales were discarded and the remaining scales were separa...

Preliminary Study on Effect of Early Defoliation on Dry Matter Accumulation and Storage of Reserves on ‘Abbé Fétel’ Pear Trees

“…Storage carbohydrates sustain the early stages of growth in spring, during budbreak and leaf growth until leaves have developed the photosynthetic capacity to independently support net carbon assimilation (Flore and Layne, 1999;Regier et al, 2010;Whiley et al, 1996a). During the dormant period (fall-winter), hydrolysis of starch and storage proteins occurs (Grochowska, 1973;Titus and Kang, 1982), supporting bud development (Keller and Loescher, 1989;Loescher et al, 1990) in the form of nucleic acid and protein synthesis (Zimmerman et al, 1970). Abbott (1970) postulated that apple buds continue developing during the entirety of the winter dormancy period.…”

Florescimento de gemas axilares em abacateiros não irrigados cultivados em clima subtropical

“…Além do aumento do número de células, as maiores dimensões das gemas podem ser atribuídas à absorção de água pelo protoplasma, a qual é maior após períodos de atividade reduzida e responsável por promover um inchaço no órgão vegetal (ZIMMERMAN, FAUST, SHREVE, 1970). Na região nordeste do estado de São Paulo, Oliveira et al (2008) Os autores mencionaram que o período foi marcado pela mudança de aparência externa e interna da gema, a qual passou de cônica, estreita e arredondada para achatada e inchada em função do aumento do diâmetro e caracterizada pelo início de formação de sépalas e brácteas no ápice meristemático, evidenciando-se uma nova conformação anatômica nas gemas de abacateiro à medida em que se tornam comprometidas com o florescimento (REECE, 1942;OLIVEIRA et al, 2008).…”

“…A presença de tais células com alta relação núcleo/citoplasmática é atribuída ao conjunto de características apresentado pelas células meristemáticas em elevada atividade metabólica, conforme observado em regiões meristemáticas das gemas de videira (BOTTI; SANDOVAL, 1990) e células pré-procambiais de embriões somáticos de pupunheira (ALMEIDA et al, 2012). Embora existam estudos sobre alterações metabólicas em espécies frutíferas (SACHER, 1982;FAUST, 1969;SHREVE, 1970;WANG;STEFFENS, 1985;BOTTI;SANDOVAL, 1990;McPHERSON et al, 1997;) e a respeito de determinações quantitativas e qualitativas de substâncias ergásticas em espécies arbóreas (KIKUCHI;SANTOS, 2007;POTIGUARA, 2009;ALMEIDA et al, 2012;GRANER, 2013), há escassez de estudos histoquímicos e informações referentes às mudanças metabólicas durante o desenvolvimento de gemas terminais e axilares de abacateiro.…”