Ribonucleic Acid and Protein Metabolism in Pea Epicotyls

Abstract

Aging of actively growing, etiolated pea Pisum sativum L. var Alaska plants was initiated by removing the plumules of plants in the third internode stage, and applying lanolin to the cut apices of otherwise intact plants. During the subsequent 4-day aging period, several degenerative events occurred in this apical 10-millimeter region. Ribosomal RNA and messenger RNA contents declined, polyribosomes disaggregated, and the protein synthesizing capacity of the polysomes decreased.Two-dimensional, silver-stained protein patterns revealed that aging altered the relative amounts of specific cellular proteins accumulated in vivo. In addition, polypeptide patterns generated by cell-free translation of total and polysomal RNA, isolated from unaged and aged tissues, showed major modifications. More than 200 spots could be resolved by two-dimensional gel fluorography of translation products using RNA from fresh tissues. Of these 200 spots, about eight appeared or increased when total RNA from aged tissue was used, and about 58 disappeared or declined. When polysomal RNA from aged tissue was used as template, about 12 spots appeared or increased, whereas about 64 disappeared or decreased. In general, the products which increased after aging were lower molecular weight and those that decreased were higher molecular weight.Aging of etiolated pea stem tissue is initiated by removal of the hook and plumule and application of lanolin to the cut end. During a 4-d period, this aging process changes actively growing tissue into nongrowing tissue presumaby because of a depletion of endogenous auxin (7).The terms aging and senescence are frequently used synonymously, but the system described here is not truly senescing. Here, aging is more aptly termed a maturation process, in contrast to senescing tissues which are undergoing a set of processes leading to death (13). The term 'aging' is also used when describing the aerobic activation of plant storage tissues (9). Since the latter is a rejuvenation event, aging in that context means nearly the opposite of what is defined here.Because this aged pea system is relatively inactive metabolically, it has served as a control to study auxin effects (e.g. 3-5, 19) and wounding effects (6,18) 'To whom all correspondence should be addressed.happen during aging are: a decline in the levels of soluble protein and nucleic acid and an increase in 3-1,3-glucanase activity (5), a slight decrease in cellulase activity (2), and a disaggregation of free polyribosomes (4).This study was initiated to provide a more detailed description of the decline in macromolecular processes which occur during aging as a prerequisite to understanding the reversal of these processes brought about by wounding (18) and by auxin treatment (19). MATERIALS AND METHODSGrowth and Treatment of Plants. Pea seeds (Pisum sativum L. var Alaska) were soaked for 20 min in 10% (v/v) Clorox and then allowed to imbibe in tap water overnight. The seeds were sown in moist vermiculite and placed in a dark room for germination and...

Ribonucleic Acid and Protein Metabolism in Pea Epicotyls

“…However, the protein synthesizing capacity of the total ribosomes increased about 90%. The RNA content per segment increased between 10 and 20% whether measured spectrophotometrically or from areas of rRNA profiles of GPS extracts (15) (Fig. 3).…”

“…Aging of etiolated pea stem tissue evokes a decline in all the components measured relating to protein synthesis (15). mRNA content, rRNA content, polysomes, and ribosomal efficiency all decrease dramatically during the 4-d aging process.…”

“…3). This methodology was preferred over in vivo labeling of the proteins for reasons discussed in Schuster and Davies (15,16). Out of more than 500 proteins resolved by this two-dimensional gel system, the patterns revealed only two spots which appeared to be affected as a result of auxin treatment.…”

“…All other procedures were identical to those described in Schuster and Davies (15 recruitment of free monosomes onto message within both populations (3). Although there is only a slight increase in the total amount of ribosomal material, the amount of mRNA doubles in the free polysomes within 6 h of hormone treatment (4).…”

Ribonucleic Acid and Protein Metabolism in Pea Epicotyls

“…The questions posed in this study are: (a) to what extent are various components involved in protein synthesis affected during wounding; (b) what factors contribute to increased polysome formation and protein synthesis; (c) are specific proteins made (and accumulated) or All of the other materials and methods were identical to those described previously (10). RESULTS …”