Nucleic Acid and Protein Changes in Relation to Cold Acclimation and Freezing Injury of Korean Boxwood Leaves

Abstract

Quantitative and qualitative differences in nucleic acids of Korean boxwood (Buxus microphylla var. Koreana) leaves were determined by methylated albumin kieselguhr chromatography at different levels of cold hardiness. During cold acclimation there was an increase in RNA, mainly ribosomal RNA, with little or no change in DNA. The increase in ribosomal RNA was closely paralleled by an increase in water soluble and membrane bound proteins. As cold hardiness increased, ribonuclease activity declined.Exposure of hardy boxwood plants to warm temperatures resulted in a rapid loss in cold resistance and a rapid synthesis of nucleic acids as judged by ' (13,14,16, 25).While this is an attractive idea, it is possible that observed autumnal increases in proteins and nucleic acids are due to reduced degradation by nucleases and proteases during sample preparation rather than increased synthesis rates. RNase activity has been shown to decrease in woody plant tissues during the autumn (8), and substantial nucleic acid degradation has been observed in boxwood leaves during lyophilization (5). Another possibility is that the nucleic acid and protein increases are real, but that these changes bear a coincidental rather than a causal relationship to cold acclimation. For example, proteins and nucleic acids may increase in the autumn as a result of a build up of precursor pools in the living bark of deciduous plants when leaves senesce and abscise.This study was designed to investigate these possibilities by examining the changes in proteins and different classes of RNA during cold acclimation in Korean boxwood leaves. The fate of nucleic acids following lethal freezing was also examined. Korean boxwood is a broad-leaved evergreen shrub which retains its leaves throughout the autumn and winter when major changes in hardiness occur. MATERIALS AND METHODSThe four general types of studies which were conducted involved: (a) characterization of cold acclimation of Korean boxwood leaves (Buxus microphylla var. Koreana) in the field with concurrent measurements of changes in nucleic acids, proteins, and RNase activity; (b) similar studies during acclimation at different photoperiods in controlled environment chambers; (c) examination of changes in the metabolism of nucleic acids during short term dehardening and rehardening when hardy plants were exposed to alternating periods of high and low temperatures; (d) a study of the fate of nucleic acids in leaves following exposure to a killing frost. GENERAL METHODSLeaf Hardiness Evaluations. The leaves of boxwood were the basic experimental unit for all analytical and hardiness evaluations in this study. The overwintering leaves are mature, differentiated organs which do not undergo cell division or other visible signs of growth and development during the autumn, winter, and spring when their cold resistance changes significantly. Since Korean boxwood is an evergreen species, this choice of material reduces the problem of a major build up in precursor pools such as that which occurs...

Nucleic Acid Metabolism during Germination of Pima Cotton (Gossypium barbadense)

“…To determine the periods of active RNA synthesis during germination, germlings were labeled with 10 [tCi of 3H-uridine, and the experiment was conducted as described for the DNA analysis. After incubation, the plants were rinsed in cold, distilled H20 and ground in To get some insight into which RNAs were synthesized at each 6-hr time interval, the RNAs were fractionated in a linear sucrose gradient (5-25% sucrose in acetate-EDTA medium) with a Spinco SW-50 rotor at 40,000 rpm for 5 hr and the radioactivity was analyzed as described.…”

“…To determine if response to chilling temperatures is mediated, in part, through alterations in nucleic acid metabolism (10,16), it is imperative to have some insight into the metabolic patterns that occur during germination under ideal growth conditions. It has been shown by Waters and Dure (8,26) that the metabolism of ribosomal RNA nation in upland short staple cotton exhibits characteristic patterns.…”

Ribosomal Changes during Induction of Cold Hardiness in Black Locust Seedlings

“…There have been many suggestions that protein synthesis plays a role in cold hardening (1, 4, 9, 13, 23). Among the many changes found during induction of cold hardiness are those which occur in RNA (13, 26) and protein (3, 4,9,13,26) metabolism. This study was undertaken to examine the ribosome as related to induction of cold hardiness.…”

Protein synthesis and freezing tolerance in plant cells

“…DNA levels remained constant during acclimation in boxwood leaves, 33 black locust, 34 red osier dogwood, 29 and mimosa epicotyls and hypocotyls. 35 Drought-induced freezing tolerance was also associated with constant DNA levels.…”

“…45 -46 There was a 50% increase in the rate of rRNA synthesis in boxwood leaves during acclimation. 33 Similarly, increases in rRNA were reported to accompany freezing tolerance in potato. 42 Paldi and Devay 46 attributed increased RNA synthesis during acclimation to a lack of disruption of the synthetic process.…”