Protein, Nucleotide, & Ribonucleid Acid Metabolism in Corn During Germination Under Water Stress

Abstract

While the influence of sub-optimal water levels on gross aspects of plant growth has been investigated extensively (3,5,6,13,19), little is known about the effect of water stress on metabolic processes. More information on specific effects is needed to establish the influence of environmental-water stress on plant growth and development. One research approach is to follow, in plants under water stress, the composition changes of constituents that have been associated with seedling growth.During normal germination and growth, changes which occur in some of the storage organs and seedlings have been reported. Schulze (21) determined that during germination in the dark, embryo-amino acids originated from the degradation of seed protein. Oota and Osawa (17) found that the RNA3 of the seed contributed to the RNA of the embryo. Recent investigations by Cherry and Hageman (2) showed that protein and RNA of corn scutellum decreased during 4 days of germination and that radicle protein and RNA increased. Soluble nucleotides increased in both the scutellum and the radicle but at a faster rate in the radicle.When the water content was reduced in leaf cells, Petrie and Wood (20) showed that the production of amino acids and formation of protein from amino acids was reduced. Presumably, any influence of water stress on plant development would alter the metabolic reactions involved in protein formation because rapid and orderly production of enzymatic and structural protein is required in growth. Materials & MethodsApproximately 110 corn (Zea mays L. doublecross hybrid, var. Dixie 18) seeds were placed embryo down on a paper towel supported by 750 ml of acid-washed gravel in a 9 X 14 inch glass dish. To the dishes, 350 ml of 10-4 M CaCl,, 0.2 M, 0.4 M, or 0.6M mannitol were added to impose water stress equivalent to 0.02 (check), 4.9, 9.8, and 14.7 atmospheres of osmotic pressure, respectively.The plants were grown in darkness for 1 to 6 days under conditions of 100 % relative humidity and constant temperature of 29 C. The seedling, consisting of the entire epicotyl, hypocotyl, and radicle (hereafter referred to as the seedling) was separated from the endosperm and scutellum (called endospermscutellum). Duplicate samples of 10 endospermscutella and seedlings were blotted dry with tissue paper and fresh and dry weights were determined.

Metabolic changes associated with the germination of corn. II. Nucleic acid metabolism.

“…These data and the previous work with barley (5) suggest that the nucleic acids stored in the endo- (2), and a similar decrease in the RNA content of the endosperm plus scutellum in which 90 % of the RNA was lost (19) have been reported. As previously discussed (7), however, it is thought that the method of RNA extraction and estimation used by these workers was unsuitable for the tissues under investigation, and is responsible for the differences in the results.…”

Effect of Fluoride on Nucleotides and Ribonucleic Acid in Germinating Corn Seedling Roots

“…Adenine was depressed significantly only by the highest fluoride treatment. The 'present finding of the altered RNA base raltios is presumably associated with the modified nucleotide species (table I) since the changes in RNA base ratios have been reported to be influenced by altered ratios of nucleotides (13,14,23).…”

“…Changes in toltal RNA ba)se ratios induced by fluoride would be a reflection of changes in base ratios of either soluble RNA and/or ribosomal RNA (23). Changes in soluble RNA base ratios also have been reported to be correlated with temperature-con,trolled growth rate (3).…”

“…Factor(s) whiich influence (s) RNA metaboilism and/or protein synthesis therefore ishould be reflected in the growth rate (5,24). Environmentall factors affecting growth such as soditum anid potassium (20), temperature (3), and water stress (23), ihave been reported to influence, respectively, .synthesis of RNA fractions and nucleotides, base .co,mposition of RNA, and relative ra'tios of nucleotide species in higher plants. However Fractionation of Nucleotide Species.…”

“…Since fluoride modifies ratios of nucleotide species with the greatest alteration in those of the triphosphate nucleotides, the production of nucleotide species altered in their relative ratios presumably could influence protein formation and in turn growth through possible alterations in amino acid activation, RNA metabolism or both (23 The 4 bases of perchloric acid-hydrolyzed RNA were stuccessfully separated in control and filuoridetreated materialls by the present procedure. Table IHI shows that fluoride alters markedily the base composition of the corn seedling root RNA.…”