Changes in Amino Acid Content of Excised Leaves During Incubation I. The Effect of Water Content of Leaves and Atmospheric Oxygen Level

Abstract

Simum ary. Excise(d leaves xwere inculbate(1 at various water contenits to dletermince the effect of water statuis on amino acid compositioni. Conisiderable proteoly sis took place dutiring incllbation Nx-ith a resultant increase iI each amino acid in the non-pr-oteill fractioni. However, serine, proline, y-aminobutyric acid and methylcysteine suilfoxide were the only amino aci(ls in which there was an accuimulationl (i.e., net synthesis). Serine showeed a small but conisistenit accutmullationi lastilng for 6 days. Proline showed a greater acculmuilatioln lut this ceased after 2 days.To learn more alout the conitrol of the proliine acctniillation (Iiring xvilting, tuirgid andl wiltedI leaves Nwere inculbated under aerobic and anaerobic conditiolns. The amino aci(I analyses showed that tuirgid leaves did niot accumnutilate proline and( that proline and methylcysteinie sillfoxide acculmuilation wx'as abolished )y naerobliosis. \Vith other amino acids, relative concentrationi changes between wilted and noni-xNilted leaves were less striking than the difference betweeni -aerobic and anaerobic coII-(litiomus.Und ( (diurnal). \Water insuifficieincy in a growing plant resuilts in wilting xxhich has profouind effects (9, 10, 38) on1 photosynthesis (4/7 ), respiration (23) iiucleic acids (8,29 ) and oIn nlitrogen metabolism (2,3,13,26,40,49). In order to iin(lerstanch and possibly control the effects of xvater deficiency on a plant, more nee(ls to be knoNx-n about the effects of dehydration at the cellullar anid suibcelluilar- le-vel THOMPSON ET AL.-AMINO ACIDS DURING WILTING AND ANAEROBIOSIS Materials and MethodsLeaves from greenhouse-grown turnips (Brassica rapa L. var. Shogoin) were used for most experiments. The leaves were excised and the midribs removed. One-half of each of 6 leaves were killed immediately after cutting to serve as controls. The other halves of these 6 leaves were incubated in the various treatments. Half leaf samples obtained in this way were similar in composition when compared on a fresh weight basis. The total amino nitrogen valuies were equivalent (on a fr wt basis) between paired half leaf samples to an average of 3.0 % (6 pairs), whereas the total uncombined amino nitrogen valutes agreed to an average of 2.5 %. The total amount of individual amino acids in comparable samples were equal to within ±5 %. The levels of individual uncombined amino acids in one half leaf sample were within ±10 % of the level in the other half leaf sample, except for valine and tyrosine which were equal to ±+15 % and asparagine to within ±30 %. Although these differences are relatively small, consideration of the effects of treatment has been restricted to changes of at least 20 % for total amino acids and of 100 % for uncombined amino acids.In the first experiment, leaves were dried in light (200 ft-c) at 200 until they had lost 50 % of their fresh weight (1-2 hrs). The leaf samples (6 half leaves) were then rolled loosely and placed in 100 ml bottles which were closed to prevent further water loss. The bottles ...

Rapid Accumulation of γ-Aminobutyric Acid and Alanine in Soybean Leaves in Response to an Abrupt Transfer to Lower Temperature, Darkness, or Mechanical Manipulation

“…Similar changes in the amino acid composition of detached leaf tissue, as described in this investigation, have been reported by others. There are several reports of an increase in alanine and Gaba and decrease in glutamate and aspartate when leaves were incubated under anaerobic conditions (6,22,24). Unlike the rapid changes we have demonstrated, a treatment of at least 1 h under anoxia was necessary to give the same accumulation of Gaba and alanine in radish leaves (22).…”

Anaerobic Accumulation of γ-Aminobutyric Acid and Alanine in Radish Leaves (Raphanus sativus, L.)

“…Alanine and GAB reached levels approximately equivalent to 7-and 100-fold accumulations, respectively. The anaerobic depletion of aspartate and glutamate in leaves has been reported previously (7,25), but in studies where roots were exposed to anaerobiosis for periods of 1 to 7 days, glutamate content increased in most tissues (6, 11) while aspartate content remained approximately the same (11). Proteolysis may have contributed significantly to glutamate content over the extended incubation periods used in the studies with roots.…”

“…Changes in enzyme content did not explain the changes in reaction rates in vivo. Most of the aspartate may be converted anaerobically to alanine via oxalacetate and pyruvate.Several reports on the anaerobic accumulation of -y-aminobutyrate in higher plant tissues have appeared in the last 10 years (6,7,10,11,25). GAB2 becomes markedly more radioactive under anaerobic than aerobic conditions when labeled glutamate (18) or CO2 (8) is administered to plants.…”

“…GAB2 becomes markedly more radioactive under anaerobic than aerobic conditions when labeled glutamate (18) or CO2 (8) is administered to plants. Uncom-bined alanine accumulated anaerobically in quantities greater than those of GAB (6,7,11,25). Anaerobiosis also induces accumulations of GAB in Chlorella (14,29) and in mammalian brain tissue (31).…”

Osmoregulation of a Pyrroline-5-Carboxylate Reductase Gene in Arabidopsis thaliana

“…The mechanisms by which Pro accumulates are mainly de novo synthesis from glutamate (Morris et al, 1969;Boggess et al, 1976;Wang et al, 1982;Badzinski Buhl and Stewart, 1983;Rhodes et al, 1986;Venekamp and Koot, 1988;Venekamp et al, 1989) and, to a lesser extent, a stress-induced decrease in protein incorporation (Dungey and Davies, 1982), inhibition of Pro oxidation (Stewart et al, 1977), and enhanced proteolysis (Thompson et al, 1966). The Pro biosynthetic pathway is poorly known in higher plants and is thought to occur as in microorganisms, from glutamate via three enzymic steps.…”