Protein and free amino acids in field-grown cowpea seeds as affected by water stress at various growth stages

Abstract

KEY WORDSAmino acids Cowpea Proteins Water stress SUMMARY This study was undertaken to evaluate water stress effects during vegetative, flowering, and podfilling stages ofcowpea plants ( Vigna unguiculata L.) grown under natural field conditions in southern California on seed yield and protein and free amino acid content of the cowpea seeds.The lowest concentration of N was found in the seeds of the control treatment plants while the seed yield from these treatments was the highest as compared with the N concentration and yield of seeds from plants subjected to water stress during flowering and podfilling stages. The concentration of N in the seeds was inversely related to the seed dry weight yield.Protein arginine, -threonine, -serine, -cystine, -valine, -methionine, and -isoleucine were significantly affected by water stress at the three growth stages. There was no consistent pattern in the effect of water stress on the individual amino acids. The sum of protein amino acids in the cowpea seeds was not significantly influenced by the various treatments since some of the protein amino acids increased and others decreased producing an averaging effect on the figures comprising the sums of the amino acids.Water stress during the flowering and pod-filling stages increased the free amino acid pool, and at the same time, inhibited incorporation of the amino acids into the protein chain-thus lowering the protein amino acid fraction simultaneously.With the exception of methionine plus cystine, the essential amino acids in the seeds were present at concentrations equal to or greater than recommended by the World Health Organization and FAO. It is of particular importance to note that the concentration oflysine in the cowpeas was substantially higher than that found in wheat grain. It is also important to note that the amount of essential amino acids per gram of protein was not measurably affected by the water stress treatments during any of the growth stages.

Rhizobium -Legume Symbiosis and Nitrogen Fixation under Severe Conditions and in an Arid Climate

“…In these plants, positive correlations were found between proline accumulation and drought tolerance. Other compounds, e.g., the free amino acids and low-molecular-weight solutes such as pinitol (o-methylinositol), accumulate in several tropical legumes under drought stress (112,185). Potassium is known to improve the resistance of plants to environmental stress.…”

Selected Abiotic and Biotic Environmental Stress Factors Affecting Two Economically Important Sugarcane Stalk Boring Pests in the United States

“…Osmotic stress in plants involves several interconnected molecular pathways that transmit signals and produce stress-response metabolites [73,74], and gene transcripts associated with signaling can be up-or down-regulated within minutes of stress induction [75,76]. As drought conditions continue, plants often have relatively low osmotic potential [77][78][79], heightened oxidative stress [80,81], and to reduce water loss to the extent possible, accumulations of osmolytes such as antioxidants, amino acids, carbohydrates, and inorganic ions, altering the attractiveness and nutritional value of the plant to herbivorous arthropods [68][69][70]82]. Chemical cues (semiochemicals) emitted by plants, frequently involving volatiles, have a major role in host plant selection and utilization by herbivorous arthropods [83][84][85][86][87][88][89][90].…”

Elucidation of Abiotic Stress Signaling in Plants

“…Drought stress may cause a decline in protein content and an increase in the level of amino acids (Labanauskas et al 1981 ;Navari-Izzo et al 1990 ;Sudachkova et al 1996 ;Hirel and Lea 2001 ). Low relative water content (RWC) was evidenced to stimulate the transcription and translation of genes of enzymes (e.g., 1-pyrroline-5carboxylase reductase) involved in the synthesis of glutamate that was argued to cause enhancement in the production of proline.…”