Activity Of Pea Research Articles

Enhanced accumulation of phenolics in pea (Pisum sativum L.) seeds upon foliar application of selenate or zinc oxide.

Selenium (Se) and zinc (Zn) are essential antioxidant enzyme cofactors. Foliar Se/Zn application is a highly effective method of plant biofortification. However, little is known about the effect of such applications on the concentration of trace elements and phytochemicals with pro-oxidant or antioxidant activity in pea (Pisum sativum L.). A 2-year pot experiment (2014/2015) was conducted to examine the response of two pea varieties (Ambassador and Premium) to foliar-administered sodium selenate (0/50/100 g Se/ha) and zinc oxide (0/375/750 g Zn/ha) at the flowering stage. Concentrations of selected trace elements (Fe, Cu, and Mn), total phenolic content (TPC), total flavonoid content (TFC), and total antioxidant activity (ABTS, FRAP) of seeds were determined. Se/Zn treatments did not improve the concentration of trace elements, while they generally enhanced TPC. Among examined treatments, the highest TPC was found in Ambassador (from 2014) treated with 100 g Se/ha and 750 g Zn/ha (2,926 and 3,221 mg/100 g DW, respectively) vs. the control (1,737 mg/100 g DW). In addition, 50 g of Se/ha increased TFC vs. the control (261 vs. 151 mg/100 g DW) in Premium (from 2014), 750 g of Zn/ha increased ABTS vs. the control (25.2 vs. 59.5 mg/100 g DW) in Ambassador (from 2015), and 50 g of Se/ha increased FRAP vs. the control (26.6 vs. 18.0 mmol/100 g DW) in Ambassador (from 2015). In linear multivariable regression models, Zn, Mn, Cu, and TPC best explained ABTS (R = 0.577), while Se, Cu, and TPC best explained the FRAP findings (R = 0.696). This study highlights the potential of foliar biofortification with trace elements for producing pea/pea products rich in bioactive plant metabolites beneficial for human health.

Response of Oxidative Stress and Antioxidant System in Pea Plants Exposed to Drought and Boron Nanoparticles.

Pea plants are sensitive to water shortages, making them less attractive to farmers. Hoping to reduce the adverse effects of drought on peas and considering the benefits of boron, this study aimed to investigate the impact of boron nanoparticles on the antioxidant system and oxidative stress biomarkers in drought-stressed peas. Experiments were performed in a greenhouse. Pea plants were treated with a suspension of B2O3 nanoparticles at 12.5, 25, and 50 ppm concentrations before ten days of water shortage. Drought effects were induced by maintaining 30% substrate moisture. This study investigated the properties of the nanoparticle suspension and different application methods for spraying and watering pea plants. The effects of B2O3 nanoparticles and drought were determined on pea growth indicators, oxidative stress biomarkers, and enzymatic and non-enzymatic antioxidants. Spraying with B2O3 nanoparticles at 12.5 ppm most effectively stimulated phenol accumulation; FRAP, DPPH, and ABTS antioxidant capacity; and APX, SOD, GPX, and CAT enzyme activity in pea leaves exposed to drought. In addition, B2O3 nanoparticles reduced the amount of MDA and H2O2 in pea plants grown on a substrate with insufficient moisture. The most substantial positive effect was found on peas affected by drought after spraying them with 12.5 ppm of B2O3 nanoparticles. B2O3 nanoparticles positively affected the pea height, leaf area, number of nodules, and yield.

Role of biostimulants (ascorbic acid and fulvic acid) to synergize Rhizobium activity in pea (Pisum sativum L. var. Meteor)

Biostimulants such as ascorbic acid (AA) and fulvic acid (FA)can enhance the efficiency of root-nodulating bacteria. This study investigates optimum concentration of these two biostimulants to maximize the Rhizobium activity and increase root size, nodulation capability, NPK uptake, yield and quality. Interaction with nitrogenase enzyme through molecular docking was also studied by using both AA and FA as ligands to better understand their inhibitory role in excess amounts. The findings of the study suggest: the combined application of both FA and AA at 200 ppm concentrations proved to be more effective than the individual application. Excellent vegetative growth was noticed which translated into an increased reproductive growth i.e statistically significant increase in number of pods per plant, fresh and dry weight of pods per plant, number of seeds per pod, total chlorophyll, carotenoids and chemical constituents of pea seeds i.e. N (16.17%), P (40.47%), K (39.96%) and protein (16.25%). These findings were substantiated by molecular docking of nitrogenase enzyme with ascorbic acid and fulvic acid. The XP docking score of ascorbic acid (−7.07 kcal mol-1) and fulvic acid (−6.908 kcal mol-1) exhibited that the optimum doses (200 ppm) should be used as higher dose or their excess amount can hinder the Rhizobium activity of nitrogen fixation by interacting with the nitrogenase enzyme.

Nitric Oxide Enhances Salt Tolerance through Regulating Antioxidant Enzyme Activity and Nutrient Uptake in Pea

Background: Salinity is one of the environmental stress factors that restrict the crop production by endangering agricultural areas. Nitric oxide (NO) protects plants from damage caused by oxidative stress conditions in various biological ways. Methods: In this greenhouse investigation during 2018, pea plants were irrigated with three levels of NaCl (0, 50 and 100 mM) solutions. NO solutions were prepared with three different doses (0, 75 and 100 µM SNP). These solutions were applied to the seeds before sowing and then to the leaves of the pea cultivars. The study was conducted to analyze the impact of NO on growth, malondialdehyde (MDA), hydrogen peroxide (H2O2), antioxidant enzyme activity and nutrient uptake in two pea cultivars under salinity conditions. Result: Salinity reduced fresh-dry weight, relative water content (RWC), and chlorophyll a and b content of pea. However, NO enhanced these parameters under salt stress. Salinity increased tissue electrical conductance (TEC), H2O2 and MDA content, which were decreased by combined application of NaCl and NO. Salinity caused an increase in antioxidant enzyme activity in pea and NO made a significant improvement in their activities under salinity conditions. Salinity treatments decreased the ratio of K+/Na+ and Ca2+/Na+ in both cultivars, and application of NO elevated them as compared to the control under salt stress. In conclude, exogenous NO treatment could help pea to tolerate salinity stress by increasing the chlorophyll content and regulating antioxidant enzyme activity and nutrient uptake.

A polygalacturonase localized in the Golgi apparatus in Pisum sativum.

Pectin is a plant cell wall constituent that is mainly composed of polygalacturonic acid (PGA), a linear α1,4-d-galacturonic acid (GalUA) backbone. Polygalacturonase (PG) hydrolyzes the α1,4-linkages in PGA. Nearly all plant PGs identified thus far are secreted as soluble proteins. Here we describe the microsomal PG activity in pea (Pisum sativum) epicotyls and present biochemical evidence that it was localized to the Golgi apparatus, where pectins are biosynthesized. The microsomal PG was purified, and it was enzymatically characterized. The purified enzyme showed maximum activity towards pyridylaminated oligogalacturonic acids with six degrees of polymerization (PA-GalUA6), with a Km value of 11 μM for PA-GalUA6. The substrate preference of the enzyme was complementary to that of PGA synthase. The main PG activity in microsomes was detected in the Golgi fraction by sucrose density gradient ultracentrifugation. The activity of the microsomal PG was lower in rapidly growing epicotyls, in contrast to the high expression of PGA synthase. The role of this PG in the regulation of pectin biosynthesis or plant growth is discussed.

Effects of polyaromatic hydrocarbons on photosystem II activity in pea leaves

The acute effects of three typical polyaromatic hydrocarbons (PAHs): naphthalene (Naph), phenanthrene (Phen) and fluoranthene (Flu) on photochemical activity of photosystem II (PSII) in detached leaves of 3-week-old pea plants were studied. The leaves were exposed in water with PAHs under white light for 0.5–72 h. The activity of PSII was examined by prompt and delayed chlorophyll a (Chl a) fluorescence. The effects of PAHs depended on their concentration and exposure time. This dependency was more significant in the presence of chemical stressors (Triton X-100 or acetone) or under high intensity irradiance. Increased content of PAHs and long-term exposure (24–72 h) led to significant reduction of the maximum photochemical quantum efficiency (Fv/Fm) of PS II, changes in the polyphasic fluorescence induction (OJIP), and to decreasing amplitudes of fast and slow components of delayed Chl a fluorescence. The damage of PSII depended on water solubility of a given type of PAHs, their concentration and exposure time. During short-time exposure the compound with highest water-solubility – naphthalene – revealed the strongest effect. During long-time exposure the compounds with low water-solubility –Phen, Flu-revealed the strongest effect as the corresponding PAH accumulates in the thylakoids especially when the solution is oversaturated containing a solid phase. The reduction of PSII activity at the presence of naphthalene (30 mg L−1) was accompanied by transient generation of H2O2 as well as swelling of thylakoids and distortion of cell plasma membranes, which was indicated by electron microscopy images. Distortion of thylakoid membranes due to accumulation of PAHs as well as the development of oxidative stress seems to be the main pathways of PAHs influencing the photochemical activity of PS II.

GH3 expression and IAA-amide synthetase activity in pea (Pisum sativum L.) seedlings are regulated by light, plant hormones and auxinic herbicides

The formation of auxin conjugates is one of the important regulatory mechanisms for modulating IAA action. Several auxin-responsive GH3 genes encode IAA-amide synthetases that are involved in the maintenance of hormonal homeostasis by conjugating excess IAA to amino acids. Recently, the data have revealed novel regulatory functions of several GH3 proteins in plant growth, organ development, fruit ripening, light signaling, abiotic stress tolerance and plant defense responses. Indole-3-acetyl-aspartate (IAA-Asp) synthetase catalyzing IAA conjugation to aspartic acid in immature seeds of pea (Pisum sativum L.) was purified and characterized during our previous investigations. In this study, we examined the effect of auxin and other plant hormones (ABA, GA, kinetin, JA, MeJA, SA), different light conditions (red, far-red, blue, white light), and auxinic herbicides (2,4-D, Dicamba, Picloram) on the expression of a putative GH3 gene and IAA-amide synthesizing activity in 10-d-old pea seedlings. Quantitative RT-PCR analysis indicated that the PsGH3-5 gene, weakly expressed in control sample, was visibly induced in response to all plant hormones, different light wavelengths and the auxinic herbicides tested. Protein A immunoprecipitation/gel blot analysis using anti-AtGH3.5 antibodies revealed a similar pattern of changes on the protein levels in response to all treatments. IAA-amide synthetase activity determined with aspartate as a substrate, not detectable in control seedlings, was positively affected by a majority of treatments. Based on these results, we suggest that PsGH3-5 may control the growth and development of pea plants in a way similar to the known GH3 genes from other plant species.

NAD pattern and NADH oxidase activity in pea (Pisum sativum L.) under cadmium toxicity

Seeds of pea (Pisum sativum L.) were germinated for 5days by soaking in distilled water or 5mM cadmium chloride. Compared to the control, cadmium (Cd) caused a reduction in percent germination and embryo growth. Pyridine nucleotide coenzyme concentrations were determined in cotyledons and embryonic axis. Nicotinamide adenine dinucleotide (NADH) oxidase activity was examined. Cd treatment caused a restriction in levels of reduced coenzyme form in the mitochondria and the post-mitochondrial fraction of cotyledons, and embryonic axis. The oxidized coenzyme form has been accumulated by Cd-treated mitochondria of both tissues. It was also found that NADH oxidase activity was stimulated. The relationship between coenzyme levels, seed germination, pea growth, and Cd stress has been reported.

Degradation of DNA and endonuclease activity associated with senescence in the leaves of pea of normal and aphyllous genotypes

Senescence and wilting of the leaves of pea (Pisum sativum L.) of normal (AfAf) and aphyllous (afaf) genotypes were accompanied by DNA degradation. In young (12th–9th) subapical leaves of AfAf plants, total DNA was high-polymeric; in the 6th leaf, DNA degradation was appreciable; and in the 4th and 3rd leaves, hydrolysis of DNA was pronounced. Similar degradation of DNA was also observed in senescing leaves of aphyllous plants, but there it started later than in the plants of normal type. The extent of DNA degradation was closely related to the elevation of total nuclease activity in pea leaves associated with the age. The leaves of plants of different genotypes distinctly differed in the activity of acid and alkaline nucleases. Senescence of the leaves was accompanied by the induction of Ca2+-and Mg2+-dependent nucleases with mol wts of 42, 37, 34, 26, and 21 kD. In different stages of leaf senescence, different sets of nucleases were detected.

Amino acid transporter expression and localisation studies in pea (Pisum sativum).

Expression of the amino acid permeases PsAAP1 and PsAAP2 was analysed in developing pea (Pisum sativum L.) plants. Both transporters were expressed in seed coats and cotyledon epidermal transfer cells and storage parenchyma cells. AAP expression is developmentally regulated and coincides with the onset of storage protein synthesis. Nitrogen was shown to induce AAP expression and AAP transcript levels were upregulated during the photoperiod. Analysis of Arabidopsis thaliana AAP1 promoter activity in pea, using promoter-β-glucuronidase (promotor-GUS) studies, revealed targeting of GUS to seed coats and cotyledon epidermal transfer cells. Expression was found in the nutritious endosperm during the early stages of seed development, whereas GUS staining in embryos was detected from the heart stage onward. In addition, AAP1 expression was observed in the phloem throughout the plant. This finding equally applied to PsAAP1 expression as shown by in situ mRNA hybridisation, which also demonstrated that PsAAP1 expression was localised to companion cells. Overall, PsAAP1 expression patterns and cellular localisation point to a function of the transporter in phloem loading of amino acids for translocation to sinks and in seed loading for development and storage protein accumulation.

A quantitative in silico analysis calculates the angiotensin I converting enzyme (ACE) inhibitory activity in pea and whey protein digests

Angiotensin I converting enzyme (ACE) inhibitory peptides can induce antihypertensive effects after oral administration. By means of an ACE inhibitory peptide database, containing about 500 reported sequences and their IC 50 values, the different proteins in pea and whey were quantitatively evaluated as precursors for ACE inhibitory peptides. This analysis was combined with experimental data from the evolution in ACE inhibitory activity and protein degradation during in vitro gastrointestinal digestion. Pea proteins produced similar in silico scores and were degraded early in the in vitro digestion. High ACE inhibitory activity was observed after the simulated stomach phase and augmented slightly in the simulated small intestine phase. The major whey protein β-lactoglobulin obtained the highest in silico scores, which corresponded with the fact that degradation of this protein in vitro only occurred from the simulated small intestine phase on and resulted in a 10-fold increase in the ACE inhibitory activity. Whey protein obtained total in silico scores of about 124 ml/mg, compared to 46 ml/mg for pea protein, indicating that whey protein would be a richer source of ACE inhibitory peptides than pea protein. Although β-lactoglobulin is only partially digested, a higher ACE inhibitory activity was indeed found in the whey (IC 50 = 0.048 mg/ml) compared to the pea digest (IC 50 = 0.076 mg/ml). In silico gastrointestinal digestion of the highest scoring proteins in pea and whey, vicilin and albumin PA2, and β-lactoglobulin, respectively, directly released a number of potent ACE inhibitory peptides. Several other ACE inhibitory sequences resisted in silico digestion by gastrointestinal proteases. Briefly, the quantitative in silico analysis will facilitate the study of precursor proteins on a large scale and the specific release of bioactive peptides.

Engineering the Rhizobium leguminosarum bv. viciae Hydrogenase System for Expression in Free-Living Microaerobic Cells and Increased Symbiotic Hydrogenase Activity

Rhizobium leguminosarum bv. viciae UPM791 induces hydrogenase activity in pea (Pisum sativum L.) bacteroids but not in free-living cells. The symbiotic induction of hydrogenase structural genes (hupSL) is mediated by NifA, the general regulator of the nitrogen fixation process. So far, no culture conditions have been found to induce NifA-dependent promoters in vegetative cells of this bacterium. This hampers the study of the R. leguminosarum hydrogenase system. We have replaced the native NifA-dependent hupSL promoter with the FnrN-dependent fixN promoter, generating strain SPF25, which expresses the hup system in microaerobic free-living cells. SPF25 reaches levels of hydrogenase activity in microaerobiosis similar to those induced in UPM791 bacteroids. A sixfold increase in hydrogenase activity was detected in merodiploid strain SPF25(pALPF1). A time course induction of hydrogenase activity in microaerobic free-living cells of SPF25(pALPF1) shows that hydrogenase activity is detected after 3 h of microaerobic incubation. Maximal hydrogen uptake activity was observed after 10 h of microaerobiosis. Immunoblot analysis of microaerobically induced SPF25(pALPF1) cell fractions indicated that the HupL active form is located in the membrane, whereas the unprocessed protein remains in the soluble fraction. Symbiotic hydrogenase activity of strain SPF25 was not impaired by the promoter replacement. Moreover, bacteroids from pea plants grown in low-nickel concentrations induced higher levels of hydrogenase activity than the wild-type strain and were able to recycle all hydrogen evolved by nodules. This constitutes a new strategy to improve hydrogenase activity in symbiosis.

THE STIMULATION OF PHENOLICS AND ANTIOXIDANT ACTIVITY IN PEA (PISUM SATIVUM) ELICITED BY GENETICALLY TRANSFORMED ANISE ROOT EXTRACT

A series of dark germination experiments demonstrate the potential of an Agrobacterium rhizogenes-transformed, high cytokinin root extract of anise (Pimpinella anisum), to stimulate phytophenolic and enhance antioxidant activity in pea (Pisum sativum) seedlings. Average shoot weight increased 40–60% after imbibing seeds for 24 h in a 1.5 to 2.0% extract of the anise root clone AR-10. Phenolic concentration was positively correlated with shoot weight, suggesting that the total phenolic content was related to seedling vigor. Antioxidant protection factor in pea shoots was also stimulated by AR-10 extracts. Free proline concentrations were 2–3 times higher in shoots collected from AR-10 treated peas versus controls. However, proline content also increased as shoot weight declined after being subjected to an overdose of AR-10 extract in 25% ethanol. G6PDH specific activity, the first committed step of the pentose phosphate pathway, was negatively associated with shoot growth and proline concentrations.

Regulation of the Growth Processes in Pea (Pisum sativumL.) by Oxylipin (9Z)-12-hydroxy-9-dodecenic Acid

Early in seed germination, tissue lipoxygenases are activated, and the genes encoding these enzymes are rapidly expressed [1]. This evidence indicates that lipoxygenases play a physiologically important role at the initial stages of development. Such a multifunctional profile [2] of lipoxygenases presumes that they participate in cell proliferation. To illustrate, jasmonates are involved in the synthesis of taxol, a microtubule-stabilizing agent, in plant cells [3, 4]. (9 Z )-12hydroxy-9-dodecenic acid (12-HDA) was shown to promote the growth of callus derived from young soybean epicotyl [5]. Young callus consists mostly of meristematic cells, and therefore we suggest that 12-HDA particularly promotes cell divisions. That is why we studied the effect of oxylipin on the mitotic activity of root meristem and other indices of growth activity in pea. The relative numbers of dividing cells were assessed in the root meristem of pea plants, cv. Tatarstan. To follow the effects of 12-HDA on cell division, the etiolated seedlings were transferred for 0.5, 1, 2, 4, and 5 h to 10 —9 and 10 —6 M oxylipin solutions. Roots were fixed and stained with acetic orcein, and cell numbers were counted under an NU 2/E microscope (Carl Zeiss, Germany) at 500 〈 magnification. To follow the growth function, seeds were germinated for three days in the same 12-HDA solutions. Amylases were extracted with NaCl solutions, and amylase activity (AA) was assayed by incubating the enzyme extract with starch solution and determining spectrophotometrically the nonnhydrolized starch residue [6]. The data on mitotic activity were processed using Student’s t test; in the case of the growth function and AA, the confidence intervals at p 05 were calculated on the basis of the standard errors.

The Effect of Abscisic Acid and Methyl Jasmonate on Carbonic Anhydrase Activity in Pea

Short-term (2 h) treatment with 10 µM abscisic acid decreased stomatal conductance and net photosynthetic rate, and increased carbonic anhydrase activity in pea seedlings. The treatment with 10 µM methyl jasmonate did not significantly affect these parameters.

Effects of NaCl on growth and nitrogen fixation and assimilation of inoculated and KNO 3 fertilized Vicia faba L. and Pisum sativum L. plants

Faba bean ( Vicia faba L. var. minor cv. Alborea) and pea ( Pisum sativum L. cv. Lincoln) plants, inoculated with Rhizobium leguminosarum biovar. viciae strain GRA19, were treated with salt (100 mM NaCl) and/or nitrate (8 mM KNO 3) to test whether plants grown with inorganic-nitrogen are more tolerant to salinity than plants entirely reliant upon fixed nitrogen. According to the growth inhibition recorded, pea plants dependent on dinitrogen fixation proved more tolerant to salt stress than those N-fertilized, in contrast to results obtained for faba bean plants. This study therefore confirms that plants dependent on nitrogen fixation are not always more sensitive to salinity than are N-fertilized plants. Nitrate addition did not reduce the specific nitrogenase activity in pea, but did in faba bean. However, nodulation was inhibited in both legumes. The specific nitrogenase activity was more affected by salt treatment in N-fertilized plants for both legumes. The activity of the enzymes mediating ammonium assimilation in nodules (GS, NADH-GOGAT) was inhibited by salt stress both in N-fixing and in N-fertilized pea and faba bean plants.

Cloning, expression and characterization of a gene which encodes a topoisomerase I with positive supercoiling activity in pea.

We have isolated and sequenced the full length cDNA for topoisomerase I. Using degenerate primers, based on the conserved amino acid sequences of five eukaryotic topoisomerase I, a 386 bp fragment was PCR amplified using pea cDNA as template. This fragment was used as a probe to screen a pea cDNA library. Two partial cDNA clones were isolated which were truncated at the 5' end. RACE-PCR was employed to isolate the remaining portion of the gene. The total size of the gene was 3055 bp with an open reading frame of 2676 bp. The deduced structure of pea topoisomerase I contain 892 amino acids with a calculated molecular weight of 100 kDa and an estimated pI of 9.3. A comparison of the deduced amino acid sequences of the pea topo I with the other eukaryotic topoisomerases clearly suggested that they are all related. Pea topoisomerase I has been overexpressed in E. coli system and the recombinant topoisomerase purified to homogeneity. The purified protein relaxes both positive and negative supercoiled DNA in the absence of divalent cation Mg2+. In the presence of Mg2+ ions the purified enzyme introduces positive supercoils a unique property not reported in any other organism except in archaebacterial topoisomerase I. Polyclonal antibodies were raised against recombinant topoisomerase I and western blotting with sub-cellular fractions indicated the localization of this topoisomerase in pea nuclei.

Neemazal, a product of neem (Azadirachta indica), induces resistance in pea (Pisum sativum) againstErysiphe pisi

The efficacy of neemazal, a natural product from neem (Azadirachta indica Juss.), against pea (Pisum sativumL.) powdery mildew (Erysiphe pisiDC.) was studied in detached leaf and intact plant experiments. Neemazal significantly retarded several growth parameters of the pathogen, viz. multiple germ tube formation, numbers of germ tubes, branches and haustoria, and colony size on pea leaves. Neemazal induced hypersensitive reaction (HR), as evidenced by browning of host cells associated with appressoria. Furthermore, increase in protein concentration of intercellular fluids followed treatment with neemazal. Heat-shock of neemazal treated leaves reduced HR. Pre-inoculation treatment with neemazal was more effective in controlling disease development than post-inoculation application. The effect of the compound on the disease development was correlated with increased phenylalanine ammonia lyase (PAL) activity in pea leaves following treatment with neemazal.

Topography and Function of Golgi Uridine-5[prime]-Diphosphatase from Pea Stems.

Golgi UDPase is an enzyme that has been shown to function in polysaccharide biosynthesis, but its role in this process is not yet clear. In this study we identified Golgi UDPase activity in pea (Pisum sativum) stems and differentiated it from another UDPase activity. We demonstrated that Golgi UDPase is an integral membrane protein, based on specific partitioning of this activity into Triton X-114. Analysis of its topology using sealed, right-side-out Golgi vesicles and treatment with proteinase K suggested that its active site faces the Golgi lumen. Studies aimed at understanding the function of Golgi UDPase by incubating Golgi vesicles with [beta]-32P]UDP-glucose (Glc) to generate [beta]-32P]UDP upon Glc transfer in situ showed that 32Pi, but not [beta]-32P]UDP, was formed, suggesting that UDPase quickly hydrolyzed the UDP formed during Glc polymerization. We found that the Golgi UDPase was highly active in the elongating region of the third internode, whereas no activity was detected in the first and second internodes of etiolated pea seedlings. These results suggest that UDPase removes the UDP formed during Glc polymerization and could be important in the mechanism of polysaccharide biosynthesis.

Developmental Regulation of Respiratory Activity in Pea Leaves.

The developmental pattern of mitochondrial respiratory activity in pea (Pisum sativum) leaves has been investigated in an attempt to determine changes in mitochondrial function as plant cells mature. NADH and succinate dehydrogenase and cytochrome c oxidase activities remained relatively constant during cell maturation (from d 0 to d 14). Alternative oxidase and glycine decarboxylase activity, however, were low in young leaf tissue (d 0-6) but increased substantially as the tissue matured (d 7-14) and gained photorespiratory activity. Western blot analysis of the alternative oxidase protein revealed that it was primarily in an oxidized state in young leaves (d 0-6) but switched dramatically to the reduced form of the protein as the pea cells matured (d 7-14). The switch to the reduced form of the protein correlated with an increase in alternative oxidase activity. Results are discussed in terms of the changing function of plant mitochondria during leaf development.