短日照对休眠诱导期油桃花芽两条电子传递途径的调控

以油桃品种“曙光”为试材,采用呼吸抑制剂法研究了短日照处理下花芽在休眠诱导期两条电子传递途径的发生和运行情况.结果表明:花芽总呼吸速率(Vt)和细胞色素电子传递途径呼吸速率(ρ'Vcyt)均呈双峰曲线变化,短日照可同步诱导两者的一次峰前移、二次峰后延,抑制ρ’Vcyt,但对Vt无显著影响.交替途径容量(Valt)和实际运行活性(ρValt)亦呈双峰曲线,两者基本同步变化,短日照可以显著诱导Valt和ρValt的前期高峰期提前,提高Valt和ρValt,对后期高峰期无明显作用.细胞色素电子传递途径呼吸速率下降和交替途径呼吸速率上升是油桃花芽休眠诱导期的重要特点.从两条电子传递途径的呼吸速率对总呼吸速率的贡献率来看,细胞色素电子传递途径仍是主要电子传递途径,交替途径起辅助与分流作用.     

Influence of the alternative respiratory pathway on the adenylate pools in heterotrophic Euglena gracilis

Etiolated Euglena gracilis Pringsheim, strain Z, were cultured in a lactate medium either in the presence of 2 μ M antimycin A for cells adapted to this inhibitor, or in the absence of antimycin A for controls. The adenylates (ATP, ADP and AMP) and the energy charge (EC) were followed during the growth of both types of cells. The effects of KCN, salicylhydroxamic acid (SHAM) and rotenone on the respiration and the adenylate pool, were investigated during the exponental and stationary phases. EC values of controls and antimycin-adapted cells were not significantly different during culture. In the logarithmic phase, EC of controls was unaffected by 3 m M SHAM, an inhibitor of the alternative pathway, but markedly decreased by 0.3 m M KCN, which inhibits the cytochrome pathway. In contrast, in antimycin-adapted Euglena , in which the cytochrome pathway was blocked, ATP content and EC were markedly lowered in the presence of SHAM but slightly increased by 0.3 m M KCN. The combination of the preceeding treatments, as well as 15 m M KCN alone, were deleterious for both types of cells, in the logarithmic and the late stationary phases. The data indicate that the energy level in Euglena was dependent on the alternative pathway when the cytochrome pathway was blocked. Such dependence could be explained by the engagement of the first rotenone-sensitive site of phosphorylation. Indeed, 50 μ M rotenone caused a similar relative decrease of oxygen consumption and ATP content in controls and in antimycin-adapted Euglena . In the absence of cytochrome respiration, the alternative pathway allowed electrons to flow through this first segment of the respiratory chain, and ATP production by the first site of phosphorylation.     

Leaf Respiration in Light and Darkness (A Comparison of Slow- and Fast-Growing Poa Species)

We investigated whether leaf dark respiration (nonphotorespiratory mitochondrial CO2 release) is inhibited by light in several Poa species, and whether differences in light inhibition between the species are related to differences in the rate of leaf net photosynthesis. Four lowland (Poa annua L., Poa compressa L., Poa pratensis L., and Poa trivialis L.), one subalpine (Poa alpina L.), and two alpine (Poa costiniana Vick. and Poa fawcettiae Vick.) Poa species differing in whole plant relative growth rates were grown under identical controlled conditions. Nonphotorespiratory mitochondrial CO2 release in the light (Rd) was estimated according to the Laisk method. Photosynthesis was measured at ambient CO2 partial pressure (35 Pa) and 500 [mu]mol photons m-2 s-1. The rate of photosynthesis per unit leaf mass was positively correlated with the relative growth rate, with the slow-growing alpine Poa species exhibiting the lowest photosynthetic rates. Rates of both Rd and respiration in darkness were also substantially lower in the alpine species. Nonphotorespiratory CO2 release in darkness was higher than Rd in all species. However, despite some variation between the species in the level of light inhibition of respiration, no relationship was observed between the level of inhibition and the rate of photosynthesis. Similarly, the level of inhibition was not correlated with the relative growth rate. Our results support the suggestion that rates of leaf respiration in the light are closely associated with rates in darkness.     

Cyanide-resistant respiration in roots and leaves. Measurements with intact tissues and isolated mitochondria

A comparison was made between the oxygen uptake of roots and leaves and of mitochondria isolated from the same tissues. Ten species were included in this study: three legumes, one C3-monocotyledon, one C4-monocotyledon, the rest non-leguminous C3-dicotyledons. Root and leaf respiration in all species examined displayed substantial resistance to KCN (0.1–1.0 mM) and the cyanide-resistant respiration was completely inhibited by salicylhydroxamic acid (SHAM; 10–20 mM). SHAM alone inhibited oxygen uptake to varying degrees, depending on the species. Mitochondria were isolated from roots and leaves of many of the species examined and also displayed cyanide-resistant oxygen uptake, which was sensitive to both SHAM and tetraethylthiuram disulfide (disulfiram). Concentrations of SHAM greater than 2 mM caused inhibition of the cytochrome path as well as of the alternative path in isolated mitochondria. Respiration rates of intact roots and leaves in the presence of varying concentrations of SHAM alone were plotted against those obtained in the presence of both SHAM and KCN. This plot showed that in vivo the cytochrome pathway was not affected by 10 or 20 mM SHAM in the external solution. We conclude that the activity of the alternative pathway in intact roots and leaves can be reliably estimated by comparing SHAM-sensitivity and cyanide-resistance of respiration.     

成熟和褐变荔枝果实呼吸作用和脂氧合酶活性

荔枝果实完全成熟和果皮变鮮红时,呼吸速率降低,仅相当于果皮带绿时的39.4％。此时果皮和果肉的脂氧合酶活性亦明显降低,分别相当于后者的60.2％和49.1％。成熟荔枝果实果皮呼吸作用对KCN抑制敏感。2mM KCN抑制果皮总呼吸的91.8％,而仅抑制果肉的56.9％。荔枝果皮呼吸的电了传递主要是通过细胞色素氧化酶途径,而果肉則可能一半是通过其它氧化酶途径。2mKCN和1.5mM SHAM抑制成熟果皮总呼吸97.9％,为SHAM抑制的交替途径呼吸占总呼吸5.28％。相同浓度KCN和SHAM抑制褐变果皮总呼吸79.7％,则SHAM抑制的交替途径呼吸占27.1％。果实褐变时,果成交替途径呼吸比例增高。这一变化可能促进H_2O_2积累、乙烯产生和果皮褐变深化。     

Cyanide-resistant respiration in light- and dark-grown soybean cotyledons

Measurements of respiration were made on intact tissue and mitochondria isolated from soybean (Glycine max [L.] Merr. cv `Corsoy') cotyledons from seedlings of different ages grown in light and darkness. Effects of cyanide (KCN) and salicylhydroxamic acid (SHAM) on O₂ uptake rates were determined. O₂ uptake was faster in light-grown tissue and was inhibited by both KCN and SHAM in all except light-grown tissue older than 9 days. Both inhibitors stimulated O₂ uptake in tissues more than 9 days old. Mitochondria in which O₂ uptake was coupled to ATP synthesis were isolated from all tissues. O₂ uptake by mitochondrial preparations from light- and dark-grown cotyledons was equally sensitive to KCN. Similarly, age did not affect KCN sensitivity, but sensitivity to SHAM declined with age both in the presence and absence of KCN. Estimated capacities of the cytochrome and alternative pathways of the mitochondrial preparations indicated considerably larger cytochrome than alternative pathway capacities. The cytochrome pathway capacities paralleled the state 3 mitochondrial respiration rates, which increased from day 5 to day 7 then declined thereafter. The alternative pathway capacities were not affected by light. The uncoupler, p-trifluoromethoxycarbonylcyanide phenylhydrazone (FCCP), increased the flow of electrons through the cytochrome pathway at the expense of flow through the alternative pathway in isolated mitochondria. However, the combined capacities did not exceed the rate in the presence of FCCP. The results are interpreted to indicate that the stimulation of respiration by KCN and SHAM observed in the 12-day-old green cotyledons and previously observed in older soybean leaves is not explained by characteristics of the mitochondria.     

Effects of KCN and Salicylhydroxamic Acid on Respiration of Soybean Leaves at Different Ages

Measurements of respiration were made on leaf discs from glasshouse-grown soybean (Glycine max [L.] Merr. cv `Corsoy') plants in the presence and absence of cyanide (KCN) and salicylhydroxamic acid (SHAM). O₂ uptake by mature leaves measured at 25°C was stimulated by 1 millimolar KCN (63%) and also by 5 millimolar azide (79%). SHAM, an inhibitor of the alternative oxidase and a selection of other enzymes, also stimulated O₂ uptake by itself at concentration of 10 millimolar. However, in combination, KCN and SHAM were inhibitory. The rate of O₂ uptake declined consistently with leaf age. The stimulation of O₂ uptake by KCN and by SHAM occurred only after a certain stage of leaf development had been reached and was more pronounced in fully expanded leaves. In young leaves, O₂ uptake was inhibited by both KCN and SHAM individually. The uncoupler, p-trifluoromethoxy carbonylcyanide phenylhydrazone, stimulated leaf respiration at all ages studied, the stimulation being more pronounced in fully expanded leaves. The uncoupled rate was inhibited by KCN and SHAM individually. The capacity of the cytochrome path declined with leaf age, paralleling the decline in total respiration. However, the capacity of the alternative path peaked at about full leaf expansion, exceeding the cytochrome capacity and remaining relatively constant. These results are consistent with the presence in soybean leaves of an alternative path capacity that seems to increase with age, and they suggest that the stimulation of O₂ uptake by KCN and NaN₃ in mature leaves was mainly by the SHAM-sensitive alternative path. The stimulation of O₂ uptake by SHAM was not expected, and the reason for it is not clear.     

Leaf respiration in Piper species native to a Mexican rainforest

We measured leaf respiration with a Clark-type oxygen-electrode in 6 species of the genus Piper (Piperaceae) growing naturally in wet evergreen rainforest, in microsites characterized by a broad range of light availabilities. Species normally found in large gaps and clearings ( Piper auritum and P. umbellatum ) had approximately twice the dark respiration per unit of leaf area or dry mass as species found predominantly in shaded understory sites ( P. aequale, P. lapathifolium and P. amalago ). within a species, dark respiration was lower in the individuals growing in low-light sites than in the individuals growing in high-light sites. Over all species, leaf respiration was positively correlated with the average daily photosynthetically active photon flux density (PFD) at each site, and negatively correlated with mean leaf longevity. Respiration was insensitive to leaf age in a shade species. ( P. lapathifolium ) and in a generalist ( P. hispidum ) but decreased with increasing leaf age in a gap specialist ( P. aurtium ).
In experiments on greenhouse-grown plants, we titrated respiration with potassium cyanide (KCN) and/or salicylhydroxamic acid (SHAM) to determine the cytochrome and alternative pathway components to respiration in 4 Piper species. All 4 species, representing gap, generalist and shade species, exhibited alternative pathway respiration. Engagement of the cytochrome pathway (ϱ_cyt) varied from 0.69 in P. auritum to 1.04 in P. lapathifolium and engagement of the alternative pathway (ϱ_alt varied from 0.41 to 1.02. Although the shade species had lower respiration rates than the gap species, the capacities for cytochrome and alternative pathway respiration made up similar or greater fractions of total respiration in shade species.     

A critique of the use of inhibitors to estimate partitioning of electrons between mitochondrial respiratory pathways in plants

The contribution of individual plant mitochondrial respiratory pathways to total respiration is commonly assessed by titration with specific inhibitors of different components in the branched electron transport chain. A pathway's contribution is equal to the activity when the other branch is blocked by an inhibitor multiplied by the degree (0-1.0) to which this activity is engaged when both pathways are operating. According to Bahr and Bonner (1973. J. Biol. Chem. 218: 3441–3445) the plot of the activities of identical titrations, one performed in the absence and the other in the presence of a specific inhibitor of the other branch of the respiratory chain, yields a straight line whose slope indicates the engagement of the titrated pathway during uninhibited respiration. An initial slope of zero may occur if electron flux is diverted between pathways during titrations. However, beyond the breakpoint (representing the point of pathway saturation), a straight line is obtained with a slope representing engagement. This technique assumes that the kinetics of inhibiting a specific component of the respiratory chain are independent of the absolute rate of electron flux through the total pathway. To test this assumption, the activity of respiratory pathways in isolated soybean (Glycine max [L]. Merr. cv. Stevens) mitochondria was titrated with specific inhibitors of the cytochrome and alternative oxidases. Under these conditions, the electron flux through a given pathway was manipulated by poising the rate of succinate oxidation with the succinate dehydrogenase inhibitor malonate. Construction of activity plots in the presence versus absence of malonate failed to result in straight lines for either KCN (when titrating the cytochrome pathway) or salicylhydroxamic acid (when titrating the alternative pathway). Rather, the resultant plots were always curvilinear whenever the activity in the presence of malonate divided by the activity in the absence of malonate was less than 1.0. In no case could the real engagement of the pathway be precisely estimated from the titration data. Titrations of cytochrome pathway activity in isolated potato tuber (Solanum tuberosum L. cv. Sabago and Canabex) mitochondria (which lack the alternative oxidase) showed that as the inhibitor concentration was increased, so did the reduction status of the ubiquinone pool, to a new steady state. The dependence of inhibition kinetics on the rate of flux through the pathway, and the increase in ubiquinone pool reduction upon KCN addition, are explained in terms of the elasticity of component enzymes as outlined in the theory of metabolic control analysis. The implications of this finding for the use of titrations to estimate engagement of plant respiratory pathways are discussed.     

Respiratory pathways in aged soybean seeds

Respiratory activities in soybean seeds (Glvcine max (L.) Merr. cv. Chippewa 64) have been examined in the first minutes after water imbibition and after three hours of imbibition, using either particles or intact axes. Cyanide and azide were utilized as inhibitors of the cytochrome oxidase pathway of respiration, and SHAM inhibitions were interpreted as effects on the alternative pathway, since in unaged axes inhibitions by SHAM were obtained only when respiratory activity had either been restricted with inhibitors of the cytochrome oxidase pathway or expanded by an uncoupler (CCCP). From the experiments with these inhibitors, it is suggested that unaged seeds utilize both respiration pathways in the cotyledon but only the cytochrome pathway in the axis. Accelerated aging causes a marked deterioration of respiration, especially that through the cytochrome pathway, and there is an associated engagement of the alternative pathway in the seed axis. It is suggested that the lowering of respiratory activity and the shift in respiratory pathways may play a major role in the decline of germinability and vigor.     

The regulation of glycolysis and electron transport in roots

The respiration of roots and isolated root mitochondria was investigated in Phaseolus vulgaris L., Spinacea oleracea L.; Triticum aestivum L., and Zea mays L. Although the respiration of both intact roots and isolated mitochondria displayed resistance to cyanide and sensitivity to SHAM, the percentage resistance and inhibition in roots was not the same as that in the mitochondria, with the exception of wheat. Adding FCCP to roots stimulated oxygen uptake and equalized the effects of SHAM and cyanide on roots and mitochondria. In spinach and maize roots, FCCP stimulated both the cytochrome and alternative pathways, while in bean roots, only the alternative pathway was stimulated. FCCP had little effect on wheat root respiration rates. Potential in vivo rates of oxygen uptake were estimated by expressing rates obtained with isolated mitochondria on a fumarase activity basis, and fumarase activity on a root weight basis. In wheat roots the potential rate was approximately equal to the measured in vivo rate; in the other species the potential rates were substantially greater than measured rates, but approximately equal to uncoupled in vivo rates. Key glycolytic intermediates in roots were measured, and it was found that the phosphofructokinase and pyruvate kinase reactions were displaced far from equilibrium, the degree of displacement being approximately equal in roots with little, and roots with substantial, alternative path engagement. Thus, although glycolysis is controlled, the regulation of this pathway appears to be quite flexible. The results are discussed in terms of possible regulatory mechanisms.     

The Role of the Alternative Oxidase in Stabilizing the in Vivo Reduction State of the Ubiquinone Pool and the Activation State of the Alternative Oxidase

A possible function for the alternative (nonphosphorylating) pathway is to stabilize the reduction state of the ubiquinone pool (Q_r/Q_t), thereby avoiding an increase in free radical production. If the Q_r/Q_t were stabilized by the alternative pathway, then Q_r/Q_t should be less stable when the alternative pathway is blocked. Q_r/Q_t increased when we exposed roots of Poa annua (L.) to increasing concentrations of KCN (an inhibitor of the cytochrome pathway). However, when salicylhydroxamic acid, an inhibitor of the alternative pathway, was added at the same time, Q_r/Q_t increased significantly more. Therefore, we conclude that the alternative pathway stabilizes Q_r/Q_t. Salicylhydroxamic acid increasingly inhibited respiration with increasing concentrations of KCN. In the experiments described here the alternative oxidase protein was invariably in its reduced (high-activity) state. Therefore, changes in the reduction state of the alternative oxidase cannot account for an increase in activity of the alternative pathway upon titration with KCN. The pyruvate concentration in intact roots increased only after the alternative pathway was blocked or the cytochrome pathway was severely inhibited. The significance of the pyruvate concentration and Q_r/Q_t on the activity of the alternative pathway in intact roots is discussed.     

Studies on the import and processing of the alternative oxidase precursor by isolated soybean mitochondria

Import of the synthetic precursor of the alternative oxidase from soybean was shown to be dependent on a membrane potential and ATP. The membrane potential in soybean mitochondria may be formed either by respiration through the cytochrome pathway, or through the alternative oxidase pathway with NAD⁺-linked substrates. Import of the alternative oxidase precursor in the presence of succinate as respiratory substrate was inhibited by KCN. Import in the presence of malate was insensitive to KCN and SHAM added separately, but was inhibited by KCN and SHAM added together (inhibitors of the cytochrome and alternative oxidases respectively). Import of the alternative oxidase was accompanied by processing of the precursor to a single 32 kDa product in both cotyledon and root mitochondria. This product had a different mobility than the two alternative oxidase bands detected by immunological means (34 and 36 kDa), suggesting that the enzyme had been modified in situ. When the cDNA clone of the alternative oxidase was modified by a single mutation (–2 Arg changed to –2 Gly), the processing of the precursor was inhibited.     

Reversion from light-induced inhibition of seed germination by respiratory inhibitors

Treating of the dark-imbibed lettuce (Lactuca sativa L.) seeds prior to light irradiation with 1 millimolar KCN or NaN₃ in the dark for 3 hours prevented blue light and far-red light-induced inhibitions of phytochrome-mediated germination. Similarly, salicylhydroxamic acid (SHAM) at 10 millimolar counteracted the blue and far-red light inhibitions, the combined application of KCN and SHAM being more effective than KCN or SHAM alone in some experiments. These respiratory inhibitors slightly inhibited phytochrome-mediated lettuce seed germination. These results indicate that both CN-sensitive, conventional cytochrome oxidase and CN-resistant (SHAM-sensitive), alternative respiration may be involved in the light inhibition or that an appropriate balance of both may be necessary for the light inhibition.     

Importance of oxidative electron transport over oxidative phosphorylation in optimizing photosynthesis in mesophyll protoplasts of pea (Pisum sativum L.)

The role of mitochondrial respiration in optimizing photosynthesis was assessed in mesophyll protoplasts of pea ( Pisum sativum L., cv. Arkel) by using low concentrations of oligomycin (an inhibitor of oxidative phosphorylation), antimycin A (inhibits cytochrome pathway of electron transport) and salicylhydroxamic acid (SHAM, an inhibitor of alternative oxidase). All three compounds decreased the rate of photosynthetic O₂ evolution in mesophyll protoplasts, but did not affect chloroplast photosynthesis. The inhibition of photosynthesis by these mitochondrial inhibitors was stronger at optimal CO₂ (1.0 m M NaHCO₃) than that at limiting CO₂ (0.1 m M NaHCO₃). We conclude that mitochondrial metabolism through both cytochrome and alternative pathways is essential for optimizing photosynthesis at limiting as well as at optimal CO₂. The ratios of ATP to ADP in whole protoplast extracts were hardly affected, despite the marked decrease in their photosynthetic rates by SHAM. Similarly, the decrease in the ATP/ADP ratio by oligomycin or antimycin A was more pronounced at limiting CO₂ than at optimal CO₂. The mitochondrial oxidative electron transport, through both cytochrome and alternative pathways, therefore akppears to be more important than oxidative phosphorylation in optimizing photosynthesis, particularly at limiting CO₂ (when ATP demand is expected to be low). Our results also confirm that the alternative pathway has a significant role in contributing to the cellular ATP, when the cytochrome pathway is limited.     

Effects of KCN and NaN3 Pretreatment on the Cyanide-Resistant Respiration in Tobacco Callus

The effects of KCN (0.5mmol/L) and NaN3 (0.01 mmol/L) pretreatment on the operation of the alternative pathway in subcultured tobacco (Nicotiana rustica L. cv. Gansu yellow flower) callus were analyzed. After treatment with KCN and NaN3 for 12 h, the total respiration rate (Vt) decreased by 12% and 17%, whereas oxygen consuption by the cytochrome pathway decreased by 22% and 28% respectively. The capacity of the alternative pathway (Valt) remained constant, while the activity of the alternative pathway (ρ· Valt ) inreased slightly. This changing pattern led to a declined contribution of the cytochrome pathway to the total respiration rate and an increased activity of the alternative pathway. Treatment with KCN for 24 h brought about a slight rise of oxygen consumption by the cytochrome pathway as compared with that in callus treated for 12 h, but the oxygen consumption was still lower than that in the untreated callus. Treatment with NaN3 for 24 h resulted in a profound decrease of the cytochrome pathway operation and a continuing increase of the alternative pathway operation. These data indicated that the enhanced operation of the alternative pathway played a compensatory role to the total respiration when the cytochrome pathway was partially inhibited in tobacco callus.     

Alternative respiration and heat evolution in plants

The alternative respiratory pathway dissipates most of the chemical energy of respiratory substrates as heat. We have shown that this heat can be quantified by microcalorimetry and is a measure of alternative pathway activity in vivo. The alternative pathway is known to increase in aged potato (Solanum tuberosum) slices and in chill-stressed leaves. Aging of potato slices for 24 hours was accompanied by an almost fourfold increase in the rate of heat evolution. This heat increase was resistant to KCN but could be blocked by an alternative pathway inhibitor, salicylhydroxamic acid (SHAM). In cucumber (Cucumis sativus) leaves subjected to chilling stress (between 4 and 16°C), the rate of heat evolution was inversely related to temperature. As in aged potato slices, the increased rate of heat evolution in cucumber leaves was blocked by SHAM, but not by KCN. Nitrogen or the combination of SHAM and KCN blocked most of the heat evolution in both aged potato slices and chill-stressed cucumber leaves. Calorimetric measurements of the alternative pathway corresponded to respiration measurements performed using an oxygen electrode.     

Cytochrome and alternative pathway respiration in green algae : measurements using inhibitors and o(2) discrimination

Inhibitor titration curves and discrimination against ¹⁸O₂ by mitochondrial respiration in three strains of green algae (Selenastrum minutum [Naeg.] Collins, and two strains of Chlamydomonas reinhardtii Dangeard) with differing respiratory capabilities were determined. Discrimination for cytochrome pathway respiration ranged from 19.89 to 20.43%. Discrimination for alternative pathway respiration by wild-type C. reinhardtii (measured in the presence of KCN) was 25.46%, while discrimination values for a cytochrome oxidase deficient mutant of C. reinhardtii ranged from 24.24 to 24.96%. In the absence of KCN, the alternative pathway was not engaged in wild-type C. reinhardtii, the only algal strain that possessed both cytochrome and alternative pathway capacities.     

Inhibition and stimulation of root respiration in pisum and plantago by hydroxamate : its consequences for the assessment of alternative path activity

The contribution of the alternative pathway in root respiration of Pisum sativum L. cv Rondo, Plantago lanceolata L., and Plantago major L. ssp major was determined by titration with salicylhydroxamate (SHAM) in the absence and presence of cyanide. SHAM completely inhibited the cyanide-resistant component of root respiration at 5 to 10 millimolar with an apparent K_i of 600 micromolar. In contrast, SHAM enhanced pea root respiration by 30% at most, at concentrations below 15 millimolar. An unknown oxidase appeared to be responsible for this stimulation. Its maximum activity in the presence of low SHAM concentrations (1-5 millimolar) was 40% of control respiration rate in pea roots, since 25 millimolar SHAM resulted in 10% inhibition. In plantain roots, the maximum activity was found to be 15%. This hydroxamate-activated oxidase was distinct from the cytochrome path by its resistance to antimycin. The results of titrations with cyanide and antimycin indicated that high SHAM concentrations (up to 25 millimolar) block the hydroxamate-activated oxidase, but do not affect the cytochrome path and, therefore, are a reliable tool for estimating the activity of the alternative path in vivo. A considerable fraction of root respiration was mediated by the alternative path in plantain (45%) and pea (15%), in the latter because of the saturation of the cytochrome path.