Mitochondrial response in the apical and lateral flower buds of the Hanfu apple to cold stress during the dormancy stage

In order to study the different physiological bases of cold tolerance in the apical flower buds (AFB) and the lateral flower buds (LFB) of the Hanfu apple (Malus domestica Borkh), we used 4-year-old grafted Hanfu plants as material and evaluated the physiological characteristics of mitochondria in the flower buds, such as electron transport chains (cytochrome pathway and alternative pathway), H₂O₂ content, mitochondrial membrane permeability transition (mPT), and MDA content. AFBs and LFBs showed different changes in total respiratory rate (V_t) during low-temperature stress, except that both reached the lowest V_ts at ?30 °C. The AFB V_t increased to a peak at ?25 °C and decreased sharply to its minimal value at ?30 °C, and then remained relatively low. In contrast, the LFB V_t decreased to its minimal value at ?30 °C and increased sharply to a peak at ?35 °C and then decreased again. In both AFBs and LFBs, the cytochrome pathway was still the main electron transport chain throughout the whole process, and the contributions of the cytochrome pathway (ρV_cyt/V_t) and of the alternative pathway (ρV_alt/V_t) showed similar tendencies to those of V_t as temperature changed. Changes in the AFB mPT were different from those of AFB V_t. LFB mPT zigzagged from peaks at ?25 °C and 35 °C. The H₂O₂ content of the LFBs increased from ?10 °C to ?30 °C, then decreased slightly from ?30 °C to ?35 °C, and then increased again. H₂O₂ content in AFBs went up steadily throughout the whole process. During the early stage of low-temperature treatment, before temperatures reached ?35 °C, LFB MDA content remained relatively low and later increased. MDA content in AFBs began to increase from the beginning of treatment. It can be concluded that the higher cold tolerance of LFBs relative to AFBs could be closely related to their higher V_t and ρV_alt/V_t, which may aid adaptations to stress by supplying energy and metabolic substrates under low-temperature stress conditions.     

Studies on the relationship between cyanide-resistant respiration and expression of alternative oxidase in mung bean using antibodies prepared by synthetic polypeptide

Twelve peptides, including eight conservative amino acid residues in the amino acid sequence of hydrophilic S helix of the alternative oxidase (AOX), were synthesized by solid-phase method. The polypeptide was coupled with α-chymotrypsinogen, and the antibodies were obtained through immunizing domestic rabbit by injecting this complex. By using these antibodies, which were raised to immunoreact with total proteins of purified mitochondria from different organs of mung bean seedlings, we find that there are two hybridizable AOX bands in mitochondria. Their molecular weights are about 35 and 38 ku, respectively. Moreover, the respiratory parameters of hypocotyl, true leaf and cotyledon of mung bean seedlings show that true leaf has the highest total respiration (Vt), alternative pathway (AP) capacity (Valt) and the activity of AP (ρValt) among the three organs. Vt and ρValt of cotyledon ranked the second. Hypocotyl has the lowest V, and ρValt, but its Valt is higher than that of cotyledon. These result     

Studies on the relationship between cyanide-resistant respiration and expression of alternative oxidase in mung bean using antibodies prepared by synthetic polypeptide

Twelve peptides, including eight conservative amino acid residues in the amino acid sequence of hydrophilic S helix of the alternative oxidase (AOX), were synthesized by solid-phase method. The polypeptide was coupled with α-chymotrypsinogen, and the antibodies were obtained through immunizing domestic rabbit by injecting this complex. By using these antibodies, which were raised to immunoreact with total proteins of purified mitochondria from different organs of mung bean seedlings, we find that there are two hybridizable AOX bands in mitochondria. Their molecular weights are about 35 and 38 ku, respectively. Moreover, the respiratory parameters of hypocotyl, true leaf and cotyledon of mung bean seedlings show that true leaf has the highest total respiration (V_t), alternative pathway (AP) capacity (V_alt) and the activity of AP (ρV_alt) among the three organs. V_t andρV _alt of cotyledon ranked the second. Hypocotyl has the lowest V_t andρV _alt, but its V_alt is higher than that of cotyledon. These results are consistent with the analysis of Western blotting of expression of AOX. The highest V_t andρV _alt in true leaf are accompanied two hybridizable polypeptides of AOX protein, 35 ku and 38 ku respectively. The next is cotyledon V_t andρV _alt with only one 38 ku hybridizable polypeptide of AOX protein. HypocotylV _t andρV _alt is the lowest and its immunoblotting band is similar to that of cotyledon, but the expressive amount of 38 ku protein is less than that of cotyledon. The results suggest that the 35 ku AOX may contribute mainly to true leafρV _alt.     

UV-A Inhibition of Alternative Respiration in Pea Leaves and a Unicellular Green Alga Chlamydomonas reinhardtii

Total respiration (v_T) increased after exposure to UV, but a decrease in the capacity of SHAM-sensitive-alternative respiration (V_alt) was accompanied by an increase in residual respiration (v_res). The capacity for CN sensitive-cytochrome c respiration (V_cyt) was not inhibited by UV-A. After 4 h of irradiation of high-CO₂-grown cells of Chlamydomonas reinhardtii with UV-A (2 μW. CM^?2) in the presence of white light (300μE.m^?2.s^?1), the capacity of Vast was reduced from 10 to 4 μmol O₂. mg^?1Chl.h^?1, a 60 % reduction. After a similar exposure to UV-A, the capacity of V_alt in pea leaves was reduced from 13 to 5 μmol O₂.g^?1 fr wt.h^?1. Exposure to UV-C was not inhibitory, but UV-B caused up to 25% inhibition of the V^alt. Twenty to 48 h after exposure to UV-A radiation, the capacity of alternative respiration had recovered. UV-A inhibition of the alternative respiration was consistent with UV-A absorption by quinones, except that UV-A did not inhibit the cyt c pathway of electron transport that also involves the ubiquinones.     

Regulation of the activity of the alternative oxidase in callus forming discs from potato tubers

Callus-forming discs from potato tubers lose 80% of their starch during one month of incubation on nutrient medium containing either 0, 3 or 6% (w/v) sucrose. The content of soluble sugar in the discs varies from 5 mg (incubated without sucrose) to 22 mg (on 3% sucrose) and 40 mg (on 6% sucrose) per g fresh weight. The activity of the cytochrome pathway (V_cyt) increases during the first week of incubation on all media. Thereafter V_cyt decreases again on 0% sucrose medium, while it remains constant on 3 and 6% sucrose media. Alternative pathway capacity (V_alt), absent in freshly sliced tissue, shows a sharp increase during the first days of incubation, independent of the sucrose concentration in the medium. This capacity further increases during prolonged incubation on 3 and 6% sucrose but decreases on 0% sucrose. The in vivo activity of the alternative pathway (the participation in uninhibited respiration, ?V_alt) varies with the sucrose concentration and with the culture time. In tissue incubated for 2-3 weeks on 6% sucrose as much as 45% of the electrons are transfered to oxygen via the alternative pathway. In this tissue the factor Q (the part of the alternative pathway capacity that is operative) is about 0.8, while in tissue incubated on 0 and 3% sucrose media p generally does not exceed 0.5. When chloramphenicol, an inhibitor of mitochondrial protein synthesis, is added to the medium together with 3% sucrose, the increase in V_yet does not occur, while the induction of V_alt during the first week of incubation is the same as without chloramphenicol. A greater part of the alternative pathway capacity becomes operative in this tissue, leading to values of Q of almost 1 after prolonged incubation. Apparently, incubation on high sugar medium leads to extra participation in respiration of the energetically inefficient alternative oxidase pathway Excess sugar leads to wasteful respiration suggesting that the alternative oxidase functions as an ‘energy overflow’.     

Alternative pathway activities in aged potato tuber slices measured by three methods

To find a simple and reliable oxygen electrode-based method to estimate the values of alternative pathway activity (V _alt) and its contribution to total respiration V _alt/V _t) in aged potato (Solanum tuberosum L.) tuber slices, we compared conventional hydroxamate-inhibiting method, improved hydroxamate-inhibiting method with 2,6-dichlorophenol indophenol (DCPIP), and the oxygen isotope discrimination (OID) method. The values of V _alt and V _alt/V _t obtained with an improved hydroxamate-inhibiting method with DCPIP in 12-h- and 24-h-aged slices were about twice higher than those with the conventional hydroxamate-inhibiting method. Only a relatively small difference in the values of V _alt and V _alt/V _t obtained by the OID method and the improved hydroxamate-inhibiting method with DCPIP in 12-h and 24-h-aged slices was observed. These results indicated that the improved hydroxamate-inhibiting method with DCPIP could be considered as a new, simple, and reliable technique for the noninvasive assay of the AP activity.From Fiziologiya Rastenii, Vol. 52, No. 2, 2005, pp. 311–315.Original English Text Copyright © 2005 by Hou, Zhou, Kong, Liang, Zhang.This article was submitted by the authors in English.This revised version was published online in April 2005 with a corrected cover date.     

光照下菜豆叶片抗氰呼吸与光合作用关系的分析北大核心CSCD

为了进一步了解光照下植物呼吸作用的内在机理以及呼吸作用和光合作用的关系,该文研究了在光照下菜豆(Phaseolus vulgaris)叶片抗氰呼吸与光合作用的关系。研究发现,将黑暗下生长的菜豆幼苗叶片转到光照下10 h,总呼吸、抗氰呼吸以及抗氰呼吸在总呼吸中的比例均逐步上升;光照也导致了叶片叶绿体光合放氧和CO2固定的出现及其速率的增加,但光合放氧和CO2固定速率的增加均滞后于抗氰呼吸的增加。将黑暗下生长的叶片转到光照下之前用抗氰呼吸的抑制剂水杨基氧肟酸(SHAM)处理叶片,发现用SHAM处理并没有导致叶片在光照下光合放氧和CO2固定速率的明显变化,这也提示了黑暗下生长的叶片转至光照的过程中,抗氰呼吸和光合作用没有产生偶联。进一步研究发现,在黑暗中对叶片施加短时间的光照能够增加抗氰呼吸在总呼吸中的比例,但短时间的光照对叶片光合CO2固定速率没有影响。这些结果表明了光照对抗氰呼吸的诱导可以不依赖于光合作用,光照可能是作为一种直接的信号去诱导抗氰呼吸。     

Possible Participation of Active Oxygen Species in the Induction of Cyanide-Resistant Pathway at the Initial Senescence of Tobacco Callus

Changes in active oxygen species (AOS) and respiration, with special reference to the alternative pathway of respiration, were followed in callus of tobacco (Nicotiana rusticaL.) during its growth and senescence. Two peaks of the total respiration rate were observed: the first one appeared on day 11, and the second one on day 19 (in senescing callus). H₂O₂and O^– ₂contents increased gradually and reached the greatest values when callus senescence initiated (by day 11 and day 15, respectively), and then declined. The peaks of H₂O₂and O^– ₂before the onset of senescence coincided with the peaks of capacity V _altand activity V _altof alternative pathway, respectively. After the onset of senescence, ·OH accumulated abundantly and maintained at a relatively high level from then on, accompanied by the decrease in both V _altand V _alt. The conclusion is that these three active oxygen species operated coordinately to regulate the alternative pathway during growth and senescence of tobacco callus, as confirmed by the callus treatments with AOS scavengers, exogenous ·OH, and inhibitors of antioxidant enzymes. The possibility of AOS-induced alternative pathway respiration at the initial senescence of tobacco callus is discussed.     

The responses of photosynthetic rate and stomatal conductance of Fraxinus rhynchophylla to differences in CO2 concentration and soil moisture

The photosynthetic parameters in leaves of three-year-old seedlings of Fraxinus rhynchophylla L. were studied under different soil water conditions and CO₂ concentrations ([CO₂]) with a LI-COR 6400 portable photosynthesis system. The objective was to investigate the response of photosynthesis and stomatal conductance (g _s) to various [CO₂] and soil water conditions, and to understand the adaptability of F. rhynchophylla to such conditions. The results showed that the soil water content (RWC) required to maintain high photosynthetic productivity in F. rhynchophylla was 49.5–84.3%; in this range, net photosynthetic rate (P _N) rose with [CO₂] increasing from 500 to 1,400 μmol mol^?1. Outside this RWC range, P _N decreased significantly. The apparent maximum photosynthetic rate (P _max,c) and carboxylation velocity (V _c) increased with increasing RWC and remained relatively high, when RWC was between 49.5 and 96.2%. CO₂ compensation points and photorespiration rate exhibited a trend opposite to that of P _max,c and V _c, indicating that moderate water stress was beneficial for increasing plant assimilation, decreasing photorespiration, and increasing production of photosynthates. g _s declined significantly with increasing [CO₂] under different water supplies, but the RWC range maintaining high g _s increased. g _s reached its maximum, when RWC was approximately 73% and then decreased with declining RWC. The maximal g _s was found with increasing RWC. Thus, based on photosynthetic characteristics in artificial, vegetation construction in semiarid loess hill and gully area, F. rhynchophylla could be planted in habitats of low soil water content.     

Physiomorphological response of rose-scented geranium (Pelargonium spp.) to irrigation frequency

The effect of irrigation frequency on leaf physiomorphological processes of rose-scented geranium (Pelargonium capitatum × P. radens cv. Rose) was investigated in a glasshouse study at the Hatfield Experimental Farm of the University of Pretoria, Pretoria, South Africa, from November 2005 to October 2006. Daily, and every 2nd, 3rd, 4th^, and 5th day irrigation were applied as treatments. Leaf samples for electron-microscopic observations were taken one week prior to harvesting, whereafter all plants were re-watered. For each of the irrigation frequency treatments, 50% of the plants were then exposed to a one-week irrigation withholding period (brief stress treatment) prior to harvesting. During this period, physiological properties were recorded on a daily basis to identify or monitor change. Higher irrigation frequency and a brief water stress period increased essential oil yield. Lower irrigation frequency tended to increase the citronellol to geraniol (C:G) ratio to unacceptably high levels (C:G > 3). Upon re-watering, stomatal conductance (G_s) and transpiration rate (R_t) were significantly lower for the lower irrigation frequency treatments, compared to the higher irrigation frequency treatments, while no noticeable differences were observed in water potential (ψ_w) and relative water content (RWC). At the end of the one-week stress period, G_s, R_t, ψ_w and RWC were lower for the plants that were more frequently irrigated compared to the less frequently irrigated treatments. Water stress reduced leaf size, and apparently increased trichome density, whereas the total number of trichomes per leaf remained more or less the same, indicating that total essential oil yield is mainly affected by leaf number (and not by leaf size or trichome number). Stomatal closure was the main water stress avoiding/adaptation mechanism. These results demonstrate that rose-scented geranium plants can make physiomorphological adaptations to save water. However, such a water saving strategy was counter-productive, since it resulted in lower essential oil yield and lower water-use efficiency.     

Responses of Quercus ilex from Different Provenances to Experimentally Imposed Water Stress

Responses of Quercus ilex L. seedlings from three different localities in Italy to experimentally imposed drought stress were analysed. Predawn (Ψ_pd) and midday (Ψ_m) leaf water potential of stressed seedlings decreased on an average until −4.0 and −4.2 MPa, respectively, in the severe water stress. At the end of the severe water stress the relative water content (RWC) was 72.5 – 83.6 % and the photosynthetic rates (P_N) near zero. The critical threshold value of Ψ_pd for complete stomatal closure was from −4.0 to −4.5 MPa. The leaf damage after the severe water stress was significantly greater in seedlings originated from the acorns of climax area (45 % total leaf injured area and 40 % fallen leaves) than in the other seedlings (on an average 20.5 % total leaf injured area and 21 % fallen leaves). This revised version was published online in July 2006 with corrections to the Cover Date.     

The production of an inducible antisense alternative oxidase (Aox1a) plant

Plant mitochondria contain an alternative oxidase (AOX) acting as a terminal electron acceptor of the alternative pathway in the electron transport chain. Here we describe the production of inducible antisense Aox1a plants of Arabidopsis thaliana (L.) Heynh. and the procedures used to determine the resulting alternative pathway activity. The Arabidopsis Aox1a cDNA sequence was cloned behind a copper-inducible promoter system in the antisense orientation. Arabidopsis thaliana (Columbia) plants were transformed by in-planta vacuum infiltration with Agrobacterium containing the antisense construct. Whole-leaf ethanol production was used as a measure to investigate alternative pathway activity in the presence of antimycin A. After 24 h, leaves from the copper-induced, antisense line F1.1 produced up to 8.8 times more ethanol (via aerobic fermentation) than the non-induced and wild-type leaves, indicating effective cytochrome pathway inhibition by antimycin A and a decreased alternative pathway activity in induced F1.1 leaves. Transgene expression studies also revealed no expression in non-induced leaves and up until 24 h post-induction. Copper-induced transgenic leaves were less susceptible to alternative pathway inhibition than non-induced transgenic leaves, as seen via tissue-slice respiratory studies, and mitochondrial respiration, using F1.1 cell cultures, also supported this. These results demonstrate the successful production of a transgenic line of Arabidopsis in which the alternative pathway activity can be genetically manipulated with an inducible antisense system. Received: 31 March 2000 / Accepted: 10 May 2000     

Alternative oxidases in Arabidopsis: A comparative analysis of differential expression in the gene family provides new insights into function of non-phosphorylating bypasses

The emergence of Arabidopsis as a model plant provides an opportunity to gain insights into the role of the alternative oxidase that cannot be as readily achieved in other plant species. The analysis of extensive mRNA expression data indicates that all five Aox genes (Aox1a, 1b, 1c, 1d and 2) are expressed, but organ and developmental regulation are evident, suggesting regulatory specialisation of Aox gene members. The stress-induced nature of the alternative pathway in a variety of plants is further supported in Arabidopsis as Aox1a and Aox1d are amongst the most stress responsive genes amongst the hundreds of known genes encoding mitochondrial proteins. Analysis of genes co-expressed with Aoxs from studies of responses to various treatments altering mitochondrial functions and/or from plants with altered Aox levels reveals that: (i) this gene set encodes more functions outside the mitochondrion than functions in mitochondria, (ii) several pathways for induction exist and there is a difference in the magnitude of the induction in each pathway, (iii) the magnitude of induction may depend on the endogenous levels of Aox, and (iv) induction of Aox can be oxidative stress-dependent or -independent depending on the gene member and the tissue analysed. An overall role for Aox in re-programming cellular metabolism in response to the ever changing environment encountered by plants is proposed.     

The Ca2+-extruding ATPase of the human platelet creates and responds to cytoplasmic pH changes,consistent with a 2 Ca2+/nH+ exchange mechanism

The Ca²⁺-extruding ATPase pump of the human platelet was studiedin situ by measuring Ca²⁺ extrusion from quin2-overloaded platelets (Johansson, J.S., Haynes, D.H. 1988.J. Membrane Biol. 104:147–163). Cytoplasmic pH (pH_cyt) was measured by BCECF fluorescence in parallel experiments. The pump was studied by raising the cytoplasmic free Ca²⁺ to 2.5 μM and monitoring active Ca²⁺ extrusion into a Ca²⁺-free medium. The pump was shown to perturb pH_cyt, to not respond to changes in membrane potential and to respond to imposed changes in pH_cyt in a manner consistent with the Ca²⁺ pump acting as a 2 Ca²⁺/nH⁺ exchanger. (i) Raising the external pH (pH_ext) from 7.40 to 7.60 lowers the V_max of the pump in basal condition (V_max,1) from 110±18 to 73±12 μM/min (=μmol/liter cell volume/min). (ii) Lowering pH_ext to 7.13 raised V_max,1 to 150±15 μM/min. (iii) In an N-methyl-d-glucamine (NMDG⁺) medium, the pump operation against high [Ca²⁺]_cyt acidifies the cytoplasm by −0.36±0.10 pH units, and the pump becomes self-inhibited. (iv) Use of nigericin to drive pH_cyt down to 6.23 reduces the V_max,1 to 18±11 μM/min. (v) Alkalinization of the cytoplasm by monensin in the presence of Na⁺ raises the V_max,1 (basal state withK _m,1=80 nM) to 136±24 μM/min, but also activates the pump fourfold (V_max,2=280±28 μM/min;K _m,2=502±36 nM). (vi) Transient elevation of pH_cyt by NH₄Cl at high [Ca²⁺]_cyt activates the pump eightfold (V_max,2≥671±350 μM/min). The large activation by alkaline pH_cyt at high [Ca²⁺]_cyt can be explained by Ca²⁺-calmodulin activation of the pump (Valant, P.A., Adjei, P.N., Haynes, D.H. 1992.J. Membrane Biol. 130:63–82) and by increased Ca²⁺ affinity of calmodulin at high pH.     

Gas exchange and leaf water relations in two peanut cultivars of different drought tolerance

In summer seasons of 1991 and 1992 the gas exchange and leaf water relations were analysed in two peanut cultivars: drought tolerant cv. GG 2 (DT) and drought sensitive cv. JL 24 (DS). Soil moisture stress was imposed by withholding irrigation at pod development phase. The decrease in photosynthesis (P_N) under stress was associated with a decrease in stomatal conductance (g_s) and relative water content (RWC). The P_N and RWC were significantly higher under stress in DT than DS. On relief of stress the g_s and RWC recovered more quickly in DT than DS. The maintenance of higher RWC (>80 %), g_s and P_N under stress appears to be imparting drought tolerance in peanut.     

High Ambient Carbon-Dioxide does not Affect Respiration by Suppressing the Alternative, Cyanide-resistant Pathway

Total dark respiration (v_t), cytochrome pathway (v_eyt), alternativepathway (v_alt) and residual (v_res) respiration were measuredin Lemna gibba plants, by the use of pathway inhibitors. NaCNwas used to inhibit v_eyt and SHAM (salicylhydroxamic acid) toinhibit v_alt. Residual respiration (v_res) was about 5% of v_t.The effect of high (100 Pa) and low (0 Pa) carbon dioxide partialpressure ([CO₂]) on v_t, v_eyt and v_alt was determined from bothCO₂ efflux and O₂ uptake measurements. The higher [CO₂] suppressedv_t by about 30%. When respiration operated through the cytochromepathway only, in the absence of v_alt, it was suppressed by about12% as measured by the O₂ uptake of submerged Lemna fronds orby about 40% as measured by CO₂ efflux from floating fronds.The higher [CO₂] treatment had only a small effect on respiration,when v_alt alone operated. There was no evidence of a specificsuppression of the v_alt pathway by high [CO₂]. Succinic dehydrogenaseactivity of the mitochondria of roots of Medicago sativum wasreduced by 18%, when the mitochondria were pre-treated with120 as compared to 34 Pa [CO₂]. There was no such effect oncytochrome c oxidase activity of mitochondria under the sameconditions. It is concluded that there is no evidence for the hypothesisthat the high [CO₂] suppression of respiration is a result ofa CO₂ effect on the non-phosphorylating alternative respirationpathway.Copyright 1995, 1999 Academic Press Lemna gibba, Medicago sativum, respiration, cytochrome pathway, alternative pathway, cyanide-insensitive pathway, carbon dioxide, succinic dehydrogenase, cytochrome c oxidase     

Respiration metabolism in mitochondria of pea seedlings of different age under water deficit and rewatering

The effects of an osmoticum (mannitol) on growth, water content, respiration, and proline content in epicotyls of etiolated two-day-old (S₂) and three-day-old (S₃) pea (Pisum sativum L., cv. Flora-2) seedlings were studied. Water deficit was produced by placing plant roots in 0.6 M mannitol for 2–4 days. Control S₃ epicotyls contained more water than S₂ epicotyls; they were also characterized by more intense mitochondrial activity (in state 3, V ₃) and by the higher value of the respiratory control (RC) due to a fourfold decrease of proportion of weakly phosphorylating cyanide-resistant respiration (CRR). After 2-day-long treatment with the osmoticum, S₂ epicotyls lost more water than S₃; water deficit in them attained 40% (28% in S₃). In S₃ treatment, epicotyls continued to grow at the almost unchanged rate, and the content of proline in them changed insignificantly, whereas in S₂ seedlings epicotyl growth stopped, and proline accumulated in them. In the presence of the osmoticum, V ₃ and RC reduced, but in S₃ treatment they retained higher than in treatment S₂. In mitochondria of S₃ subjected to dehydration, the proportion of the cytochromic pathway of oxidation (V _cyt) remained high, but the absolute values of the respiration rate reduced, whereas in S₂ both these indices reduced and the proportion of CRR increased. After rewatering, indices of mitochondrial activity (the rate of substrate oxidation, RC value) were restored, but in S₃ they were higher. The ratio of V _cyt to CRR in S₃ shifted toward CRR, whereas in S₂, in contrast, it was shifted toward V _cyt. When temperature during seedling growth and experiment performing was declined from 22°C (in control) to 18°C, growth of S₃ epicotyls was retarded to the rate characteristic of S₂ at 22°C. Under the effect of osmoticum, they, like S₂, acquired a capacity to accumulate proline. Nevertheless, mitochondrial activity in such S₃ turned out to be higher than in S₂ grown at 22°C. The results obtained than, as distinct from traditional notes, 3-day-old pea seedlings manifested the higher tolerance to water deficit than 2-day-old seedlings.