Homeoviscous and functional adaptations of mitochondrial membranes to growth temperature in soybean seedlings

The present study investigated whether the cold‐sensitive character of soybean is reflected at the level of mitochondrial membranes. When exposed to an increase of temperature (from 25 to 35 °C), mitochondrial membranes were characterized by a higher phosphatidylcholine : phosphatidylethanolamine ratio and a lower content in 18 : 3 fatty acid. After a reduction of temperature (from 25 to 18 °C) the opposite changes were found. Lipid lateral diffusion and local microviscosity appeared to be comparable in mitochondria from plantlets grown at 25 or 35 °C when assayed at the respective growth temperatures. Some functional aspects (cytochrome c oxidase activity or membrane conductance) tended to this behaviour whereas others (respiration rate or maximum membrane potential) did not. On the other hand, membranes from plants grown at 18 °C were more rigid. Moreover, as illustrated by cytochrome c oxidase activity or respiration rate, functional measurements suggested that these membranes were less active at this temperature. Thus the dynamic characteristics and functional properties measured in mitochondrial membranes were in favour of an adaptive trend at 35 °C, but not at 18 °C despite changes in lipid composition, in accordance with the cold‐sensitive character of the plant.     

Photosynthetic acclimation to low temperature by western red cedar seedlings

Imposition of low, but above freezing, temperatures resulted in a gradual increase in the cold hardiness of western red cedar seedlings. This was associated with a decrease in the maximum rates of photosynthetic CO₂ fixation and O₂ evolution, and changes in chlorophyll a fluorescence transients which indicated that photoinhibition had occurred. Maximum photosynthetic rates declined approximately 40% during cold hardening. The leaves changed colour from green to red-brown during the hardening process. The colour change was due to the synthesis of large amounts of the carotenoid rhodoxanthin. Lutein levels doubled, while chlorophyll declined slightly. Dehardening resulted in the rapid recovery of photosynthesis to control levels, the rapid disappearance of rhodoxanthin, and the return of lutein levels to control. It is suggested that rhodoxanthin accumulation at low temperature functions to decrease the light intensity reaching the photosynthetic apparatus. The combination of photoinhibition and rhodoxanthin synthesis probably serves to protect the photosynthetic capacity of the seedlings at low temperature.     

Intraspecific variations in antioxidant defense responses and sensitivity of soybean varieties to ambient UV radiation

Field experiments were conducted to determine the effects of exclusion of UV-A/B and UV-B alone on growth parameters, activity of antioxidant enzymes, level of antioxidants and yield, to evaluate the intra-specific variations in sensitivity of these responses in eight soybean (Glycine max) varieties (PK-472, PK-1029, Pusa-24, JS-7105, JS-335, Hardee, NRC-7 and Kalitur). The plants were grown in specially designed UV-exclusion chambers which lined with selective UV filters to exclude either UV-B (<320 nm) or UV-A/B (<400 nm). Plants grown under UV-exclusion filters were compared with those grown under polythene filter which transmitted ambient UV-B and UV-A radiation. The results indicate that the exclusion of solar UV-B and UV-A/B enhanced the vegetative growth (plant height and leaf area), total biomass accumulation and yield (number of seeds and seed weight) of all the varieties as compared with those grown under ambient UV. The activities of SOD, GPX, APX and GR, and levels of ASA were significantly decreased, while α-tocopherol increased after the exclusion of UV-B and UV-A/B in all varieties. These results suggest that the ambient level of UV-B and UV-A radiation evoked some active oxygen species to accumulate, which in turn retarded the growth, development and yield of soybean varieties. On the basis of biomass, UV-B (280–315 nm) sensitivity can be arranged in decreasing order as PK-472 > Hardee > JS-335 > Kalitur > JS 71-05 > Pusa-24 > NRC-7 > PK-1029 and UV-A/B sensitivity can be arranged in decreasing order as PK-472 > Kalitur > JS-335 > Hardee > Pusa-24 > JS 71-05 > NRC-7 > PK-1029. The results indicate var. PK-472 is more sensitive than other varieties and PK-1029 is least sensitive to ambient level of UV radiation. This study in the area of UV-B and UV-A/B stress provides an extensive data that can be used as a predictive basis in crop sciences to further investigate some of the tolerant varieties in field studies.     

Differing sensitivity of photosynthesis to low leaf water potentials in corn and soybean

Rates of net photosynthesis were studied in soil-grown corn (Zea mays) and soybean (Glycine max) plants having various leaf water potentials. Soybean was unaffected by desiccation until leaf water potentials were below −11 bars. Rates of photosynthesis in corn were inhibited whenever leaf water potentials dropped below −3.5 bars.     

Daily variations in the influence of noradrenaline on preferred ambient temperature of the Siberian hamster

Daily variations in sensitivity to noradrenaline (NA) and the activation of nonshivering thermogenesis (NST) are important for survival under a potentially wide range of environmental conditions. However, little is known regarding the ability of the Siberian hamster and other species to activate NST in the day and night when they may be subjected to marked variations in environmental temperature. In this study, the effects of acclimation temperature and time of day on the behavioral thermoregulatory response to NA injections in Siberian hamsters (Phodopus sungorus) was investigated. Hamsters were acclimated for 4 weeks to 23 degrees C and a L:D 12:12 h photoperiod. After acclimation, preferred ambient temperatures (PT(a)) in saline- and NA-injected animals were measured continuously in the temperature gradient system. NA (0.6 mg/kg; s.c.) was given every 4 h while PT(a) was monitored. After NA injections there was a rapid drop in PT(a), decreasing to approximately 15 degrees C within 10-20 min after each NA injection. Following 4 weeks of acclimation to 10 degrees C and a L:D 8:16 h photoperiod, the same hamsters were re-tested in the temperature gradient system. Cold acclimation led to an accentuation in the behavioral response with a decrease in PT(a) of approximately 10 degrees C. The maximal decrease in preferred ambient temperatures was recorded during the light phase of the day and during the second part of the night. Lowering of PT(a) after NA allows for rapid dissipation of the heat from NST. Overall, the behavioral response reflects the daily changes in brown adipose tissue sensitivity to NA and thus capacity for NST.     

Effect of low temperature on ethanolic fermentation in rice seedlings

Rice seedlings (Oryza sativa L.) were incubated at 5-30 degrees C for 48 h and the effect of temperature on ethanolic fermentation in the seedlings was investigated in terms of low-temperature adaptation. Activities of alcohol dehydrogenase (ADH, EC 1.1.1.1) and pyruvate decarboxylase (PDC, EC 4.1.1.1) in roots and shoots of the seedlings were low at temperatures of 20-30 degrees C, whereas temperatures of 5, 7.5 and 10 degrees C significantly increased ADH and PDC activities in the roots and shoots. Temperatures of 5-10 degrees C also increased ethanol concentrations in the roots and shoots. The ethanol concentrations in the roots and shoots at 7.5 degrees C were 16- and 12-times greater than those in the roots and shoots at 25 degrees C, respectively. These results indicate that low temperatures (5-10 degrees C) induced ethanolic fermentation in the roots and shoots of the seedlings. Ethanol is known to prevent lipid degradation in plant membrane, and increased membrane-lipid fluidization. In addition, an ADH inhibitor, 4-methylpyrazole, decreased low-temperature tolerance in roots and shoots of rice seedlings and this reduction in the tolerance was recovered by exogenous applied ethanol. Therefore, production of ethanol by ethanolic fermentation may lead to low-temperature adaptation in rice plants by altering the physical properties of membrane lipids.     

Differing sensitivity of pyruvate orthophosphate dikinase to low temperature in maize cultivars

Cold lability of pyruvate Pi dikinase was examined by incubatingdie enzyme at 0°C using crude extracts obtained from 20maize cultivars which exhibit different growth responses toclimatic conditions in this country. The results provide evidencefor a possible correlation between cold lability of the enzymeand the cultivars. (Received March 24, 1976; )     

Responses of Rubisco and Rubisco activase in cucumber seedlings to low temperature and weak light

Using 'Jinyou 3' cucumber seedlings as test materials, this paper studied their photosynthetic rate (P(n)), Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) and Rubisco activase (RCA) activities, and gene expression of Rubisco and RCA under optimal temperature and weak light (WL: 25 degrees C/18 degrees C, 100 micromol x m(-2) x s(-1)), suboptimal temperature and weak light (ST+WL: 18 degrees C/12 degrees C, 100 micromol x m(-2) x s(-1)), and low temperature and weak light (LT+WL: 10 degress C/5 degrees C, 100 micromol x m(-2) x s(-1)). Comparing with the control (25 degrees C/18 degrees C, 400 micromol x m(-2) x s(-1)), treatments WL, ST+WL, and LT+WL all led to a remarkable decrease in leaf area and dry matter mass. At initial stage, the P(n), Rubisco activity, rbcL and rbcS expression, RCA activity, and CsRCA expression in the three treatments declined by a big margin; 5-7 days later, these parameters tended to be less changed in treatment WL, ascended slowly in treatment ST+WL, and decreased continuously in treatment LT+WL. These results suggested that the photosynthetic apparatus of test cucumber seedlings could gradually adapt to weak light or suboptimal temperature and weak light. The Rubisco and RCA activities and the gene expression of Rubisco and RCA showed the similar responses to low temperature and weak light as the P(n), suggesting that the decline in Rubisco and RCA activities and gene expression in cucumber seedlings under low temperature and weak light could be the important reason leading to the decrease of P(n).     

Rhythmical changes in the sensitivity of cotton seedlings to herbicides

Cotton (Gossypium hirsutum L.) seedlings that were grown under a photoperiod of 12 hours darkness and 12 hours light showed oscillations in their sensitivity to the herbicides sodium 5-(2-chloro-4-trifluoromethyl)-phenoxy)-2-nitrobenzoate (acifluorfen), butyl 2-(4-((5-(trifluoromethyl)-2-pyridinyl)oxy)phenoxy)propanoate (fluazifop) and 3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide (bentazon). Sensitivity was expressed in appearance of necrotic areas on the cotyledons and in decreased growth of the shoot. The seedlings were least sensitive in the beginning and middle of the light period, then the sensitivity increased and reached its maximum during the beginning and middle of the dark period and then declined. Seedlings grown from germination under continuous light exhibited very small or no oscillations in sensitivity. The oscillations in sensitivity were entrained by one cycle of darkness and light. A cycle of 12 hours darkness and 12 hours light triggered the greatest oscillations while either increasing or decreasing the duration of the dark period resulted in smaller oscillations. Apparently, these oscillations in sensitivity to herbicides were endogenously controlled since after entrainment they continued irrespective of the light conditions.     

苯丙氨酸解氨酶在诱导黄瓜幼苗抗寒性中的作用

为了探讨苯丙氨酸解氨酶(PAL)在诱导黄瓜幼苗抗寒性中的作用,采用喷施特异抑制剂(AOPP)的方法控制PAL活性,测定幼苗抗寒性的变化.结果表明： 低温可以诱导黄瓜幼苗叶片中PAL的基因表达和活性升高;喷施AOPP显著抑制了叶片中PAL活性,减少了酚类和类黄酮物质的积累.低温对黄瓜幼苗造成显著伤害,AOPP预处理加剧了低温对幼苗的损伤,幼苗抗寒性降低.与对照相比,幼苗叶片中相对电解质渗漏率和丙二醛(MDA)含量显著升高,PSII最大光化学效率(F_v/F_m)降低,光化学猝灭参数Y(NO)升高,胁迫相关基因(PR1-1a、COR47、P5CS、HSP70)的诱导表达受到抑制.低温导致黄瓜幼苗叶片中H₂O₂积累,还原型抗坏血酸(AsA)含量降低,脱氢抗坏血酸(DHA)含量升高,AsA∶DHA减小;喷施AOPP的幼苗中抗氧化酶(过氧化氢酶CAT、抗坏血酸过氧化物酶APX)活性显著低于对照,H₂O₂过量积累,AsA∶DHA更低.施用H₂O₂清除剂可以有效缓解喷施AOPP引起的低温损伤加剧,而施用CAT抑制剂的幼苗对低温胁迫更敏感.表明低温诱导了PAL活性升高,促进了苯丙烷类次生代谢产物的合成,提高了胞内抗氧化酶活性,可有效清除活性氧分子,维持AsA氧化还原状态,缓解低温引起的光损伤和氧化损伤.     

QTL analysis of low temperature induced browning in soybean seed coats

Exposure of soybean [Glycine max (L.) Merr.] to chilling temperatures at flowering stage induces browning around the hilum of the seed coats. The brown pigmentation spoils the external appearance of soybean seeds and reduces their commercial value. Our previous studies revealed that pigmentation was controlled by a few major genes, and one of the genes is closely associated with a maturity gene. This study was conducted to further investigate inheritance of pigmentation using DNA markers. Fifty-eight F(2) plants derived from a cross between a tolerant cv. Koganejiro and a sensitive cv. Kitakomachi were exposed to 15 degrees C for 2 weeks beginning 8 days after anthesis. Genotypes of 522 genetic markers were determined using the F(2) plants. Composite interval mapping revealed 5 quantitative trait loci (QTLs) for pigmentation, pig1 to pig5 (pig1 in molecular linkage group A2 [MLG A2], pig2 in MLG B1, pig3 in MLG C2, pig4 in molecular linkage group (MLG), and pig5 in MLG N) and 4 QTLs for flowering date, fd1 to fd4 (fd1 in MLG C1, fd2 in MLG C2, fd3 in MLG J, and fd4 in MLG L). Based on the relative location with markers, fd2 and fd4 probably correspond to E1 and E3, respectively. pig3 and fd2 were found at a similar position, and logarithm of odds (LOD) score plots for pigmentation and flowering date almost overlapped around this region. Considering the fact that pig3 had the most intense effects on pigmentation, E1 is presumed to be the maturity gene that profoundly affects pigmentation. Further, E3 has a small effect on pigmentation in accordance with the previous reports. These results support the idea that soybean maturity genes control low temperature-induced pigmentation with various intensities specific to each maturity gene. QTLs for seed coat pigmentation with small or no impact on maturity identified in this study may be useful in breeding for chilling tolerance.     

Alterations in phenylpropanoid content in soybean roots during low temperature acclimation

L-Phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) activity, growth and phenolic acid content during low temperature acclimation in soybean (Glycine max. (L.) Merr.) roots were investigated. Elongation of soybean roots was inhibited after the transfer of 3-d-old seedlings grown at 25 to 10 °C. Extractable PAL activity as well as the total amount of phenolics increased 24 h after plant transfer to low temperature. The high pressure liquid chromatography analyses revealed the presence of six phenolic acids in soybean roots: p-hydroxybenzoic, vanillic, syringic, anisic, p-coumaric and ferulic. Analyses of different fractions of phenolic acids showed that during 24 h of low temperature exposure, an increase in the relative level of ester-bound-soluble phenolic acids occurred. The highest increase in this fraction was observed for ferulic acid (26 %). At the same time, a decrease in phenolic glycosides took place. The amount of phenolic acids released after alkaline treatment of the cell wall material was strongly inhibited (3-fold), which may suggest an alteration of the physical properties of the wall in acclimation to low temperature. The possible role of phenolics in acclimation to low temperature in roots is discussed.     

Arginase activity in the cotyledons of soybean seedlings

The influence of naphthylacetic acid, abscisic acid, gibberellic acid and kinetin on the formation of aerenchyma in seedling roots of Zea mays L. cv. Capella has been studied in relation to reported changes of their concentration in poorly aerated roots, which readily form aerenchyma, and to the effects of these hormones on the production of ethylene, a major factor promoting aerenchyma formation. Because the absence of nitrate accelerates aerenchyma formation in aerated roots, their influence on these roots was compared. The growth regulators were added to roots growing in non-aerated and aerated nutrient solutions, and aerenchyma formation and the production and endogenous concentration of ethylene were measured. Naphthylacetic acid prevented aerenchyma formation in both aerated roots without nitrate and in non-aerated roots although it enhanced the ethylene concentration of the roots. Abscisic acid also prevented aerenchyma formation, but without affecting the ethylene concentration. Gibberellic acid promoted aerenchyma formation in aerated roots only, but ethylene production in both aerated and non-aerated roots. Kinetin promoted aerenchyma formation in both aerated and non-aerated roots. It stimulated ethylene production in aerated roots, but slightly inhibited it in non-aerated roots. Co²⁺ and Ag⁺, which suppress ethylene production and action, respectively, reduced the promoting effects of gibberellic acid, but not those of kinetin. It is concluded that the effects of the plant growth regulators on aerenchyma formation in maize roots were, with a possible exception for gibberellic acid, not the result of altered ethylene concentrations in the roots. Their influence on aerenchyma formation is discussed in relation to their reported actions on cell membranes.     

Osmoregulation,solute distribution,and growth in soybean seedlings having low water potentials

Soybean (Glycine max (L.) Merr.) seedlings osmoregulate when the supply of water is limited around the roots. The osmoregulation involves solute accumulation (osmotic adjustment) by the elongating region of the hypocotyls. We investigated the relationship between growth, solute accumulation, and the partitioning of solutes during osmoregulation. Darkgrown seedlings were transplanted to vermiculite containing 1/8 (0.13 x) the water of the controls. Within 12–15 h, the osmotic potential of the elongating region had decreased to-12 bar, but it was-7 bar in the controls. This osmoregulation involved a true solute accumulation by the hypocotyls, since cell volume and turgor were virtually the same regardless of the water regime. The hypocotyls having low water potentials elongated slowly but, when deprived of their cotyledons, did not elongate or accumulate solute. This result indicated a cotyledonary origin for the solutes and a dependence of slow growth on osmotic adjustment. The translocation of nonrespired dry matter from the cotyledons to the seedling axis was unaffected by the availability of water, but partitioning was altered. In the first 12 h, dry matter accumulated in the elongating region of the 0.13 x hypocotyls, and osmotic adjustment occurred. The solutes involved were mostly free amino acids, glucose, fructose, and sucrose, and these accounted for most of the increased dry weight. After osmotic adjustment was complete, dry matter ceased to accumulate in the hypocotyls and bypassed them to accumulate in the roots, which grew faster than the control roots. The proliferation of the roots resulted in an increased root/shoot ratio, a common response of plants to dry conditions.Osmotic adjustment occurred in the elongating region of the hypocotyls because solute utilization for growth decreased while solute uptake continued. Adjustment was completed when solute uptake subsequently decreased, and uptake then balanced utilization. The control of osmotic adjustment was therefore the rate of solute utilization and, secondarily, the rate of solute uptake. Elongation was inhibited by unknown factors(s) despite the turgor and substrates associated with osmotic adjustment. The remaining slow elongation depended on osmotic adjustment and represented some optimum between the necessary inhibition for solute accumulation and the necessary growth for seedling establishment.     

Molecular characterization of the soybean L-asparaginase gene induced by low temperature stress

L-asparaginase (EC 3.5.1.1) catalyzes the hydrolysis of the amide group of L-asparagine, releasing aspartate and NH4+. We isolated a low temperature-inducible cDNA sequence encoding L-asparaginase from soybean leaves. The full-length L-asparaginase cDNA, designated GmASP1, contains an open reading frame of 1,258 bp coding for a protein of 326 amino acids. Genomic DNA blotting and fluorescence in situ hybridization showed that the soybean genome has two copies of GmASP1. GmASP1 mRNA was induced by low temperature, ABA and NaCl, but not by heat shock or drought stress. E. coli cells expressing recombinant GmASP1 had 3-fold increased L-asparaginase activity. A possible function of L-asparaginase in the early response to low temperature stress is discussed.