Changes in response to drought stress of triticale and maize genotypes differing in drought tolerance

Direct effects and after-effects of soil drought for 7 and 14 d were examined on seedling dry matter, leaf water potential (ψ), leaf injury index (LI), and chlorophyll (Chl) content of drought (D) resistant and sensitive triticale and maize genotypes. D caused higher decrease in number of developed leaves and dry matter of shoots and roots in the sensitive genotypes than in the resistant ones. Soil D caused lower decrease of ψ in the triticale than maize leaves. Influence of D on the Chl b content was considerably lower than on the Chl a content. In triticale the most harmful D impact was observed for physiologically younger leaves, in maize for the older ones. A period of 7-d-long recovery was too short for a complete removal of an adverse influence of D.     

Content of Plant Pigments in the Bottom Sediments of the Water Bodies of Vietnam

Data on the content of plant pigments in the bottom sediments (BSs) of the water bodies of Central and South Vietnam are given for the first time. The average concentration of chlorophyll a and phaeopigments (Chl + Ph) in total reaches up to 3.9 μg/g dry matter in rivers, 5.6 in ponds, 13.8 in sand quarries, 56.8 in reservoirs, and 245 in lakes. Most frequently, the concentrations of Chl + Ph in the coastal zones of watercourses and water bodies fall in the oligotrophic category, and those in the central areas are in the hypertrophic category. Relationships between concentrations of Chl + Ph and water depth, content of oxygen near the bottom, moisture content, volumetric mass, and concentrations of organic matter (OM) in the BSs are found. The content of sedimentary pigments in tropical waters of Vietnam is similar to that in freshwater ecosystems of temperate latitudes, despite the substantial differences of climatic zones in temperature and light regimes.     

Differences in pigment composition, photosynthetic rates and chlorophyll fluorescence images of sun and shade leaves of four tree species.

The differential pigment composition and photosynthetic activity of sun and shade leaves of deciduous (Acer pseudoplatanus, Fagus sylvatica, Tilia cordata) and coniferous (Abies alba) trees was comparatively determined by studying the photosynthetic rates via CO(2) measurements and also by imaging the Chl fluorescence decrease ratio (R(Fd)), which is an in vivo indicator of the net CO(2) assimilation rates. The thicker sun leaves and needles in all tree species were characterized by a lower specific leaf area, lower water content, higher total chlorophyll (Chl) a+b and total carotenoid (Cars) content per leaf area unit, as well as higher values for the ratio Chl a/b compared to the much thinner shade leaves and needles that possess a higher Chl a+b and Cars content on a dry matter basis and higher values for the weight ratio Chls/Cars. Sun leaves and needles exhibited higher rates of maximum net photosynthetic CO(2) assimilation (P(Nmax)) measured at saturating irradiance associated with higher maximum stomatal conductance for water vapor efflux. The differences in photosynthetic activity between sun and shade leaves and needles could also be sensed via imaging the Chl fluorescence decrease ratio R(Fd), since it linearly correlated to the P(Nmax) rates at saturating irradiance. Chl fluorescence imaging not only provided the possibility to screen the differences in P(N) rates between sun and shade leaves, but in addition permitted detection and quantification of the large gradients in photosynthetic rates across the leaf area existing in sun and shade leaves.     

Influence of soil type and natural Zn chelates on flax response, tensile properties and soil Zn availability

A greenhouse experiment was conducted on weakly acidic and calcareous soils to evaluate the relative efficiencies of three natural Zn chelates [Zn-aminelignosulphonate (Zn-AML), Zn-polyhydroxyphenylcarboxylate (Zn-PHP) and Zn-S,S-ethylenediaminedisuccinate (Zn-S,S-EDDS)] applied to a crop textile flax (Linum ussitatisimum L.) at application rates of 0, 5 and 10 mg Zn kg^?1. In the flax plant, the following parameters were determined: dry matter yield, soluble and total Zn concentrations in leaf and stem, chlorophyll, crude fibre, and tensile properties. For the different soil samples, the following parameters were determined: available Zn (DTPA-AB and Mehlich-3 extractable Zn), easily leachable Zn (BaCl₂-extractable Zn), the distribution of Zn fractions, pH and redox potential. On the basis of the use of added Zn by flax, or Zn utilization, it would seem recommendable to apply Zn-S,S-EDDS at the low Zn rate in both soils. In contrast, adding the high Zn rate of this chelate to the weakly acidic soil produced an excessive Zn concentration in the plant, which caused a significant decrease in both dry matter yield and chlorophyll content. Furthermore, assessing available Zn with the DTPA-AB method proved the best way of estimating the level of excess Zn in flax plants. The soluble Zn concentration, which was established with 2-(N-morpholino)ethanesulfonic acid reagent (MES), of plant fresh and dry matter could be used as an alternative way of diagnosing the nutritional status of Zn in flax plants. In this experiment, the highest soil pHs were associated with the lowest redox potentials, which coincided with the smallest amounts of available Zn and water soluble Zn in soil, and the lowest levels of Zn uptake by flax plants.     

Effect of zinc and cadmium on physiological and production characteristics in <Emphasis Type="Italic">Matricaria recutita</Emphasis>

Effects of zinc (12–180 μM) alone and in mixtures with 12 μM Cd on metal accumulation, dry masses of roots and shoots, root respiration rate, variable to maximum fluorescence ratio (F_V/F_M), and content of photosynthetic pigments were studied in hydroponically cultivated chamomile (Matricaria recutita) plants. The content of Zn in roots and shoots increased with the increasing external Zn concentration and its accumulation in the roots was higher than that in the shoots. While at lower Zn concentrations (12 and 60 μM) the presence of 12 μM Cd decreased Zn accumulation in the roots, treatment with 120 and 180 μM Zn together with 12 μM Cd caused enhancement of Zn content in the root. Presence of Zn (12–120 μM) decreased Cd accumulation in roots. On the other hand, Cd content in the shoots of plants treated with Zn + Cd exceeded that in the plants treated only with 12 μM Cd. Only higher Zn concentrations (120 and 180 μM) and Zn + Cd mixtures negatively influenced dry mass, chlorophyll (Chl) and carotenoid content, F_V/F_M and root respiration rate. Chl b was reduced to a higher extent than Chl a.     

The combined effects of acidification stress and kinetin on chlorophyll content,dry matter accumulation and transpiration coefficient inSorghum bicolor plants

Increasing soil acidity (from pH 6.5 to pH 2.0) decreased chlorophyll (Chl)a andb contents, dry matter accumulation by plants and the transpiration coefficient. Chl stability to heat significantly increased with increased soil acidity. The Chla/b ratio was increased significantly at pH 5 and 4 and decreased at pH 3 and 2. SprayingSorghum shoots with kinetin solutions counteracted the above adverse effects on Chl content and dry matter accumulation. Kinetin-treated plants showed a lower transpiration coefficient than the untreated plants.     

四季竹对土壤水分胁迫的生理适应

以四季竹2年生竹苗为材料,采用每天补水控制土壤含水量的方法,设置土壤相对含水率为<30%(T1)、40%～50%(T2)、60%～70%(T3)、80%～90%(T4)和竹蔸部完全水淹(T5)5个土壤水分含量水平,研究四季竹叶片在水分胁迫下的生理活性变化,以探讨四季竹对土壤水分的适应能力。结果表明:(1)随处理时间的延长,T1处理叶片离子渗漏率、MDA含量、叶绿素a/b值、SOD和POD活性、脯氨酸和可溶性蛋白含量均迅速升高,叶绿素含量、类胡萝卜素含量和叶绿素/类胡萝卜素比值迅速下降。(2)T5处理14d后叶片各生理指标随处理时间的延长与T1处理表现出相同的变化规律(类胡萝卜素和脯氨酸除外),并且分别在T1处理14d和T5处理28d后四季竹叶片全部干枯脱落。(3)随处理时间的延长,T2、T3、T4处理的四季竹叶片各生理指标经过一段时间的适应后最终稳定在处理前水平,且处理间均无显著差异。研究发现,四季竹在土壤相对含水率小于30%的土壤中生长不良,甚至死亡,在相对含水率40%～90%的土壤中能正常生长;四季竹耐受水淹胁迫的时间阈值是28d。     

Zinc efficiency of oilseed rape (t Brassica napus and t B. juncea) genotypes

Twenty five genotypes of oilseed rape (canola and mustard) were tested under varied supply of Zn (+Zn: 2 mg kg^–1 soil, -Zn: no Zn added) in two pot experiments in soil culture to determine the genotypic variation in tolerance to the Zn-deficient conditions, that is, to identify the Zn-efficient genotypes. On the basis of performance of genotypes in pot experiments, ten genotypes were tested in 1995 for their performance under varied supply of Zn (+Zn: 3.5 kg ha^–1, -Zn: no Zn added) on a Zn-deficient field in South Australia.Zn efficiency (ratio of shoot dry matter in -Zn to shoot dry matter in +Zn treatment and expressed in percentage) in pot Experiment 1 varied from 35% for 92-13 to 74% for Siren. Narendra, Dunkeld, Barossa, Oscar and Xinza 2 performed well under -Zn treatment. Zn efficiency in Experiment 2 varied from 32% for Wuyou 1 to 62% for Pusa Bold. Pusa Bold and CSIRO-1(mustard genotypes) were the most efficient in terms of dry matter production among all the oilseed rape genotypes tested. Root dry matter accumulation was significantly higher in Zn-efficient genotypes. Zn efficiency (ratio of seed yield in -Zn to seed yield in +Zn and expressed in percentage) in field experiment varied from 62% for Huashang 2 to 76% for Dunkeld. With few exceptions, the ranking of genotypes in pot and field experiments indicates similarity in their response to Zn deficiency. There looks to be genetic control over Zn concentration in tissues. Zn-efficient genotypes had lower Zn concentration in roots and higher Zn concentration in youngest fully opened leaf blades, indicating a better transport of Zn. This, together with a higher Zn uptake, appears to be the basis of expression of Zn efficiency.     

A study of the role of root morphological traits in growth of barley in zinc-deficient soil

Zinc (Zn) deficiency reduces crop yields globally. This study investigated the importance of root morphological traits, especially root hairs, in plant growth and Zn uptake. Wild-type barley (Hordeum vulgare) Pallas and its root-hairless mutant brb were grown in soil and solution culture at different levels of Zn supply for 16 d. Root morphological traits (root length, diameter, and surface area) were measured using the WinRHIZOPro Image Analysis system. In soil culture, Pallas had greater shoot dry matter, shoot Zn concentration, shoot Zn content, and Zn uptake per cm(2) root surface area than brb, primarily under zinc deficiency. Both Pallas and brb developed longer roots under Zn deficiency. Development of root hairs was not affected by plant Zn status. In solution culture, there were no significant genotypic differences in any of the parameters measured, indicating that mutation in brb does not affect growth and Zn uptake. However, both Pallas and brb developed longer and thinner roots, and root hair growth was less than in soil culture, and was not affected by plant Zn status. The better growth and greater Zn uptake of Pallas compared with brb in Zn-deficient soil can be attributed primarily to greater root surface area due to root hairs in Pallas rather than other root morphological differences.     

Role of kinetin in alleviation of copper and zinc toxicity in Lupinus termis plants

The effect of exogenous kinetin application on the growth and some physiological processes of Lupinus termis plants growing in metal containing solutions with excess concentrations of Cu and Zn ion were studied. Generally, plants growing in these solutions had a lower chlorophyll (Chl.) content, leaf relative water content (RWC) and produced less biomass than the control plants. Proline content was higher in metal-treated plants than in untreated controls. Chromatography of cell-free-extracts of roots and shoots indicated three main protein peaks with molecular weights about 170, 75--70 and 5--45 kDa. These peaks were coincident with Cu or Zn maxima. Addition of kinetin reduced the decline in Chl. content in metal-treated plants, improved water status of the plants and enhanced growth of the shoots and roots. The Cu or Zn content expressed on a per mg protein basis was raised when kinetin was applied to the growing shoots. Kinetin (Kin), Cu and Zn, singly and in the presence of kinetin (Cu × Kin and Zn × Kin), significantly affected the parameters tested. Only the effects of Cu × Kin and Zn × Kin interactions on shoot fresh weight and Cu × Kin on root length were statistically insignificant. Based on the calculated coefficient of determination ( ²) the roles of Cu and Zn in affecting Chl. content and growth were dominant in comparison to kinetin. Kinetin effect was dominant for root length and proline content, but the role of the interaction was subdominant. The results of this study indicate that kinetin can alleviate the harmful effects of Cu and Zn on the growth of lupin plants through stimulation of Cu and Zn incorporation into metal-binding proteins.     

Triadimefon enhances growth and net photosynthetic rate in NaCl stressed plants of Raphanus sativus L.

The effect of sodium chloride and triadimefon (TDM) on the chlorophyll (Chl) content, net photosynthetic rates (P_N), rate of transpiration (E), and intercellular CO₂ concentration (C_i) in Raphanus sativus was studied. The effect of NaCl salinity was partially ameliorated by TDM which caused increase in Chl content, P_N, and C_i. TDM also increased root dry matter production, decreased E, and increased the water use efficiency.     

Effect of crop and soil management practices on soil compatibility in maize and groundnut plots in a Paleustult in Southeastern Nigeria

Frequent occurrences of soil compaction damage resulting from high raindrop impact energy, and from human and animal trafficking during field operations pose a problem to farmers around the tropics. We studied the effect of some crop and soil management practices (manure, mulch, NPK applications, tillage and crop type) on some soil compactibility indices (dry bulk density, cone index, total soil porosity, gravimetric soil water content) in a Typic Paleustult in southeastern Nigeria. The study was carried out for three consecutive planting seasons using two tillage systems and four other soil management practices (poultry droppings + NPK, mulch + NPK, NPK alone and no amendment). These were laid out as split-plot in a RCB design replicated three times and using maize (Zea mays L.) and groundnut (Arachis hypogea) as test crops. Results indicate that the different soil management techniques adopted influenced dry bulk density, penetration resistance, total soil porosity and gravimetric soil water content at 44 and 66 days after planting (DAP) whereas only gravimetric soil water content was affected at 90 DAP. The dry bulk density of tilled maize and groundnut plots increased significantly (P<0.05) by between 2 and 14% relative to no-till plots at 44 and 66 DAP. In both maize and groundnut plots, dry bulk density decreased significantly (P<0.05) in plots amended with poultry droppings +NPK relative to the control plots by 3–10% at 44 and 66 DAP. Tilled maize and groundnut plots had 37–45% lower (P< 0.05) penetration resistance than their corresponding no-till plots at both 44 and 66 DAP. Penetration resistance measurements were lower by 16.5–25% in plots amended with poultry droppings + NPK relative to unamended plots at 44 and 66 DAP. Cumulative (1996, 1997, 1998) data indicate that gravimetric soil water content in maize and groundnut plots generally increased significantly (P<0.05) in no-till plots relative to tilled plots by 18–27% at both 44 and 66 DAP. Plots amended with poultry droppings + NPK had between 24 and 111% increase (P<0.05) in soil gravimetric soil water content at both 44 and 66 DAP. Results are indicative that all soil compactibility indices measured were not affected at 90 DAP except for soil gravimetric soil water content in 1996 and 1998. Results from this work demonstrate that some crop and soil management practices could be used to reduce soil compactibility problems thus increasing productivity of such soils.     

Effects of vesicular-arbuscular mycorrhizae on growth and phosphorus and zinc nutrition of peanut (Arachis hypogaea L.) in an Oxisol from subtropical Australia

Peanut plants (cv. Shulamit) were grown in an Oxisol soil in pots in the glasshouse to assess effects of soil sterilization and inoculation with spores of vesicular-arbuscular mycorrhizal fungi (VAMF) on the response to five rates of phosphorus (0 to 240 kg P ha^–1) and two rates of zinc (0 and 10 kg Zn ha^–1) fertilizers.Both P and Zn nutrition were affected by VAMF activity but the dominant role of VAMF in this soil type was in uptake of P. In the absence of VAMF there was a clear threshold level of P application (60 kg P ha^–1) below which plants grew poorly, which resulted in a sigmoidal response of dry matter to applied P. The maximum response was not fully defined because dry matter production continued to increase up to 240 kg P ha^–1. Tissue P concentration of non-mycorrhizal plants increased linearly with P rate and was always significantly less than that in mycorrhizal plants.Mycorrhizal plants responded without threshold to increasing P rate, attaining maximum dry matter at 120 kg P ha^–1 in inoculated sterilized soil and at 30 kg P ha^–1 in nonsterile soil. These differences in maximal P rates and in the greater dry matter produced in sterile soil at high P rates were attributed to the negative effects of the root-knot nematodeMeloidogyne hapla in nonsterile soil.Plant weight did not respond to zinc fertilizer but tissue Zn concentration increased with applied Zn. Tissue Zn concentration and uptake were increased by VAMF.     

Response of flooded rice grown on a vertisol from northern nigeria to zinc sources and methods of application

Summary Greenhouse and laboratory studies were conducted to study the effect of zinc sources and methods of application on correcting zinc deficiency in flooded rice grown on Vertisol from Ngala, northern Nigeria, using the variety IR-20.Plant dry matter yield was similar for ZnSO₄, ZnEDTA, metallic Zn and fritted Zn with mixed soil application. Zinc uptake was affected in the following order; ZnSO₄ > ZnEDTA > metallic Zn > fritted Zn. Comparable dry matter yield and zinc uptake were obtained with mixing, surface broadcasting and banding of ZnEDTA. Mixing the fritted Zn gave higher dry matter yield and zinc uptake than broadcasting or banding.Seed soaking with a suspension of fritted Zn resulted in higher dry matter yield and zinc uptake than with ZnEDTA solution. Seed soaking for 24 hours with fritted Zn suspension at a concentration of about 0.5 per cent Zn appeared to be a suitable method for applying zinc with direct seeded rice.     

Dry matter production and distribution of zinc in bread and durum wheat genotypes differing in zinc efficiency

Six bread wheat (Triticum aestivum cvs. Kiraç-66, Gerek-79, Aroona, ES 91-12, ES-14 and Kirkpinar) and four durum wheat (Triticum durum cvs. BDMM-19, Kunduru-1149, Kiziltan-91 and Durati) genotypes were grown under controlled environmental conditions in nutrient solution for 20 days to study the effect of varied supply of Zn (0 to 1 µM) on Zn deficiency symptoms in shoots, root and shoot dry matter production, and distribution of Zn in roots and shoots.Visual Zn deficiency symptoms, such as whitish-brown lesions on leaves, appeared rapidly and severly in durum wheats, particularly in Kiziltan-91 and Durati. Among the durum wheats, BDMM-19 was less affected by Zn deficiency, and among the bread wheats Kiraç-66, ES 91-12, Aroona and Gerek-79 were less affected than ES-14 and Kirkpinar.Under Zn deficiency, shoot dry matter production was decreased in all genotypes, but more distinctly in durum wheat genotypes. Despite severe decreases in shoot growth, root growth of all genotypes was either not affected or even increased by Zn deficiency. Correspondingly, shoot/root dry weight ratios were lower in Zn-deficient than in Zn-sufficient plants, especially in durum wheat genotypes.The distinct differences among the genotypes in sensitivity to Zn deficiency were closely related with the Zn content (Zn accumulation) per shoot but not with the Zn concentration in the shoot dry matter. On average, genotypes with lesser deficiency symptoms contained about 42% more Zn per shoot than genotypes with severe deficiency symptoms. In contrast to shoots, the Zn content in roots did not differ between genotypes. Shoot/root ratios of total Zn content were therefore greater for genotypes with lesser deficiency symptoms than for genotypes with severe deficiency symptoms (i.e. all durum wheat genotypes).The results suggest that the enhanced capacity of genotypes for Zn uptake and translocation from roots to shoot meristems under deficient Zn supply might be the most important factor contributing to Zn efficiency in wheat genotypes. The results also demonstrate that under severe Zn deficiency, Zn concentration in the shoot dry matter is not a suitable parameter for distinguishing wheat genotypes in their sensitivity to Zn deficiency.     

‘东红’猕猴桃果园土壤养分与果实品质的多元分析

以四川蒲江32家果园的猕猴桃(Actinidia)品种‘东红’(A. chinensis var. chinensis ‘Donghong’)为材料, 对果园土壤养分含量和果实品质进行检测, 应用典型相关性分析和多元回归分析, 筛选出影响果实品质的主要土壤因子, 并找出调查果园存在的土壤问题.结果显示: ‘东红’采收干...     

Effect of water deficit on photosynthetic and other physiological responses in grapevine (Vitis vinifera L. cv. Riesling) plants

The grapevine (Vitis vinifera L. cv. Riesling) plants subjected to water deficit were studied for changes in relative water content (RWC), leaf dry mass, contents of chlorophyll (Chl), total leaf proteins, free amino acids, and proline, and activities of ribulose-1,5-bisphosphate carboxylase (RuBPC), nitrate reductase (NR), and protease. In water-stressed plants RWC, leaf dry matter, Chl content, net photosynthetic rate (P _N), and RuBPC and NR activities were significantly decreased. The total leaf protein content also declined with increase in the accumulation of free amino acids. Concurrently, the protease activity in the tissues was also increased. A significant two-fold increase in proline content was recorded.     

万寿菊属不同品种初花期抗旱特性分析

以万寿菊属(Tagetes)9个品种为试验材料,研究了自然持续干旱胁迫对它们初花期的花最大直径、叶色、旱害指数等形态指标以及叶绿素含量(Chl a+b,Ch a/b)、叶片相对含水量(RWC)、叶片保水力(WHC)、叶片和花的脯氨酸、可溶性糖和可溶性蛋白含量等生理指标的影响,以揭示其抗旱特性及其生理机制.结果显示:(1)持续6d干旱胁迫条件下,万寿菊9个品种花的最大直径显著降低,叶绿素含量和相对含水量均呈明显下降趋势.(2)万寿菊叶片的脯氨酸、可溶性蛋白和可溶性糖含量均呈上升趋势;而花的脯氨酸含量持续上升,可溶性蛋白含量呈下降趋势,但可溶性糖含量变化趋势复杂.(3)万寿菊旱害指数与其叶片相对含水量、叶绿素总含量、叶片和花的脯氨酸含量、叶片可溶性蛋白含量呈极显著相关.研究表明,抗旱性强的品种可以通过调节自身的渗透调节物质含量减轻干旱伤害;9个品种初花期抗旱性强弱依次为:珍妮>金门>鸿运>拳王>巨人>发现>小英雄>大英雄>迪阿哥.     

土壤水分胁迫对红砂幼苗叶绿素荧光和抗氧化酶活性的影响

以红砂(Reaumuria soongorica)2年生幼苗为材料,研究不同土壤水分处理下其叶绿素荧光参数、叶绿素含量和抗氧化酶活性等光合生理指标的变化特征。取得如下结果。(1)与对照组(CK)相比,中度胁迫(MS)和重度胁迫(SS)处理下红砂叶绿素含量分别降低了15.3%和25.7%,叶绿素(a/b)含量分别增加了7.4%和36.9%。表明胁迫处理导致色素含量和捕光色素复合体II含量下降,减少了其对光能的捕获,降低了光合机构遭受破坏的风险。(2)随着胁迫的加剧,初始荧光(Fo)呈升高趋势,而最大荧光(Fm)、PSII潜在光化学效率(Fv/Fo)和PSII最大光化学效率(Fv/Fm)呈明显降低趋势。说明胁迫使PSII结构与功能受到一定程度的损伤和破坏。(3)在胁迫处理下,抗氧化酶活性和丙二醛含量也发生了一定程度的变化,反映出红砂对胁迫环境有较强的耐受性。     

Zinc ion-DNA polymer interactions

The adjacent GN7-M-GN7 cross-linking and adjacent G-M-G sandwich-complex models for DNA metal ion binding were evaluated both with native DNAs differing in GC content as well as with the synthetic polymers poly [(dGdC)]2, poly[(dAdT)]2, and poly[(dAdC)(dGdT)]. The effect of Zn2+ was studied in depth, and limited studies were also performed with Co2+ and Mg2+. The results were compared to the extensive information available on Cu2+ binding to native DNAs and poly[(dAdT)]2. At high ratios of metal/base (R), Zn2+ caused all native DNAs to denature with the same melting temperature Tm, approximately 61 degrees C. A similar pattern was reported previously for Cu2+, but the typical Tm was approximately 35 degrees C. The extent of renaturation on cooling DNAs denatured in the presence of Zn2+ increased with GC content, as reported previously for Cu2+. These results, together with previously reported similarities, strongly indicate that the DNA binding characteristics of the two cations are similar. By comparison of the Tm values and hyperchromicity changes monitored at 260 and 282 nm, it is clear that, during thermal denaturation in the presence of Zn2+, both AT and GC regions were denatured, even at high R. The Tm vs R profile for the native DNAs was typical. The rise at low R and subsequent decrease at high R were inversely and directly related, respectively, to GC content. Except for poly[(dAdT)]2, where Tm increased with R, the other synthetic polymers exhibited the increase/decrease pattern. Poly[(dAdC)(dGdT)] gave a Tm value at high R of 54 degrees C. In the absence of Zn2+, this polymer exhibited little hypochromicity on cooling of denatured polymer. However, in the presence of Zn2+, nearly complete hypochromicity was observed, although the midpoint of the cooling curve was lower than the Tm value by approximately 15 degrees C at R = 10. These characteristics were similar to those with native DNAs, although viscosity and CD studies suggested that the "renatured" polymer was not identical to the unheated polymer. Furthermore, addition of Zn2+ after denaturation nearly completely reversed the absorption increase. This finding contrasts with those for native DNAs, where the Zn2+ must be present during denaturation in order to reverse the absorption increase nearly completely on cooling. With some caveats, poly[(dAdC)(dGdT)] appears to be a good model for native DNAs since its properties, including CD and uv changes on addition of Zn2+ to premelted and melted polymer, parallel those of the native polymers.(ABSTRACT TRUNCATED AT 400 WORDS)