Recent studies on chilling tolerance mechanisms in revealed a significant positive correlation between genotypic chilling tolerance and chilling-induced accumulation of the stress hormone () under controlled chamber conditions. Based on this and other results, the hypothesis was developed that chilling tolerance in is related to the ability to accumulate large amounts of rapidly, as a protection against chilling injury. The objective of the present study was to test this hypothesis under field conditions during natural cold weather periods in spring, which often cause severe chilling injury in fields. In two experiments at two locations in Europe with contrasting climates, eight genotypes with different genotypic chilling tolerance were cultivated in spring in the field according to agronomic practice for . Before and at the end of cold weather periods, levels and contents were determined in the third leaves. It was found that chilling-tolerant genotypes accumulated higher amounts of during the chilling period than chilling-sensitive genotypes. A significant positive correlation between chilling tolerance and the levels of in the leaves was found. These results support the above-mentioned hypothesis. In contrast to earlier studies performed under chamber conditions, the content in chilled leaves was mostly higher than in non-chilled leaves. The increase in is therefore not attributable to chilling-induced deficit, but probably to the low temperature itself.

AbstractCold is a typical environmental stress factor that limits the geographical distribution and growth of various plants. It affects crop quality and productivity. In the contemporary years, with the plant cold-resistant genetic engineering development, great progress was obtained in this field. This paper gave a general statement about the development of plant cold resistantance on the level of unsaturated fatty acids, protective enzymes, functional genes and regulation genes, aiming to provide some useful information and ideas to researchers who work on plant cold breeding and the mechanism of cold resistance. As research continues, we could develop further multiple resistant plant species.

Unfavourable environmental conditions such as cold induce the transcription of a range of genes in plants in order to acclimate to these growth conditions. To better understand the cold acclimation of maize ( Zea mays L.) it is important to identify components of the cold stress response. For this purpose, cold-induced genes were analysed using the PCR-select cDNA subtraction method. We identified several novel genes isolated from maize seedling exposed for 48 h to 6 C. Of 18 Zea mays cold-induced genes ( ZmCOI genes) characterized, the majority share similarities with proteins with known function in signal transduction and photosynthesis regulation. RT CR was conducted for a selected group of genes, namely ZmCOI6.1, ZmACA1, ZmDREB2A and ZmERF3, confirming the induction by low temperature. In addition, it was found that their expression was strongly induced by other abiotic stresses such as drought and high salt concentration, by stress signalling molecules such as jasmonic acid, salicylic acid and abscisic acid, and by membrane rigidification. These results suggest that this group of genes is involved in a general response to abiotic stresses.

ABSTRACT Introduction. Maize is a crop of great economical importance. Despite its tropical origin and its high sensitivity to low temperatures, maize is now cultivated in a wide range of latitudes. To maintain competitive yields, many genetic and agricultural adaptations have been implemented. Literature. Plant responses to environmental stresses such as drought or cold have been extensively studied. This article reviews the progress and current knowledge regarding the effects of non-freezing cold temperatures on maize plants, from germination to floral transition. During the early stages of development, cold alters plant phenology and productivity, mainly because of its negative impact on photosynthesis. Plant growth is affected and secondary osmotic and oxidative stresses induce cell damage. Conclusions. A better understanding of the effects of cold will allow the development of new strategies for improving plant tolerance through the use of various physiological, genetic and molecular approaches. 2015, FAC UNIV SCIENCES AGRONOMIQUES GEMBLOUX. All rights reserved.

The objective of the present paper was to study the relationship between chilling tolerance and chilling-induced abscisic acid (ABA) accumulation in maize. Ten maize genotypes, five classified as chilling tolerant and five as chilling sensitive, were used. Two of them, Co 125 and F 7, with significant differences in chilling tolerance, were studied in detail. Seedlings at the third leaf stage, without and with previous acclimation, were chilled at 5 C and at relative humidities (RH) of 65 and 100%. Immediately before and during chilling the ABA content in the third leaf was measured by RIA. Water content, osmotic potential, and - after recovery - the degree of necrotic injuries were also determined. Chilling of non-acclimated seedlings at 65 % RH caused accumulation of ABA in all ten genotypes. The ABA accumulation was significantly higher in the chilling tolerant genotypes than in the chilling sensitive ones. Chilling of non-acclimated seedlings at 100 % RH, studied in the two inbreds, caused ABA accumulation only in the chilling tolerant inbred F 7, although there were no significant changes in the water relations. Acclimation (4 days at 14/12 C, 70 % RH) had only marginal influence on the ABA content but increased the chilling tolerance markedly. The higher chilling tolerance of acclimated seedlings was accompanied by the ability for greater ABA accumulation during chilling, especially in the chilling tolerant inbred F 7. Thresholds of water content and osmotic potential for the rise of ABA were higher in tolerant than in sensitive genotypes. It is suggested that higher chilling tolerance is related to the ability for greater and faster ABA accumulation and better stabilization of water status in response to chilling. Evidence is presented that the rise in ABA is induced indirectly by chilling-induced water deficit as well as directly by the chilling temperature.

The role of ABA in freezing resistance in nonacclimated and cold‐acclimated barley ( Hordeum vulgare L.) was studied. Eleven nonacclimated cultivars differed in their LT 50 , ranging from 6110.8 to 614.8°C. Sugars, free proline, soluble proteins and ABA were analyzed in nonacclimated cultivars and during cold acclimation of one cultivar. There was an inverse correlation between LT 50 and both ABA and sucrose contents. Exogenous ABA caused a decrease in the freezing point of leaf tissue in the cultivar with the lowest level of endogenous ABA, but not in the cultivar with the highest level, suggesting that ABA in the latter may be near the optimum endogenous level to induce freezing tolerance. Plants of cv. Aramir treated with ABA or allowed to acclimate to cold temperature increased their soluble sugar content to a similar level. The LT 50 of leaves of cold‐acclimated cv. Aramir decreased from 615.8 to 6111.4°C, with biphasic kinetics, accumulating proline and soluble sugars with similar kinetics. The biphasic profile observed during cold acclimation could be a direct consequence of cryoprotectant accumulation kinetics. ABA and soluble protein accumulation showed a single step profile, associated mainly with the second phase of the LT 50 decrease. Thus, a significant increase in endogenous ABA is part of the response of barley to low temperature and may be required as a signal for the second phase of cold acclimation. Endogenous ABA contents in the nonacclimated state may determine constitutive freezing tolerance.

Abstract To elucidate how physiological and biochemical mechanisms of chilling stress are regulated by abscisic acid (ABA) pretreatment, pepper variety (cv. 'P70') seedlings were pretreated with 0.57 mM ABA for 72 h and then subjected to chilling stress at 10 /6 C (day/night). Chilling stress caused severe necrotic lesions on the leaves and increased malondialdehyde and H(2)O(2) levels. Activities of monodehydroascorbate reductase (DHAR), dehydroascorbate reductase, glutathione reductase, guaiacol peroxidase, ascorbate peroxidase, ascorbate, and glutathione increased due to chilling stress during the 72 h, while superoxide dismutase and catalase activities decreased during 24 h, suggesting that chilling stress activates the AsA-GSH cycle under catalase deactivation in pepper leaves. ABA pretreatment induced significant increases in the above-mentioned enzyme activities and progressive decreases in ascorbate and glutathione levels. On the other hand, ABA-pretreated seedlings under chilling stress increased superoxide dismutase and guaiacol peroxidase activities and lowered concentrations of other antioxidants compared with untreated chilling-stressed plants. These seedlings showed concomitant decreases in foliage damage symptoms, and levels of malondialdehyde and H(2)O(2). Induction of Mn-SOD and POD was observed in chilling-stressed plants treated with ABA. The expression of DHAR1 and DHAR2 was altered by chilling stress, but it was higher in the presence than in the absence of ABA at 24 h. Overall, the results indicate that exogenous application of ABA increases tolerance of plants to chilling-induced oxidative damage, mainly by enhancing superoxide dismutase and guaiacol peroxidase activities and related gene expression.

Two chilling-tolerant genotypes, that is, weedy rice WR03-45 and cultivated rice Lijiangxintuanheigu and two chilling-sensitive genotypes, that is, weedy rice WR03-26 and cultivated rice Xiuzinuo were used in this study to investigate the effects of exogenous abscisic acid (ABA) on protection against chilling damage as well as on changes in physiological features. The results showed that under chilling stress the increased levels of superoxide radical (), hydrogen peroxide (H2O2) and malondialdehyde (MDA) in WR03-45 and Lijiangxintuanheigu were lower than those in WR03-26 and Xiuzinuo. Activities of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR)) and non-enzymatic antioxidants (ascorbate acid (AsA) and reduced glutathione (GSH)) were enhanced in WR03-45 and Lijiangxintuanheigu, whereas they were decreased significantly in WR03-26 and Xiuzinuo. Application of exogenous ABA reduced the chilling damage in the four genotypes. The pre-treatment with ABA decreased the levels of , H2O2 and MDA caused by chilling stress in the four genotypes through increasing the activities of SOD, CAT, APX, GR and the contents of AsA and GSH in the four genotypes under chilling stress. Moreover, pre-treatment with Fluridone, the ABA biosynthesis inhibitor, prohibited the effects of ABA through enhancing the oxidative damages and suppressing the antioxidant defence systems under chilling stress. The results indicate the mechanism for rice with chilling tolerance is to enhance the capacity of antioxidant defence systems under chilling stress. Furthermore, ABA plays important roles in the tolerance of rice against chilling stress for it could induce the capacity of whole antioxidant defence systems including enzymatic and non-enzymatic constitutions under chilling stress.

【目的】探讨花后高温和外源脱落酸（ABA）对不同持绿型小麦籽粒胚乳细胞增殖、籽粒灌浆和内源激素的影响，为高温逆境下采用激素调控措施提高粒重提供理论依据。【方法】选用持绿型汶农6号和非持绿型济麦20，花后1—5 d，用透明聚乙烯塑料膜搭设增温棚进行高温处理，同时花后1—3 d喷施10 mg?L-1的ABA于穗部，用量100 mL?m-2，3次重复。定期取籽粒样，用高效液相色谱法测定4种内源激素，用简易胚乳细胞计数法测定胚乳细胞数目，Richard方程对籽粒增重及胚乳细胞增殖动态模拟并计算相关参数。【结果】高温处理显著降低了两品种强弱势籽粒的胚乳细胞数目，降低胚乳细胞增殖速率，但延长了籽粒胚乳细胞活跃分裂期和实际分裂终期；显著降低两品种弱势籽粒的灌浆速率，缩短了两品种弱势粒的生长活跃期及实际灌浆终期。高温处理显著降低两品种千粒重和穗粒数，其中汶农6号强、弱势粒分别减少3.7和8.2 粒/穗，济麦20强、弱势粒分别减少1.3和4.3 粒/穗；显著降低两品种产量，汶农6号和济麦20产量分别降低19.65%和26.22%。常温及高温下喷施ABA均显著提高了两品种灌浆速率，提高了籽粒胚乳细胞增殖速率，扩大胚乳细胞数目。高温处理降低了强弱势籽粒ZR含量，显著提高了济麦20强、弱势粒花后3—27 d的GA3含量，显著提高汶农6号花后12—27 d的GA3含量；但降低了弱势粒花后15—27 d的IAA含量。高温处理下喷施ABA，降低了济麦20强势粒花后3—9 d ZR含量，但显著提高济麦20强势粒花后3—28 d内源ABA含量，显著提高汶农6号强势粒花后3—18 d ABA含量。常温下喷施ABA显著降低了济麦20和汶农6号强、弱势粒的GA3含量；高温下喷施ABA，显著降低了汶农6号强弱势粒的GA3含量，降低济麦20强势粒花后3—12 d的GA3含量，显著降低弱势粒花后6—15 d的GA3含量。常温下喷施ABA显著提高济麦20强势粒花后12—18 d的IAA含量；提高了汶农6号强势粒花后6—18 d IAA含量，显著提高两品种弱势粒花后6—27 d IAA含量。持绿型汶农6号的千粒重和产量均显著大于非持绿型济麦20。【结论】高温胁迫对非持绿型品种的产量和两品种弱势粒粒数影响较大，高温降低了两品种籽粒胚乳细胞数目，降低籽粒灌浆速率，最终导致粒重及产量降低。喷施外源ABA通过调节内源激素水平，促进胚乳细胞分裂，扩大了常温及高温下籽粒库容量，提高了籽粒灌浆速率，从而提高了籽粒产量。

The effects of exogenous application of abscisic acid (ABA) on anti-oxidant enzyme activities and photosynthetic capacity in 090004Sultana090005 grapevine (Vitis vinifera L.) were investigated under cold stress. When vines had an average of 15 leaves, 0 (control), 50, 100, or 200 0008M ABA was sprayed to run-off on all leaves of each plant. Twenty-four hours after foliar spraying with ABA, half (n = 5) of the water-only control vines and half (n = 5) of each group of ABA-treated plants were subjected to 400°C for 12 h, followed by a recovery period of 3 d under greenhouse conditions (2500°/1800°C day/night). The remaining plants in each treatment group were kept at 2400°C. Cold stress increased H2O2 and malondialdehyde (MDA) concentrations in vine leaves, whereas all foliar ABA treatments significantly reduced their levels. Chilled plants showed marked increases in their total soluble protein contents in response to each ABA treatment. ABA significantly increased the activities of superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase in cold-stressed grapevine leaves. In contrast, cold stress markedly decreased the rates of leaf photosynthesis (A) and evaporation (E), stomatal conductance (gs), and chlorophyll concentrations in leaves, but increased intercellular CO2 concentrations (Ci) in leaves. Treatment with all concentrations of ABA resulted in lower leaf A, E, and gs values, but higher Ci values at 2400°C. However, following cold stress, ABA-treated vines showed higher leaf A, E, and gs values, but lower Ci values compared to control vines without ABA treatment. The application of 50090009200 0008M ABA allowed chilled vines to recover more quickly when re-exposed to normal temperatures, enabling the vines to resume their photosynthetic capacity more efficiently following cold stress. These results showed that, by stimulating anti-oxidant enzyme systems and alleviating cold-induced stomatal limitations, ABA reduced the inhibitory effect of cold stress on the rate of CO2 fixation in 090004Sultana090005 grapevine plants.

以1年生雷公藤扦插苗为试材,研究低温胁迫下不同浓度外源脱落酸（ABA，0、5、10、15、20、25 mg&middot;L^-1)叶面喷施处理对雷公藤叶片光合作用及叶绿素荧光参数的影响.结果表明：喷施20 mg&middot;L^-1的ABA能显著提高雷公藤幼苗的抗冷性,减缓低温下雷公藤叶片净光合速率(<em>P</em>_n)、蒸腾速率(<em>T</em>_r)、气孔导度(<em>g</em>_s)、胞间CO₂浓度(<em>C</em>_i)的下降幅度,提高幼苗叶片的光合能力.低温处理6 d后,随着ABA浓度上升,雷公藤叶片的初始荧光(<em>F</em>_o)下降,最大荧光(<em>F</em>_m)和PSII最大光化学效率(<em>F</em>_v/<em>F</em>_m)上升,PSII实际光化学量子产量(<em>&Phi;</em>_PS_Ⅱ)、光化学猝灭系数(<em>q</em>_P)先下降后上升,而非光化学猝灭系数(<em>q</em>_N)呈下降－上升－下降趋势.<em>P</em>_n、<em>g</em>_s、<em>q</em>_P、<em>F</em>_m和<em>F</em>_v/<em>F</em>_m均在20 mg&middot;L^-1ABA处理时达到峰值.不同浓度ABA的相对电子传递速率(rETR)随着光化光强度增加呈先上升后下降的趋势,当光化光强度(PAR)达到395 &mu;mol&middot;m^-2s^-1时,各处理的rETR达到最高值,其中25 mg&middot;L^-1和20 mg&middot;L^-1ABA处理分别比对照高17.1%和5.2%.雷公藤叶片<em>&Phi;</em>_PSⅡ的光响应曲线均随光化光强度升高而下降,<em>q</em>_N的光响应曲线则呈相反趋势.

脱落酸(ABA)是低温逆境下的重要信号因子,为了探讨外源 ABA 对低温胁迫下玉米幼苗的生长调节作用,以耐低温玉米品种久龙5号为试验材料,采用不同浓度(5、15、25、35 mg L–1) ABA于玉米三叶一心时喷雾于叶片,并进行低温梯次处理。分析处理后玉米叶片相对电导率、抗氧化酶活性及内源激素ABA、IAA的含量变化,并采用Real-time PCR明确Asr1基因表达水平变化。结果表明,低温胁迫下不同浓度外源ABA处理的玉米叶片相对电导率整体呈上升趋势, SOD和POD活性加强,15 mg L–1和25 mg L–1ABA处理的SOD活性均显著高于未应用ABA处理,玉米內源ABA和IAA合成水平上升,应用ABA后Asr1基因相对表达水平上调,其中5、15和25 mg L–1浓度处理基因表达上调显著。相关分析表明, ABA含量与Asrl基因相对表达量、SOD活性均表现为极显著正相关,与POD活性显著正相关。说明Asr1基因表达受ABA的介导调控, Asr1基因表达量的提升,也促进了内源ABA的合成,抗氧化酶活性加强,提升了应用ABA后玉米的抗低温能力。但外源ABA的介导调控具有一定浓度效应,表现为低促高抑。

以3个玉米品种为试验材料,通过盆栽试验,研究低温胁迫下电导率和叶绿素荧光参数的变化。结果表明,3个品种的抗低温性为金玉5〉兴垦3〉吉单198,随着低温处理时间的延长,3个品种叶片电导率和初始荧光（F0）上升,Fv/Fm、Fv/F0、NPQ整体上均呈下降趋势。说明低温胁迫使叶绿素所吸收的光能被用于光合作用的部分减少,玉米叶光系统Ⅱ（PSⅡ）活性中心受损。

Non-invasive, high-throughput screening methods are valuable tools in breeding for abiotic stress tolerance in plants. Optical signals such as chlorophyll fluorescence emission can be instrumental in developing new screening techniques. In order to examine the potential of chlorophyll fluorescence to reveal plant tolerance to low temperatures, we used a collection of nine Arabidopsis thaliana accessions and compared their fluorescence features with cold tolerance quantified by the well established electrolyte leakage method on detached leaves. We found that, during progressive cooling, the minimal chlorophyll fluorescence emission rose strongly and that this rise was highly dependent on the cold tolerance of the accessions. Maximum quantum yield of PSII photochemistry and steady state fluorescence normalized to minimal fluorescence were also highly correlated to the cold tolerance measured by the electrolyte leakage method. In order to further increase the capacity of the fluorescence detection to reveal the low temperature tolerance, we applied combinatorial imaging that employs plant classification based on multiple fluorescence features. We found that this method, by including the resolving power of several fluorescence features, can be well employed to detect cold tolerance already at mild sub-zero temperatures. Therefore, there is no need to freeze the screened plants to the largely damaging temperatures of around -15 C. This, together with the method easy applicability, represents a major advantage of the fluorescence technique over the conventional electrolyte leakage method.

Cold injuries are frequently seen in Hydrangea macrophylla but not in Hydrangea paniculata. This may be ascribed to different levels of hardiness in the non-acclimated and the acclimated state, and to differences in responses to short day (SD) and low temperature (LT) and hence in the ability to cold acclimate. In this study H. macrophylla ssp. macrophylla (Thunb.) Ser. ‘Blaumeise’ and H. paniculata Sieb. ‘Kyushu’ were exposed to short photoperiod (10-h) and 4 °C in controlled conditions for 25 days, with measurements and samplings carried out at regular intervals. Chlorophyll fluorescence measurements revealed significant alterations in O–J–I–P fluorescence kinetics and decreases in the photochemical efficiency of photosystem II in stressed plants, followed by less chlorophyll contents. Perturbations of the photosynthetic apparatus were relatively greater in H. macrophylla than in H. paniculata. Likewise, induction of a transient increase in xylem sap abscisic acid concentrations ([ABA] xylem) and accumulation of soluble sugars in leaves and stems were different in the two species. Stem cold hardiness in the non-acclimated state did not differ between H. macrophylla and H. paniculata, indicating equal sensitivity to sudden temperature drops in the growing season. Despite adaptive responses induced by the treatment neither species developed increased stem cold hardiness, suggesting that cold acclimation in Hydrangea may require exposure to temperatures below ca. 4 °C.

The objective of this study was to examine several cultivars of Ocimum basilicum L. (green, red, cinnamon, lettuce leaf, lemon, and Thai basils) for photosynthetic performance, chlorophyll a fluorescence, and chlorophyll content under chilling stress conditions of 6°C in comparison to non-stressed controls (18°C). The basil plants were grown in a peat substrate for 8 weeks and then exposed to chilling for 8 or 16 days, under a 300 μmol61m -2 61s -1 photosynthetic photon flux. After chilling, significant reductions in both the transpiration ( E ) and net photosynthetic ( P N ) rates were observed in basil plants, while the intercellular CO 2 concentration ( C i ) was higher in the plants treated with 6°C in comparison to the controls. The decrease in P N and E was associated with decreased water use efficiency (WUE) and stomatal conductance ( g s ). The greatest impairment of photosynthesis for Thai basil leaves was observed after 8 days of chilling, and for green basil after the 16-day low temperature treatment. The photosystem II (PSII) activity (F v /F m ) and variable-to-initial chlorophyll fluorescence (F v /F 0 ) were decreased after chilling. PSII activity was most affected in lettuce leaf basil after 8 days, and in Thai and red basil plants after the prolonged temperature treatment. Low temperatures did not significantly alter the chlorophyll concentration but did increase the Chl a/b ratio in leaves of basil. The results indicated that the decrease in photosynthesis was not attributable mainly to damage to PSII, but rather to chilling-induced photoinhibition of PSI. The knowledge gained in this study on the genotypic variation in basil response should be helpful for future selection of plants with low chilling sensitivity.

Spermidine (Spd) is known to be involved in the regulation of plant responses to chilling stress and counteract the adverse effect of stress conditions. Antioxidant activities, endogenous hormones and ultrastructure change under chilling stress were investigated inindica-japonicahybrid rice seedlings. 12-d-old seedlings were subjected to exogenous Spd (1 mmol L 1) and then a chilling stress (6 C, 4 d) was induced, followed by a subsequent recovery (25 C, 4 d). Results showed that malondialdehyde (MDA) and proline content were enhanced significantly, whereas shoot fresh and dry weights decreased during chilling stress and after recovery; chlorophyll content of chilling-stressed seedlings increased slightly but declined after recovery; additionally, total soluble sugar, sucrose, fructose and starch contents increased significantly during chilling stress, and only soluble sugar and fructose contents were observed in increase after recovery; chilling stress-induced increases in superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities, but declined after recovery, and the level of ascorbate peroxidase was lower during chilling stress and after recovery; however, endogenous indole-3-acetic acid (IAA), zeatin riboside (ZR), gibberellic acid (GA3), and abscisic acid (ABA) levels were induced decreased compared with Spd pretreatment. The microscopic analysis revealed that chilling stress-induced destruction of the chloroplast envelope during chilling stress and increased the number of plastoglobuli along with aberrations in thylakoid membranes after recovery. In contrast, exogenous Spd protected rice seedlings from chilling-induced injuries in terms of lower malondialdehyde, proline and carbohydrates accumulation coupled with increased endogenous hormones metabolism. After recovery, Spd pretreatment chilling-exposed seedlings showed higher activities of antioxidant enzymes and normal physiological function of chloroplasts. These results suggest that Spd could promote effectively chilling tolerance which might be largely attributable to the integrity of cell structure and normal metabolism of endogenous hormones inindica-japonicahybrid rice seedlings.

Growth and photosynthesis of grapevine ( Vitis vinifera L.) planted on two sloping cool climate vineyards were measured during the early growth season. At both vineyards, a small difference in mean minimum air temperature (1–3 °C) between two microsites accumulated over time, producing differences in shoot growth rate. The growth rates of the warmer (upper) microsite were 34–63% higher than the cooler (lower) site. Photosynthesis measurements of both east and west canopy sides revealed that the difference in carbon gain between the warmer and cooler microsites was due to low temperatures restricting the photosynthetic contribution of east-facing leaves. East-facing leaves at the warmer microsite experienced less time at suboptimal temperature while being exposed to high irradiance, contributing to an average 10% greater net carbon gain compared to the east-facing leaves at the cooler microsite. This chilling-induced reduction in photosynthesis was not due to net photo-inhibition. Further analysis revealed that CO 2 - and light-saturated photosynthesis of grapevines was restricted by stomatal closure from 15 to 25 °C and by a limitation of RuBP regeneration and/or end-product limitation from 5 to 15 °C. Changes in photosynthetic carboxylation efficiency implied that Rubisco activity may also play a regulatory role at all temperatures. This restriction of total photosynthetic carbon gain is proposed to be a major contributor to the temperature dependence of growth rate at both vineyards during the early season growth period.

In our previous study, it was found that abscisic acid (ABA) improved the chilling resistance of Stylosanthes guianensis . In order to determine the effects of ABA on photosynthesis and photochemistry of S. guianensis , an experiment was conducted under controlled condition to determine the effects of exogenous ABA on stomatal conductance ( g s ), transpiration ( E ), photosynthetic rate ( A ) and chlorophyll a fluorescence of this pasture legume. The results showed that ABA treatment reduced A , g s , and E under both chilling (802°C) and control temperature (2802°C). A of the ABA treated plants returned to a high rate, while that of the water-treated plants remained low when plants were rewarmed after chilling treatment. ABA-treated plants had higher maximum photochemical efficiency ( F v / F m ), non-photochemical quenching (NPQ), quantum efficiency of PS II photochemistry (Φ ps02ii ) than water-treated ones during chilling. Although the biomass of S. guianensis was reduced by ABA under control temperature, ABA-treated plants had higher biomass than water-treated ones after 702days of recovery.

The functional activities of the photosynthetic apparatus of two grapevine genotypes ( Vitis vinifera L. cvs. Müller-Thurgau and Lagrein) were investigated after low night temperature (LNT) treatment for 7 d. LNT caused important reductions of the net photosynthetic rate (P N ) of Lagrein plants due to non-stomatal components. These non-stomatal effects were not evident in Müller-Thurgau. At LNT treatment, the contents of photosynthetic pigments decreased significantly in Lagrein, but in Müller-Thurgau the contents of chlorophyll (Chl) remained unchanged whereas the contents of carotenoids (Car) increased. An increase and decrease of Chl a/b was shown in Mü ller-Thurgau and Lagrein stressed plants, respectively. RuBPC activity and content of soluble proteins were also significantly reduced in Lagrein. Under LNT treatment, photosystem (PS) 2 was markedly more inhibited in Lagrein than in Müller-Thurgau. The decrease in PS 2 activity in Lagrein was mostly due to the marked loss of D1, 47, 43, 33, 28-25, 23 and 17 kDa proteins determined by immunological and SDS-PAGE studies.

AbstractDrought is a major limitation of maize cultivation in Brazil. Agronomic and physiological practices have been considered to overcome this stress and consequently, increase grain production. The present study investigated the role of abscisic acid (ABA) application in some physiological parameters, in two hybrids with contrasting drought resistance (DKB 390 and BRS 1030 resistant and sensitive, respectively). Contrasting resistance to drought in these genotypes was determined in previous studies. Water deficit was imposed for 10 days at flowering stage, in association with the application of 100 M abscisic acid on plant canopy. Evaluations of gas exchange, chlorophyll fluorescence, relative water content (RWC), and endogenous ABA content were performed during stress period and also at water recovery (recovery irrigation). A significant functional relationship was observed between RWC and the parameters of gas exchange and fluorescence. During water recovery, no differences were observed among the treatments. DKB 390 presented higher photosynthesis rate () and electron transport rate (ETR) under water stress, while BRS 1030 presented higher intercellular CO concentration () and lower photochemical quenching (qP), non-photochemical quenching (NPQ), and lower / ratio. DBK 390 was more responsive to ABA application than BRS 1030, presenting higher endogenous ABA content in the first day of stress. DBK 390 with ABA application reduced the effect of water stress through maintenance of water status, an increase of photosynthetic parameters, and a decrease of decline in the functions of photosystem II during stress.