梯度干旱胁迫对水稻叶片光合和水分状况的影响

采用温室营养液培养方式,通过添加0%、10%、20%、30%PEG6000模拟干旱胁迫,对水稻幼苗叶片的光合作用和水分状况进行比较分析。结果表明:1)在干旱胁迫下,水稻叶片的光合速率、气孔导度、叶肉导度、总导度和叶绿体内CO2浓度等都显著降低;2)在干旱胁迫条件下,限制光合作用的非气孔限制值并没有显著提高,而气孔限制值则大幅提高;与正常水分条件相比,扬稻6号和汕优63在30%PEG干旱胁迫下气孔限制值分别提高了42%和81%;3)光合速率与气孔导度、叶肉导度、总导度及叶绿体内CO2浓度呈正相关;4)在重度干旱胁迫下(20%和30%),叶片水势和含水量都显著下降,并且叶片水势与气孔导度、叶肉导度和总导度呈正相关。因此,气孔关闭导致的叶绿体内CO2浓度降低是限制光合作用的最主要因素,同时叶片水势的降低增加了叶片内CO2传输的阻力。     

Studies on Mechanisms of Dehydration Postponement in Cassava Leaves under Short-term Soil Water Deficits

Abstract

Cassava (Manihot esculenta Crantz) can produce a high crop yield even in an environment with irregular rains. This is mainly attributed to its abilities to maintain leaf area under drought conditions and rapidly regrow after rain. In this study, we investigated the mechanism of leaf maintenance under water deficits through measurement of photosynthetic rate and water potential changes in leaves. The cassava plants were grown in pots and exposed to water deficits, and the diurnal changes in water potentials, rates of photosynthesis and transpiration and stomatal conductance were measured. The relationship between leaf water potential (ψW) and photosynthetic rate with decreasing soil water, and osmotic adjustment were also investigated. With respect to water supply in leaves, the movement of water in plants was measured using stem heat balance. Under water deficits, photosynthesis occurred only in the early morning. The water loss was reduced by stomatal closure in the mid-day. This was attributed to the complete closure of the stornata during the decrease in ψW to a range between –1.0 and –1.4 MPa. Furthermore, the firm stomatal closure is caused by the consistency of osmotic potential under decreases in soil water, i.e., to a lack of osmotic adjustment. Water stored in the pith parenchyma of stem flowed into leaves in the morning. From these results, we conclude that cassava can consistently maintain an adequate water level in leaves via water storage and the sensitivity of stornata to water deficits, thereby avoiding leaf dehydration.     

Wx基因对灌浆期小麦不同叶位叶片光合特性的影响

为了解Wx基因对小麦光合作用的影响,对8个小麦Wx近等基因系的不同叶位叶片光合参数进行了测定和分析。结果表明,小麦叶片净光合速率、气孔导度、胞间CO2浓度和蒸腾速率在叶位和基因型间均有极显著差异,缺失单个Wx基因使叶片光合参数下降,且降幅表现为Wx-D1Wx-A1Wx-B1;胞间CO2浓度不影响光合作用,不同叶位叶片光合参数明显呈旗叶倒二叶倒三叶,但WxABD(糯小麦)光合参数在叶位间没有显著差异;Wild type和WxABD总体光合能力和产量相对较高。以上结果说明,Wx基因的缺失会引起叶片光合能力下降,不利于小麦产量形成。     

氮肥水平对限制灌溉下冬小麦旗叶光合性能及产量的影响

为了解氮素营养供应与小麦节水效果的关系,以周麦22为材料,采取大田试验研究了不同氮肥水平对限制灌条件下冬小麦旗叶光合性能及产量的影响。结果发现,与正常灌水相比,限制灌溉降低了小麦旗叶叶绿素含量、净光合速率、气孔导度和蒸腾速率,提高了小麦旗叶胞间CO2浓度;限制灌溉条件下,与不施氮肥相比,增施氮肥能明显改善小麦旗叶光合性能。从产量来看,充分灌水有利于小麦产量提高,而限制灌溉条件下,灌水时期提前或增施氮肥能不同程度提高小麦产量。以上结果说明,增施一定量的氮肥能明显改善限制灌溉条件下冬小麦花后旗叶光合性能,提高小麦产量和水分利用效率。     

Identification of Chromosomal Regions Controlling the Leaf Photosynthetic Rate in Rice by Using a Progeny from Japonica and High-yielding Indica Varieties

Abstract

The whole-leaf photosynthetic rate in rice plants is controlled by various physiological processes. In a high-yielding indica rice variety, Habataki, the leaf photosynthetic rate (LPR) of the uppermost fully expanded leaves was approximately 130 to 140% of that in a japonica variety, Sasanishiki, from booting to the early ripening stage. We characterized the difference in the LPR between Habataki and Sasanishiki. Leaves of Habataki contained higher levels of nitrogen and, as a consequence, of Rubisco, and had higher stomatal conductance that was associated with higher hydraulic conductance from roots to leaves than those of Sasanishiki. These features were responsible for the higher LPR of Habataki. An analysis of chromosome segment substitution lines (CSSLs) in which chromosome segments from Habataki were substituted into the genetic background of Sasanishiki showed that three genetic regions on chromosomes 4, 5 and 11 were responsible for the increase in the LPR. Each of these regions was estimated to increase the LPR by 15 to 30%, and we showed that they were associated with higher activity of mesophyll photosynthesis due to higher leaf nitrogen content and greater stomatal conductance. Leaf nitrogen content and stomatal conductance may be useful parameters for further quantitative trait locus analysis of efficient photosynthesis in leaves.     

PEG模拟干旱胁迫对五唇兰光合系统的影响

以3年生红背型五唇兰组培苗为试验材料,分别用5%、10%、20%的PEG 6000溶液处理模拟干旱胁迫,研究不同程度的干旱对五唇兰光合系统的影响,结果表明：（1）干旱导致叶片的气孔密度、开度、长度逐渐降低,且随PEG胁迫时间的延长下降趋势越明显,处理15 d后PEG 10%以上处理与CK差异达显著水平。（2）干旱导致叶片中苹果酸含量逐渐降低,随着PEG处理时间的延长,五唇兰叶片的苹果酸含量下降趋势减缓,凌晨叶片的苹果酸含量显著高于傍晚,处理15 d后PEG 20%处理下傍晚的苹果酸含量差异达显著水平,与CK相比降低了27.16%。（3）干旱导致叶片的净光合速率、蒸腾速率、气孔导度逐渐降低,随PEG胁迫时间的延长下降越显著,胞间CO₂浓度的变化趋势则相反,水分利用效率呈先升高后降低的趋势,处理后第15天PEG 5%以上处理与CK差异均达显著水平。（4）干旱导致五唇兰叶片叶绿素的初始荧光值（F_o）逐渐升高,可变荧光值（F_v）、最大荧光值（F_m）、PSⅡ实际光化学效率（F_v/F_m）、PS Ⅱ潜在光化学效率（F_v/F_o）则逐渐降低,表观电子传递速率（ETR）、光化学淬灭系数（qP）、PSⅡ实际光量子效率（Yield）随着PEG胁迫程度的增加而逐渐降低。非光化学淬灭系数（NPQ）随PEG胁迫浓度的增加显著提高,处理15 d后PEG 5%以上处理与CK差异达显著水平。结果表明,10%、20% PEG处理能够在较短时间内通过影响叶片的气孔关闭、降低气孔密度进而降低光合作用和阻碍光合代谢产物苹果酸的合成,同时影响五唇兰叶片对光能的吸收传递以及光化学转换,5% PEG处理在处理10 d后才表现出光合生理受到抑制的现象,说明中度、重度干旱能够在较短时间内影响五唇兰叶片的气孔性状,进而降低叶片的光合能力,导致光合产物的合成受阻,最终导致光合系统受到抑制。     

Varietal Differences in Photosynthetic Rates in Rice Plants,with Special Reference to the Nitrogen Content of Leaves

Abstract

The photosynthetic rate in the fl ag leaf of rice at the full heading stage was examined in three japonica varieties, Koshihikari, Aikoku and Asanohikari, and the indica high-yielding variety Takanari at the same level of leaf nitrogen. At an ambient CO₂ concentration of 350 µL L-₁, Takanari had a higher photosynthetic rate and stomatal conductance than the japonica varieties when plants were compared at a leaf nitrogen content of approximately 1.5 g m-₂. Stomatal conductance increased considerably with increases in leaf nitrogen content in the japonica varieties. As a result, at a leaf nitrogen content of approximately 2.0 g m-₂, differences in terms of the photosynthetic rate among varieties were small. By contrast, there were no clear varietal differences in Rubisco content at any identical nitrogen content of leaves. We conclude that stomatal conductance is responsible for the varietal differences in photosynthetic rate examined at the same leaf nitrogen content.     

Some characteristics of reduced leaf photosynthesis at midday in maize growing in the field

Maize was grown in the high-radiation arid summer environment of Davis, California, and its leaf photosynthetic rate was measured over diurnal courses on cloudless days with the leaf held perpendicular to the sunlight. On days of high atmospheric vapor pressure deficit (VPD), leaf photosynthesis reached a maximum in the late morning and then decreased gradually as the day progressed, though the soil was well irrigated. When CO₂ concentration in the measurement chamber was raised to about 1000 μmol mol⁻¹, photosynthesis was enhanced, but more in the afternoon than in the morning. As a result, rates measured at high CO₂ in the morning and afternoon were essentially the same. There was also no difference in the curves of photosynthetic rate (A) versus intercellular CO₂ concentration (C_i) for the morning and afternoon. Hence, photosynthetic capacity was similar for the two periods and there was no evidence of photoinhibition by the high photosynthetic photon flux density at noon. Further, C_i and photosynthetic rates A measured over a range of photon flux density were lower in the afternoon than in the morning. These results indicate that A at noon and early afternoon was more limited than in the morning by epidermal conductance (mostly stomatal). On a day of low VPD, however, midday depression in A and epidermal conductance were not evident for the well-irrigated plants. Without irrigation and with leaves at a lower midday water potential, midday reduction in conductance and A was much more marked, beginning late in the morning. Epidermal conductance of maize grown in the field in Davis is are not sensitive to VPD. Therefore, the midday reduction in conductance and A was more likely the result of low leaf water potential caused by high transpiration rates.     

Regulation of root-to-leaf Na and Cl transport and its association with photosynthetic activity in salt-tolerant soybean genotypes

ABSTRACT

Soil salinity is a major constraint to sustainable crop production. Genetic improvements are needed for growing soybean in salinity-prone environments. Salt-tolerant soybean genotypes alleviate a reduction in photosynthesis and growth under saline conditions; however, the detailed mechanisms involved remain unclear. Here, we aimed to clarify how Na and Cl root-to-leaf transport is quantitatively regulated, and to identify whether photosynthetic tolerance depends on traits associated with either stomata or with mesophyll tissues. Two pairs of pot-grown soybean near-isogenic lines (NILs) consisting of tolerant and susceptible counterparts, derived from a cross between salt-tolerant FT-Abyara and salt-sensitive C01, were subjected to salinity treatment in a rainout greenhouse. Comparison of photosynthetic responses between genotypes indicated that genotypic differences in salinity tolerance depended on the ability for sustained CO₂ assimilation in mesophyll tissues, rather than stomatal conductance. The ratio of photosynthetic rate to intercellular CO₂ concentration (A/Ci) declined exponentially with increasing Na and Cl concentration regardless of genotype, but tolerant genotypes effectively kept both elements at significantly low levels. Under saline conditions, tolerant genotypes reduced Na and Cl content at the two transport pathways: from root to stem, and from stem to leaf, but the reduction of Cl at each pathway was only minor. These results suggest that integrating genetic capacity for Cl transport regulation and osmotic adjustment should be an important target in salinity-tolerance soybean breeding.     

Structural and physiological responses of the C4 grass Sorghum bicolor to nitrogen limitation

Nitrogen (N) is one of the major nutrients influencing photosynthesis and productivity of C₄ plants as well as C₃ plants. C₄ photosynthesis operates through close coordination between mesophyll (M) and bundle sheath (BS) cells. However, how the development of structural and physiological traits in leaves of C₄ plants is regulated under N limitation remains uncertain. We investigated structural and physiological responses of leaves of the NADP-ME-type C₄ grass Sorghum bicolor to N limitation. Plants were grown under four levels of N supply (.05 to .6 g N per 5-L pot). Decreasing N supply resulted in decreases in net photosynthetic rate, stomatal conductance, leaf N and chlorophyll contents, and the activity ratio of phosphoenolpyruvate carboxylase to ribulose 1,5-bisphosphate carboxylase/oxygenase and increases in δ¹³C values and photosynthetic N use efficiency. Low-N leaves were thinner and had smaller photosynthetic cells, especially in M, resulting in lower M/BS tissue area ratio, and contained smaller and fewer chloroplasts. The BS chloroplasts in the low-N leaves accumulated abundant starch grains. The number of thylakoids per granal stack was reduced in M chloroplasts but not in BS chloroplasts. The low-N leaves had thicker cell walls, especially in the BS cells, which might be associated with less negative δ¹³C values, and fewer plasmodesmata in the BS cells. These data reveal structural and physiological responses of C₄ plants to N limitation, most of which would be related to cellular N allocation, light use, CO₂ diffusion and leakiness, and metabolite transport under N limitation.     

迟播对冬小麦灌浆后期高温胁迫下旗叶光合能力和产量的影响

为了解迟播对冬小麦灌浆后期高温胁迫下旗叶光合的调控效应,在大田条件下设置2个播期(常规播期10月8日、推迟播期10月22日)和2种灌浆期温度(开放式增温、自然温度),分析了迟播小麦旗叶光合能力的变化及其对灌浆后期高温胁迫的响应。结果表明,灌浆期高温降低了小麦旗叶光合速率、花后干物质生产量、粒重和产量。与常规播期相比,迟播提高了高温胁迫下小麦旗叶叶绿体类囊体膜不饱和脂肪酸指数,保持类囊体膜相对稳定,减轻高温对旗叶光合机构的损伤;增强了旗叶活性氧清除能力,保障能量传输,减少热耗散,提高光化学反应中可利用能量的分配比例,保持较高的光合系统同化力;提高了气孔导度和胞间CO_2浓度,增加光合作用底物供应。总之,迟播小麦的旗叶可在灌浆期高温胁迫下保持较高的光合能力,有利于提高粒重和产量。     

干旱胁迫对不同肥水类型小麦旗叶光合特性及产量的影响

为给小麦抗旱育种和节水高产栽培提供理论和技术支持,在防雨旱棚池栽条件下研究了干旱胁迫对6个不同肥水类型小麦品种旗叶光合特性和产量的影响。结果表明,干旱胁迫条件下,小麦开花后旗叶的净光合速率、气孔导度、蒸腾速率、气孔限制值和单叶水分利用效率均呈下降趋势,而胞间CO₂浓度有所升高。其中,水浇地品种烟农21、烟农24和济麦22净光合速率、气孔导度、蒸腾速率、气孔限制值和单叶水分利用效率较低且下降幅度大,而旱地品种青麦6号、济旱5034和鲁麦21的净光合速率、气孔导度、蒸腾速率、气孔限制值和单叶水分利用效率较高且下降较为缓慢,而胞间CO₂浓度较低。青麦6号具有较高的抗旱指数,在干旱胁迫条件下能够保持较好的叶片结构和功能状况,是其获得高产的重要原因。     

酸性黄棕壤中钼磷配施对甘蓝型油菜苗期碳氮代谢的影响

利用酸性黄棕壤进行盆栽试验,研究了钼磷配施对甘蓝型油菜苗期碳氮代谢的影响。结果表明,施钼和施磷均显著增加叶片叶绿素含量、光合速率、可溶性总糖含量以及地上部干物质重和可溶性蛋白质含量,显著降低油菜苗期叶片硝态氮含量;且钼肥和磷肥配施对促进油菜苗期碳氮代谢存在协同效应。钼肥和磷肥提高油菜光合速率的机制有所不同,钼肥主要提高叶肉细胞光合活性,而磷肥则增加气孔导度。     

Variations in structural,biochemical, and physiological traits of photosynthesis and resource use efficiency in Amaranthus species (NAD-ME-type C4)

C₄ plants show higher photosynthetic capacity and productivity than C₃ plants owing to a CO₂-concentrating mechanism in leaves, which reduces photorespiration. However, which traits regulate the photosynthetic capacity of C₄ plants remains unclear. We investigated structural, biochemical, and physiological traits associated with photosynthesis and resource use efficiency in 20 accessions of 12 species of Amaranthus, NAD-malic enzyme-type C₄ dicots. Net photosynthetic rate (P_N) ranged from 19.7 to 40.5 μmol m^?2 s^?1. P_N was positively correlated with stomatal conductance and nitrogen and chlorophyll contents of leaves and was weakly positively correlated with specific leaf weight. P_N was also positively correlated with the activity of the C₃ enzyme ribulose-1,5-bisphoshate carboxylase/oxygenase, but not with the activities of the C₄ enzymes phosphoenolpyruvate carboxylase and NAD-malic enzyme. Structural traits of leaves (stomatal density, guard cell length, leaf thickness, interveinal distance, sizes of mesophyll and bundle sheath cells and the area ratio between these cells) were not significantly correlated with P_N. These data suggest that some of the biochemical and physiological traits are involved in interspecific P_N variation, whereas structural traits are not directly involved. Photosynthetic nitrogen use efficiency ranged between 260 and 458 μmol mol^?1 N s^?1. Photosynthetic water use efficiency ranged between 5.6 and 10.4 mmol mol^?1. When these data were compared with previously published data of C₄ grasses, it is suggested that common mechanisms may determine the variations in resource use efficiency in grasses and this dicot group.     

Photosynthetic components associated with differential senescence of maize hybrids following ear removal

The effect of ear removal on carbon exchange rate (CER), leaf resistance, transpiration and internal CO₂ concentration of leaves for two field-grown maize (Zea mays L.) hybrids was determined using a portable photosynthesis system. Ears were removed 15 days after anthesis and measurements were made at intervals during grain development on the first leaf above the ear. Leaf CER and transpiration of earless cv. B73 × Mo17 plants were lower than controls by 4 days after ear removal (DAER) and were not detectable by 18 DAER. In contrast, ear removal from cv. FS854 plants did not affect leaf CER or transpiration relative to eared controls until 9 DAER, and leaves retained 20% of maximum CER and transpiration by 29 DAER. The decline in CER in both hybrids did not appear to be due to stomatal closure, as initial internal CO₂ concentrations were sufficient to support adequate CER. The levels of CER, transpiration, and leaf resistance were consistent with visual estimates of leaf senescence.Grain harvested from the eared plants used for CER measurements showed that FS854 plants had more (23%) and heavier (4%) kernels than B73 × Mo17 plants. For FS854, the larger kernel number of comparable weight was attributed to the maintenance of a relatively higher level of leaf photosynthesis during the later stages of grain fill. The differences in CER and visual ratings indicate that the rate of leaf senescence following ear removal may be useful in identifying hybrids with late-season photosynthetic capabilities and high production potential.     

烟嘧磺隆对糯玉米光合特性和叶绿素荧光参数的影响

以沈糯509抗、不抗近等基因系为试材,研究烟嘧磺隆除草剂对玉米光合色素含量、叶片光合特性和叶绿素荧光参数的影响。结果表明,烟嘧磺隆处理使沈糯509抗、不抗近等基因系的叶绿素含量、净光合速率和PSⅡ光化学效率等均不同程度的降低,使胞间CO₂浓度和非光化学猝灭系数呈升高趋势,且表现出一定的剂量-效应关系。在供试浓度范围内,抗系各参数变化幅度均小于不抗系,说明抗系具有较强的光合调节机制,用以减轻或消除烟嘧磺隆的胁迫反应。     

Photosynthesis, symbiotic N and C accumulation in leaves of 30 nodulated cowpea genotypes grown in the field at Wa in the Guinea savanna of Ghana

Cowpea is a major food legume in Africa with relatively little information on N and C nutrition under field conditions in the continent. The aim of this study was to assess the relationship between leaf symbiotic N nutrition and photosynthetic carbon assimilation in cowpea genotypes grown under field conditions in the Guinea savanna of Ghana. The experiments were conducted in a randomized complete block design in Ghana, using 30 nodulated cowpea genotypes. Data collected from gas-exchange studies showed that genotypes with high photosynthetic rates expectedly exhibited greater stomatal conductance, high transpiration rates and increased water-use efficiency, leading to greater dry matter yield. In contrast, those with low photosynthetic rates revealed low stomatal conductance, low transpiration rates and low water-use efficiency. Quantification of symbiotic N in photosynthetic leaves indicated greater N₂ fixation in genotypes with higher photosynthetic rates, leaf transpiration and better water-use efficiency. Furthermore, measurement of C in leaves also indicated greater accumulation in genotypes with higher symbiotic N yield and total N, clearly indicating a link between C and N metabolism in photosynthetic leaves. Additionally, measures of photosynthetic N-use efficiency showed that genotypes with high levels of C-fixed per unit leaf total N also exhibited greater C-fixed per unit leaf N-fixed. Data suggest that where symbiotic legumes derive a large proportion of their N from N₂ fixation, photosynthetic C yield is much enhanced.     

Chlorophyll fluorescencein vivo as an indicator of water stress in potato leaves

Potato plants, cv. Desirée, were exposed to a -0.3 MPa polyethylene glycol-induced water stress for 24 h in a hydroponic system. Leaves with a Leaf Plastochron Index of 3 to 3.99, 4 to 4.99 and 6 to 6.99 were measured for total, osmotic and pressure potential, leaf conductance andin vivo chlorophyll fluorescence transients F_o, F_p and F_T. Leaf conductance and F_o significantly declined with leaf age in unstressed leaves. Water potential components and leaf conductance were significantly lower after 4 h of water stress whereas all three chlorophyll fluorescence transients measured after 24 h were significantly higher. The increase in fluorescence transients suggested that PSII electron acceptors were reduced faster than PSI and the Calvin cycle could oxidize them.In vivo chlorophyll fluorescence provides a greater understanding of the physiological effects of water stress but it requires additional experimentation to make it useful in screening for water stress tolerance.     

氮水平对水稻汕优64和金南风光合特性的影响

 以缺氮、低氮、中氮、高氮、超高氮盆栽土培的汕优64和金南风为材料，测定植株和叶片的生长状况、叶片总N含量、光合速率、光呼吸速率、气孔导度和叶肉导度的变化。结果表明，供试两品种随着施N量的增加，植株的分蘖数增多,株高增加,气孔密度减少, 叶片总N含量、叶绿素含量、光呼吸速率、叶肉导度等均增加。供试两品种的净光合速率变化存在差异，金南风叶片的净光合速率随着施N量的增加而增加,但汕优64在高氮和超高氮的条件下净光合速率反而下降,说明在高氮和超高氮的条件下光氧化环增加的幅度大于光合还原环。     

胡椒园间作槟榔对胡椒光合效应和产量的影响

为揭示槟榔胡椒间作体系中胡椒间作产量优势的光合机理,2009~2012年在海南胡椒与槟榔间作优势区,研究4种间作和单作条件下,胡椒不同生育期完全展开叶的光合有效辐射、净光合速率、气孔导度、蒸腾速率和胞间二氧化碳浓度等光合参数以及叶面积和叶绿素的含量。结果表明:胡椒与槟榔间作明显提高胡椒产量,偏土地当量比(PLER-M)高于其所占面积比例的134%~189%,表现出明显的间作产量优势。分析胡椒光合参数与产量相关关系,发现胡椒灌浆期光合参数与产量显著或极显著正相关,其中气孔导度对产量的正效应最大,以气孔导度为解释变量与因变量产量做回归分析,发现灌浆期对产量的贡献率达52%。胡椒与低密度槟榔间作提高或显著提高了胡椒灌浆期叶片光合作用,增强二氧化碳的固定,这可能是胡椒产量间作优势的主要来源。