Non-leaf Organs Research Articles

Responses of photosynthetic characteristics of oat flag leaf and spike to drought stress.

Raising crops production via improving photosynthesis has always been focused. Recently excavating and increasing the photosynthetic capacity of non-leaf organs becomes an important approach to crops yield increase. Here we studied the photosynthetic characteristics of the flag leaf and the non-leaf organs including the sheath, the glume and the lemma under greenhouse. The relative water content (RWC), the stomatal characteristics, the photosynthetic pigment contents, the enzyme activities in C3 and C4 pathway and the malate content of the flag leaf and the non-leaf organs on 7, 14, 21, and 28 days after anthesis (denoted by 7DAA, 14DAA, 21DAA, and 28DAA) were determined under well-watered (CK) and water-stressed (D) treatments. Drought stress significantly reduced the RWC of the flag leaf and the non-leaf organs, while the variation of RWC in the glume and the lemma was lower than in the flag leaf. The chlorophyll a content, the chlorophyll b content, the total chlorophyll content and the xanthophyll content in the flag leaf were significantly decreased under D. However, drought stress significantly increased the photosynthetic pigment contents in the glume at the late stage (21DAA and 28DAA). In addition, the induced activities of PEPC, NADP-MDH, NADP-ME, NAD-ME, and PPDK in non-leaf organs under drought stress suggested that the C4 photosynthetic pathway in non-leaf organs compensated the limited C3 photosynthesis in the flag leaf. Non-leaf organs, in particular the glume, showed the crucial function in maintaining the stable photosynthetic performance of oat.

The dynamics of carbohydrate and associated gene expression in the stems and roots of upland cotton (Gossypiumhirsutum L.) during carbon remobilization

Carbohydrates remobilization in non-leaf organs has a potential association with the formation of cotton yield. However, our understanding of the physiological and molecular mechanisms regulating carbon remobilization during flowering is still limited. The objectives of the study were to: i) evaluate the potential of carbohydrate remobilization in stems and roots to yield formation; ii) unravel the carbon metabolism and transport associated gene expression patterns regulating carbon remobilization. Two cotton lines 4003-6 and 4003-10 were employed to examine leaf photosynthesis, reproductive biomass accumulation, and carbon dynamics in stems and roots during reproductive growth. The results showed that decreasing leaf photosynthetic capacity combined with rapidly increasing reproductive biomass and leaf area index is accompanied by the initiation of carbohydrate remobilization during first flowering to peak flowering. The proportion of sucrose to total nonstructural carbohydrate was also decreased at that period. The upper and lower of stem recorded higher soluble sugars and starch concentrations, respectively compared to the two others. The gross contribution rate of carbon remobilization to seed cotton yield ranged from 2.83% to 7.12%. Key genes and sugar transporters related to starch and sucrose metabolism in the lower stem exhibited significant up- or down-regulated expressions indicating their important roles in carbon reserves remobilization. Three pivotal sugar transporters SWEET1, TMT2, and ERLD5 presented higher transcript levels at peak flowering suggesting more active sugar movement occurring at that stage. The present study provides potential target genes for engineering carbohydrate metabolism and transport to improve the remobilization efficiency of nonstructural carbohydrates.

氮添加对黄河三角洲滨海湿地芦苇养分再吸收效率的影响

大气氮沉降增加能改变土壤养分可利用性，影响滨海湿地植物的养分再吸收。目前研究多关注氮沉降量对养分再吸收过程的影响，且研究集中于叶片，鲜有研究区分不同形态氮素对植物不同器官养分再吸收过程的影响。通过两年的野外控制实验，研究硝态氮、铵态氮添加对黄河三角洲滨海湿地芦苇（Phragmites australis）叶、茎养分再吸收效率的影响。结果表明：两类氮添加均显著增加叶、茎的氮、磷含量（P<0.001），增幅达32.74%-43.22%（氮）、30.91%-36.51%（磷）。叶片氮的再吸收效率为54.14%-67.66%，茎氮的再吸收效率为50.60%-62.85%。叶片磷的再吸收效率为56.80%-70.38%，茎磷的再吸收效率为77.43%-84.95%。两类氮添加均显著降低氮、磷的再吸收效率（P<0.001），但两类氮添加处理下的养分再吸收效率无差异。叶、茎氮的再吸收效率无差异，但茎磷的再吸收效率明显高于叶（P<0.01）。总之，氮添加降低芦苇对氮、磷的再吸收效率，且茎对养分的再吸收也具有不可忽略的贡献。;Increased atmospheric nitrogen (N) deposition may adjust the nutrient resorption efficiency of the plant species in the coastal wetlands due to the changing of soil nutrients availability. Most studies concentrated on the nutrient resorption of the leaf, whereas the nutrient resorption of the non-leaf organs, such as culm, is still less known. Moreover, little attention is concentrated on differentiating the effects of nitrate and ammonium additions on nutrient resorption. In this study, an in situ experiment was conducted to investigate the effects of nitrate and ammonium additions on the nutrient resorption efficiency of leaf and culm for reed (Phragmites australis) in the coastal wetlands of the Yellow River Delta, China. Results showed that N additions increased the concentrations of N and phosphorus (P) in senesced organs, ranging from 32.71% to 43.22% for N, and ranging from 30.91% to 36.51% for P. The N resorption efficiency (NRE) ranged from 54.14% to 67.66% for the leaf and ranged from 50.60% to 62.85% for the culm. The P resorption efficiency (PRE) ranged from 56.80% to 70.38% for the leaf and ranged from 77.43% to 84.95% for the culm. Both two types of N addition had similar and negative effects on nutrient resorption efficiency (P<0.001). The NRE of leaf was similar to that of culm, whereas the culm had larger PRE than leaf (P<0.01). Overall, both N additions decreased the NRE and PRE of reed. Furthermore, the culm of reed had a non-negligible contribution to nutrient resorption.

Progress in research on the photosynthetic characteristics of green non-leaf organs in plants

Progress in research on the photosynthetic characteristics of green non-leaf organs in plants

Boll-leaf system gas exchange and its application in the analysis of cotton photosynthetic function.

Estimating the boll development and boll yield from single-leaf photosynthesis is difficult as the source-sink relationship of cotton (Gossypium hirsutum L.) is complicated. As the boll-leaf system (BLS), which includes the main-stem leaf, sympodial leaf, and non-leaf organs, is the basic unit of the cotton source-sink relationship and yield formation, the concept of "BLS photosynthesis" is introduced in this study. We speculate that the characteristics of BLS gas exchange can more accurately reflect the photosynthetic function of the system, thus revealing the law of photosynthesis in the process of boll development. The results showed that the photosynthetic rate of single leaves measured by a BLS chamber was consistent with that measured by a standard single-leaf chamber. BLSs exhibited typical light response curves, and the shape of the curves was similar to those of single leaves. The light compensation point and respiration rate of BLSs were higher than those of single leaves, while the apparent quantum efficiency of BLSs was lower. Compared with single leaves, the duration of the photosynthetic function of BLSs was longer. Increasing plant density decreased the gas exchange rate per unit BLS more significantly under field conditions. There was a better linear correlation between the net CO2 assimilation rate, respiration rate of BLSs and boll biomass. Therefore, we think that the gas exchange of BLSs can better reveal the changes in photosynthetic function of BLSs and boll development. This provides a new basis for analyzing the mechanism and regulation of cotton yield formation.

Single boll weight depends on photosynthetic function of boll-leaf system in field-grown cotton plants under water stress.

Cotton has many leaves and even more bolls, which results in a complicated source-sink relationship. Under water stress, the single boll weight (SBW) of cotton remains relatively stable, while both the leaf area and leaf photosynthetic rate decrease greatly. It is therefore difficult to understand how the formation of SBW is regulated under water stress solely by considering single-leaf photosynthesis. Considering the cotton boll-leaf system (BLS: including the main-stem leaf, sympodial leaves, and non-leaf organs) as the basic unit of the cotton canopy, we speculated that the formation of SBW may depend on photosynthesis in the corresponding BLS under water stress. To verify this hypothesis, five water treatments were set up in the field. The results showed that with increasing water stress, the relative water content (RWC) of the main-stem and sympodial leaves decreased gradually, and the decrease in the sympodial leaves was more obvious. The SBW and the number of BLSs decreased slightly with increasing water stress, while the number of bolls per plant decreased significantly. The area of the BLS decreased gradually with increasing water stress, and the area of sympodial leaves decreased more than that of the main-stem leaves. Gas exchange showed that the photosynthetic rate of the BLS (Pn(BLS)) decreased gradually with increasing water stress. In addition, the single-leaf photosynthesis and carboxylation efficiency (CE) decreased progressively and rapidly with the increase of water stress. Compared with the main-stem leaf, the photosynthetic function of the sympodial leaf decreased more. Further analysis showed that compared with leaf photosynthetic rate, there was a better correlation between Pn(BLS) and SBW. Thus, the formation of SBW mainly depends on Pn(BLS) under water stress, and the increase of BLS to boll is also helpful to maintain SBW to some extent. In BLS, the photosynthesis of the main-stem leaf plays a very important role in maintaining the stability of SBW, while the photosynthetic performance in sympodial leaves may be regulated plastically to influence SBW.

The net photosynthetic rate of the cotton boll-leaf system determines boll weight under various plant densities

The yield of cotton (Gossypium hirsutum L.) can be effectively maximized through high planting density. Estimating the yields from single-leaf photosynthesis under various plant densities is difficult as the source-sink relationship of cotton is complicated. By considering the boll-leaf system (BLS: including the main-stem leaf, sympodial leaf and non-leaf organs) as the basic unit of the cotton canopy, the present study asserts that the photosynthetic function of BLS determines single boll weight. This hypothesis was tested by establishing plant densities to explore changes in photosynthesis of the cotton BLS and the consequent effects on boll weight. The results showed that high plant density increased total boll number per unit ground area, whereas single boll weight remained relatively stable, thereby increasing cotton yield. High plant density significantly limited the biomass of the BLS and reduced the distribution ratio of assimilate to sympodial leaves, whereas the dry matter proportion of cotton bolls increased. Although the leaf area and photosynthetic rate of both the main-stem and sympodial leaves of the BLS decreased with increasing plant density, the extent of decrease in the latter was greater. CO2 assimilation within the BLS decreased slightly with increasing plant density, and significant decreases in CO2 assimilation were only evident in extremely high plant densities. A significant positive linear correlation was observed between CO2 assimilation of the BLS and single boll weight. Therefore, photosynthesis of the BLS was identified as the primary factor maintaining boll weight under various plant densities. The main-stem leaf plays a key role in maintaining photosynthesis of the BLS, whereas BLS photosynthesis can be improved by plastically regulating the photosynthetic performance in sympodial leaves.

Glutathione and ethylene biosynthesis reveal that the glume and lemma have better tolerance to water deficit in wheat

As senescence progresses, the sensitivity of wheat organs to plant hormones during the grain-filling stages cannot be ignored. Especially under water deficit situation, non-leaf organs (spikes) have better photosynthesis and drought-tolerance traits than flag leaves. However, the mechanism of ethylene synthesis in wheat organs under water deficit remains unclear. We have studied the influence of water deficit in wheat flag leaves and spike bracts on photosynthetic parameters and on the expression of key enzymes involved in the ethylene biosynthesis pathway during the late grain-filling stages. More stable chlorophyll content (Chl), maximum PSII quantum yield (Fv/Fm), nonphotochemical quenching (NPQ) and maximal efficiency of PSII photochemistry under light adaptation (Fv’/Fm’) were observed in the spike bracts than that in the flag leaves during the late grain-filling stages. In addition, the activity of glutathione reductase (GR), γ-glutamylcysteine synthetase (γ-ECS), 1-aminocyclopropane-1-carboxylic (ACC) acid synthase (ACS), and ACC oxidase (ACO) induced ethylene synthesis and influenced plant growth. Further analysis of genes encoding cysteine-ethylene related proteins (γ-ECS, GR, ACO, ACS1, and ASC2) demonstrated that ear organs and flag leaves exhibited different expression patterns. These findings will facilitate future investigations of the regulatory senescence response mechanisms of cysteine interaction with ethylene in wheat under conditions of drought stress.

Participation of stem and ear photosynthesis in formation of the crop and its quality in wheat

Photosynthesis of various organs and their contribution to formation of ear caryopsis were measured using14CO2 labeled carbon in the phase of caryopsis formation of spring wheat plants (Moskovskaya-35). It turned out that inclusion of14C into amino acids is more than twice as high in photosynthesis of an ear. Among labeled low molecular weight compounds in caryopsis, during a short exposure (2 hours) after photosynthesis, the most of the labeled carbon in the14CO2 was found from the photoassimilates of the flag leaf (70.4%); from the ear (55.8%), and the least – from the stem under the flag (41.5%). The difference in inclusion of14C into the caryopsis’ total proteins was observed only with a short exposure of the photosynthesizing organ (2 hours). Water-soluble proteins, as products of photosynthesis of the flag leaf, were synthesized for the most in the caryopsis (flag – 73.9%; stem – 46.4% and ear – 44.8%), and in the synthesis of complex proteins, which are soluble in alkali and Triton X-100, most of14C was from the products of photosynthesis of non-leaf organs (10.5; 21.5; 28.4 and 4.3; 12.5; 13.4), respectively.

Impact of K deficiency on leaves and siliques photosynthesis via metabolomics in Brassica napus

Potassium (K) deficiency is known for its impact on photosynthesis via the synthetic constraints of CO2 diffusion and assimilation. However, insights in the different responses of net photosynthetic rate (A) to K depletion inside primary metabolites, produced specifically by each organ, remain to be elucidated. Leaves and siliques of Brassica napus were investigated to clarify the responses of A, the CO2 conductance and that of main metabolism pathways under K deficiency. Leaves were far more sensitive to K deficiency, displaying simultaneous decreases in A and CO2 diffusion reflected in a broader range of metabolites. To compensate the carbon starvation under K deficiency, leaf metabolic profile was adaptively regulated thorough downregulation of the carbon flux into carbohydrates and organic acids and upregulation of nitrogen-rich amino acids. Significant relationships between leaf A and sugars, organic acids and amino acids were observed. In comparison with leaves, the carbon shortage observed in siliques was negligible or even absent, with no obvious change in carbon flux through the glycolysis and tricarboxylic acid cycle pathways. Proline represented the only metabolite that correlated positively with silique A. These results provide new insights into differences in photosynthetic responses to K deficiency between leaf and non-leaf organs based on the potential metabolic processes involved.

Nitrogen and phosphorus concentrations and allocation strategies among shrub organs: the effects of plant growth forms and nitrogen-fixation types

We aimed to explore the influences of plant functional groups on nutrient concentrations and allocation strategies among shrub organs, as well as to examine the effects of climate, soil and species on nutrient concentrations in shrubs of different plant functional groups. We investigated the nitrogen (N) and phosphorus (P) concentrations in roots, stems and leaves and their influencing factors of 187 shrub species in the shrublands across southern China, and we also examined the relationships between N and P among various organs using scaling analysis. The scaling relationships of N and P tended to be allometric between leaf and non-leaf organs, while they tended to be isometric among non-leaf organs. Plant functional groups affected nutrient allocation among shrub organs, where a higher proportion of nutrients were present in the stems and roots of evergreen shrubs and non-legume shrubs when compared to deciduous shrubs and legume shrubs as nutrients within a plant increased. Among organs, N and P concentrations were higher in leaves than in stems and roots. Among functional groups, evergreen shrubs and legume shrubs were more P-limited than deciduous shrubs and non-legume shrubs, respectively. The N and P concentrations in evergreen shrubs were lower and more sensitive to environmental change than in deciduous shrubs. Both N and P contents in legume shrubs were higher and more homeostatic than those of non-legume shrubs. Plant growth forms and N-fixation types exerted strong effects on nutrient concentrations and allocations among shrub organs. The influences of climate and soil on shrub N and P concentrations differed by plant functional groups.

Establishment of ANEDr model for evaluating absorbed-nitrogen effects on wheat dry matter production

Applying mathematic models to evaluate absorbed-N effects on dry matter production at different developmental stages would help determine proper nitrogen management according to crop demands and yield target. Two field trials were carried out for establishing absorbed-N effects on dry matter production (ANEDr) model, using uniform design in 2010–2011 and 2012–2013 winter wheat growing seasons in Hebei Province, China. Another field trial was carried out in 2010–2011 for model validation. Dry matter and N concentration in leaf and non-leaf organs were measured at setting, jointing, anthesis, and maturity. Theory of best linear unbiased prediction (BLUP) was applied to analyse the N effects of leaf and non-leaf organs on dry matter production. Within ANEDr model, four N-affected phases at each stage were concerned, leaf absorbed-N effect before this stage, non-leaf organ absorbed-N effect before this stage, leaf absorbed-N effect at this stage, and non-leaf organ absorbed-N effect at this stage. In addition, developmental processes, genotype characters and temperature were three factors that determine each N effect. It was demonstrated that ANEDr model can precisely quantify absorbed-N effects on dry matter production with high correlation coefficient (r=0.95). Comparing with other models, ANEDr model considered both leaf and non-leaf organs according to developmental processes of winter wheat, showed higher flexibility and simplicity, thus could be applied to different environments, cultivars and crops after parameter adjustment.

Effect of High Temperature on Photosynthetic Capability and Antioxidant Enzyme Activity of Flag Leaf and Non-leaf Organs in Wheat

Winter wheat in North China has been subject to high temperature stress during grain filling. The purpose of this study was to determine the effect of high temperature on the photosynthetic capability of flag leaf and the antioxidant system of flag leaf and non-leaf organs in winter wheat cultivars Shijiazhuang 8(tolerant to high temperature) and Henong 341(sensitive to high temperature). High temperature(HT) stress was imposed with a plastic shed from the 8th to the 22 nd day after anthesis, and normal temperature was used as the control. Under HT, the photosynthetic rate and chlorophyll content of flag leaf decreased by 18.7%–24.9% and 5.7%–6.2%, respectively; whereas the malodialdehyde(MDA) and proline(Pro) contents in flag leaf blade, sheath, peduncle, glume and grain increased in different levels. The increased percentage of MDA was higher in flag leaf than in non-leaf organs and that of Pro was higher in non-leaf organs than in flag leaf. Superoxide dismutase(SOD) in flag leaf, glume and grain, catalase(CAT) in flag leaf, sheath and grain, and peroxidases(POD) in flag leaf, sheath and glume were induced at early stage(4 d after treatment) by HT treatment, while the activities of antioxidant enzymes in other organs increased at later stage(7 d after treatment). Thereafter, the activities of antioxidant enzymes in various organs maintained lower levels compared with those of the control. At the 26 th day after anthesis when HT stress was relieved for four days, the SOD activity in sheath, peduncle and glume and the POD activity in flag leaf, glume and grain began to increase, but the effects of HT on the SOD and POD activities in other organs and the CAT activity in all organs seemed irreversible. In general, the non-leaf organs exhibited higher antioxidant capability and heat tolerance than flag leaf. Compared with Henong 341, Shijiazhuang 8 exhibited higher cell membrane stability and antioxidant activity in leaf and non-leaf organs, leading to a tolerance to HT stress of the whole plant. This might be the physiological basis of smaller percentage of yield loss in Shijiazhuang 8 than in Henong 341 under HT stress. Our results indicate that non-leaf organs of wheat play an important role in adaptability to climate warming.

Photosynthetic Characteristics after Flowering and Contribu-tion of Non-leaf Green Organs of Cotton to Yield under Mulching-drip Irrigation with Water Deficiency

Leaf is one of the main photosynthetic organs, while other green parts of plant also retain or develop chlorophyll and have photosynthesis. To better understand the whole plant photosynthesis production potential and contribution to cotton yield, we selected Xinluzao 33 and Xinluzao 45 (two common cultivars in Northern Xinjiang) with three irrigation treatments (CI, conven- tional irrigation; SDI, slight deficit irrigation; MDI, moderate deficit irrigation) to measure the chlorophyll content (Chl), net pho- tosynthetic rate (Pn), stomatal conductance (gs) and photosynthate accumulation in leaf and non-leaf green organs during different growth stages and the contribution of non-leaf green organs to yield. The results showed that the Pn and Chl in non-leaf organs were relatively insensitive to soil moisture stress, decreasing by only a small amount between 25 and 45 days after anthesis. With reduction of water supply, the dry matter production in non-leaf green organs played more important roles in cotton yield forma- tion. Cotton boll weight in the moderate deficit irrigation treatment decreased by 16.8% to 34.9% when the bolls (capsule walls plus bracts) were shaded and by 7.6% to 17.5% when the stalks were shaded. Hence, limiting-irrigation treatment is important to maintain high leaf photosynthetic rates. It is also important to develop the potential photosynthetic capacity of non-leaf green or- gans. This is especially important when leaf photosynthesis capacity declines due to leaf aging or water stress.

Effects of favorable alleles for water-soluble carbohydrates at grain filling on grain weight under drought and heat stresses in wheat.

Drought, heat and other abiotic stresses during grain filling can result in reductions in grain weight. Conserved water-soluble carbohydrates (WSC) at early grain filling play an important role in partial compensation of reduced carbon supply. A diverse population of 262 historical winter wheat accessions was used in the present study. There were significant correlations between 1000-grain weight (TGW) and four types of WSC, viz. (1) total WSC at the mid-grain filling stage (14 days after flowering) produced by leaves and non-leaf organs; (2) WSC contributed by current leaf assimilation during the mid-grain filling; (3) WSC in non-leaf organs at the mid-grain filling, excluding the current leaf assimilation; and (4) WSC used for respiration and remobilization during the mid-grain filling. Association and favorable allele analyses of 209 genome-wide SSR markers and the four types of WSC were conducted using a mixed linear model. Seven novel favorable WSC alleles exhibited positive individual contributions to TGW, which were verified under 16 environments. Dosage effects of pyramided favorable WSC alleles and significantly linear correlations between the number of favorable WSC alleles and TGW were observed. Our results suggested that pyramiding more favorable WSC alleles was effective for improving both WSC and grain weight in future wheat breeding programs.

Scaling of nitrogen and phosphorus across plant organs in shrubland biomes across Northern China.

Allocation of limiting resources, such as nutrients, is an important adaptation strategy for plants. Plants may allocate different nutrients within a specific organ or the same nutrient among different organs. In this study, we investigated the allocation strategies of nitrogen (N) and phosphorus (P) in leaves, stems and roots of 126 shrub species from 172 shrubland communities in Northern China using scaling analyses. Results showed that N and P have different scaling relationships among plant organs. The scaling relationships of N concentration across different plant organs tended to be allometric between leaves and non-leaf organs, and isometric between non-leaf organs. Whilst the scaling relationships of P concentration tended to be allometric between roots and non-root organs, and isometric between non-root organs. In arid environments, plant tend to have higher nutrient concentration in leaves at given root or stem nutrient concentration. Evolutionary history affected the scaling relationships of N concentration slightly, but not affected those of P concentration. Despite fairly consistent nutrients allocation strategies existed in independently evolving lineages, evolutionary history and environments still led to variations on these strategies.

Combined effects of nitrogen addition and litter manipulation on nutrient resorption of Leymus chinensis in a semi‐arid grassland of northern China

Plant growth in semi-arid ecosystems is usually severely limited by soil nutrient availability. Alleviation of these resource stresses by fertiliser application and aboveground litter input may affect plant internal nutrient cycling in such regions. We conducted a 4-year field experiment to investigate the effects of nitrogen (N) addition (10 g N·m(-2) ·year(-1)) and plant litter manipulation on nutrient resorption of Leymus chinensis, the dominant native grass in a semi-arid grassland in northern China. Although N addition had no clear effects on N and phosphorus (P) resorption efficiencies in leaves and culms, N fertilisation generally decreased leaf N resorption proficiency by 54%, culm N resorption proficiency by 65%. Moreover, N fertilisation increased leaf P resorption proficiency by 13%, culm P resorption proficiency by 20%. Under ambient or enriched N conditions, litter addition reduced N and P resorption proficiencies in both leaves and culms. The response of P resorption proficiency to litter manipulation was more sensitive than N resorption proficiency: P resorption proficiency in leaves and culms decreased strongly with increasing litter amount under both ambient and enriched N conditions. In contrast, N resorption proficiency was not significantly affected by litter addition, except for leaf N resorption proficiency under ambient N conditions. Furthermore, although litter addition caused a general decrease of leaf and culm nutrient resorption efficiencies under both ambient and enriched N conditions, litter addition effects on nutrient resorption efficiency were much weaker than the effects of litter addition on nutrient resorption proficiency. Taken together, our results show that leaf and non-leaf organs of L. chinensis respond consistently to altered soil N availability. Our study confirms the strong effects of N addition on plant nutrient resorption processes and the potential role of aboveground litter, the most important natural fertiliser in terrestrial ecosystems, in influencing plant internal nutrient cycling.

Preliminary Study on the Physiological Characteristics of Transgenic Wheat with Maize C4-pepcGene in Field Conditions

To explore the physiological characteristics of the pepc gene in transgenic wheat (Triticum aestivum) plants, PEPC activities in various organs of T3 plants were analyzed at Feekes 6.0, Feekes 10.3 and Feekes 11.1, and compared to control, untransformed wheat cultivar Zhoumai 19. Net photosynthetic rates (Pn) in leaves were also measured at the same stages. At Feekes 11.1, both transgenic and control plants were treated with DCDP. Yield traits were surveyed after harvest. The results indicated that Pn and PEPC activity in the flag leaf of transgenic wheat were significantly higher than those of the control at different stages. At Feekes 10.3, Pn reached the highest value at 28.2 μmol m−2 s−1 and PEPC activity reached the highest value at 104.6 μmol h−1 mg−1. Both factors significantly increased by 21% compared to the control at Feekes 11.1. PEPC activity in the flag leaf of transgenic plants was significantly higher than that of non-leaf organs. Pn of transgenic plants was greatly reduced after DCDP treatment. In the flag leaf of transgenic wheat, Pn was significantly correlated to PEPC activities at 0.01 probability level with a correlation coefficient of 0.8957**. The yield traits of transgenic line 1-27-3, such as 1000-grain weight, single spike weight and harvest index were higher than those of the control. Additionally, the spike weight of 1-27-3 showed an increase of approximately 9.5% compared to the control. These results indicated that the expression of maize (Zea mays) pepc gene was different across various organs of transgenic wheat and across every growth stage. Therefore, we conclude that introducing maize pepc gene into wheat plants can increase their Pn and improve production.

Contributions of nonleaf organs to the yield of cotton grown with different water supply.

The objectives of this experiment were (i) to determine the effect of water supply on the photosynthetic capacity of leaves, bracts, capsule walls, and stalks of cotton at different growth stages and (ii) to determine the contributions of these nonleaf organs to whole plant photosynthesis. Water deficit reduced the total surface area per plant but increased the proportion of nonleaf to total plant surface area. Net photosynthetic rates of leaves declined rapidly beginning 25 days after anthesis. In contrast, the net photosynthetic rates of bracts and capsule walls were insensitive to soil moisture stress and decreased by a small amount between 25 and 45 days after anthesis. The relative contribution of bracts and stalks to canopy apparent photosynthesis (CAP) increased under water deficit conditions. Cotton seed weight in the conventional irrigation treatment decreased by 10.1–29.7% when the bolls (capsule walls plus bracts) were darkened and by 5.3–9.9% when the stalks were darkened. On a percentage basis, both boll photosynthesis and stalk photosynthesis contributed more to seed weight when the plants were grown under water deficit conditions rather than nondeficit conditions. In conclusion, nonleaf organs contribute significantly to yield when cotton plants are under water stress during late growth stages.

Spatial patterns of photosynthesis in thin- and thick-leaved epiphytic orchids: unravelling C3-CAM plasticity in an organ-compartmented way.

A positive correlation between tissue thickness and crassulacean acid metabolism (CAM) expression has been frequently suggested. Therefore, this study addressed the question of whether water availability modulates photosynthetic plasticity in different organs of two epiphytic orchids with distinct leaf thickness. Tissue morphology and photosynthetic mode (C3 and/or CAM) were examined in leaves, pseudobulbs and roots of a thick-leaved (Cattleya walkeriana) and a thin-leaved (Oncidium 'Aloha') epiphytic orchid. Morphological features were studied comparing the drought-induced physiological responses observed in each organ after 30 d of either drought or well-watered treatments. Cattleya walkeriana, which is considered a constitutive CAM orchid, displayed a clear drought-induced up-regulation of CAM in its thick leaves but not in its non-leaf organs (pseudobulbs and roots). The set of morphological traits of Cattleya leaves suggested the drought-inducible CAM up-regulation as a possible mechanism of increasing water-use efficiency and carbon economy. Conversely, although belonging to an orchid genus classically considered as performing C3 photosynthesis, Oncidium 'Aloha' under drought seemed to express facultative CAM in its roots and pseudobulbs but not in its leaves, indicating that such photosynthetic responses might compensate for the lack of capacity to perform CAM in its thin leaves. Morphological features of Oncidium leaves also indicated lower efficiency in preventing water and CO2 losses, while aerenchyma ducts connecting pseudobulbs and leaves suggested a compartmentalized mechanism of nighttime carboxylation via phosphoenolpyruvate carboxylase (PEPC) (pseudobulbs) and daytime carboxylation via Rubisco (leaves) in drought-exposed Oncidium plants. Water availability modulated CAM expression in an organ-compartmented manner in both orchids studied. As distinct regions of the same orchid could perform different photosynthetic pathways and variable degrees of CAM expression depending on the water availability, more attention should be addressed to this in future studies concerning the abundance of CAM plants.