Sub-stomatal CO2 Research Articles

Photosynthetic Adaptation to Length of Day Is Dependent on S-Sulfocysteine Synthase Activity in the Thylakoid Lumen

Arabidopsis (Arabidopsis thaliana) chloroplasts contain two O-acetyl-serine(thiol)lyase (OASTL) homologs, OAS-B, which is an authentic OASTL, and CS26, which has S-sulfocysteine synthase activity. In contrast with OAS-B, the loss of CS26 function resulted in dramatic phenotypic changes, which were dependent on the light treatment. We have performed a detailed characterization of the photosynthetic and chlorophyll fluorescence parameters in cs26 plants compared with those of wild-type plants under short-day growth conditions (SD) and long-day growth conditions (LD). Under LD, the photosynthetic characterization, which was based on substomatal CO(2) concentrations and CO(2) concentration in the chloroplast curves, revealed significant reductions in most of the photosynthetic parameters for cs26, which were unchanged under SD. These parameters included net CO(2) assimilation rate, mesophyll conductance, and mitochondrial respiration at darkness. The analysis also showed that cs26 under LD required more absorbed quanta per driven electron flux and fixed CO(2). The nonphotochemical quenching values suggested that in cs26 plants, the excess electrons that are not used in photochemical reactions may form reactive oxygen species. A photoinhibitory effect was confirmed by the background fluorescence signal values under LD and SD, which were higher in young leaves compared with mature ones under SD. To hypothesize the role of CS26 in relation to the photosynthetic machinery, we addressed its location inside of the chloroplast. The activity determination and localization analyses that were performed using immunoblotting indicated the presence of an active CS26 enzyme exclusively in the thylakoid lumen. This finding was reinforced by the observation of marked alterations in many lumenal proteins in the cs26 mutant compared with the wild type.

Photosynthetic characteristics of hybrid and conventional rice plants as a function of plant competition

The objective of this work was to evaluate the characteristics related to the photosynthetic ability of hybrid and inbred rice varieties, as a way to assess which of the two presented higher potential to stand out under conditions of competition. The trial was set in a greenhouse in completely randomized block design and 2 x 6 factorial scheme with four replications. Factor A consisted of rice varieties (hybrid or inbred) and factor B by competition levels. Treatments consisted in maintaining one plant of either BRS Pelota (inbred) or Inov (hybrid) variety at the center of the plot, under competition with 0, 1, 2, 3, 4 or 5 plants of the variety BRS Pelota at the periphery of the experimental unit, according to the treatment. Fifty days after emergence (DAE), sub-stomatal CO2 concentration (Ci - mmol mol-1), photosynthetic rate (A - mmol m-2 s-1) and CO2 consumed (DC - mmol mol-1) were quantified, as well as shoot dry mass(SDM).Hybrid plants present higher photosynthesis capacity than inbred plants, when competing with up to 3 times its own density. When under the same competitive intensity, hybrid plants surpass the inbred. However, it should be emphasized that, when in farm condition, the lower competitive capacity with weeds often attributed to the hybrid varieties, probably is due to their lower planting density, but if weed competition is kept at low levels, hybrid rice plants may perform in the same way or usually better than inbred plants.

Alleviation of Adverse Effects of Drought Stress on Growth and Some Potential Physiological Attributes in Maize (Zea mays L.) by Seed Electromagnetic Treatment

Effects of varying preseed magnetic treatments on growth, chlorophyll pigments, photosynthesis, water relation attributes, fluorescence and levels of osmoprotectants in maize plants were tested under normal and drought stress conditions. Seeds of two maize cultivars were treated with different (T0 [0 mT], T1 [100 mT for 5 min], T2 [100 mT for 10 min], T3 [150 mT for 5 min] and T4 [150 mT for 10 min]) electromagnetic treatments. Drought stress considerably suppressed growth, chlorophyll a and b pigments, leaf water potential, photosynthetic rate (A), stomatal conductance (g(s)) and substomatal CO(2) concentration (C(i)), while it increased leaf glycinebetaine and proline accumulation in both maize cultivars. However, pretreated seeds with different magnetic treatments significantly alleviated the drought-induced adverse effects on growth by improving chlorophyll a, A, E, g(s), C(i) and photochemical quenching and nonphotochemical quenching, while it had no significant effect on other attributes. However, different magnetic treatments negatively affected the g(s) and C(i) particularly in cv. Agaiti-2002 under drought stress conditions. Of all magnetic treatments, 100 and 150 mT for 10 min were most effective in alleviating the drought-induced adverse effects. Overall, preseed electromagnetic treatments could be used to minimize the drought-induced adverse effects on different crop plants.

Photosynthetic responses to heat treatments at different temperatures and following recovery in grapevine (Vitis amurensis L.) leaves.

BackgroundThe electron transport chain, Rubisco and stomatal conductance are important in photosynthesis. Little is known about their combined responses to heat treatment at different temperatures and following recovery in grapevines (Vitis spp.) which are often grown in climates with high temperatures.Methodology/FindingsThe electron transport function of photosystem II, the activation state of Rubisco and the influence of stomatal behavior were investigated in grapevine leaves during heat treatments and following recovery. High temperature treatments included 35, 40 and 45°C, with 25°C as the control and recovery temperature. Heat treatment at 35°C did not significantly (P>0.05) inhibit net photosynthetic rate (P n). However, with treatments at 40 and 45°C, P n was decreased, accompanied by an increase in substomatal CO2 concentration (C i), decreases in stomatal conductance (g s) and the activation state of Rubisco, and inhibition of the donor side and the reaction center of PSII. The acceptor side of PSII was inhibited at 45°C but not at 40°C. When grape leaves recovered following heat treatment, P n, gs and the activation state of Rubisco also increased, and the donor side and the reaction center of PSII recovered. The increase in P n during the recovery period following the second 45°C stress was slower than that following the 40°C stress, and these increases corresponded to the donor side of PSII and the activation state of Rubisco.ConclusionsHeat treatment at 35°C did not significantly (P>0.05) influence photosynthesis. The decrease of P n in grape leaves exposed to more severe heat stress (40 or 45°C) was mainly attributed to three factors: the activation state of Rubisco, the donor side and the reaction center of PSII. However, the increase of P n in grape leaves following heat stress was also associated with a stomatal response. The acceptor side of PSII in grape leaves was responsive but less sensitive to heat stress.

Water-deficit tolerance in citrus is mediated by the down regulation of PIP gene expression in the roots

Water deficit (WD) is a growing problem in agriculture. In citrus crops, genetically-determined rootstock characteristics are important factors influencing plant responses to WD. Aquaporins are involved in regulating the water supply to the plant by mediating water flow through the cell membranes. Recent studies support a direct role for aquaporins in plant water relations and demonstrate their involvement in WD tolerance. This study investigates the relationship between photosynthetic and water-balance parameters with aquaporin expression levels and hydraulic conductance of roots (Kr) in conditions of moderate WD in citrus rootstocks. The plant materials used were the rootstocks Poncirus trifoliata (L.) Raf. (PT), Cleopatra mandarin (Citrus reshni Hort ex Tan.) (CM) and 030115 (a hybrid of the two former rootstocks), all grafted with the citrus variety ‘Valencia Late’ (C. sinensis (L.) Osb). Plants were irrigated with two differents irrigation doses (normal irrigation and moderate WD) during 70 days and leaf water potential (ψs), net CO2 assimilation (ACO2), transpiration, stomatal conductance (gs) and substomatal CO2 concentration (Ci) were measured periodically under both irrigation conditions. Kr and PIP1 and PIP2 gene expression levels in fine roots of control plants and plants subjected to WD on day 43 of the experiment were determined. Under WD conditions, the hybrid 030115 drastically reduced aquaporin expression and Kr, accompanied by a loss of plant vigour but without reducing the net CO2 assimilation (ACO2). PT maintained the same aquaporin expression level and similar Kr under WD as under normal irrigation conditions, but suffered a sharp reduction in ACO2. CM, which has lower Kr and aquaporin expression than PT under both normal irrigation conditions and WD, responded better to water stress conditions than PT. Low aquaporin levels, or down-regulated aquaporin expression, accompanied by decreased plant vigour led to decreased plasma membrane permeability, thereby facilitating water retention in the cells under water stress conditions. This may induce water stress tolerance in citrus rootstocks.

Influência de Brachiaria brizantha nas características fisiológicas relacionadas a fotossíntese e uso eficiente da água em cana-de-açúcar

O aumento da população das plantas daninhas eleva a habilidade competitiva dessas com as plantas cultivadas, podendo causar interferência nos aspectos fisiológicos das culturas. Objetivou-se com o trabalho avaliar a interferência de populações de Brachiaria brizantha nas características relacionadas a atividade fotossintética e o uso eficiente da água das cultivares de cana-de-açúcar RB72454, RB867515 e SP80-1816. Foi conduzido um experimento a campo, onde os tratamentos foram constituídos por 12 populações de plantas de B. brizantha que emergiram juntamente com a cultura. Aos 120 dias após a emergência da cana-de-açúcar foram realizadas as avaliações da concentração de CO2 subestomático (Ci - µmol mol-1), a atividade fotossintética (A - µmol m-2 s-1), a condutância estomática (Gs - mol m-1 s-1), a taxa de transpiração (E), a eficiência do uso da água (EUA) e a massa seca da parte aérea (SDM - g por planta) da cultura. Todas as variáveis fisiológicas e a massa seca da cultivar RB72454 foram afetadas pelo aumento da densidade das plantas de B. brizantha, bem como a transpiração da cultivar RB867515. A cultivar RB72454 apresenta menor habilidade competitiva com as plantas daninhas e a atividade fotossintética é limitada por fatores que reduzem o influxo de CO2 para o interior da folha.

Effect of high temperature on active oxygen species, senescence and photosynthetic properties in cucumber leaves

To gain a physiological understanding of the effects of high temperatures on cucumber ( Cucumis sativus L.), we subjected seedlings to heat treatment at daytime temperatures of 28 °C, 32 °C, and 36 °C for 7 h a day for 30 days. The amount of active oxygen species, indicators of senescence, and photosynthetic properties in the second and third leaves were determined at the start of temperature treatment and on the 15th and 30th days of treatment. The amount of active oxygen species superoxide in leaves was greatest in the high temperature zones on the 15th day of treatment, and the amount of hydrogen peroxide was greatest in the high temperature zones on both the 15th and 30th days of treatment. The reduction in the amount of protein and the increase in the amount of malondialdehyde, both indicators of senescence, were greatest in the high temperature zones on both the 15th and 30th days of treatment, and the amount of chlorophyll was lowest in the 36 °C zone on the 15th day, and lower in the high temperature zones on the 30th day. It is clear from these results that a large amount of active oxygen species is generated and accumulated in the leaves at high temperatures, and senescence is significantly accelerated. The photosynthetic properties of stomatal conductance, sub-stomatal CO 2 concentration, and transpiration rate were at the same level on both the 15th and 30th days of treatment in all three temperature treatment zones. No significant difference was seen in the net photosynthesis rate between the 28 °C and 32 °C zones, was lower in the 36 °C zone than the 32 °C zone on the 15th day, and lowest in the 36 °C zone on the 30th day. CO 2 intake and water absorption are only mildly affected by high temperatures, and the reduction in net photosynthesis rate due to the 36 °C high temperature stress suggests that the large amount of active oxygen species induces inhibition of photosynthesis and damage to the mechanism of photosynthesis.

Differing responses to carbon dioxide enrichment by a dwarf and a normal-sized soybean cultivar may depend on sink capacity

Responses to CO2 enrichment were determined for a dwarf (MiniMax) and a normal-sized (Fiskeby) soybean [Glycine max (L.) Merr.]. Plants were grown in growth chambers with ambient (36 Pa) or elevated (98 Pa) CO2 using a 2 × 2 × 2 factorial design. Harvests for MiniMax and Fiskeby were increased 6 and 26 d, respectively, by CO2 enrichment. At final maturity, mean biomass for MiniMax and Fiskeby was 53 and 197 g, respectively, in the ambient CO2 treatment and these values were 48 and 199% greater, respectively, in response to CO2 enrichment. Root development was constrained in MiniMax and, unlike Fiskeby, all of the biomass attributed to CO2 enrichment was in the shoot. Cultivar differences were not detected for CO2 assimilation rates, stomatal conductance or substomatal CO2 concentrations. Foliar sucrose was 43% greater (P < 0.05) in MiniMax than in Fiskeby. Pods per plant, total seed mass per plant, seed number per plant and seed oil content were greater for Fiskeby than MiniMax. Seeds of Fiskeby were 75% greater by mass than those of MiniMax. Seed mass of Fiskeby increased about 50% in response to CO2 enrichment, whereas MiniMax was unchanged. Root growth, seed size, seeds per pod and starch accumulation rates for MiniMax were unaffected by CO2 enrichment. The above findings suggested that growth of the dwarf genotype under elevated CO2 was sink limited.Key words: Elevated CO2, atmospheric change, photosynthate partitioning, harvest index, soybean genotypes

Enhancement of morphological, anatomical and physiological characteristics of seedlings of the mangrove Avicennia marina inoculated with a native phosphate-solubilizing isolate of Oceanobacillus picturae under greenhouse conditions

One hundred and twenty-nine rock phosphate (RP) solubilizing bacteria were isolated from the mangrove Avicennia marina rhizosphere sediment deficient in available phosphorus (P), in the United Arab Emirates (UAE). Among these isolates, an outstanding isolate of Oceanobacillus picturae grown in Pikovskaya’s liquid medium amended with RP, caused the highest percentage of RP solubilization (97%), the most pronounced drop in the medium pH and produced a variety of organic acids, as well as acid and alkaline phosphatases. Greenhouse experiments were carried out to investigate the effect of sediment inoculation with O. picturae (Op) with or without RP amendment on the growth, nutrient uptake, conducting tissue and photosynthetic gas exchange characteristics of mangrove seedlings. The application of Op to sediments amended with RP significantly promoted the growth of roots and shoots of seedlings compared with those grown in sediment amended with RP only. O. picturae significantly increased available sediment P, decreased sediment pH, positively enhanced nutrient uptake parameters in roots and shoots, increased stem circumference, number of xylem vessels, mean xylem diameter, and the hydraulically weighted xylem vessel diameter, compared with plants grown in non-inoculated sediment amended with only RP. Mechanistic analysis of A:Ci response curves (Assimilation versus sub-stomatal CO2 concentration) showed that photosynthetic gas exchange characteristics were significantly enhanced by Op + RP treatment compared with RP alone or control treatment. The maximal Rubisco-catalyzed carboxylation velocity (Vc,max), increased by more than two fold in plants treated with RP + Op, over the control. Application of Op + RP greatly increased the maximal electron transport rate values (Jmax) by 185%, over the control plants. In addition, the triose phosphate utilization rate (VTPU) increased three fold in plants treated with RP + Op over the control. To the best of our knowledge, this is the first published report of Op from mangrove sediments and also the first report of this organism as a phosphate-solubilizing bacterium. These results have clearly shown that Op has the potential to be applied as an effective and economical treatment in association with RP amendment for mangrove reforestation programs in arid environments such as those found in the UAE.

Water use efficiency and photosynthesis of glyphosate-resistant soybean as affected by glyphosate

Previous studies comparing cultivars of different maturity groups in different soils demonstrated that early maturity group cultivars were more sensitive to glyphosate injury than those of other maturity groups. In this work, we evaluated the effect of increasing rates of glyphosate on water absorption and photosynthetic parameters in early maturity group cultivar BRS 242 GR soybean. Plants were grown in a complete nutrient solution and subjected to a range of glyphosate rates either as a single or sequential leaf application. Net photosynthesis, transpiration rate, stomatal conductance, sub-stomatal CO 2, carboxylation efficiency, fluorescence, maximal fluorescence and chlorophyll content were monitored right before and at different stages after herbicide application; water absorption was measured daily. All photosynthetic parameters were affected by glyphosate. Total water absorbed and biomass production by plants were also decreased as glyphosate rates increased, with the affect being more intense with a single full rate than half the rate applied in two sequential applications. Water use efficiency (WUE) was significantly reduced with increasing rates of glyphosate.

Influência de herbicidas na atividade fotossintética de genótipos de cana-de-açúcar

Objetivou-se com este trabalho avaliar em campo os efeitos de herbicidas sobre a atividade fotossintética de genótipos de cana-de-açúcar. Para isso, foi realizado um experimento em blocos casualizados, em parcelas subdivididas, com quatro repetições. Nas parcelas principais alocaram-se os herbicidas ametryn (2.000 g ha-1), trifloxysulfuron-sodium (22,5 g ha ¹), a mistura de ametryn + trifloxysulfuron-sodium (1.463 + 37,0 g ha-1) e uma testemunha capinada. Nas subparcelas foram avaliados seis genótipos de cana-de-açúcar (RB72454, RB835486, RB855113, RB867515, RB947520 e SP80-1816). Aos 70 dias após o plantio e 15 dias após a aplicação dos herbicidas, foram realizadas as avaliações da taxa de fluxo de gases pelos estômatos (U - μmol s-1), concentração de CO2 subestomática (Ci = μmol mol-1), taxa fotossintética (A - μmol m ² s-1) e CO2 consumido (ΔC - μmol mol-1), na primeira folha da cana-de-açúcar com a lígula visível (dewlap visível). O ametryn causou danos significativos nas características fisiológicas ligadas à atividade fotossintética da cana-de-açúcar, em comparação com o trifloxysulfuron-sodium. Os genótipos de cana-de-açúcar apresentam sensibilidade diferencial aos herbicidas. Os mais suscetíveis ao ametryn foram o RB835486 e RB867515, e os mais tolerantes, o RB72454, RB855113, RB947520 e SP80-1816. Quanto às características avaliadas, não se observou diferença entre os genótipos tratados com o trifloxysulfuron-sodium e a mistura de ametryn + trifloxysulfuron-sodium.

Photorespiration and photoprotection of grapevine (Vitis vinifera L. cv. Cabernet Sauvignon) under water stress

In order to investigate the photoprotective function of photorespiration in grapevine under water stress, potted grapevines (Vitis vinifera L. cv. Cabernet Sauvignon) were randomly divided into three uniform groups for well-watered [watered every morning to keep the relative water content (RWC) of soil over 70 %], water-stress adapted (drought-adapted at 30 % relative soil water content for 30 days), and water stress without adaptation treatment (water-stressed to 30 % relative soil water content for 3 days). Net assimilation rate (A N), stomatal conductance (g s), substomatal CO2 concentration (C i), transpiration rate (E), actual photochemical efficiency of PSII (ΦPSII), and maximum photochemical efficiency of PSII (Fv/Fm) were recorded by combining measurements of gas exchange and chlorophyll fluorescence. Gross photorespiration (Pr), photosynthetic electron partitioning (JC/JT), photochemical quenching coefficient (qP), and non-photochemical quenching (NPQ) were also calculated. The ratio of net assimilation rate to transpiration rate (A N/E) was used as an indicator of water use efficiency (WUE). A N, apparent Pr, ΦPSII, Fv/Fm, qp, and g s decreased, NPQ increased, and gross Pr sustained at a high level under water stress. This suggests that both photorespiration and energy dissipation play important roles in protecting photosynthetic apparatus against photoinhibition. C i in water-stressed plants without adaptation treatment increased, which indicates the leaves suffered a non-stomatal limitation, while the water-stress adaped plants only suffered a stomatal limitation indicated by low C i.

Mesophyll conductance to CO2 transport estimated by two independent methods: effect of variable CO2 concentration and abscisic acid

Mesophyll conductance (g(m)) and stomatal conductance (g(s)) are two crucial components of the diffusive limitation of photosynthesis. Variation of g(m) in response to CO(2) concentration was evaluated by using two independent methods based on measurements of variable electron transport rate (J) and instantaneous carbon isotope discrimination, respectively. Both methods of g(m) estimation showed a very similar shape of the g(m)/C(i) relationship, with an initial increase at low substomatal CO(2) concentrations (C(i)), a peak at 180-200 micromol mol(-1) C(i), and a subsequent decrease at higher C(i). A good correlation was observed between values of g(m) estimated from the two methods, except when C(i) <200 micromol mol(-1), suggesting that the initial increase of g(m) at low C(i) was probably due to unreliable estimates over that range of C(i). Plants were also treated with abscisic acid (ABA), which induced a reduction in g(s) without significantly affecting the rate of photosynthesis, g(m) or the photosynthetic capacity. The present results confirm, using two independent methods, that g(m) is strongly sensitive to C(i), and that the relationship between g(s) and g(m) is not conservative, differing between control and ABA-treated plants.

Silicon supply in soilless cultivations of zucchini alleviates stress induced by salinity and powdery mildew infections

In the present study, the hypothesis was tested as to whether silicon supplied via the nutrient solution is capable of enhancing the tolerance of hydroponically grown zucchini squash ( Cucurbita pepo L. cv. ‘Rival’) to salinity and powdery mildew infections. Two experiments were conducted involving a low (2.2 dS m −1, 0.8 mM NaCl) and a high salinity level (6.2 dS m −1, 35 mM NaCl) in combination with a low (0.1 mM) and a high (1.0 mM) Si level in the nutrient solution supplied to the crop. The exposure of the plants to high external salinity restricted significantly the vegetative growth as well as the fruit yield of zucchini due to a reduction of both the number of fruits per plant and the mean fruit weight. However, the inclusion of 1 mM of Si in the salinized nutrient solution mitigated the salinity-associated suppression of both growth and yield. Part of the growth and fruit yield suppression at high salinity was due to restriction of net photosynthesis. The stomatal conductance was also restricted by salinity, whereas the substomatal CO 2 concentration was not affected by the NaCl or Si treatments. The supply of 1 mM of Si via the nutrient solution mitigated the inhibitory effect of salinity on net photosynthesis and this effect was associated with lower Na and Cl translocation to the epigeous plant tissues. Furthermore, the supply of Si via the nutrient solution suppressed appreciably the expansion of a powdery mildew ( Podosphaera xanthii) infection in the leaves at both salinity levels. These results indicate that the supply of at least 1 mM of Si via the nutrient solution is capable of enhancing both tolerance to salinity and resistance to powdery mildew in soilless cultivations of zucchini squash.

Effect of cadmium on photosynthesis, nutrition and growth of mungbean

Contamination of soils with cadmium is a major threat to ecosystems. Root uptake of cadmium from contaminated soils induces physiological changes such as a decrease in plant growth. Plant species and varieties show differential physiological mechanisms of cadmium tolerance. Here, we studied the effect of cadmium chloride on leaf chlorosis, gas exchange attributes and some essential nutrients in the shoots of selected tolerant and sensitive mungbean (Vigna radiata) varieties at the seedling, vegetative and reproductive growth stages. Our results show that elevated concentrations of cadmium led to accumulation of cadmium in the shoot and roots, intervein chlorosis of leaves and loss of pigments. Tolerant mungbean showed steady-state contents of potassium, magnesium, manganese and iron, and photosynthetic pigments at all growth stages. A decrease in the net photosynthesis, increase in substomatal CO2 level and a decline in the ratio of net photosynthesis and substomatal CO2 level revealed that cadmium prevented CO2 fixation by Rubisco. Correlations of shoot cadmium concentration and chlorosis with its nutrient and pigment content, although negative in both varieties, were closer in the tolerant but absent, or weaker if present, in the sensitive mungbean. Most nutrients had close association with the content of photosynthetic pigments of tolerant mungbean, which indicated their involvement in maintaining steady levels of pigments. This finding indicates the involvement of nutrients and pigments in cadmium tolerance. In conclusion, cadmium tolerance in mungbean was attributed to low cadmium uptake and its accumulation in the shoot, leaf chlorosis, improved pigment, nutrient levels and carboxylation efficiency of Rubisco throughout the mungbean phenology. Based on these findings the tolerant mungbean can be grown in moderately cadmium-contaminated soils.

Effect of chromium species on phytochemical and physiological parameters in Datura innoxia

In soil, chromium can be found in two main valence states: hexavalent Cr(VI) and trivalent Cr(III). In this study, we investigated the impact of Cr on photosynthetic gas exchange, photosystem II (PSII) activity, Cr translocation and accumulation, proline content and alkaloids production, i.e. scopolamine and hyoscyamine, in Datura innoxia. Cr uptake was influenced by its oxidation state and its concentration in growth medium. The plant roots were determined as being the main organ of Cr accumulation. Cr(VI) was more toxic than Cr(III) as indicated by reduction in plant biomass and net photosynthesis. The stomatal conductance showed a similar trend to that of photosynthetic capacity. Cr(III) and Cr(VI) had a different impact on substomatal CO 2 concentration then Cr toxicity was related to its oxidation states. In plants stressed with a Cr(VI) excess, a down regulation of PSII activity was observed with an impairment of photochemical activity. Indeed, the maximum quantum yield of PSII ( F v/ F m), the quantum yield of PSII (ΦPSII) and the efficiency of excitation capture by open centers ( F v ′ / F m ′ ) decreased. Cr(III) had little effects on PSII primary photochemistry, whatever its form induces an increase of scopolamine content without changes in hyoscyamine content in leaves of D. innoxia. These results provide that chromium contamination can change the secondary metabolites composition of leaves, thereby, impacting the quality, safety and efficacy of natural plant products synthesized by D. innoxia plants.

Photosynthetic Responses to Sink–Source Manipulation in Five Peach Cultivars Varying in Maturity Date

Five peach cultivars [Prunus persica (L.) Batch] with different maturity dates were subjected to sink–source manipulation by girdling to isolate 1-year-old fruit-bearing shoots. Four treatments were performed: fruit were removed (−fruit); one fruit (+1 fruit) and two fruit (+2 fruit) were kept inside two girdling cuts; and two fruit were kept outside two girdling cuts (−fruit*). Photosynthetic responses for the five cultivars were similar and did not show genotypic differences. Generally, net photosynthetic rate (Pn), stomatal conductance (g s), and transpiration rate (E) were higher, and leaf temperature (Tl) was lower in +2 fruit than in +1 fruit, followed by −fruit and −fruit* which were not different. The results also indicated that water outflow from fruit into leaves did not influence photosynthesis, and lower photosynthesis in −fruit treatment was not due to water status of source leaves influenced by removing fruit. Pn tended to increase with Tl until Tl reached a critical level. Beyond the critical temperature level, Pn generally decreased. The critical Tl was roughly identified as 34–37 °C for the five cultivars. Both higher and lower substomatal CO2 (Ci) levels occurred in −fruit and −fruit* treatments than in +1 fruit and +2 fruit treatments, indicating that decreased Pn could be due to both nonstomatal and stomatal limitations. Further analysis of the relationship between Ci and photosynthetically active radiation (PAR) showed that nonstomatal limitation under low sink demand took place mostly under high PAR. Thus, high light intensity, combined with Tl may play an important role in leaf photosynthetic regulation.

Artificially-induced leaf nitrate accumulation affects photosynthesis in micropropagated apple plants with different water supply

SummaryOne-year-old micropropagated ‘Gala’ apple (Malus domestica Borkh.) plants with split root systems were supplied with tungsten (Na2WO4), an inhibitor of nitrate reductase activity, and NaNO3, separately, or in combination. The chemicals were supplied either through the xylem (40 ml 0.3 mM Na2WO4 or 3 mM NaNO3), or as foliar sprays (30 mM NaNO3 and 20 mM Na2WO4). When applied separately, neither increased the NO3– content of leaves, although Na2WO4 inhibited foliar nitrate reductase activity completely, and NaNO3 supplied additional nitrate to the leaves. However, when both were applied together, either through the xylem or as sprays, NO3– accumulated in the leaves of well-irrigated plants, as well as in those subjected to half- or whole-root drought stress. Such artificially induced NO3– accumulation in leaves significantly decreased the net photosynthetic rate, stomatal conductance, and rate of transpiration at approx. 12.00 h following the application, compared to controls supplied with deionised water. Net photosynthesis, stomatal conductance, and transpiration rate were negatively correlated with the foliar concentration of NO3–. None of the treatments influenced leaf temperatures or sub-stomatal CO2 concentrations, indicating that the decrease in net photosynthesis was not due to stomatal limitation. It is concluded that low foliar NO3– concentrations are a characteristic of the species, and important for efficient photosynthesis in apple.

Growth of Avocado Plants Under Saline Conditions

ABSTRACT Avocado (Persea americana Mill.) is an important multipurpose tree crop. A study was conducted to investigate the growth and gas exchange characteristics of avocado seedlings growing under different salinity levels. Plants were grown in 4.5 liter plastic pots containing soil were subjected to 0 (control), 15, 30, 45 and 60 mM NaCl salinity treatments. Growth, net photosynthetic rate (PN), stomatal conductance (gs), transpiration rate (E), water use efficiency (WUE) and chlorophyll (chl) concentration decreased in response to increasing salt concentration. Substomatal CO2 concentration (Ci) and chloride content increased as salt concentration increased. The findings from this study demonstrate that salinity inhibits growth and gas exchange of avocados.

Safflower yield, chlorophyll content, photosynthesis, and water use efficiency response to nitrogen fertilization under rainfed conditions

Safflower ( Carthamus tinctorius L.) is a deep-rooted crop which can tolerate water stress and can be grown in rotation with other crop species. Nitrogen is very important for the growth and yield of safflower, however, the effect of N level on chlorophyll content, assimilation rate, transpiration rate, stomatal conductance, substomatal CO 2 concentration, and water use efficiency (WUE) have not been determined. A 2-year field study was conducted with the objective to determine the effect of N fertilization on yield, yield components, chlorophyll content, photosynthetic characteristics, and WUE of safflower grown under rainfed conditions. Three rates of N were used (0, 100, and 200 kg N ha −1) and two hybrids (CW9048 and CW9050). N fertilization increased seed yield by an average of 19%, the seed weight per plant by 60%, the seed weight per head by 18%, the number of heads per plant by 32%, and the number of seeds per plant by 41% compared with the control. N level also affected chlorophyll content, N concentration at anthesis, protein, and oil yield. N application increased assimilation rate by an average of 51%, stomatal conductance of water vapour by an average of 27%, and WUE by an average of 60% over the 2 years of the study when compared to the control. The present study indicates that N fertilization can affect yield, yield components, photosynthetic efficiency, and physiology of safflower under rainfed conditions.