Responses of dominant desert species <Emphasis Type="Italic">Artemisia ordosica</Emphasis> and <Emphasis Type="Italic">Salix psammophila</Emphasis> to water stress

Morphology, biomass accumulation and allocation, gas exchange, and chlorophyll fluorescence were compared for one-year-old seedlings of Salix psammophila and Artemisia ordosica, two dominant desert species, in response to two water supplies (equivalent to 315.0 mm for present precipitation in growing season and to 157.5 mm for future decreasing precipitation) during 105 d. For both species, photochemical efficiency of photosystem 2 (F_v/F_m), net photosynthetic rate, transpiration rate, stomatal conductance, biomass accumulation in different organs, tree height, number of leaves, and leaf area were reduced in response to the decrease in water supply. For both species, instantaneous water use efficiency was not affected by the water deficit. However, diurnal patterns of gas exchange and biomass allocation were affected in different ways for the two species, with notably a decrease in specific leaf area and an increase in root : shoot ratio for S. psammophila only. Overall, S. psammophila was more responsive to the decreasing precipitation than A. ordosica.     

Gas exchange characteristics and water relations in two cultivars of <Emphasis Type="Italic">Hibiscus esculentus</Emphasis> under waterlogging

Thirty-day-old plants of two okra cultivars, Sabzpari and Chinese-red, were subjected for 30 d to normal watering or continuous flooding. Continuous flooding did not cause any adverse effect on shoot fresh and dry biomass. Leaf water potential and pressure potential of both cultivars increased significantly due to waterlogging, but there was a slight increase in leaf osmotic potential. Chlorophyll a and b contents decreased significantly and chlorophyll a/b ratio increased. Waterlogging caused a significant reduction in net photosynthetic rate, water use efficiency and intrinsic water use efficiency, but stomatal conductance and intercellular CO₂/ambient CO₂ ratio remained unchanged.     

Drought tolerance in the Mediterranean species <Emphasis Type="Italic">Quercus coccifera,Quercus ilex,Pinus halepensis</Emphasis>, and <Emphasis Type="Italic">Juniperus phoenicea</Emphasis>

We investigated the strategies of four co-occurring evergreen woody species Quercus ilex, Quercus coccifera, Pinus halepensis, and Juniperus phoenicea to cope with Mediterranean field conditions. For that purpose, stem water potential, gas exchange, chlorophyll (Chl) fluorescence, and Chl and carotenoid (Car) contents were examined. We recognized two stress periods along the year, winter with low precipitation and low temperatures that led to chronic photoinhibition, and summer, when drought coincided with high radiation, leading to an increase of dynamic photoinhibition and a decrease of pigment content. Summer photoprotection was related to non-photochemical energy dissipation, electron flow to alternative sinks other than photosynthesis, decrease of Chl content, and proportional increase of Car content. Water potential of trees with deep vertical roots (Q. coccifera, Q. ilex, and P. halepensis) mainly depended on precipitation, whereas water potential of trees with shallow roots (J. phoenicea) depended not only on precipitation but also on ambient temperature.     

The impact of <Emphasis Type="Italic">trans</Emphasis>-zeatin <Emphasis Type="Italic">O</Emphasis>-glucosyltransferase gene over-expression in tobacco on pigment content and gas exchange

The responses of tobacco plants over-expressing trans-zeatin O-glucosyltransferase gene under constitutive or senescence-inducible promoter (35S:ZOG1 and SAG12:ZOG1) and of wild type (WT) plants to water stress and subsequent rehydration were compared. In plants sufficiently supplied with water, both transgenics have higher net photosynthetic rate (P_N) in upper and middle leaves and higher stomatal conductance (g_s) in middle leaves than WT. Water use efficiency (WUE = P_N/E) was higher in both transgenics than in WT. During prolonged water stress, both P_N and E declined to a similar extent in both transgenics and WT plants. However, 7 d after rehydration P_N in SAG:ZOG (upper and middle leaves) and 35S:ZOG (upper leaves) was higher than that in WT plants. Increased content of endogenous CKs in 35S:ZOG plants did not prevent their response to ABA application and the results obtained did not support concept of CK antagonism of ABA-induced stomatal closure. The chlorophyll (Chl) a+b content was mostly higher in both transgenics than in WT. During water stress and subsequent rehydration it remained unchanged in upper leaves, decreased slightly in middle leaves only of WT, while rapidly in lower leaves. Total degradation of Chl, carotenoids and xanthophyll cycle pigments (XCP) was found under severe water stress in lower leaves. Carotenoid and XCP contents in middle and upper leaves mostly increased during development of water stress and decreased after rehydration. While β-carotene content was mostly higher in WT, neoxanthin content was higher in transgenics especially in 35S:ZOG under severe stress and after rehydration. The higher content of XCP and degree of their deepoxidation were usually found in upper and middle leaves than in lower leaves with exception of SAG:ZOG plants during mild water stress.     

Effects of silicon on photosynthesis,water relations and nutrient uptake of <Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> under NaCl stress

A greenhouse experiment was conducted to investigate the effects of silicon application on Phaseolus vulgaris L. under two levels of salt stress (30 and 60 mM NaCl in the irrigation water). Salinity significantly reduced growth, stomatal conductance and net photosynthetic rate, and increased Na⁺ and Cl⁻ content mainly in roots. Silicon application enhanced growth of salt stressed plants, significantly reduced Na⁺ content especially in leaves and counterbalanced the effects of NaCl on gas exchange; the effect was more evident at 30 mM NaCl. Cl⁻ content in shoots and roots was not significantly modified by silicon application; the drop in K⁺ content caused by salinity was partially counterbalanced by silicon, especially in roots.     

Photosynthetic characteristics of <Emphasis Type="Italic">Hordeum,Triticum, Rumex</Emphasis>, and <Emphasis Type="Italic">Trifolium</Emphasis> species at contrasting altitudes

Photosynthetic characteristics were compared between plants of low altitude (LA) grown at LA (Palampur; 1 300 m) and at high altitude, HA (Kibber; 4 200 m), and plants naturally occurring at different altitudes (Palampur, 1 300 m; Palchan, 2 250 m; and Marhi, 3 250 m). Net photosynthetic rate (P _N) was not significantly different between altitudes. However, the slopes of the curve relating P _N to intercellular CO₂ concentration (C _i) were higher in plants at Palchan, Marhi, and Kibber compared to those at Palampur, indicating that plants had higher efficiency of carbon uptake (the initial slope of P _N/C _i curve is an indication) at HA. They had also higher stomatal conductance (g _s), transpiration rate, and lower water use efficiency at HA. g _s was insensitive to photosynthetic photon flux density (PPFD) for plants naturally occurring at Palampur, Palchan, and Marhi, whereas plants from LA grown at Palampur and Kibber responded linearly to increasing PPFD. Insensitivity of g _s to PPFD could be one of the adaptive features allowing wider altitudinal distribution of the plants.This research is supported by the Department of Biotechnology (DBT), Government of India vide grant number BT/PR/502/AGR/08/39/966-VI.     

Photosynthesis,transpiration, and water use efficiency of <Emphasis Type="Italic">Leymus dasystachys</Emphasis> on the Hunshandake desert

Net photosynthetic rate (P _N), transpiration rate (E), and stomatal conductance (g _s) declined from upper leaves to the lower ones during dry and rainy seasons, indicating that long-term carbon budget should take into account P _N variations for different leaf types. Relatively greater P _N in the dry season suggested that this species is more able to maintain higher P _N under drought, but the relatively higher E in the dry season might reduce water use efficiency (P _N/E) for the species. Significant correlations between P _N and g _s indicated that g _s may be the critical factor for P _N variability in the desert region.     

Comparative photosynthesis characteristics of <Emphasis Type="Italic">Calycanthus chinensis</Emphasis> and <Emphasis Type="Italic">Chimonanthus praecox</Emphasis>

Calycanthus chinensis is an endangered plant of the national second-grade protection of China restricted in a small area in Zhejiang Province. We studied parameters of photosynthesis, chlorophyll (Chl) contents, and Chl fluorescence (minimum fluorescence, F₀, maximum fluorescence, F_m, variable fluorescence, F_v, and F_v/F_m) of C. chinensis and Chimonanthus praecox. C. chinensis had lower compensation irradiance but higher saturation irradiance than C. praecox. Hence C. chinensis has more advantage in obtaining and utilizing photon energy and higher Chl content, and is more adaptive to higher temperature and propitious to thermal dissipation than C. praecox. In addition, C. chinensis produces abundant, well-preserved seed with a higher germination rate and a wider adaptability to temperature than C. praecox. Thus C. chinensis is prone to survival and viability, and gets rid of the endangered plant species of the national second-grade protection of China.     

Photosynthetic water use efficiency in tree crowns of <Emphasis Type="Italic">Shorea beccariana</Emphasis> and <Emphasis Type="Italic">Dryobalanops aromatica</Emphasis> in a tropical rain forest in Sarawak,East Malaysia

Photosynthetic water use efficiency (PWUE), stomatal conductance (g _s), and water potential were measured at two different positions in the tree crown of two emergent tropical tree species (Shorea beccariana Burck, Dryobalanops aromatica Gaertn. f.). The trees were about 50 m high, in a tropical rain forest in Sarawak, East Malaysia. In both species, g _s at the upper crown position at midday was lower than at the lower crown position, even though both positions were exposed to full sunlight; the difference was greater in S. beccariana. Hydraulic limitation occurs in the upper crown position in both species. A midday depression was observed in the photon saturated photosynthetic rate in both species, especially at the upper crown. However, PWUE was markedly higher in the upper crown than the lower crown at midday, even though no morphological adjustment was observed in the leaves; this difference was greater in S. beccariana.     

Phosphomannose-isomerase (<Emphasis Type="Italic">pmi</Emphasis>) gene as a selectable marker for <Emphasis Type="Italic">Agrobacterium</Emphasis>-mediated transformation of rapeseed

Nodal segments (4 ± 1 mm long) of Hibiscus moscheutos (hardy hibiscus) were excised from in vitro proliferating microshoots and utilized to evaluate initial factors involved in bulk alginate encapsulation. The factors evaluated were; storage vessel type, volume and multiple rinse effects of CaCl₂ solutions, and sodium alginate concentrations (2.5, 2.75, 3.0 or 3.25%) for bulk alginate encapsulation. Results indicate that vessels utilized for bulk alginate encapsulation should have a lower base area (L × W) to height ratio to reduce the amount of alginate matrix shrinkage resulting in exposure of nodal segments. Increased volumes and multiple 50 mM CaCl₂ solution rinses did not have an effect on alginate solidification. Shoot length, root number, and root length significantly decreased in a linear manner from nodal explants stored for 4 weeks with increasing concentrations of sodium alginate. This research suggests an innovative technique for alginate encapsulation of H. moscheutos utilizing bulk methods as an alternative to single bead alginate encapsulation.     

Changes in leaf photosynthesis of transgenic rice with silenced <Emphasis Type="Italic">OsBP-73</Emphasis> gene

In comparison with its wild type (WT), the transgenic (TG) rice with silenced OsBP-73 gene had significantly lower plant height, grain number per panicle, and leaf net photosynthetic rate (P _N). Also, the TG rice showed significantly lower chlorophyll (Chl), ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO), RuBPCO activase, and RuBP contents, photosystem 2 (PS2) photochemical efficiency (F_v/F_m and ΔF/F_m′), apparent quantum yield of carbon assimilation (Φ_c), carboxylation efficiency (CE), photosynthetic electron transport and photophosphorylation rates as well as sucrose phosphate synthase activity, but higher intercellular CO₂ concentration, sucrose, fructose, and glycerate 3-phosphate contents, and non-photochemical quenching of Chl fluorescence (NPQ). Thus the decreased P _N in the TG rice leaves is related to both RuBP carboxylation and RuBP regeneration limitations, and the latter is a predominant limitation to photosynthesis.     

Effects of soil and air drought on growth,plant water status and leaf gas exchange in three Mediterranean cedar species: <Emphasis Type="Italic">Cedrus atlantica</Emphasis>, <Emphasis Type="Italic">C. brevifolia</Emphasis> and <Emphasis Type="Italic">C. libani</Emphasis>

Three- and four-year-old potted, greenhouse-grown cedar seedlings were subjected to two different watering regimes: half received full water supply and the other half was submitted to moderate drought (50% of the full water supply). Height growth was the greatest for C. atlantica and the most-limited for C. brevifolia in the well-watered set. However, in the dry set, height growth was less affected by drought conditions for C. brevifolia than for C. atlantica. Cedrus libani gave intermediate results for both watering regimes. Moderate drought provoked a decrease in osmotic potential at full leaf turgor and a long-lasting osmotic adjustment. When irrigation was withheld completely to induce severe soil drying, gas exchange decreased and then stopped at predawn water potentials of −3.0 MPa for C. brevifolia, between −2.6 and −2.8 MPa for C. libani, and at −2.4 MPa for C. atlantica, irrespective of watering regime. For all species, the dry set showed lower net photosynthesis (A) and stomatal conductance (g _s) than the plants in the well-watered set. A and g _s responded to variations in atmospheric water-vapour pressure deficit (VPD). As VPD increased, A and g _s decreased, and this trend was proportionate to initial values at low VPD, but remained independent of previous watering treatments, plant water status or species. To conclude, C. brevifolia appears to be a species with limited growth potential but strong soil drought tolerance whereas C. atlantica has strong growth potential when an adequate water supply is available but is more sensitive to soil drought. C. libani shows an intermediate behaviour for growth and drought tolerance.     

Midday depression of photosynthesis in <Emphasis Type="Italic">Enkleia malaccensis</Emphasis>, a woody climber in a tropical rainforest

We measured the diurnal changes in net photosynthetic rate (P _N) and stomatal conductance (g _s) of the leaves of a liana, Enkleia malaccensis Griff. (Thymelaeaceae), at the canopy level in the lowland tropical rainforest at Pasoh, Peninsular Malaysia. The measurements were made from a canopy walkway system, 30 m from the ground for 3 d in March 2003. P _N increased with increasing photosynthetically active radiation (PAR) before noon, though P _N was not enhanced by the strong radiation hit in the afternoon. Plotting g _s at saturating PAR (>0.5 mmol m⁻² s⁻¹) against the vapour pressure deficit (VPD) failed to reveal a significant correlation between VPD and g _s, and g _s became very low at VPD >2.5 kPa. The relationship between P _N and g _s was fitted on the same regression line irrespective of measuring day, indicating that this relationship was not influenced by either VPD or leaf temperature (T _L). Therefore, in the liana E. malaccensis, an increase in VPD leads to partial stomatal closure and, subsequently, reductions in P _N and the midday depression of P _N of this plant.     

Evaluation of physiological traits for improving drought tolerance in faba bean (<Emphasis Type="Italic">Vicia faba</Emphasis> L.)

Among grain legumes, faba bean is becoming increasingly popular in European agriculture due to recent economic and environmental interests. Faba bean can be a highly productive crop, but it is sensitive to drought stress and yields can vary considerably from season to season. Understanding the physiological basis of drought tolerance would indicate traits that can be used as indirect selection criteria for the development of cultivars adapted to drought conditions. To assess genotypic variation in physiological traits associated with drought tolerance in faba bean and to determine relationships among these attributes, two pot experiments were established in a growth chamber using genetic materials that had previously been screened for drought response in the field. Nine inbred lines of diverse genetic backgrounds were tested under adequate water supply and limited water conditions. The genotypes showed substantial variation in shoot dry matter, water use, stomatal conductance, leaf temperature, transpiration efficiency, carbon isotope discrimination (Δ¹³C), relative water content (RWC) and osmotic potential, determined at pre-flowering vegetative stage. Moisture deficits decreased water usage and consequently shoot dry matter production. RWC, osmotic potential, stomatal conductance and Δ¹³C were lower, whereas leaf temperature and transpiration efficiency were higher in stressed plants, probably due to restricted transpirational cooling induced by stomatal closure. Furthermore, differences in stomatal conductance, leaf temperature, Δ¹³C and transpiration efficiency characterized genotypes that were physiologically more adapted to water deficit conditions. Correlation analysis also showed relatively strong relationships among these variables under well watered conditions. The drought tolerant genotypes, ILB-938/2 and Melodie showed lower stomatal conductance associated with warmer leaves, whereas higher stomatal conductance and cooler leaves were observed in sensitive lines (332/2/91/015/1 and Aurora/1). The lower value of Δ¹³C coupled with higher transpiration efficiency in ILB-938/2, relative to sensitive lines (Aurora/1 and Condor/3), is indeed a desirable characteristic for water-limited environments. Finally, the results showed that stomatal conductance, leaf temperature and Δ¹³C are promising physiological indicators for drought tolerance in faba bean. These variables could be measured in pot-grown plants at adequate water supply and may serve as indirect selection criteria to pre-screen genotypes.     

Acclimation of photosynthesis to temperature in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> and <Emphasis Type="Italic">Brassica oleracea</Emphasis>

Plants differ in how much the response of net photosynthetic rate (P _N) to temperature (T) changes with the T during leaf development, and also in the biochemical basis of such changes in response. The amount of photosynthetic acclimation to T and the components of the photosynthetic system involved were compared in Arabidopsis thaliana and Brassica oleracea to determine how well A. thaliana might serve as a model organism to study the process of photosynthetic acclimation to T. Responses of single-leaf gas exchange and chlorophyll fluorescence to CO₂ concentration measured over the range of 10–35 °C for both species grown at 15, 21, and 27 °C were used to determine the T dependencies of maximum rates of carboxylation (V_Cmax), photosynthetic electron transport (J_max), triose phosphate utilization rate (TPU), and mesophyll conductance to carbon dioxide (g’_m). In A. thaliana, the optimum T of P _N at air concentrations of CO₂ was unaffected by this range of growth T, and the T dependencies of V_Cmax, J_max, and g’_m were also unaffected by growth T. There was no evidence of TPU limitation of P _N in this species over the range of measurement conditions. In contrast, the optimum T of P _N increased with growth T in B. oleracea, and the T dependencies of V_Cmax, J_max, and g’_m, as well as the T at which TPU limited P _N all varied significantly with growth T. Thus B. oleracea had much a larger capacity to acclimate photosynthetically to moderate T than did A. thaliana.     

Water-use efficiency and carbon isotope discrimination of <Emphasis Type="Italic">Acacia ampliceps</Emphasis> and <Emphasis Type="Italic">Eucalyptus camaldulensis</Emphasis> at different soil moisture regimes under semi-arid conditions

Acacia ampliceps Maslin and Eucalyptus camaldulensis Dehnh. were grown for one year in lysimeters at three soil moisture regimes: 100 % (well-watered), 75 % (medium-watered) and 50 % (low-watered) of total plant available water. Biomass yield of both species increased with increase in soil moisture. Water-use efficiency (WUE) of E. camaldulensis decreased and that of A. ampliceps increased markedly with decrease in available soil moisture. A. ampliceps showed 4 – 5 times more biomass yield than E. camaldulensis grown at similar soil moisture. A. ampliceps showed almost 5, 9 and 12 times higher WUE than E. camaldulensis under low-, medium- and well-watered treatments, respectively. Significant negative correlation of ¹³C with WUE (r = –0.99) was observed in A. ampliceps. In contrast, ¹³C of E. camaldulensis showed a significant positive correlation with WUE (r = 0.82).     

<Emphasis Type="Italic">Ty</Emphasis>1<Emphasis Type="Italic">/copia</Emphasis>- and <Emphasis Type="Italic">Ty</Emphasis>3<Emphasis Type="Italic">/gypsy</Emphasis>-like DNA sequences in <Emphasis Type="Italic">Helianthus </Emphasis>species

Two repeated DNA sequences isolated from a partial genomic DNA library of Helianthus annuus, p HaS13 and p HaS211, were shown to represent portions of the int gene of a Ty3 /gypsy retroelement and of the RNase-Hgene of a Ty1 /copia retroelement, respectively. Southern blotting patterns obtained by hybridizing the two probes to BglII- or DraI-digested genomic DNA from different Helianthus species showed p HaS13 and p HaS211 were parts of dispersed repeats at least 8 and 7 kb in length, respectively, that were conserved in all species studied. Comparable hybridization patterns were obtained in all species with p HaS13. By contrast, the patterns obtained by hybridizing p HaS211 clearly differentiated annual species from perennials. The frequencies of p HaS13- and p HaS211-related sequences in different species were 4.3x10(4)-1.3x10(5) copies and 9.9x10(2)-8.1x10(3) copies per picogram of DNA, respectively. The frequency of p HaS13-related sequences varied widely within annual species, while no significant difference was observed among perennial species. Conversely, the frequency variation of p HaS211-related sequences was as large within annual species as within perennials. Sequences of both families were found to be dispersed along the length of all chromosomes in all species studied. However, Ty3 /gypsy-like sequences were localized preferentially at the centromeric regions, whereas Ty1/ copia-like sequences were less represented or absent around the centromeres and plentiful at the chromosome ends. These findings suggest that the two sequence families played a role in Helianthusgenome evolution and species divergence, evolved independently in the same genomic backgrounds and in annual or perennial species, and acquired different possible functions in the host genomes.     

Seasonal water-use efficiency and chlorophyll fluorescence response in alpha grass (<Emphasis Type="Italic">Stipa tenacissima</Emphasis> L.) is affected by tussock size

Abstact  Twelve randomly chosen Stipa tenacissima L. individuals were grouped into three tussock size classes, small (ST), medium (MT), and large (LT) with 5.6±0.8, 34.1±4.2, and 631.9±85.8 g of dry green foliar matter, respectively, in three plots with different S. tenacissima cover. Instantaneous (WUE_i) and long-term (WUE_l) water-use efficiencies were measured in two seasons of contrasting volumetric soil water content (early winter 21.0±0.8 % and summer 5.8±0.3 %). Maximum photochemical efficiency of photosystem 2 and stomatal conductance in summer assessed the extent of water and irradiance stress in tussocks of different size. WUE_i was lower in MT and ST “water spender” strategies than in LT during the high water-availability season. In summer net photosynthetic rate and WUE_i were higher and photoinhibition was lower in LT than in MT and ST. Significant spatial variability was found in WUE_i. Water uptake was competitive in stands with denser alpha grass and more water availability in summer, reducing their WUE_i. However, WUE_l showed a rising tendency when water became scarce. Thus it is important to explicitly account for plant size in ecophysiological studies, which must be combined with demographic information when estimating functional processes at stand level in sequential scaling procedures.     

Diurnal and seasonal trends in photosynthetic performance of <Emphasis Type="Italic">Dalbergia sissoo</Emphasis> Roxb. and <Emphasis Type="Italic">Hardwickia binata</Emphasis> Roxb. from a semi-arid ecosystem

Diurnal and seasonal trends in net photosynthetic rate (P _N), stomatal conductance (g), transpiration rate (E), vapour pressure deficit, temperature, photosynthetic photon flux density, and water use efficiency (WUE) were compared in a two-year-old Dalbergia sissoo and Hardwickia binata plantation. Mean daily maximum P _N in D. sissoo ranged from 21.40±2.60 μmol m⁻² s⁻¹ in rainy season I to 13.21±2.64 μmol m⁻² s⁻¹ in summer whereas in H. binata it was 20.04±1.20 μmol m⁻² s⁻¹ in summer and 13.64±0.16 μmol m⁻² s⁻¹ in winter. There was a linear relationship between daily maximum P _N and g _s in D. sissoo but there was no strong linear relationship between P _N and g _s in H. binata. In D. sissoo, the reduction in g _s led to a reduction in both P _N and E enabling the maintenance of WUE during dry season thereby managing unfavourable environmental conditions efficiently whereas in H. binata, an increase in g _s causes an increase of P _N and E with a significant moderate WUE.     

Biomass production,photosynthesis, and leaf water relations of <Emphasis Type="Italic">Spartina alterniflora</Emphasis> under moderate water stress

The perennial smooth cordgrass, Spartina alterniflora, has been successfully introduced in salty ecosystems for revegetation or agricultural use. However, it remains unclear whether it can be introduced in arid ecosystems. The aim of this study was to investigate the physiological response of this species to water deficiency in a climate-controlled greenhouse. The experiment consisted of two levels of irrigation modes, 100 and 50% field capacities (FC). Although growth, photosynthesis, and stomatal conductance of plants with 50% FC were reduced at 90 days from the start of the experiment, all of the plants survived. The water-stressed plants exhibited osmotic adjustment and an increase in the maximum elastic modulus that is assumed to be effective to enhance the driving force for water extraction from the soil with small leaf water loss. An increase in the water use efficiency was also found in the water-stressed plants, which could contribute to the maintenance of leaf water status under drought conditions. It can be concluded that S. alterniflora has the capacity to maintain leaf water status and thus survive in arid environment.