Differences In Plant Response Research Articles

Generalist and specialist lepidopteran larvae elicit different transcriptional responses in Nicotiana attenuata, which correlate with larval FAC profiles

AbstractUnlike generalist herbivores, specialists are believed to share a history of evolutionary interactions with their host plants. We determine whether a specialist lepidopteran species alters plant metabolism differently from two generalist species despite similarities in feeding mode and larval elicitors. With a cDNA microarray enriched in defence‐related genes, we compared the transcriptional responses elicited in the native tobacco Nicotiana attenuata by the oligophagous larvae of Manduca sexta and the polyphagous larvae of Heliothis virescens and Spodoptera exigua, which are all members of N. attenuata's natural herbivore community. We found the differences in plant responses to be correlated with the profile of larval elicitors [fatty acid–amino acid conjugates (FAC)] and discuss how variation in FAC composition may shape the interaction between generalist or specialist lepidopteran larvae and plants.

Physiological Responses of Cotton to Two‐Spotted Spider Mite Damage

Spider mites are important pests of cotton (Gossypium hirsutum L.), capable of dramatically affecting growth, yield, and fiber quality. This study investigated the physiological response of cotton leaves to feeding damage by the two‐spotted spider mite (Tetranychus urticae Koch) in two experiments in the field over two seasons. Mite colonies initially established and developed in the basal areas of leaves, where the leaf blade joins the petiole. These infestations caused rapid and severe reductions in photosynthetic rate, stomatal conductance, transpiration, transpiration efficiency (TE), and chlorophyll content. In basal areas, a peak of 68 adult female mites per leaf caused photosynthesis to decline to zero, while undamaged leaves averaged 33 μmol CO2 m−2 s−1 Differences in plant responses to mites occurred between seasons despite similar infestation levels, possibly related to later timing of infestation and harder leaves in the second season. Compensation for mite damage was not apparent at the leaf level, since photosynthesis was reduced on undamaged portions of damaged leaves. The sequence of mite damage events on the undamaged leaf portions was determined to be: first, reduction of stomatal conductance; second, reduction of transpiration; third, reduction of photosynthetic rate; and finally, reduction of transpiration efficiency. At the leaf level, the overall effect of mite damage on photosynthesis was greater than expected because undamaged areas surrounding those visibly damaged were also affected.

Physiological Responses of Cotton to Two-Spotted Spider Mite Damage

Spider mites are important pests of cotton (Gossypium hirsutum L.), capable of dramatically affecting growth, yield, and fiber quality. This study investigated the physiological response of cotton leaves to feeding damage by the two-spotted spider mite (Tetranychus urticae Koch) in two experiments in the field over two seasons. Mite colonies initially established and developed in the basal areas of leaves, where the leaf blade joins the petiole. These infestations caused rapid and severe reductions in photosynthetic rate, stomatal conductance, transpiration, transpiration efficiency (TE), and chlorophyll content. In basal areas, a peak of 68 adult female mites per leaf caused photosynthesis to decline to zero, while undamaged leaves averaged 33 μmol CO2 m−2 s−1 Differences in plant responses to mites occurred between seasons despite similar infestation levels, possibly related to later timing of infestation and harder leaves in the second season. Compensation for mite damage was not apparent at the leaf level, since photosynthesis was reduced on undamaged portions of damaged leaves. The sequence of mite damage events on the undamaged leaf portions was determined to be: first, reduction of stomatal conductance; second, reduction of transpiration; third, reduction of photosynthetic rate; and finally, reduction of transpiration efficiency. At the leaf level, the overall effect of mite damage on photosynthesis was greater than expected because undamaged areas surrounding those visibly damaged were also affected.

Seasonal differences in plant responses to flooding and anoxia

Strategies for surviving an environmental stress in winter can differ from those that provide protection from the same stress when it occurs in summer. During the growing season, escape mechanisms from stresses tend to prevail, as periods of adversity are generally brief. In winter, adverse environmental conditions have a high probability of persisting for lengthy periods and consequenctly, survival depends on tolerance. Spring is a period of uncertainty as to whether the risk of flooding has passed, and seeds differ markedly in their ability to resume germination if interrupted by re-imposition of winter conditions. When growing plants are flooded in summer, brief periods of accelerated anaerobic metabolism can alleviate energy shortages while improved aeration tissues develop, which then remove the dangers of prolonged anaerobiosis. By contrast, overwintering species, if they are highly tolerant of prolonged anoxia, may down-regulate metabolism when flooded and thus reduce the risk of exhausting carbohydrate supplies. Ventilation of underground organs in winter is still possible but is dependent on specialized mechanisms that can provide a through flow of air from emergent stems to buried or submerged organs. The tree form also presents metabolic and morphological problems for surviving wet conditions at critical seasons.Key words : anoxia, flooding summer, winter stress, plants, crops.

The response of forest floor vegetation and tree regeneration to deer exclusion and disturbance in a riparian deciduous forest, central Japan

The response of forest floor vegetation and regeneration of major treespecies to deer exclusion in a riparian forest were studied for 3 years withtheinteractive effects of natural disturbances. At the start of this study, deerdensity had quickly increased to a fairly high level (29–31 individualskm−2) during the last decade and had severely reduced theamount of forest floor vegetation in the study area. Dwarf bamboos, which weredominant before, had almost diminished from the forest floor. During the studyperiod, aboveground biomass increased steadily but species diversity did notchange much in the exclosures. Outside the exclosures, the seedlings of alltreespecies were damaged greatly by deer browsing, especially the taller ones. Deerbrowsing had little effect on the emergence of tree seedlings, but deertrampling might have accelerated emergence indirectly by disturbing the soilsurface for some species. Differences in plant responses were also observed fordeer browsing and the presence of dwarf bamboo that strongly inhibits therecruitment of tree seedlings. The nine major species were classified intothreegroups according to the response of seedlings to deer browsing and disturbance.Group 1 consists of the species whose seedling survival is affected bybrowsing,but seldom by disturbances (Phellodendron amurense,Kalopanax pictus, Quercus crispulaandMalus toringo). Groups 2 and 3 consist of species adaptedto tree-fall disturbance (Betula spp.) and ripariandisturbance (Alnus hirsuta var.sibirica, Ulmus davidiana var.japonica, Populus maximowiczii andSalix sachalinensis), respectively, and seedling survivalof these two groups is principally affected by light conditions. The effect ofdeer browsing on seedling survival and growth was greater for Group 2 than forGroup 3.

Variability of soybean germplasm in relation to phosphorus uptake and use efficiency

Plant efficiency for phosphorus uptake and utilization may contribute to improve crop yield potential in situations of low P availability. Twenty nine soybean [Glycine max (L.) Merr.] cultivars were evaluated and classified in relation to the response to phosphorus (P) levels in nutrient solution. P uptake and use efficiency were estimated by the variables: shoot and root dry matter (DM) yield, P-concentrations and contents in plant parts and P-efficiency index (EI). The experiment was conducted in a greenhouse, during 1999, at Campinas, State of São Paulo, Brazil. The experimental design consisted of randomized complete blocks, arranged in split-plots, with three replications. The main plots were the P levels in the nutrient solution (64.5; 129; 258 and 516 mmol L-1), and the subplots were the twenty-nine soybean cultivars, grouped according days to maturity. The plants were harvested at flowering, separated in shoots and roots for dry matter determination and chemical analysis. The analyses of variance indicated differences in plant responses to P-levels and cultivars. Multivariate analysis showed high correlation among the variables shoot-DM, total-DM and shoot P-concentration and P-efficiency index (EI). Cultivars were classified in efficient-responsive (ER)-- 'IAC-1', 'IAC-2', 'IAC-4', 'IAC-5', 'IAC-6', 'IAC-9', 'Sta. Rosa' and 'UFV-1'; efficient-non-responsive (ENR) -- 'IAC-7', 'IAC-11', 'IAC-15', 'S. Carlos' and 'Cristalina'; inefficient-responsive (IR) -- 'IAC-8', 'IAC-10', 'IAC-14', 'Bossier' and 'Foscarin'; and inefficient-non-responsive (INR) -- 'IAC-12', 'IAC-13', 'IAC-16', 'IAC-17', 'IAC-18', 'IAC-19', 'IAC-20', 'IAC-22', 'Paraná', 'IAS-5' and 'BR-4'. The efficient-responsive soybean cultivars showed the highest values for shoot and total DM and EI, and the lowest shoot P-concentrations.

Greenhouse Growth of Marigolds in Three Leached Sources of Spent Mushroom Compost over a 3-Year Period

Though high electrical conductivity (EC) levels are commonly held to be the primary limiting factor for using spent mushroom compost (SMC) as a growing substrate, EC can be reduced by leaching. This allowed SMC to be successfully used for growing plants. Leaching reduced EC of the substrate solution from as high of 30 dS·m-1 (mmhos·cm-1) to 2 to 3 dS·m-1, a level acceptable for growing plants. The initial EC and container capacity determined the number of leachings and total volume of water required to lower EC of SMC substrates to acceptable levels. As the concentration of SMC was increased, a higher number of leachings or larger volume of water were required to adequately reduce EC levels. In trials spanning 2.5 years, SMC was effectively used as a substrate in the production of marigold (Tagetes patula) `Yellow Girl'. Benefits to plant growth from SMC incorporation included a slow release of nutrients as the SMC decomposed and a good air-filled pore space/water-holding capacity when amended with a commercial nursery mix. From these trials, it is recommended that SMC be incorporated at rates of 25% to 50%. It is not recommended that SMC be used in concentrations over 50% because the EC may be too difficult to manage and the high levels of air-filled pore space of SMC. Though season may affect the initial EC level of SMC, such variation is minimized by leaching while differences in plant response are more likely to be attributed to environmental conditions. No differences in plant growth were observed among SMC sources.

A Rapid Method to Determine Cereal Plant Response to Glyphosate1

A rapid method for determining the response of cereals to glyphosate is described. This method detects the differential responses of plants in 4 d, allowing for the rapid selection of glyphosate-tolerance response. Two types of tests determined the efficacy of this rapid method: differential response to different dosages of herbicide in a coleoptile growth test and in sprayed plants. In seedling assay, barley cultivars showed a higher level of tolerance to glyphosate (the dose that causes 50% of the total effect [I50] = 0.066 and I50 = 0.060 mM) than wheat cultivars (I50 = 0.018 and I50 = 0.014 mM). The response in seedling assay is well correlated (r2 = 0.95 and r2 = 0.98) with the response in plant-sprayed assays. The method was employed to verify the tolerance level of a sensitive barley cultivar and the four tolerant and sensitive mutant lines derived from it.Nomenclature: Glyphosate; barley, Hordeum vulgare L.; wheat, Triticum aestivum L.Additional index words: Herbicide response.Abbreviations: AN, Amaji Nijo; ANOVA, analysis of variance; CS, Chinese Spring; DAT, days after treatment; I50, dose that causes 50% of the total effect.

Continuous measurement of stem-diameter growth response of Pinus pinea seedlings mycorrhizal with Rhizopogon roseolus and submitted to two water regimes

Linear variable differential transformer (LVDT) sensors were used to detect continuous diameter growth responses of Pinus pinea (stone pine) seedlings inoculated with the ectomycorrhizal fungus Rhizopogon roseolus. Colonised and non-colonised seedlings provided with sensors were submitted to different water regimes in two consecutive experiments established in a controlled-temperature greenhouse module (cycle1), and in an adjacent module without temperature control (cycle2). Under regular irrigation, colonised seedlings showed significantly higher growth than non-colonised seedlings. Water-stressed seedlings showed no benefit from inoculation in terms of growth. Also, seedlings with a high colonisation level recovered more slowly from water stress than control seedlings. A significant positive relationship between maximum daily shrinkage (amplitude of the daily stem contraction) and global radiation was observed only in the first water-stress period in cycle1 and in regularly irrigated seedlings in both cycles. However, no differential responses due to inoculation were observed. The mycorrhizal colonisation of the seedlings at the end of the experiment was related with the initial colonisation level. Mycorrhizal colonisation by R. roseolus in old roots was maintained at significantly higher levels in seedlings which had an initial colonisation level >50% than in seedlings with <50% initial colonisation. Also, more newly formed roots became colonised in seedlings which had an initial colonisation level >50% than in seedlings with an initial colonisation <50%, which had almost no new root colonisation. From the results obtained, it can be concluded that LVDT sensors can be used to detect a differential response of plants according to water supply, mycorrhizal status and, in some cases, to their colonisation level. The results are discussed in relation to the predictive possibilities of the method for the selection of efficient mycorrhizal fungi for the promotion of plant growth.

Enantioselective Response of Rice and Barnyard Millet on Root Growth Inhibition by Optically Active α-Methylbenzyl Phenylureas

Abstract Optical active α-methylbenzyl p -tolylureas ( 7, 8 ) show diverse plant physiological properties. Experiments were conducted to evaluate the response of the optically active α-methylbenzyl phenylureas on root growth inhibition against rice and barnyard millet and to assess differential chiral responses of both plants from the viewpoints of activity, enantioselectivity, and cross intergenus response. A preference configuration to inhibit the root growth was not necessarily the same, and the toxicity and enantioselectivity were dependent on the substituent at the phenyl ring. To rice, the (R) -4-Pr ( 15 ) and (R) -4-Bu ( 23 ) derivatives exhibited the most potent activity with an I 50 value below 2 μM. To barnyard millet, similar to rice, the (R) -enantiomers with a lower alkyl group (2- tert Bu ( 25 ), 4-Pr ( 15 ), 2-isoPr ( 17 ), 3-Et ( 11 ), 4-Bu ( 23 ), 3-isoPr ( 19 ) and 4-Et ( 13 )) exhibited significant activity. The (R) -2-F-5-CF 3 ( 119 ) derivative was the most potent inhibitor, showing an I 50 value of 0.58 μM. The (S) -2-F ( 60 ), (S) -2,3-F 2 ( 90 ), (S) -2,5-F 2 ( 94 ) and (S) -4-COOEt ( 52 ) derivatives also inhibited the root growth of barnyard millet. Enantioselectivity and selective toxicity were quite high. Only chiral pairs of the 3-Me ( 5, 6 ) and 4-Me ( 7, 8 ) derivatives exhibited a cross intergenus response between rice and barnyard millet; rice was more affected by the (R) -enantiomers and barnyard millet by the (S) -enantiomers. Differential chiral responses including enantioselectivity and cross intergenus response between Oryza and Echinochloa plants against optically active α-methylbenzyl phenylureas were indicated in this study.

Effects of targeted replacement of the tomatinase gene on the interaction of Septoria lycopersici with tomato plants.

Many plants produce constitutive antifungal molecules belonging to the saponin family of secondary metabolites, which have been implicated in plant defense. Successful pathogens of these plants must presumably have some means of combating the chemical defenses of their hosts. In the oat root pathogen Gaeumannomyces graminis, the saponin-detoxifying enzyme avenacinase has been shown to be essential for pathogenicity. A number of other phytopathogenic fungi also produce saponin-degrading enzymes, although the significance of these for saponin resistance and pathogenicity has not yet been established. The tomato leaf spot pathogen Septoria lycopersici secretes the enzyme tomatinase, which degrades the tomato steroidal glycoalkaloid alpha-tomatine. Here we report the isolation and characterization of tomatinase-deficient mutants of S. lycopersici following targeted gene disruption. Tomatinase-minus mutants were more sensitive to alpha-tomatine than the wild-type strain. They could, however, still grow in the presence of 1 mM alpha-tomatine, suggesting that nondegradative mechanisms of tolerance are also important. There were no obvious effects of loss of tomatinase on macroscopic lesion formation on tomato leaves, but trypan blue staining of infected tissue during the early stages of infection revealed more dying mesophyll cells in leaves that had been inoculated with tomatinase-minus mutants. Expression of a defense-related basic beta-1,3 glucanase gene was also enhanced in these leaves. These differences in plant response may be associated with subtle differences in the growth of the wild-type and mutant strains during infection. Alternatively, tomatinase may be involved in suppression of plant defense mechanisms.

Expression of the ACC Deaminase Gene fromEnterobacter cloacae UW4 in Azospirillum brasilense.

The ACC deaminase structural gene (acdS) from Enterobacter cloacae UW4 was cloned in the broad host range plasmid pRK415 under the control of the lac promoter and transferred into Azospirillum brasilense Cd and Sp245. A. brasilenseCd and Sp245 transformants showed high ACC deaminase activity, similar to that observed in Enterobacter cloacae UW4. The expression of ACC deaminase improved the existing growth promoting activity of Azospirillum. The roots of tomato and canola seedlings were significantly longer in plants inoculated with A. brasilense Cd transformants than those in plants inoculated with the nontransformed strains of the same bacterium. In the case of wheat seedlings, inoculation with A. brasilense Cd transformants did not promote root growth. The difference in plant response (canola and tomato versus wheat) is attributed to the greater sensitivity of canola and tomato plants to ethylene as compared to wheat plants.

380 Differential Responses of Container-grown Ornamental Foliage Plants to Silicon Application

Silicon (Si) is the second most-abundant element in soils, and its concentration in soil solution ranges from 0.1 to 0.6 mm, which is the same concentration range as some of the major nutrient elements such as calcium, magnesium, phosphorus, and sulfur. Increasing evidence has recently suggested that Si plays important roles in improving plant growth. However, little information is available on Si effects on container-grown ornamental plants, particularly since most are grown in soilless media where Si sources are greatly limited. The objectives of this research were to evaluate Si absorption and translocation in diverse container-grown ornamental plants and to determine whether Si absorption could improve plant growth. Liners from 39 plant species were potted in peat and pine bark-based soilless media and grown in a shaded greenhouse. Plants were fertigated with a Peter's 24–8–16 water-soluble fertilizer containing 0, 50, and 100 mg·L–1 of Si. Once marketable sizes were reached, plants were harvested and fresh and dry weights determined; Si and other nutrient elements in roots and shoots were measured. Results indicated that 32 of the 39 evaluated species were able to absorb Si, with large quantities further transported to shoots. Of the 32 Si-responsive species, 17 showed significant dry weight increases, whereas the other 15 only exhibited Si absorption and translocation with no apparent growth responses. The seven non-responsive plant species showed no significant increases in neither Si absorption and translocation, nor dry weight.

Laboratory Exercises to Demonstrate Effects of Salts on Plants and Soils

The presence of salts in soil or in irrigation water can adverselyaffectplantgrowthandsoilproperties.Salinityconcerns are more common in semiarid and arid regions than in more humid regions. Furthermore, salinity is often an important concern for irrigated agriculture. Therefore, it is critical to educate students in soils courses about the effects of salts on plants and soils. Many soils laboratory manuals focus on measurement of salts in soils, but few include demonstrations of how salt effects bothplantsandsoils.Demonstratingtheeffectsofsaltsonplants andsoilsshouldenhancelearningbyprovidingtangibleimages. Our purpose was to develop laboratory exercises that demonstrate these effects for use in soils and other science courses. To demonstrate differences in plant response to salinity, a hydroponic study utilizing a range in salinities and plants with differentsaltsensitivitieswasused.Todemonstratedifferencesinhow salteffectshydraulicconductivity,astudyutilizingthreesoilsand foursaltsolutionswasused.Theseprovidevisualrepresentations of the well-established effects of salts on plants and soils. Includingplantspecieswithdifferentsalttolerances,soilswithdifferent textures, and treatments such as elevated sodium and elevated total salt levels effectively demonstrate the relative importanceofsalts.Inclusionofthesevisualdemonstrationsofthe effects of salts on plants and soils should enhance student learning.

Maize cultivars differ in tolerance to imazethapyr

The low tolerance of maize (Zea mays L.) to imazethapyr ((±)-2-[4,5-dihydro-4 methyl-4-(1 -methylethyl)-5-oxo 1H-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid) resulted in extensive crop damage in 1992/93 due to residue carry-over from resistant soybean (Glycine max L.). Pot experiments were conducted to assess the role of cultivar differences in maize tolerance, as well as the potential for synergistic interaction between imazethapyr and a fungicide. A selection of white and yellow maize cultivars were tested. The fungicide captab (3a, 4, 7, 7a- tetrahydro-2-[(trichloromethyl)thio]-1H-isoindole-1, 2(2H)-dione) was investigated in terms of its potential to exacerbate damage caused by imazethapyr to various maize cultivars. White cultivars were significantly more sensitive to imazethapyr than the yellow cultivars, with damage in shoot dry mass ranging from 13 to 63% at the lowest herbicide rate of 5 g ai ha−1. The ED50-values derived from linear regression equations for the relationship between imazethapyr rate and maize damage confirmed the differential tolerance of white and yellow cultivars, and indicated that the sensitivity of all six cultivars of the former type increased in the presence of captab. Except for one of six yellow cultivars, the same tendency was found in this group. The mechanisms involved in these differential plant responses are not known. Their elucidation could introduce flexibility into the safety (waiting) period specified for maize, through rational cultivar selection and promote the breeding of cultivars that are tolerant to the broad spectrum of acetolactate synthase (ALS)-inhibiting herbicides.

Effects of ozone depletion and increased ultraviolet-B radiation on northern vegetation

The stratospheric ozone layer has been depleted at high and mid-latitudes as a consequence of man's pollution of the atmosphere, and this results in increasing ultraviolet-B radiation at ground level. We investigate the effects of further radiation increases on plants and ecosystems by irradiating natural sub-Arctic and Arctic vegetation with artificial UV-B radiation in field experiments extending over several years. Our experimental sites are located at Abisko, in northern Sweden (68°N), and Adventdalen, on the island of Spitsbergen (78°N). Additional UV-B induced interspecific differences in plant response in terms of reduced (or, in one case, increased) growth, changed morphology and changed pigment content. In some cases effects seem to be accumulated from one year to another. Plant litter decomposition is retarded. We are also studying how UV-B enhancement may affect the interaction between species. In some experiments we combine UV-B enhancement with changes in other factors: carbon dioxide concentration, water availability, and temperature. In some cases the effect of radiation enhancement is modified, or even reversed, by such changes. Over a four year period we did not find any significant radiation induced change in species composition, but based on the effects on individual plant species, such changes can be expected to take place over a longer time.

Differential responses of UK upland plants to nitrogen deposition.

Native upland species, Nardus stricta, Eriophorum vaginatum, Erica cinerea and Vaccinium vitis-idaea were given 3 or 60 kg N ha-1 yr-1 , over 2 yr, applied as a mist (NH4 NO3 ). The high N treatment increased above-ground biomass in all four species, but only significantly in E. cinerea, E. vaginatum and N. stricta. Biomass increases in E. vaginatum and N. stricta resulted from enhanced tiller production rather than shoot elongation. Root growth increased in N. stricta, so that root∶shoot ratio in this species was unchanged by N. Root growth in E. vaginatum, E. cinerea and V. vitis-idaea did not respond to N and their root∶shoot ratios decreased. Tissue N concentrations increased in both shoots and roots of all species in response to N. The accumulated foliar N did not increase the proportion of N allocated to Rubisco and the photosynthetic capacities of N. stricta, E. vaginatum and V. vitis-idaea were unchanged. Thus growth responses to N were due to altered allocation rather than increased rate of photosynthesis per unit leaf area. The high N treatment increased flower production significantly in E. cinerea but not in the other species. Although in this experiment dwarf shrubs were more responsive than graminoids to N, in the field at current N inputs the enhanced tillering of the graminoids may be more competitively advantageous, especially where gaps develop in the canopy. Thus increasing N deposition may lead to increased grassiness of upland heath, and in particular, a spread of N. stricta.

Evidence of depleted uranium‐induced hormesis and differential plant response in three grasses

General plant response to depleted uranium (DU) was tested using three widespread range‐grass species, Aristida purpurea Nutt. (purple threeawn), Buchloe dactyloides (Nutt.) Engelm. (buffalograss), and Schizachyrium scoparium (Michx.) Nash (little bluestem). Aboveground, belowground, and total biomass measures of these grasses were analyzed over the five different DU soil concentrations of 0, 50, 500, 5,000, and 25,000 mg kg‐1. Differential plant response to DU was observed between the three grasses, wiith A. purpurea and B. dactyloides exhibiting a threshold‐type response in which no changes in biomass occurred until the highest treatment level of 25,000 mg kg‐1 was reached. Schizachyrium scoparium, however, demonstrated a large degree of growth stimulation, or hormesis, at the 50 and 500 mg kg‐1 DU concentrations. Several possible mechanisms of this hormetic response are offered.

Relationships between plant and soil water status in five field-grown cotton ( Gossypium hirsutum L.) cultivars

The objective of this study was to evaluate the possibility of using the fraction of transpirable soil water (FTSW) under field conditions, to analyse genotypic differences in plant responses to soil water deficit. Two years of field experiments were carried out on a sandy soil under sub-sahelian conditions in Senegal. Five cotton cultivars ( Gossypium hirsutum L.), with similar phenology but different yield responses to drought, were compared under two irrigation treatments differentiated after flowering. Because of differences in the rainfall pattern during the pre-flowering period, the two years resulted in marked differences in soil water hydration and effective rooting depth. Soil water deficit experienced by the plants in each elementary plot was characterized with FTSW, calculated with volumetric soil water content (measured with a neutron probe) from soil surface to the estimated effective rooting depth. Despite large differences of soil water content between years and irrigation treatments, FTSW was closely related to the predawn leaf water potential measured on the same day. Plant responses to soil water deficit were analysed with leaf water potential ( ψ l), relative water content (RWC), stomatal conductance ( g s), and crop water stress index (CWSI) measured during the crop cycle. Genotypic differences for these plant variables were found on some days, but they were frequently associated with genotypic differences in FTSW. The relationships between plant variables and FTSW, over two years of measurements and contrasting soil water profiles, were adjusted to typical logistic functions, previously used in other species. Leaf water status ( ψ l and RWC), g s and CWSI did not change appreciably until FTSW reached 0.4–0.5. Significant genotypic differences were found in the relationships of RWC and CWSI with FTSW, which allowed the ranking of the five cultivars for dehydration avoidance. The absence of genotypic differences in the relationships between g s and FTSW indicates that the higher dehydration avoidance of one of the cultivars (STAM F) is not linked to stomatal regulation, but probably to osmotic adjustment. Calculation of FTSW from soil water content measurements provided an efficient way to conduct genotypic comparison of plant response to drought in field conditions over two years of contrasted rainfall pattern.

Two different modes of early development and nitrogen assimilation in gymnosperm seedlings†

SummaryLight‐independent chloroplast development and expression of genes encoding chloroplast proteins occur in many but not all species of gymnosperms. Early development in maritime pine (Pinus pinaster) seedlings was strongly light‐independent, whereas Ginkgo biloba seedlings exhibited a typical angiosperm‐like morphogenesis with differentiated patterns in light and dark. In pine, chloroplast polypeptides were undetectable in the seed embryo and accumulated in cotyledons of both light‐ and dark‐grown plants in good correlation with light‐independent chlorophyll synthesis. In contrast, chlorophyll and chloroplast proteins were only detected in light‐grown ginkgo. Pine cytosolic glutamine synthetase (GS) and ferredoxin glutamate synthase (Fd‐GOGAT) were present at low levels in the seeds and accumulated at comparable amounts in light‐ and dark‐grown seedlings. Fd‐GOGAT was also barely detectable in the seeds of ginkgo and only accumulated in green plants with mature chloroplasts. In G. biloba seeds and etiolated plants only cytosolic GS was identified, while in light‐grown seedlings this molecular form was present at low abundance and choroplastic GS was the predominant isoenzyme. The above results have been confirmed by immunolocalization of GS protein in pine and ginkgo plantlets. In pine, GS was present in the peripheral cytoplasm of mesophyll cells and also in the phloem region of the vascular bundle. Immunocytochemical analysis showed that the labelling of mesophyll and phloem cells was only cytoplasmic. In developing ginkgo, GS antigens were present in the chloroplasts of mesophyll parenchyma cells of leaflets and green cotyledons. In contrast, a weak labelling of GS was observed in the parenchyma and phloem cells of non‐green cotyledons enclosed in the seed coat. Taking all this into account, our data indicate the existence of two different modes of GS and GOGAT regulation in gymnosperms in close correlation with the differential response of plants to light. Furthermore, the results suggest that glutamine and glutamate biosynthesis is confined to the chloroplast of mesophyll cells in species with light‐dependent chloroplast, development whereas compartmentation would be required in species with light‐independent plastid development.