油菜生长发育期间内源激素含量的变化

初花期至盛花期华双3号、华杂4号、恢5900等3个品种花蕾的iPAs含量呈明显上升趋势,而秦油2号则刚好相反(表2)。对双低品种华双3号功能叶的研究表明：苗期至盛花期IAA含量始终最高,其后依次是GA1 3;、iPAs、ABA。功能叶IAA的含量在越冬期处于整个生育期的最低水平,蕾薹期达到高峰,随后下降：GA1 3和iPAs含量随生育进程逐渐升高,并在初花期达到峰值;ABA在苗期及抽薹后一直处于很低水平,但在越冬期达到最高值(图1、2)。蕾薹期IAA主要分布在幼嫩和正在生长的器官中并起重要作用,而在功能叶中相对要少;幼叶GA1 3和iPAs含量最高,功能叶其次,花蕾最低(表1)。角果皮与籽粒的内源激素含量差异极显著,在开花后第39天,籽粒中IAA、GA1 3;、iPAs的含量大大超过角果皮(表3)。结果 表明iPAs在促进籽粒的充实饱满、物质积累转化方面发挥重要作用。     

Growth and reproduction of Arabidopsis thaliana in relation to storage of starch and nitrate in the wild-type and in starch-deficient and nitrate-uptake-deficient mutants

We have investigated the interactions between resource assimilation and storage in rosette leaves, and their impact on the growth and reproduction of the annual species Arabidopsis thaliana. The resource balance was experimentally perturbed by changing (i) the external nutrition, by varying the nitrogen supply; (ii) the assimilation and reallocation of resources from rosette leaves to reproductive organs, by cutting or covering rosette leaves at the time of early flower bud formation, and (iii) the internal carbon and nitrogen balance of the plants, by using isogenic mutants either lacking starch formation (PGM mutant) or with reduced nitrate uptake (NU mutant). When plants were grown on high nitrogen, they had higher concentrations of carbohydrates and nitrate in their leaves during the rosette phase than during flowering. However, these storage pools did not significantly contribute to the bulk flow of resources to seeds. The pool size of stored resources in rosette leaves at the onset of seed filling was very low compared to the total amount of carbon and nitrogen needed for seed formation. Instead, the rosette leaves had an important function in the continued assimilation of resources during seed ripening, as shown by the low seed yield of plants whose leaves were covered or cut off. When a key resource became limiting, such as nitrogen in the NU mutants and in plants grown on a low nitrogen supply, stored resources in the rosette leaves (e.g. nitrogen) were remobilized, and made a larger contribution to seed biomass. A change in nutrition resulted in a complete reversal of the plant response: plants shifted from high to low nutrition exhibited a seed yield similar to that of plants grown continuously on a low nitrogen supply, and vice versa. This demonstrates that resource assimilation during the reproductive phase determines seed production. The PGM mutant had a reduced growth rate and a smaller biomass during the rosette phase as a result of changes in respiration caused by a high turnover of soluble sugars ( Caspar et al. 1986 ; W. Schulze et al. 1991 ). During flowering, however, the vegetative growth rate in the PGM mutant increased, and exceeded that of the wild-type. By the end of the flowering stage, the biomass of the PGM mutant did not differ from that of the wild-type. However, in contrast to the wild-type, the PGM mutant maintained a high vegetative growth rate during seed formation, but had a low rate of seed production. These differences in allocation in the PGM mutant result in a significantly lower seed yield in the starchless mutants. This indicates that starch formation is not only an important factor during growth in the rosette phase, but is also important for whole plant allocation during seed formation. The NU mutant resembled the wild-type grown on a low nitrogen supply, except that it unexpectedly showed symptoms of carbohydrate shortage as well as nitrogen deficiency. In all genotypes and treatments, there was a striking correlation between the concentrations of nitrate and organic nitrogen and shoot growth on the one hand, and sucrose concentration and root growth on the other. In addition, nitrate reductase activity (NRA) was correlated with the total carbohydrate concentration: low carbohydrate levels in starchless mutants led to low NRA even at high nitrate supply. Thus the concentrations of stored carbohydrates and nitrate are directly or indirectly involved in regulating allocation.     

A protocol for fertility restoration of F<Subscript>1</Subscript> hybrid derived from <Emphasis Type="Italic">Lilium</Emphasis> × <Emphasis Type="Italic">formolongi</Emphasis> ‘Raizan 3’ × Oriental hybrid ‘Sorbonne’

The present study was an attempt to develop an in vitro colchicine chromosome doubling protocol to restore the fertility of an F₁ interspecific hybrid in Lilium. Basal scale segments of Lilium?×?formolongi?×?Oriental hybrid (FO) bulblets were pre-cultured for three durations (6, 15 and 25 days) and soaked in three colchicine concentrations (0.00, 1.25 and 2.50 mM) for 18, 24 and 36 h. To separate mixoploids, three cycles of adventitious bud induction were performed. The ploidy levels of the surviving plantlets were detected by flow cytometry at 30–31 weeks after induction and were confirmed by chromosome counts. The results indicated that the pre-culture duration, colchicine concentration and exposure time all had significant impacts on the tetraploid induction rate. The preferred procedure was to pre-culture the segments for 6 days and then treat them with 1.25 mM colchicine for 24 h. The morphological traits of rosette leaves were significantly different between the tetraploid and diploid plants. The adult tetraploid plants had considerably longer and wider leaves, larger flowers, and delayed flowering time (8 days later) than did diploid plants. Pollen viability tests and backcross trials of FO hybrids demonstrated fertility restoration at the tetraploid level. This protocol provides a feasible method for inducing fertile tetraploid FO hybrids for further breeding.     

The floral transition is not the developmental switch that confers competence for the Arabidopsis age-related resistance response to Pseudomonas syringae pv. tomato

Age-related resistance (ARR) is a plant defense response characterized by enhanced resistance to certain pathogens in mature plants relative to young plants. In Arabidopsis thaliana the transition to flowering is associated with ARR competence, suggesting that this developmental event is the switch that initiates ARR competence in mature plants (Rusterucci et al. in Physiol Mol Plant Pathol 66:222–231, 2005). The association of ARR and the floral transition was examined using flowering-time mutants and photoperiod-induced flowering to separate flowering from other developmental events that occur as plants age. Under short-day conditions, late-flowering plant lines ld-1 (luminidependens-1), soc1-2 (suppressor of overexpression of co 1-2), and FRI ⁺ (FRIGIDA) displayed ARR before the transition to flowering occurred. Early-flowering svp-31, svp-32 (short vegetative phase), and Ws-2 were ARR-defective, whereas early-flowering tfl1-14 (terminal flower 1-14) displayed ARR at the same time as Col-0. While svp-31, svp-32 and Ws-2 produced few rosette leaves, tfl1-14 produced a rosette leaf number similar to Col-0, suggesting that the development of a minimum number of rosette leaves is necessary to initiate ARR competence under short-day conditions. Photoperiod-induced transient expression of FT (FLOWERING LOCUS T) caused precocious flowering in short-day-grown Col-0 but this was not associated with ARR competence. Under long-day conditions co-9 (constans-9) mutants did not flower but displayed an ARR response at the same time as Col-0. This study suggests that SVP is required for the ARR response and that the floral transition is not the developmental event that regulates ARR competence.     

Uptake,distribution, and turnover rates of selenium in barley

The present communication elucidates initially the topographic distribution of selenium in barley grains. Then by the fluorimetric method the uptake of selenium (selenite) in 8–16 d old germinating barley was estimated. Finally by means of⁷⁵Se the anabolic and catabolic rates (turnover) of⁷⁵Se (selenite) was compared. The distribution of selenium in barley was evaluated after microdissection of barley grains. In dried grains the highest concentration was found in husk and pericarp with about 0.6 ppm Se. Then followed Scutellum with 0.4 and 0.3 ppm in embryon. The aleurone layer, embryonic leaves, and initial root did only have 0.2 ppm Se. In order to know more about the uptake and distribution of selenium in 8-d-old barley, the plants were cultivated for a further 8 d in the culture medium with variation in selenite concentration. In roots and leaves, the uptake did not arrive at saturation during the period studied since the dose-response curve increased up to 0.34 mM selenite in the medium, whereas the selenium levels were about 200 ppm in roots and 30 ppm in leaves. However, the uptake was linear, with concentration during 8 d of cultivation up to 0.84 μM selenite for grain and stem. At higher concentrations the dose-response curve diminished its slope. At 0.34 mM selenite the concentration in grain increased to 6.87 ppm and in the stem to 8.13 ppm. The uptake, distribution, and catabolic rate of selenium components in germinating barley were further evaluated by exposing the plants to 0.0492 μCi⁷⁵Se (12.6 μM selenite) for up to 4 d. Then the plants were moved to a selenium deficient medium for further 4 d. Then finally the medium was supplemented with high doses of cold selenite (0.126 mM selenite) for further 4 d. The first third period made it possible to estimate the rate of uptake. It was highest in roots (313 fmol/h/mg dw), i.e., about 10 times those of grains, stems, and leaves. The intermediate period where the barley was transferred to a selenium deficient medium made it possible to estimate the kinetics and eventual sparing mechanisms. The selenium losses were highest for leaves (39%), then followed by roots and stems (22 and 25%, respectively). The losses were lowest in grain with 9% Se losses. The losses were three times more pronounced during the first day than in the following 3 d. These data may argue that the selenium is distributed into different pools and that sparing mechanisms may be in function. The last period, i.e., the chase experiment, revealed the rate of elimination of selenium under conditions with surplus selenium. The catabolic rate was about 10 times faster in roots (169 fmol/h/mg dw) than in grains and about 8 times faster than in leaves.     

Ontogenic variation in response of Brassica campestris L. to cadmium toxicity

Abstract

Rapeseed (Brassica campestris L.) cv Pusa Gold plants, exposed to different cadmium (Cd) levels (0, 25, 50 and 100 mg kg^?1 soil) in greenhouse, pot culture experiment, were analyzed with reference to distribution of metal, accumulation of biomass and the degree of growth stage Cd-sensitivity. A significant maximum decrease in plant biomass was observed at Cd-exposed flowering stage followed by pre-flowering and post-flowering stages. Activities of enzymatic antioxidants such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) differentially increased; while, the concentrations of non-enzymatic antioxidants such as ascorbic acid (AsA) and glutathione (GSH) drastically decreased in plants exposed to Cd at various growth stages. However, the concentrations of GSH and AsA decreased maximally in plant groups exposed to Cd at their flowering stage. The maximum Cd-accumulation occurred in roots followed by leaves and stem. Various Cd levels inhibited also the contents of plant nutrients such as nitrogen (N), phosphorous (P), potassium (K) and sulfur (S) in leaves. The present endeavor hence concludes the existence of close relationships among growth parameters, Cd-sensitivity of phenological stages of the crop and the components of antioxidant system in rapeseed plants exposed at various growth stages.     

Changes in the Activity of the Chloroplastic and Cytosolic Forms of Dihydroxyacetone Phosphate Reductase during Maturation of Leaves

Young or mature rosette leaves from spinach (Spinacia oleracea L.) plants growing in the field, in the greenhouse, or in a growth chamber under a regimen of 8 hours light and 16 hours dark contained 15 to 50 nanomoles per minute per gram wet weight of NADH:dihydroxyacetone phosphate reductase activity. Of this activity, 75 to 87% was the chloroplastic isoform and 25 to 13% was the cytosolic form. When plants were induced to senesce, as measured by stem elongation and flowering, the percentage of the two reductase isoforms in rosette or stem leaves changed to about 12% as the chloroplastic and 88% as the cytosolic isoform. The change in enzyme activity of the rosette leaves occurred within 3 days, before phenotypic changes were observed. Likewise, when plants senesced in continuous darkness, the percentage of chloroplastic to cytosolic reductase changed from 80:20% to 25:75% after 62 hours before changes in total protein or chlorophyll occurred. The ratio of activities did not change in the first 16 hours of darkness or overnight. In each case the change in ratio resulted from about a 75% decrease in activity of the chloroplastic isoform and up to 14-fold increase in cytosolic isoform. In spinach leaves purchased at a local market primarily only the cytosolic isoform remained. When plants were returned to normal day-nights, after 62 hours in continuous darkness, the activity of the chloroplastic isoform increased, but not to control levels after 3 days, while the cytosolic enzyme decreased within 1 day to normal day-night values. Changes in activity were not due to changes during in vitro assays in activation by thioredoxin for the chloroplastic isoform or fructose 2,6-phosphate for the cytosolic isoform.     

Salicylic acid-mediated reductions in yield in Nicotiana attenuata challenged by aphid herbivory

Aphid herbivory decreases primary production in natural ecosystems and reduces crop yields. The mechanism for how aphids reduce yield is poorly understood as some studies suggest aphid feeding directly impedes photosynthesis, whereas other studies suggest a change in allocation of resources from growth to defense compounds reduces yield. To determine the mechanisms underlying reduced plant growth by aphids, Nicotiana attenuata plants, native tobacco, were infested with Myzus persicae ssp. nicotianae, tobacco-adapted green peach aphids, at low and high densities, and plant performance including fitness was assessed. To test the direct defense capacity of salicylic acid (SA) on aphid performance, we fed aphids an artificial diet with varying levels of SA and measured their survivorship and fecundity. There was no detectable effect of aphid herbivory on net photosynthesis, yet herbivory reduced plant growth, final biomass (43 % at high aphid density), and seed set (18 % at high aphid density) at both low and high aphid infestation levels. High-density aphid attack during the rosette and flowering stage caused an increase in SA levels, but caused only a transient decrease in jasmonic acid concentration at low aphid density. SA concentrations similar to those found in infested flowering plants decreased aphid fecundity, suggesting that SA was an effective chemical defense response against aphids. These results suggest that as aphid densities increased the proximal cause of reduced growth and yield was not reduced photosynthesis, but instead resources may have been mobilized for defense via the SA pathway, decreasing the availability of resources for building plant biomass.     

Pleiotropic effects of flowering time genes in the annual crucifer Arabidopsis thaliana (Brassicaceae)

Variation in flowering time of Arabidopsis thaliana was studied in an experiment with mutant lines. The pleiotropic effects of flowering time genes on morphology and reproductive yield were assessed under three levels of nutrient supply. At all nutrient levels flowering time and number of rosette leaves at flowering varied among mutant lines. The relationship between these two traits depended strongly on nutrient supply. A lower nutrient supply first led to an extension of the vegetative phase, while the mean number of leaves at flowering was hardly affected. A further reduction resulted in no further extension of the vegetative phase and, on average, plants started flowering with a lower leaf number. At low nutrients, early flowering affected the timing of production of siliques rather than the total output, whereas late flowering was favorable at high nutrients. This may explain the fact that many plant species flower at a relatively small size under poor conditions. Flowering time genes had pleiotropic effects on the leaf length, number of rosette and cauline leaves, and number of axillary flowering shoots of the main inflorescence. Silique production was positively correlated with the number of axillary shoots of the main inflorescence; the number of axillary primordia appeared to have a large impact on reproductive yield.     

The biomass and nutritive potential of Vallisneria americana Michx in navigation pool 9 of the upper Mississippi river

Vallisneria americana Michx (wild celery) was studied to determine the biomass and nutritive potential of all morphological structures. A 2.6-ha stand of uniform V. americana was sampled during the summer and autumn of 1980, and the spring and summer of 1981 in the southern portion of Navigation Pool 9 of the Upper Mississippi River.The maximum production rate of 3.2 g m^?2 day^?1 was coincident with rapid rosette production and flowering, and occurred mid- to late-July 1980. The maximum biomass of 217.3 g dry wt. m^?2 was on 1 September 1980, when fruit development was also at a maximum. Leaves composed 60–70% of the summer biomass; winter buds constituted all of the winter biomass.Winter buds and fruits had the greatest nutritive potentials. Both organs contained relatively high dry matter concentrations and were low in ash (less than 10%) and fiber content. The potentially-digestible ash-free non-cell-wall fraction (NCF) was composed of an average of 75.7 and 82.2% of the dry weight of fruits and winter buds, respectively. In contrast, the nutritive potential of leaves, rootstocks, peduncles and stolons was reduced because of high moisture (less than 8% dry matter), ash and fiber concentrations. Staminate inflorescences and pistillate flowers were high in crude protein (averaged 21.8% and 16.1% of the dry-weight, respectively) and ash-free non-cell-wall fractions, but they accounted for only 2.7% of the plant biomass. The maximum calorific content of V. americana was approximately 3200 kJ m^?2 at peak biomass on 1 September 1980.     

Inhibitory efficacy of endophytic Bacillus subtilis EDR4 against Sclerotinia sclerotiorum on rapeseed

Stem rot, caused by Sclerotinia sclerotiorum, is a serious disease of rapeseed worldwide. This paper tested the inhibitory effect of an endophytic bacterial Bacillus subtilis strain, EDR4, on the sclerotial germination and hyphal growth of S. sclerotiorum. The cell-free filtrate solution and cell suspension of strain EDR4 were sprayed on rapeseed leaves and stems one day before, at the same time and one day after inoculation in the greenhouse experiments. There was no significant difference in inhibitory efficacy between the cell-free filtrate solution and cell suspension. The best biocontrol efficacy was achieved by spraying either the cell-free filtrate solution or cell suspension at the same time as inoculation. In the field trials, the efficacy of two applications of EDR4 cell suspension at the initial flowering stage and full bloom stage was the best, but there was no significant difference in efficacy between the one-application and two-application treatments during the initial flowering stage. The efficacy decreased gradually with the culture suspension dilutions. Scanning electron microscopy revealed that EDR4 cells significantly suppressed the hyphal growth. The bacterial treatment caused shrink, cytoplasm leakage and irregular tip swelling of fungal hyphae. The hyphal cells in the treated groups had higher numbers of vacuoles in the cytoplasm than the non-treated hyphal cells. The hyphal cytoplasm was disintegrated; the hyphal biomass was reduced; the formation of infection cushions was delayed; and the infection was suppressed after spraying the bacterial culture on rapeseed leaves. The results showed that the EDR4 bacterial strain could be used to control stem rot of rapeseed.     

In vitro propagation of Dendrobium aphyllum (Orchidaceae)—seed germination to flowering

This communication describes asymbiotic seed germination, protocorm development, micropropagation and flowering in in vitro and hardened seedlings of Dendrobium aphyllum (Roxb.) C.E.C. Fischer. Effects of four culture media viz., Murashige and Skoog (MS); Phytamax (Sigma Chemical Co. USA; PM); Mitra et al. (M) and Knudson ‘C’ (KC), 6-benzylaminopurine (BAP) and 2,4-dichlorophenoxyacetic acid (2,4-D), peptone and activated charcoal were studied on seed germination and protocorm development. Maximum germination (97 %) was recorded in PM basal medium. Peptone (2.0 gl^?1) remarkably enhanced germination percentage (100 %), vigorous growth, high survival and subsequent development of protocorms, while in activated charcoal the response was not encouraging. BAP improved germination percentage, however, 2,4-D showed noticeably low seed germination. The morphogenetic response of protocorms and nodal segments of in vitro raised seedlings varied depending on type of explants and concentrations and combinations of plant growth regulators used. Stout root system was induced in 1/2PM + 0.5 mgl^?1 IAA. Approximately 10 % of the in vitro raised plants (4–5 cm) with 3–4 leaves flowered in vitro irrespective of flowering season. The well-rooted plants showed 80 % survival under green house conditions and flowering was noticed after 5–6 months in 10 % of hardened plants.     

Regrowth of spring canola (Brassica napus) after defoliation

Aims

Regrowth of dual-purpose canola after grazing is important for commercial success and the aim of this research was to investigate the effects of defoliation on the development, growth, photosynthesis and allocation of carbohydrates.

Methods

We conducted two pot experiments in which defoliation was conducted at multiple intensities with scissors. Experiment 1 determined changes in flowering date due to defoliation while Experiment 2 investigated the effects of defoliation on growth, photosynthesis and allocation of carbohydrates in canola.

Results

Time to the appearance of the first flower was delayed by up to 9 days after the removal of all leaves at the start of stem elongation (GS30), and up to 19 days if the elongating bud was also removed. Stem growth rate decreased by 56–86 % due to defoliation and tap roots did not increase in mass when plants were completely defoliated. Leaf area continued to expand at the same rate as in un-defoliated plants. The new leaf area established per gram of regrowth biomass over 20 days was 158 cm².g^-1 for the complete defoliation treatments compared with 27 cm².g^?1 for the half-defoliated treatment and 13 cm².g^?1 for the un-defoliated treatment. Despite a reduction in total biomass of up to 60 %, the proportion of dry matter partitioned to the leaves was 18 % for all treatments within 20 days after defoliation. Total non-structural carbohydrate levels were reduced rapidly in the stem by day two (predominately sucrose) and the tap root by day four (predominately starch) after defoliation and did not recover to match un-defoliated plant levels within 20 days. Residual leaves on defoliated plants maintained photosynthetic rate compared with the same leaf cohorts on un-defoliated plants in which photosynthetic rate decreased to 39 % by day 12.

Conclusions

The rapid recovery of leaf area in defoliated canola was facilitated by the sustained high photosynthetic rate in remaining leaves, rapid mobilisation of stored sugars (stem) and starch (root), and a cessation of root and stem growth.     

Selenium Modifies the Effect of Short-Term Chilling Stress on Cucumber Plants

The objective of this study was to investigate the effect of selenium (Se) supply (0, control; 2.5, 5, 10, or 20 μM) on cucumber (Cucumis sativus L.) cv. Polan F1 plants grown under short-term low temperature stress. About 14–16 day-old seedlings, grown at an optimal temperature (25/20°C; day/night), were exposed to short-term chilling stress with a day/night temperature of 10°C/5°C for 24 h, for a further 24 h at 20°C/15°C, and then transferred to 25/20°C (re-warming) for 7 days. Se did not affect the fresh weight (FW) of plants at a concentration of 2.5–10 μM, but in the presence of 20 μM Se, the biomass of shoots significantly decreased. The contents of chlorophylls and carotenoids witnessed no significant change after Se supplementation. Compared with the control, the Se-treated plants showed an increase of proline content in leaves, once after chilling and again after 7 days of re-warming. However, proline levels were much higher immediately after chilling than after re-warming. The malondialdehyde (MDA) content in the root of plants treated with 2.5–10 μM Se decreased directly after stress. This was in comparison with the plants grown without Se, whereas it increased in roots and leaves of plants exposed to 20 μM Se. Seven days later, the MDA level in the root of plants grown in the presence of Se was still lower than those of plants not treated with Se and generally witnessed no significant change in leaves. Although Se at concentrations of 2.5–10 μM modified the physiological response of cucumber to short-term chilling stress, causing an increase in proline content in leaves and diminishing lipid peroxidation in roots, the resistance of plants to low temperature was not clearly enhanced, as concluded on the basis of FW and photosynthetic pigments accumulation.     

PHYSIOLOGICAL AND MORPHOLOGICAL MODIFICATIONS OF PLANTAGO MAJOR (PLANTAGINACEAE) IN RESPONSE TO LIGHT CONDITIONS

Physiological and morphological differences between Plantago major L. (Plantaginaceae) growing in full sunlight and shaded conditions were examined. Photosynthesis of isolated leaves was saturated by irradiance around 300 μE m^−-2 sec^−-1 and 170 μE m^−-2 sec^−-1, respectively. In contrast to previous studies of sun/shade leaf responses, initial slopes of curves from shaded plants are significantly less than those taken from full-sun plants. Within the 400–500 nm and 600–700 nm ranges, leaves 5.0 cm or longer are essentially opaque, transmitting less than 1.25% of incident light. Chlorophyll content per unit leaf area is nearly equivalent for leaves from plants growing under the two extremes in light levels. Morphometric comparisons indicate shaded plants bear fewer leaves, have less leaf overlap, lower total leaf area, and longer petioles than full-sun plants. Leaf elongation rates are lower and the duration between the emergence of successive leaves is longer in shaded plants. Computer analyses of both types of rosette morphology reveal shaded plants have an equal or greater capacity to intercept light than full-sun plants, principally because of the minimization of leaf overlap and the large variation in the deflection angles of leaves in shaded rosette morphologies. Simulations, calculated on the basis of light interception, and taking into account the transition between photosynthate-importing and -exporting leaves, predict relative growth rates for full-sun and shaded rosette morphologies that are in reasonable agreement with empirically determined leaf growth rates. However, the data indicate that significant physiological and morphological differences exist among leaves from a single rosette, and among developmentally comparable leaves from rosettes growing under different ambient light environments. Differences among leaves on a single plant must be accommodated in computerized techniques attempting to simulate light interception and its consequences on potential growth rates.     

Photosynthetic characteristics and productivity of spring rape plants as related to crop density

Optimal density of spring rape (Brassica napus L.) crop stand was determined by plant photosynthetic characteristics at the beginning of flowering. As crop density increased from 100 to 350 plants/m², leaf surface index (LSI) of the crop was found to increase by 18.2–80.2%, and LSI decreased by 38.8–67.3% as compared with the sparsest crop (50–100 plants/m²). LSI depended on the rate of incident PAR reaching 0.5 and 0.25 heights of the crop stand and to the soil surface. When crop density increased from 100 to 350 plants/m², the photosynthetic potential (PP) of the crop increased 1.8 times as compared with the sparsest crop. PP of the densest rape crop stand was 3 times lower than in the sparsest crop. When the crop density increased from 100 to 250 plants/m², the daily increment in biomass calculated per leaf surface unit increased by 27.0% as compared with the sparsest crop and depended on LSI. When leaf area decreased, the daily increment in biomass calculated per leaf surface unit declined; in the densest stand, this characteristic was by 58.3% lower than in the sparsest crop. Rape productivity at the flowering stage depended on the crop density, LSI of plants, rate of PAR reaching 0.5 and 0.25 heights of the crop stand and to the soil surface, PP, and the daily increment in biomass calculated per leaf surface unit. Crop productivity at the flowering stage and the rape seed yield were associated by a significant parabolic relationship. When crop density increased from 100 to 350 plants/m², seed yield per plant considerably decreased (by 33.1–78.5%) as compared with the sparsest crop. The greatest influence on seed yield per plant was exerted by LSI and the daily increment in biomass calculated per leaf surface unit. When crop density increased to 250–300 plants/m², the seed yield considerably rose (by 28.6–58.8%) as compared with the sparsest crop; when this index reached 300–350 plants/m², the seed yield decreased because plant growth was suppressed, with the productivity reduced. The results thus obtained suggest that the photometric characteristics of spring rape were at optimum at crop density of 100–250 plants/m². The agroclimatic conditions of Lithuania ensure potential for rapid accumulation of total biomass and high seed yield.     

Flowering responses to light-breaks in photomorphogenic mutants of Arabidopsis thaliana, a long-day plant

Flowering response and plant form of photomorphogenic mutants (hy1, hy2, hy3, hy4 and hy5) of Arabidopsis thaliana (L.), a long-day plant, were examined in long and short days. There were only slight differences among genotypes including Landsberg wild type with respect to the flowering time under long days. The effect of 1 h light-(night)-breaks of far-red, red, blue and white light given in the middle of the dark period of plants grown under short days, was studied. Effects of far-red light applied at the end or the beginning of the main photoperiod on flowering and plant form were also examined. The light-breaks with all the above mentioned light qualities promoted floral initiation of all the genotypes including the wild type in terms of both the flowering time and the number of rosette leaves. In general, far-red light was most effective. It is possible to classify the hy-mutants into 3 groups by their responses to light-breaks under short day conditions: (a) Mutants hy2 and hy3, which have a reduced number of rosette leaves, and flower early. Red light is as effective as far-red light. The wavelength of light-breaks is relatively unimportant for flowering response. (b) Mutants hy4, hy5 and Landsberg wild type, which have a greater number of rosette leaves, and flower relatively late. The effectiveness of light-breaks is in the following order, far-red, blue, and red light, which is in reverse order to the transformation of phytochrome to the P_fr form. (c) Mutant hy1, which behaves anomalously with respect to relations between flowering time and number of rosette leaves; late flowering with reduced number of rosette leaves. Red, blue and far-red light are effective, but white light is ineffective for reducing the number of rosette leaves. When far-red light was given in the middle of the night or at the end of the main photoperiod, it markedly reduced the number of rosette leaves compared to those grown under short days for all the genotypes, while when applied at the beginning of the main photoperiod far-red light did not affect the number of rosette leaves. Different effects on the plant form dependent on the time of treatment with far-red light-breaks are also discussed.     

Chronic mild salinity affects source leaves physiology and productivity parameters of rice plants (Oryza sativa L., cv. Taipei 309)

Aim

In rice, the top two leaves are the major carbohydrate source during grain filling. Physiological performance of these leaves under salinity may allow estimate stress-induced yield loss.

Methods

Greenhouse grown rice plants (cv. Taipei 309) were subjected to 10 and 20 mM NaCl stress levels from germination till maturity. Plant development was measured at the flowering stage and yield parameters were quantified after complete ripening of panicles.

Results

Gas exchange in the main source leaves were not significantly affected by any of the stress levels. However, growth parameters as well as total metabolizable carbohydrates content, chlorophyll content (CCI), maximal efficiency of PSII photochemistry in dark-adapted state (F _v/F _m) and lipid peroxidation were significantly affected. Rice yield, measured as total panicle production, declined to 78 and 21 % of controls in 10 and 20 mM NaCl stress, respectively. Stress-induced yield loss was positively related with the decline in CCI, F _v/F _m and K⁺/Na⁺ ratio as well as with the increase in lipid peroxidation and total soluble carbohydrate contents.

Conclusions

Though the stress levels used in this work are below what is considered the minimal critical threshold of toxicity for rice, they induce significant negative effects on plant development and yield, when present along the whole plant life cycle.     

Differences in response to defoliation between males and females of Silene dioica

Summary The response by male and female plants to herbivory was studied by experimental defoliation of the dioecious perennial herb Silene dioica in a green-house. Male and female plants were defoliated prior to and during the early flowering phase at two intensities (50% and 100% of leaf-area removed) in two consecutive years. Defoliation resulted in a decrease in the number of flowers initiated in both sexes, while a larger delay of peak flowering and a higher mortality was observed in males compared to females. In female plants, severe defoliation resulted in a reduction in seed number per capsule and in seed size compared to control. Females showed a negative correlation between the production of flowers in the first and second season in all treatments, while flowering in males the first season was not correlated with flowering in the second season. Females also showed a lower frequency of flowering than males during the two seasons studied. However, during the flowering period, males allocated significantly more biomass to flowers than did females. This outcome supports the idea that females may have a higher total reproductive expenditure than males, but males have a higher reproductive effort during flowering. Male rosette leaves were significantly preferred by the generalist herbivore Arianta arbustorum in experiments. This preference was most pronounced in trials with leaves from fertilized plants compared to nonfertilized plants. A greater storage of resources in aboveground leaves during winter by males compared to females may explain the higher preference for male leaves and the higher male mortality following early defoliation. Furthermore, males are smaller than females and may have a lower ability than females to replace lost resources needed for reproduction when defoliated early in the season.