Irreversibility of chilling injury in zucchini squash (Cucurbita pepo L) could be a programmed event long before the visible symptoms are evident

Zucchini fruits were subjected to 2.5 or 10 degrees C for 16d, followed by transfer to 20 degrees C for 24h in order to evaluate the relationship between ripening pattern, measured as CO(2) evolution and ethylene (C(2)H(4)) production, and metabolic heat production (q). Chilling injury (CI) visible symptoms were evident after 8d at 2.5 degrees C, but none were recorded on fruits kept at 10 degrees C. In fruits held at 10 degrees C, q, C(2)H(4) production, and CO(2) evolution diminished in the course of 16d, whereas in those at 2.5 degrees C CO(2) evolution showed an early burst peaking at 8d. Both C(2)H(4) production and q also showed a burst at 2.5 degrees C but they started at 4 and 8d, respectively, and peaked at 12d. The results showed that irreversibility of chilling injury in zucchini could occur long before the appearance of visible symptoms, although the metabolic activity accompanying the irreversibility process was not noticeable by isothermal calorimetry.     

Effects of G-protein probes on interactions between auxin efflux carriers and phytotropin receptors in zucchini (Cucurbita pepo L.) microsomal membranes

Microsomal vesicles prepared from etiolated hypocotyl tissue of zucchini (Cucurbita pepo L. cv. All Green Bush) exhibited saturable N-1-naphthylphthalamic acid ([³H]NPA) binding, NPA-stimulated association of indol-3yl-acetic acid ([³H]IAA), and saturable binding of guanosine 5-O-[3-thiotriphosphate] (GTP--[³⁵S]). These vesicles were used to test the possibility that NPA receptors might interact with IAA-anion efflux carriers by coupling through a GTP-binding protein (G-protein). Unlabelled GTP--S or guanosine 5-O-[2-thiodiphosphate] (GDP--S) had no effect on saturable NPA binding or on the NPA-stimulated association of IAA with microsomes. NPA did not affect saturable binding of GTP--[³⁵S] to microsomes, either in the presence or absence of saturating concentrations of unlabelled GTP--S or GDP. It is concluded that the occupancy of phytotropin receptors is not transduced to auxin efflux carriers by a GTP-binding protein.     

Host-tissue differences in transformation of pumpkin (Cucurbita pepo L.) by Agrobacterium rhizogenes

Agrobacterium rhizogenes (wild-type strains 8196 and 15834) transformation of pumpkin (Cucurbita pepo L.) intact seedlings grown in vivo, and 6–8-day-old excised cotyledons cultured in axenic conditions was investigated. Transformed (hairy) roots were successfully induced only on the excised cotyledons with the strain 8196, while intact seedlings failed to form hairy roots with either of the two different bacterial strains. Axenic hairy-root cultures established on MS medium without hormones grew vigorously. Mannopine was detected in all transgenic root clones examined. The peroxidase activity in transformed roots was higher compared with normal roots. Electrophoretic analyses of soluble proteins and isoperoxidases showed substantial differences between transformed and normal pumpkin roots.     

Pollen gene expression analysed by micro-isoelectric focusing of proteins from isolated pollen grains in Cucurbita pepo L.

Summary Isoelectric focusing of proteins from single pollen grains of Cucurbita pepo L. has been developed for large scale study of pollen grain populations' heterogeneity. Forty to forty-five protein bands from one pollen grain are revealed after silver staining. Applications of this technique to pollen grain populations from different genotypes are described in this paper. Possible applications and limits of this technique are discussed with respect to plant breeding especially for the measure of gene frequencies in pollen grain populations.The work was partly supported by a grant from LIMAGRAIN and AGPM     

Somatic embryogenesis in pumpkin (Cucurbita pepo L.): control of somatic embryo development by nitrogen compounds

Embryogenic cultures of pumpkin (Cucurbita pepo L.) were initiated from mechanically wounded mature zygotic embryos on 2,4-D-containing MS medium, and on hormone-free, semisolid modified MS medium containing NH4Cl as the sole source of nitrogen. The habituated line was derived from the embryogenic tissue induced with 2,4-D and maintained on medium without growth regulators. Sustained subculturing of the three embryogenic lines on a medium with NH4Cl as the sole source of nitrogen enabled the establishment of highly uniform cultures in which no further development into mature embryo stages occurred. The tissue consisting of proembryogenic globules or globular stage embryos was maintained, without decline, for over six years. Globular embryos proceeded to maturity when a combination of reduced (NH4) and unreduced (NO3) forms of nitrogen was provided in the medium. Different nitrogen sources in the medium caused changes of medium pH during subculture in the pH range of 4.0-6.5. The tissue growth and embryo development were blocked on medium with pH adjusted and stabilized at 4.0 or at 3.2.     

Changes in photosynthetic capacity and polypeptide patterns during natural senescence and rejuvenation of <Emphasis Type="Italic">Cucurbita pepo</Emphasis> L. (zucchini) cotyledons

Natural senescence of Cucurbita pepo (zucchini) cotyledons was accompanied by a gradual degradation of reserve proteins (globulins) and an intensive decrease in the content of both large subunit (LSU) and small subunit (SSU) of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). The net photosynthetic rate, the primary photochemical activity of PSII, estimated by the variable fluorescence (F_v)/maximal fluorescence (F_m) ratio (F_v/F_m) and the actual quantum yield of PSII electron transport in the light-adapted state (ΦPSII) also progressively decreased during natural senescence. In contrast, the fraction of the absorbed light energy, which is not used for photochemistry (LNU) increased with progression of senescence. The decline in the photosynthetic rate started earlier in ontogenesis compared with the down-regulation of the functional activity of PSII, thus suggesting the existence of protective mechanisms which maintain higher efficiency of the photochemical electron transport reactions of photosynthesis compared with the dark reactions of the Calvin cycle during earlier stages of natural senescence. Decapitation of the epicotyl above the senescing cotyledons resulted in full recovery of the polypeptide profile in the rejuvenated cotyledons. In addition, the photosynthetic rate increased reaching values that exceeded those measured in juvenile cotyledons. The photochemical efficiency of PSII also gradually recovered, although it did not reach the maximum values measured in the presenescent cotyledons.     

Genetics of resistance to red pumpkin beetle (A ulacophora foveicollis) in summer squash (Cucurbita pepo L.)

Summary Resistance to red pumpkin beetle in summer squash was found to be controlled by polygenes. Diallel and Triple test cross analysis revealed the preponderance of non-additive and additive gene effects for resistance respectively. Absence of epistasis for resistance was indicated by both tests.     

Effect of cytokinins on ribosomal RNA gene expression in excised cotyledons of Cucurbita pepo L.

Excised pumpkin (Cucurbita pepo L.) cotyledons were used to investigate the effects of two different types of cytokinins: N⁶-benzyladenine and N₁-(2-chloro-4-pyridyl)-N₂-phenylurea on RNA synthesis in isolated nuclei. Treatment of cotyledons with both cytokinins resulted in a rapid enhancement of nuclear RNA-polymerase-I activity (EC 2.7.7.6). Maximum stimulation of RNA polymerase I, responsible for rRNA synthesis, was observed 4–6 h after the start of cytokinin action. The activity of RNA polymerase II was stimulated much more slowly and to a lesser extent. Uridine 5-monophosphate-uridine analysis of the alkalidigested nascent pre-rRNA chains showed that the stimulation of RNA-polymerase-I activity was the consequence of an increase of the polyribonucleotide-clongation rate. No significant change in the number of transcribing enzyme molecules was defected after hormone treatment (86·10³ RNA-polymerase-I molecules per diploid genome).Indications that de-novo protein synthesis is necessary for cytokinin-mediated RNA-polymerase stimulation were derived from experiments showing inhibition by cycloheximide.Abbreviations BA N⁶-benzyladenine - [PU]-30 N₁-(2-chloro-4-pyridyl)-N₂-phenylurea - UMP undine 5-monophosphate - UTP udine 5-triphosphate     

Effect of Crotalaria juncea Amendment on Nematode Communities in Soil with Different Agricultural Histories

Effect of sunn hemp (Crotalaria juncea) hay amendment on nematode community structure in the soil surrounding roots of yellow squash (Cucurbita pepo) infected with root-knot nematodes was examined in two greenhouse experiments. Soils were from field plots treated long-term (LT) with yard-waste compost or no yard-waste compost in LT experiment, and from a short-term (ST) agricultural site in ST experiment. Soils collected were either amended or not amended with C. juncea hay. Nematode communities were examined 2 months after squash was inoculated with Meloidogyne incognita. Amendment increased (P < 0.05) omnivorous nematodes in both experiments but increased only bacterivorous nematodes in ST experiment (P < 0.05), where the soil had relatively low organic matter (<2%). This effect of C. juncea amendment did not occur in LT experiment, in which bacterivores were already abundant. Fungivorous nematodes were not increased by C. juncea amendment in either experiment, but predatory nematodes were increased when present. Although most nematode faunal indices, including enrichment index, structure index, and channel index, were not affected by C. juncea amendment, structure index values were affected by previous soil organic matter content. Results illustrate the importance of considering soil history (organic matter, nutrient level, free-living nematode number) in anticipating changes following amendment with C. juncea hay.     

Genotypic variation in sulphur assimilation and metabolism of onion (Allium cepa L.). II: Characterisation of ATP sulphurylase activity

To investigate the regulation of sulphur (S)-assimilation in onion further at the biochemical level, the pungent cultivar W202A and the milder cultivar Texas Grano 438 PVP (TG) have been grown in S-sufficient (S⁺; 4 meq S⁻¹) or S-deficient (S⁻; 0.1 meq S⁻¹) growth conditions, and tissues excised at the seedling stage (pre-bulbing; ca. 10-weeks-old) and at the mature stage (bulbing; ca. 16-weeks-old). S-supply negatively influenced adenosine-5′-phosphosulphate (APS) reductase (APR) enzyme activity in both cultivars at bulbing only, and a higher abundance of APR was observed in both cultivars at bulbing in response to low S-supply. In contrast, S-supply significantly influenced ATP sulphurylase (ATPS) activity in leaf tissues of W202A only, and only at bulbing, while an increase in abundance in response to high S-supply was observed for both cultivars at bulbing. To investigate the regulation of the ATPS enzyme activity and accumulation further, activity was shown to decrease significantly in roots at bulbing in the S-deficient treatment in both cultivars, a difference that was only supported by western analyses in W202A. Phylogenetic analysis revealed that AcATPS1 groups in a broad monocot clade with the closest sequences identified in Sorghum bicolour, Zea mays and Oryza sativa, but with some support for a divergence of AcATPS1. Detection of ATPS in leaf extracts after two dimensional gel electrophoresis (2-DE) revealed that the protein may undergo post-translational modification with a differential pattern of ATPS accumulation detected in both cultivars over the developmental progression from the seedling to the bulbing stage. Treatment of leaf extracts of W202A to dephosphorylate proteins resulted in the loss of immuno-recognised ATPS spots after 2-DE separation, although enzyme activity was not influenced. These results are discussed in terms of the tiers of control that operate at the biochemical level in the reductive S-assimilation pathway in a S-accumulating species particularly during the high-S-demanding bulbing stage.     

Effect of ethylene antagonists on auxin-induced inhibition of intact primary root elongation in maize (Zeamays L.)

We tested that the hypothesis that root elongation might be controlled by altering the level of ethylene in intact primary roots of maize(Zea mays L.). We measured root elongation in a short period using a computerized root auxanometer. Compounds which regulate ethylene production were applied to intact primary roots in different time periods. Root elongation was stimulated by the treatment with ethylene antagonists such as Co²⁺, aminoethoxyvinylglycine (AVG) and L-canaline. This result suggested that root elongation was closely related to ethylene level of intact primary roots. Furthermore, IAA- and 1-aminocyclopropane-1-carboxylic acid (ACC)-induced inhibition of root elongation was reversed by treatment with Co²⁺. The application of ACC to roots which have been exposed to IAA and Co²⁺ have no significant effect on root elongation. However, the inhibition of root elongation by ACC in roots previously treated with IAA and AVG became manifest when the applied IAA concentrations were lower. These results were consistent with the hypothesis that the level of ethylene in intact roots functions to moderate root elongation, and suggested that auxin-induced inhibition of root elongation results from auxin induced promotion of ethylene production.     

Effect of mineral nitrogen on nitrogen nutrition and biomass partitioning between the shoot and roots of pea (Pisum sativum L.).

The effect of mineral N availability on nitrogen nutrition and biomass partitioning between shoot and roots of pea (Pisum sativum L., cv Baccara) was investigated under adequately watered conditions in the field, using five levels of fertiliser N application at sowing (0, 50, 100, 200 and 400 kg N ha^–1). Although the presence of mineral N in the soil stimulated vegetative growth, resulting in a higher biomass accumulation in shoots in the fertilised treatments, neither seed yield nor seed nitrogen concentration was affected by soil mineral N availability. Symbiotic nitrogen fixation was inhibited by mineral N in the soil but it was replaced by root mineral N absorption, which resulted in optimum nitrogen nutrition for all treatments. However, the excessive nitrogen and biomass accumulation in the shoot of the 400 kg N ha^–1 treatment caused crop lodging and slightly depressed seed yield and seed nitrogen content. Thus, the presumed higher carbon costs of symbiotic nitrogen fixation, as compared to root mineral N absorption, affected neither seed yield nor the nitrogen nutrition level. However, biomass partitioning within the nodulated roots was changed. The more symbiotic nitrogen fixation was inhibited, the more root growth was enhanced. Root biomass was greater when soil mineral N availability was increased: root growth was greater and began earlier for plants that received mineral N at sowing. Rooting density was also promoted by increased mineral N availability, leading to more numerous but finer roots for the fertilised treatments. However, the maximum rooting depth and the distribution of roots with depth were unchanged. This suggested an additional direct promoting effect of mineral N on root proliferation.     

Effect of anther orientation on microspore-callus production in barley (Hordeum vulgare L.)

Barley anthers from cold pretreated spikes produced no or few calluses when plated with both loculi in contact with the medium (flat). When anthers were plated with only one loculus in contact with the medium (up), a high proportion of the anthers produced calluses. The top loculus of the up anthers was most productive. Flat anthers, when compared with up anthers, were not only slower to produce multicellular pollen grains (MCPs) and microcalluses, but also produced fewer of them and ceased production earlier. The MCPs and microcalluses in flat anthers grew more slowly and few developed beyond the 30 cell stage. These results establish the importance of anther orientation for barley anther culture.     

Effect of age of seedling and phytohormones on micropropagation of indica rice (Oryza sativa L.) from Meristem Culture.

An efficient protocol forin vitro micropropagation of seven indica rice varieties was developed from meristem culture. Meristem (leaf base) was isolated from different age of seedlings and cultured on MS medium without hormones and supplemented with different concentrations of NAA and BAP. Regeneration of plantlets from meristem was observed within five days of culture. The meristem isolated from 4-day old seedlings gave highest regeneration on hormone free MS medium. Histological study of meristem (leaf base) from 4-day old seedlings confirmed the presence of meristematic cells. Regenerated plants were multiplied on MS medium supplemented with 0.05 mg/L NAA and 5 mg/L BAP. An average of five plants were obtained from single regenerated meristem. The plants regenerated from meristem showed morphological uniformity.     

Effect of nitrogen and phosphorus status on the translocation of three herbicides in field bindweed (Convolvulus arvensis L.)

Twenty-eight day old field bindweed plants grown in culture solutions deficient in nitrogen (N) or phosphorus (P) for the last seven days of growth translocated significantly less foliarly applied dicamba (3,6-dichloro-o-anisic acid) and 2,4-D [(2,4-dichlorophenoxy) acetic acid] to their roots than did plants grown in complete nutrient solutions. In contrast, N deficiency stimulated basipetal translocation of glyphosate [N-(phosphonomethyl) glycine] and inhibited its acropetal translocation in field bindweed. Deficiencies of both N and P decreased translocation of dicamba from the treated area, but had no influence on translocation of glyphosate or 2,4-D from the treated area.Journal Article No. 4406 of the Agric. Exp. Stn., Oklahoma State University.     

Effect of triacontanol on photosynthesis,alkaloid content and growth in opium poppy (Papaver Somniferum L.)

The influence of different foliar applications of Triacontanol (Tria.) on growth, CO₂ exchange, capsule development and alkaloid accumulation in opium poppy was studied in glasshouse conditions. Plant height, capsule number and weight, morphine content, CO₂ exchange rate, total chlorophyll and fresh and dry weight of the shoot were significantly maximum at 0.01 mg/l Tria. At the highest concentration (4 mg/l) total chlorophyll, CO₂ exchange rate and plant height were significantly inhibited. Thebaine and codeine contents remained unaffected at all the concentrations. The concentration of Fe, Mn, Cu in shoots were maximum at .01 and Zn at 0.1 mg/l Tria. Increase in shoot weight, leaf area ratio and chlorophyll content were significantly correlated with morphine content.CIMAP Communication No. 839.     

增强UV-B辐射和氮对谷子叶光合色素及非酶促保护物质的影响

以谷子(Setaria italica(L)Beauv.)为对象,从拔节期开始持续给予低氮(1.875 mmol/L)和高氮(15 mmol/L)两种氮供应条件并从抽穗期开始进行26 d两种强度(4.29、7.12 kJ·m-2·d-1)的增强UV-B辐射处理,研究了谷子叶中光合色素含量、类黄酮含量和苯丙氨酸解氨酶(PAL)活性的变化.结果表明:与高氮供应条件相比,低氮供应条件明显降低了谷子叶中光合色素含量但提高了类胡萝卜素/叶绿素含量比值;在开花期中段和灌浆期中段,高氮供应条件下谷子叶中光合色素含量对增强UV-B辐射比低氮供应条件下的谷子更敏感.从灌浆期开始到处理结束,两种影响因子对谷子叶中类黄酮含量均有显著影响,增强UV-B辐射导致谷子叶中类黄酮含量逐渐升高,且相同增强UV-B辐射强度下低氮供应条件下的谷子叶中类黄酮含量明显高于高氮供应条件下的谷子.谷子叶中PAL活性对两种影响因子的响应较类黄酮含量更加敏感,低氮供应条件使谷子叶中PAL活性明显提高.结合上述指标的相关性分析结果可知,低氮供应条件加强了处于繁殖期主要阶段的谷子叶中类黄酮的积累,并使谷子叶中的类胡萝卜素/叶绿素含量比值明显提高,进而有助于维持谷子叶中光合色素含量在增强UV-B辐射条件下的相对稳定性,对植株抵抗UV-B辐射伤害有利.