Compensatory acclimated mechanisms of photoprotection in a Xa mutant of Lycopersicon esculentum Mill.

To probe the role of xanthophylls in non-photochemical quenching (NPQ) and the compensatory acclimated photoprotection mechanisms, a tomato (Lycopersicon esculentum Mill. cv. Ailsa Craig) Xa mutant with deficit in lutein (L) and neoxanthin (N) contents was used. The Xa mutant showed lowered NPQ, an increased degree of de-epoxidation state [(A+Z)/(V+A+Z)], and decreases of photosystem 2 (PS2) antenna size. Although the Xa mutant had a CO₂ assimilation rate similar to that of Ailsa Craig, it exhibited a much larger stomatal conductance (g _s) than Ailsa Craig. Decreased electron flux in PS2 (J _PS2) for the Xa mutant was associated with electron flux for photorespiratory carbon oxidation (J _o) and alternative electron flux in PS2 (J _a) while electron flux for photosynthetic carbon reduction (J _c) was not different from Ailsa Craig. Moreover, the Xa mutant also exhibited higher activities of antioxidant enzymes, higher contents of ascorbate and glutathione, and lower contents of reactive oxygen species. Hence some compensatory acclimated mechanisms of photoprotection operated properly in the lack of NPQ and xanthophylls.     

番茄离体培养过程中器官发生的细胞组织学观察

对番茄下胚轴、子叶、茎段、叶片、叶柄不同类型外植体离体培养中有关细胞启动、分裂、分化以及器官发生作了细胞组织学观察。研究结果表明番茄不同类型外植体在同样的培养条件下,愈伤组织生长表现出明显差异,其中下胚轴、子叶诱导产生愈伤组织时,细胞启动最早,生长最快,其分裂方式基本为无丝分裂,未见有丝分裂,因此我们认为以不定芽方式获得转基因植株时,植株的所有性状变化,是否纯属目的基因所为,应该反复考察,不能忽视不定芽产生过程中的种种变化;下胚轴诱导愈伤组织形成时,细胞不规则的无丝分裂少于子叶,故下胚轴离体培养得到的正常芽的比例高于子叶的;番茄离体培养中不定芽通常发生在愈伤组织的周边区,也可起源于维管组织结节周围的形成层状细胞。不定根则由茎中柱鞘处发生。     

Vegetative and Reproductive Response of Lycopersicon esculentum Mill. to Photoperiods

The photoperiodic behavior of tomato cultivars differing ingrowth habit and geographical origin was investigated. Short(8 h) and long (11 to 14 h or dark interruption) photoperiodswere obtained by using the changing seasonal daylenghs. Observationson vegetative and reproductive development indicated that thetomato cultivars responded differentially to the treatments.A highly significant interaction between photoperiod and leafposition was observed. The probable cause for the diverse andcomplex responses of the tomato species to photoperiods is discussed.     

Process of meiosis in interspecific hybrid F1 Lycopersicon esculentum Mill. x Lycopersicon chilense Dun

The investigation concerns meiosis behaviour in embryo-culture-obtained Lycopersicon esculentum Mill. (mutant seedline Mo 638) x L. chilense Dun. F1 hybrid and its parental forms. It was determined that chiasma frequency decreased while univalent and meiotic disorder frequencies increased in F1 plants in comparison with parents forms. Univalent number and the percent of main disorders lowered with bud tier increasing. The conclusion was made about meiosis regularity connection with the influence of environment factors and heterozygous genotype of F1 plants Lycopersicon esculentum x L. chilense.     

In Vitro Induction of Regeneration of Fruit-Like Structure in Lycopersicon esculentum Mill.

It is possible to induce in vitro regeneration of fruit-like structures from tissue pieces excised from young pistil and young fruit of Lycopersicon esculenturn Mill. These fruit-like structures could be cultured in vitro to maturation, meanwhile they became red coloured. Under dissection it was observed that the fruit-like structure consists of fruit flesh and fruit coats without seeds and plancentae. Tests of exogenous hormones and explant ages revealed: 1. Supplement with exogenous cytokinins alone could induce the explants excised from the pistils to regenerate the fruit-like structures, and the highest induced frequency (50%) was obtained when 0. 5 mg/L zeatin was supplemented. Exogenous auxin seems unnecessary. 2. When tissues of young fruit were used as explants, all explants excised from 4—12 mm (diameter) young fruits could be induced to differentiate the fruit-like structures on medium supplemented with exogenous hormones. However, the hightest frequency of induction (62.5%) was obtained only in tissues of explants excised from 8 mm (diameter) sized fruit and cultured on medium supplemented with 2 mg/L of 6-BAP and 1 mg/L of NAA where regermination of the fruit-like structures took place. In order to investigate the expression of cell totipotency arisen in the regeneration of the fruit-like structure a concept of partial expression of plant cell totipotency was proposed and discussed.     

Primary dormancy in tomato (Lycopersicon esculentum cv. Moneymaker): studies with the sitiens mutant

Intact wild-type tomato (Lycopersicon esculentum cv. Moneymaker)seeds do not complete germination to the same percentage orat the same speed as intact ABA-deficient sitiens (sit^w) mutantseeds when seeds of both genotypes are imbibed on polyethyleneglycol (PEG) solutions of –0.3 to –1.5 MPa osmoticpotential. However, if the thicker testas of wild-type seedsare removed (stripped) from the micropyle without damaging theendosperm, both the percentage and speed of germination at lowexternal water potential are similar to that of sit^w mutantseeds. Removing the micropylar end of the testa from sit^w seedsdid not enhance either the speed or percentage of germinationon PEG solution. Despite similar germination percentage and speed between strippedwild-type seeds and either stripped or intact sit^w seeds underosmotic stress, some differences in seed metabolism are evidentbetween genotypes. The activity of endo-ß-mannanasewas greater in the endosperm of sit^w mutant seeds compared tothe endosperm of wild-type seeds when seeds were exposed toosmotic stress. Although     

Responses of nitrate assimilation and N translocation in tomato (Lycopersicon esculentum Mill) to reduced ambient air humidity

The impact of low humidity in ambient air on water relations,nitrate uptake, and translocation of recently absorbed nitrogen,was investigated in 5-week-old tomato (Lycopersicon esculentumMill cv. Ailsa Craig) plants grown hydroponically in a completenutrient solution. Plants were subjected to dry air (relativehumidity 2–4% for 6 h. The transpiration rate increasedseveral-fold and the shoot water content decreased by almost20%, whereas root water content was unaffected. No effect onin vitro nitrate reductase (NR) activity was detected when usingan EDTA-contraining assay buffer. Replacement of EDTA with Mg²⁺revealed a significant decline in shoot NR activity, which suggestsphosphorylation of the enzyme during the stress treatment. Plantswere grown in a split-root system, in which one root half wasfed ¹⁵N-nitrate during the treatment, in order to determinenitrate uptake and translocation of recently absorbed nitrogenin the plants. Uptake of nitrate was substantially inhibited,but the proportion of absorbed ¹⁵N that was translocated tothe shoots was only slightly affected. In untreated plants,71% of the ¹⁵N recovered in roots had been retranslocated fromthe shoots, whereas in plants subjected to stress the deliveryof ¹⁵N from shoots to roots appeared to be completely inhibited.The data show that lowered humidity in air has significant effectson both uptake of nitrate as well as translocation of nitrogenwithin the plants. Some of these effects appear to be commonwith those observed in plants subjected to reduced water potentialsin the root environment and point to the possibility of theshoot water relations being highly influential on nitrogen uptakeand translocation. Key words: Air humidity, nitrate assimilation, nitrate reductase activity, nitrogen translocation, tomato, water stress     

Altered patterns of senescence and ripening in gf, a stay-green mutant of tomato (Lycopersicon esculentum Mill.)

The gf tomato mutant, which retains chlorophyll during ripening, has been found to be affected in leaf senescence. The leaves of the gfmutant show an absolute stay-green phenotype. As leaf senescence and fruit ripening proceed, there is a marked difference in chlorophyll content between wild-type and gf. In both attached and detached leaf studies, or after treatment with ethylene, the leaves withered and abscised in gf with only slight loss of chlorophyll and carotenoids. Total protein content declined and free amino acids increased during leaf senescence in wild-type and gf, but Western analysis showed that LHCII polypeptides were retained at higher levels in gf. Expression of senescence-related mRNAs increased normally in gf whereas those for cab, rbcS and rbcL declined in both mutant and wild-type. The mutant possesses enzyme activity for chlorophyllase, the formation of phaeophorbide a by the action of Mg-dechelatase and the oxygenolytic opening of the porphyrin macrocycle. Analysis of chlorophyll breakdown products in fruit indicated that gf, like other stay-green mutants, accumulates chlorophyllides a and b, but phaeophorbide a does not accumulate in vivo. This may indicate that, in the mutant, in vivo the action of phaeophorbide a-oxygenase is somehow presented, either by altered accessibility or transport of components required for thylakoid disassembly or the absence of another factor.     

Identification and distribution of profilin in tomato (Lycopersicon esculentum Mill.)

Profilin is a G-actin monomer-binding protein which has been shown to participate in actin-based tipgrowth of animal cells. The abundance of profilin in pollen and its occurrence in several vegetable foods raises the question of the role of profilin in plants. First, its distribution throughout various parts of the plant needs to be determined. This paper describes observations on the presence of profilin in the tomato plant (Lycopersicon esculentum Mill.). The distribution of profilin in flower buds, stems, leaves, roots, and fruits of tomato was determined by immunoblotting and by tissue printing, showing that profilin is present in most if not all parts of the tomato plant.We gratefully acknowledge the help provided by Dr. A.T. Jagendorf and the donation of tomato seeds and maize pollen by N. Eanetta and Dr. M. Smith, respectively. The use of Dr. R. Wayne's SZH ILLD dissecting microscope is gratefully acknowledged. This work was aided by helpful discussions with C.S. Combs, Dr. C.A. Conley, and Dr. J. Andersland. This work was supported by a Hatch grant and NRI Competitive Grants Program/USDA 94-37304-1046 to MVP. This material is based upon work supported under a National Science Foundation Graduate Research Fellowship to DWD.     

Regulation of reproduction in wild and cultivatedLycopersicon esculentum Mill. by vesicular-arbuscular mycorrhizal infection

Summary We examined how mycorrhizal infection byGlomus etunicatum Becker and Gerd. affected flowering phenology and components of reproduction in eight wild accessions and two cultivars ofLycopersicon esculentum Mill. We did this by performing a detailed demographic study of flower, fruit and seed production. Mycorrhizal infection had variable effects on the ten accessions. Infection significantly decreased the time taken to initiate flowering in some accessions. In addition, infection increased flowering duration in some accessions. In many accessions, infection significantly increased seed production, primarily by increasing the number of inflorescences and infructescences. In some accessions, mycorrhizal infection also increased the proportion of flowers that produced mature fruits or the number of seeds per fruit. Among accessions, shoot phosphorus content was correlated with seed productivity for both mycorrhizal and non-mycorrhizal plants. However, non-mycorrhizal plants produced more seed biomass per mg of shoot phosphorus than mycorrhizal plants.     

Management of root-knot nematode in tomato Lycopersicon esculentum,Mill, with biogas slurry

The effect of biogas slurry application on the severity of root-knot nematode, Meloidogyne incognita, attack on tomato cv. Co-1, was tested in the green house with two levels of biogas slurry: 5% and 10% (w/w) added to soil. Both the number (3 fruits/plant) and fruit yield (35.2 g/plant) of tomato increased significantly with 10% (w/w) biogas slurry. The plants amended with biogas slurry put up more vegetative growth and tended to flower and fruit much earlier than did those of the control. The nematode population in the soil decreased thus decreasing the severity of nematode attack.     

Allelochemical stress causes inhibition of growth and oxidative damage in Lycopersicon esculentum Mill

The aim of this study was to analyse the effect of allelochemical stress on Lycopersicon esculentum growth. Our results showed that allelochemical stress caused by Sicyos deppei aqueous leachate inhibited root growth but not germination, and produced an imbalance in the oxidative status of cells in both ungerminated seeds and in primary roots. We observed changes in activity of catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD), glutathione reductase (GR) and the plasma membrane NADPH oxidase, as well as in the levels of H(2)O(2) and O(2) (*-) in seeds at 12 and 24 h, and in primary roots at 48 and 72 h of treatment, which could account for the oxidative imbalance. There were changes in levels of expression of the mentioned enzymes, but without a correlation with their respective activities. Higher levels of membrane lipid peroxidation were observed in primary roots at 48 and 72 h of treatment. No effect on the expression of metacaspase and the PR1 was observed as indicators of cell death or induction of plant defence. This paper contributes to the understanding of plant-plant interactions through the phytotoxic allelochemicals released in an aqueous leachate of the weed S. deppei, which cause a negative effect on other plants.     

Effects of Ethylene on Photosynthesis and Partitioning in Tomato, Lycopersicon esculentum Mill

The extended period of ethylene release from ethephon (2-chloroethylphosphonicacid) after application to intact tomato plants has provideda model system in which the effects of ethylene on photosyntheticmetabolism and carbon partitioning has been studied. Ethylenerelease from leaf tissue after ethephon treatment was 10 timesgreater than that from untreated control leaves. The specificactivity of 14C2H4 released from [14C] ethephon remained constantover several days demonstrating that the ethylene was derivedfrom the applied ethephon. The ethephon-treated plants exhibitedextreme epinasty of the leaves and 24 h after application theflower buds in the first visible cluster had abscised, leafexpansion at the apex had ceased and developing adventitiousroots were visible on the lower stem. Rates of steady-state photosynthesis, respiration, photorespirationand transpiration were the same in treated and control leaves24 h after ethephon application. Both treated and control leavespartitioned similar proportions of newly-fixed 14C from 14CO²into neutral (46.4%), acidic (14.0%), basic (5.0%) and insoluble(34.0%) leaf fractions under steady-state conditions. The speedof 11C-assimilate movement in the stems of control plants (3.62±0.42cm min-1 towards the apex and 4.03±0.15 cm min-1 towardsthe roots) was more rapid than in the ethephon-treated plants(2.90±0.31 cm min-1 upwards and 2.59±0.22 cm min-1downwards). Furthermore, in the control plants 20.0±5.4%of the 14C exported to the plant from the source leaf was transportedtowards the developing flower cluster and young leaves. Twenty-fourhours after ethephon application only 6.5 ±1.7% of theexported 14C was translocated towards the shoot. Contrary tosome reports ethylene did not affect steady-state gas exchangeprocesses while carbon partitioning was significantly alteredindicating that ethylene effects on photosynthetic carbon metabolismare indirect and not due to direct effects on photosyntheticprocesses per se. Key words: Ethylene, photosynthesis, partitioning     

Ethylene Exchange in Lycopersicon esculentum Mill. Leaves During Short- and Long-Term Exposures to CO2

The effects of long-term and transient exposure to elevatedCO₂ concentrations on photosynthetic gas exchange and ethylenerelease by tomato leaves were investigated. The net CO₂ assimilationrate was enhanced when leaf tissue grown at ambient (35 Pa CO₂)levels was assayed at 100 Pa CO₂. Leaf tissue grown at high(130 Pa) CO₂ exhibited a lower net CO₂ assimilation rate athigh CO₂ levels than leaf tissue grown at ambient (35 Pa) CO₂.This decrease in CO₂ exchange rate in response to growth athigh CO₂ is typical of C₃ species. Rates of endogenous and 1-aminocyclopropane-l-carboxylicacid (ACC)-stimulated ethylene release from leaf tissue wereenhanced by exposure to elevated CO₂ levels whether the leaftissue had been grown at ambient or enriched CO₂ levels. Thedata demonstrate that CO₂ enhanced C₂H₄ release from leaf tissuein response to both short-term perturbations in CO₂ concentrationand long-term growth and development under high CO₂. Prolongedgrowth at elevated CO₂ concentrations induced a higher endogenousrate of C₂H₄ release relative to that of leaf tissue grown atlower CO₂ levels. Leaf tissue from all leaf positions of plantsgrown at high CO₂ consistently evolved more C₂H₄ than correspondingtissue from ambient-grown plants when assayed under standardizedconditions. Endogenous (ACC) tissue contents and rates of ACC-stimulatedethylene release were also higher at all leaf positions in CO₂-enrichedtissue. Thus the higher rates appeared to be due to both higherendogenous precursor (ACC) levels in the tissue and greaterACC to C₂H₄ conversion capacity. Growth at elevated CO₂ levelsresulted in a persistent increase in the rate of endogenousC₂H₄ release in leaf tissue. The capacity for increased ethylenerelease in response to CO2 did not decline after prolonged growthat high CO₂. Key words: CO₂enrichment, ethylene, leaves, tomato     

Flowering in the uniflora mutant of tomato (Lycopersicon esculentum Mill.): description of the reproductive structure and manipulation of flowering time

The uniflora (uf) mutant of tomato (Lycopersicon esculentum Mill.) is known to produce solitary, normal, fertile flowers instead of inflorescences. Histological and SEM studies revealed that this unusual reproductive structure resulted from the inability of the plant to produce an inflorescence and not from post-initiation abortion processes affecting young flower buds. Development prior to floral transition was apparently not affected by the mutation since rates of germination and leaf initiation were identical in both uf and the Ailsa Craig (AC) initial cultivar. However, the time of flowering of the mutant was always delayed as compared to AC. In uf, environmental conditions markedly influenced flowering time which occurred early in all individuals in summer, but was strongly delayed during winter, with less than 20% plants reaching flowering before having initiated 40 leaves. Defoliation treatments stimulated floral transition in uf plants since 100% flowering occurred whatever the season and since the time of floral transition was usually advanced in comparison to the non-defoliated control plants. Similarly, compared to intact uf plants, flowering of terminal meristem of cuttings and upper axillary bud of decapitated plants was promoted. The involvement of correlative influences and assimilate availability in the control of flowering in tomato is suggested by these findings.